Dissertations / Theses on the topic 'Infrared optoelectronics'

Since its discovery in 2004, graphene, a one-atom-thick layer of carbon atoms arranged in a hexagonal lattice, has attracted huge interest from the scientific community due to its extraordinary electronic, mechanical, and optical properties. While most of the earliest studies focused on electronic transport, in recent years the fields of graphene photonics and optoelectronics have thriven. The goal of this thesis is to explore the use of graphene for novel optoelectronic devices, adopting different approaches to enhance the electrically tunable graphene-light interaction in a broad spectral range, from the visible to the mid-infrared. This includes investigating the sub-wavelength interaction and energy transfer between a dipole and a graphene sheet, as well as working on efficient photodetection schemes. Indeed graphene high electronic mobility, broadband absorption, flexibility and tunable optoelectronic properties (described in Chapter 1) make it extremely appealing for the development of optoelectronic applications with new functionalities. Concerning the devices, the starting point of the experiments presented in the thesis are graphene field effect transistors of different geometries, whose fabrication and characterization techniques are described in Chapter 2. The tunability of the optoelectronic properties via control over the Fermi energy is an essential feature of the fabricated devices. The change in the Fermi level is achieved applying a voltage to a back-gate or a polymer electrolyte top-gate. We address both aspects at the core of optoelectronics, i.e. the control of optical properties with electric fields and the modification of electrical quantities, such as current, with light. Therefore the first part of the thesis (comprising Chapter 3, 4 and 5) is devoted to graphene nanophotonics and plasmonics, while the second part deals with graphene-based photodetection (Chapter 6, 7, 8 and 9). In Chapter 3, the main concepts at the basis of graphene nanophotonics are presented, such as the electrical tunability and the strong field confinement of the 2D plasmons, as well as the coupling of an optical emitter to graphene plasmons or electron-hole pair excitations. Then we present two experiments showing the control of light by means of static electric fields. In Chapter 4 we show the electrical control of the relaxation pathways of erbium ions in close proximity to a graphene sheet: the energy flow from the emitters is tuned to electron-hole pairs in graphene, to free space photons and to plasmons by changing the graphene Fermi level. In Chapter 5 we present the real-space imaging and tuning of highly confined graphene plasmons in the mid-infrared, launched by the dipole of a metallized s-SNOM tip (Chapter 5). In this case modifying the graphene Fermi level leads to a change in the plasmon wavelength. In Chapter 6 we review existing schemes for graphene photodetectors and the main mechanisms enabling photodetection with graphene, with particular emphasis toward the photothermoelectric effect. Then we present three cases where graphene photoresponse is enhanced exploiting the interaction with surrounding materials. A hybrid graphene-quantum dot photodetector in the visible and near-infrared is reported in Chapter 7: a photogating effect after light absorption in the quantum dots leads to extremely high responsivities (over one million A/W). In Chapter 8 we demonstrate how the excitation of bulk phonons of a polar substrate enhances the mid-infrared photocurrent via a photothermoelectric effect. Also substrate surface phonons, launched by illuminating a metal edge with light polarized perpendicularly to it, lead to an increase in the photoresponse, as described in Chapter 9. The results presented in this thesis open new avenues in the field of graphene-based optoelectronics for active nano-photonics and sensing.
Desde su descubrimiento en 2004, el grafeno, una sola capa átomos de carbono en un retículo hexagonal, ha atraído un gran interés de la comunidad científica debido a sus propiedades electrónicas, mecánicas y ópticas extraordinarias. Los primeros estudios se centraron en el transporte electrónico, pero en los últimos años estudios en el campo de la fotónica y de las propiedades optoelectrónicas del grafeno han suscitado un mayor interés. El objetivo de esta tesis es explorar el uso del grafeno para nuevos dispositivos optoelectrónicos, adoptando diferentes enfoques para mejorar la interacción del grafeno con la luz en un amplio rango espectral, desde el rango visible hasta el infrarrojo medio. Esto incluye la investigación de la interacción y la transferencia de energía entre un dipolo y una monocapa de grafeno cercana, así como trabajar en esquemas de fotodetección eficientes. La alta movilidad electrónica, la absorción de banda ancha, la flexibilidad y las propiedades optoelectrónicas sintonizables (véase Capítulo 1) hacen que el grafeno sea extremadamente atractivo para el desarrollo de aplicaciones optoelectrónicas con nuevas propiedades funcionalidades. En cuanto a los dispositivos, el punto de partida de los experimentos presentados en esta tesis son transistores de efecto de campo con diferentes geometrías, cuya fabricación y técnicas de caracterización se describen en el Capítulo 2. La capacidad de ajuste de las propiedades optoelectrónicas a través del control de la energía de Fermi es una característica esencial de los dispositivos, y se logra con la aplicación de un voltaje de puerta. Nos dirigimos a ambos aspectos a la base de la optoelectrónica, es decir, el control de las propiedades ópticas con campos eléctricos y la modificación de magnitudes eléctricas, como la corriente con la luz incidente. Por tanto, la primera parte de la tesis (Capítulos 3, 4 y 5) se dedica al estudio de la nanofotónica y plasmónica del grafeno, mientras que la segunda parte se ocupa de fotodetección basada en grafeno (Capítulos 6, 7, 8 y 9). En el Capítulo 3, se explican los principales conceptos del campo de la nanofotónica de grafeno, como la capacidad de ajuste eléctrico y el fuerte confinamiento de los plasmones 2D, así como el acoplamiento de un emisor óptico con los plasmones o pares electrón-hueco. Luego se presentan dos experimentos que muestran el control de la luz por medio de campos eléctricos estáticos. En el Capítulo 4 se muestra el control eléctrico de las vías de relajación de iones de erbio en las proximidades de una monocapa de grafeno: el flujo de energía a partir de los emisores se puede dirigir a pares electrón-hueco en el grafeno, a fotones y a plasmones cambiando el nivel de Fermi del grafeno. En el Capítulo 5 se presenta la excitación y el ajuste de plasmones de grafeno altamente confinados en el infrarrojo medio, activado mediante el dipolo de una punta de microscopia de campo cercano (Capítulo 5). En el Capítulo 6 se revisan los fotodetectores de grafeno existentes y los principales mecanismos que permitan fotodetección con grafeno. A continuación se presentan tres casos donde la fotorrespuesta del grafeno se mejora con la explotación de la interacción con los materiales circundantes. Un fototransistor híbrido de grafeno y puntos cuánticos (véase Capitulo 7) llega a responsividad extremadamente alta en el visible y infrarrojo cercano (más de un millón de A/W). En el Capítulo 8 se demuestra cómo la excitación de fonones de bulk de un sustrato polar aumenta la fotocorriente en el infrarrojo medio a través de un efecto fototermoeléctrico. También fonones superficie del sustrato, lanzados por la iluminación de un borde de metal con luz polarizada perpendicularmente, conducen a un aumento en la fotorrespuesta (Capítulo 9). Los resultados presentados en esta tesis abren nuevos caminos en el campo de la optoelectrónica basada en el grafeno en el campo de la nano-fotónica activa y de los sensores

Les nanocristaux colloïdaux sont des objets cristallins obtenus par voie chimique. Ces objets étant confinés, leurs propriétés optiques dépendent de leur taille, et peuvent donc être ajustées à la demande. Les nanocristaux de tellurure de mercure et de séléniure de mercure possèdent notamment des propriétés d’absorption dans l’infrarouge: l’énergie de bande interdite (interbande) des nanocristaux de HgTe peut-être variée du SWIR au MWIR, tandis que les nanocristaux de HgSe, grâce à un auto-dopage électronique dégénéré, présentent des transitions intrabande ajustables du MWIR au LWIR. Un contrôle fin de la chimie de surface de ces objets permet de les intégrer dans des dispositifs électroniques et de créer des détecteurs infrarouge à bas coût. Dans mon travail de thèse, je me suis intéressé à différentes manières de sonder la dynamique des porteurs dans ces dispositifs, soit via la mesure du photocourant, soit par des observations directes de la relaxation des porteurs photogénérés. A partir d’études sur la dynamique dans HgSe, j’ai identifié les limitations apportées par le fort dopage de ces nanocristaux : le transport est dominé par la forte densité électronique, conduisant à des faibles performances pour la détection IR. En reprenant les concepts développés pour les hétérostructures de semi-conducteurs III-V, je propose différentes approches fructueuses pour découpler les propriétés optiques et le transport de charges dans des dispositifs de détection MWIR à base de nanocristaux de HgSe
Colloidal nanocrystals are crystalline objects grown by colloidal chemistry approaches. Thanks to quantum confinement, their optical properties depend on their size, and can then be tuned accordingly. Using mercury selenide and mercury telluride, we grow infrared-absorbing nanocrystals. While HgTe nanocrystals interband gap can be tuned from the NIR to the MWIR, HgSe nanocrystals display self-doping and intraband transitions in the MWIR to LWIR. With a careful control of their surface chemistry, those nanocrystals can be integrated into electrical devices to create cheap infrared photodetectors. In my PhD work, I am interested in probing carrier dynamics in those devices using various time-resolved techniques, either based on photocurrent measurements or on direct observation of the photocarriers relaxation. From dynamic study of HgSe intraband devices, I identify the issue brought by the degenerative doping level of those nanocrystals: transport is driven by the doping of this material, resulting in very poor IR-sensing performances. By taking inspiration from the III-V semiconductor developments, I propose several successful approaches to uncouple optical and transport properties in HgSe-based, MWIR detectors

Optoelectronic devices operating in the mid-wave (3-5 Μm) and long-wave (8-12 Μm) infrared (IR) regions of the electromagnetic spectrum are of a great interest for academic and industrial applications. Due to the lack of atmospheric absorption, devices operating within these spectral bands are particularly useful for spectroscopy, imaging, and dynamic scene projection. Advanced IR imaging systems have created an intense need for laboratory-based infrared scene projector (IRSP) systems which can be used for accurate simulation of real-world phenomena occurring in the IR. These IRSP systems allow for reliable, reproducible, safe, and cost-effective calibration of IR detector arrays. The current state-of-the-art technology utilized for the emitter source of IRSP systems is thermal pixel arrays (TPAs) which are based on thin film resistor technology. Thermal pixel array technology has fundamental limitations related to response time and maximum simulated apparent temperature, making them unsuitable for emulation of very hot (> 700 K) and rapidly evolving scenes. Additionally, there exists a need for dual wavelength emitter arrays for IRSP systems dedicated to calibration of dual wavelength detector arrays. This need is currently met by combining the spectral output from two separate IRSP systems. This configuration requires precise alignment of the output from both systems and results in the maximum radiance being limited to approximately half that of the capability of a given emitter array due to the optics used to combine the outputs. The high switching speed inherent to IR light-emitting diodes (LEDs) and the potential for high power output makes them an appealing candidate to replace the thermal pixel arrays used for IRSP systems. To this end, research has been carried out to develop and improve the device performance of IR LEDs based on InAs/GaSb type-II superlattices (T2SLs). A common method employed to achieve high brightness from LEDs is to incorporate multiple active regions, coupled by tunnel junctions. Tunnel junctions must provide adequate barriers to prevent carrier leakage, while at the same time remain low in tunneling resistance to prevent unwanted heating. The performance of two tunnel junction designs are compared in otherwise identical four stage InAs/GaSb superlattice LED (SLED) devices for application in IRSP systems. This research culminated in the development of a 48 Μm pitch, 512$times512 individually addressable mid-wave IR LED array based on a sixteen stage, InAs/GaSb T2SL device design. This array was hybridized to a read-in integrated circuit and exhibited a pixel yield greater than 95 %. Projections based on single element emitter results predict this array will be able to achieve a peak apparent temperature of 1350 K within the entire 3-5 Μm band. These results demonstrate the feasibility of emitter arrays intended for IRSP systems based on InAs/GaSb SLED devices. Additionally, a dual wavelength 48 Μm pitch, 8x8 emitter array based on InAs/GaSb T2SL LEDs was developed and demonstrated. This design incorporates two separate, 16 stage InAs/GaSb SL active regions with varying InAs layer thicknesses built into a single vertical heterostructure. The device architecture is a three terminal device allowing for independent control of the intensity of each emission region. Each emitter region creates a contiguous pixel, capable of being planarized and mated to drive electronics.

The year 2015 was defined the international year of light and light-based technologies. This title did not come unexpected, the research activity in solid-state lighting intensified during the last decade striving to improve solid-state light sources in terms of power consumption and fabrication costs. Emerging technologies are going to improve and amplify the scope of applicability of current solid-state lighting technology. This work would like to give a contribution to scientific research in solid-state lighting on two fronts. First, by contributing to the determination of the optical properties of germanium and germanium-tin alloy and second, by searching for remedies to the temperature dependent efficiency loss in GaN/InGaN based blue light emitting diodes. On these premises, this work has been splitted in two parts. In part one, the Auger recombination properties of germanium and radiative and Auger recombination properties for germanium-tin alloy have been calculated. In case of germanium, the application of a minimum biaxial tensile strain turns the material to a direct gap semiconductor, suitable for active and passive optoelectronic applications. On the other hand, the germanium-tin alloy is even more interesting due to its tunable band-gap energy and the capability to turn into a direct gap material above a certain molar fraction. On top of that, both materials may represent cheaper alternatives to materials currently used for the fabrication of high performance photodetectors and active optoelectronic devices. For both materials, the Auger and radiative recombination properties have been determined through a novel numerical approach that applies a Green’s function based model to the full band structure of the material. In part two, the temperature dependent efficiency loss, experimentally detected in a reference GaN/InGaN based single quantum well light emitting diode, has been numerically studied by measn of a commercial simulation software Crosslight APSYS © . The charge transport mechanism in the device has been modeled through an improved drift-diffusion scheme and compared to the real device current-voltage characteristics. Once an agreement between real and simulated current-voltage characteristics was achieved, the impact of Shockley-Read-Hall recombination mechanism on the device internal quantum efficiency function of temperature has been throughfully studied.

L’imagerie infrarouge refroidie est portée par une demande forte pour des applications dans les secteurs militaire, industriel et spatial. Les enjeux actuels de ce marché sont le fonctionnement à haute température et la fonctionnalisation spectrale des détecteurs.Ces enjeux peuvent être adressés grâce à l’utilisation de résonateurs optiques et leur faculté à concentrer le champ électromagnétique. Ce travail de thèse montre comment des résonateurs plasmoniques peuvent être intégrés dans la filière HgCdTe.La théorie temporelle des modes couplés a été utilisée, de manière analytique, pour optimiser à travers la condition de couplage critique, l’absorption dans un résonateur plasmonique chargé par un semiconducteur. La conception d’une photodiode HgCdTe ultramince plasmonique est ensuite détaillée. Elle repose sur l’utilisation d’un mode optique résultant du couplage entre un mode plasmon de surface et un mode gap plasmon de cavité
The market for cooled infrared imaging technologies is growing fast due to a range of applications covering military, commercial and space. Current research for innovative systems focuses on high operating temperature and multispectral detectors.To achieve these aims, optical resonators can be used to concentrate electromagnetic fields in thin absorbing media. This thesis investigates the possibility of using plasmonic resonators for HgCdTe photodetection.Temporal coupled-mode theory is used to optimise analytically the absorption in a plasmonic resonator incorporating an absorbing semiconductor subject to the critical coupling condition. A design of a thin plasmonic HgCdTe diode is then described. This includes a hybrid plasmonic mode arising from the coupling between a surface plasmon and a cavity gap-plasmon mode

We use spectroscopy to study infrared optoelectronic inter and intraband semiconductor carrier dynamics. The overall aim of this thesis was to study both III-V and Pb chalcogenide material systems in order to show their future potential use in infrared emitters. The effects of bandstructure engineering have been studied in the output characteristics of mid-IR III-V laser diodes to show which processes (defects, radiative, Auger and phonon) dominate and whether non-radiative processes can be suppressed. A new three-beam pump probe experiment was used to investigate interband recombination directly in passive materials. Experiments on PbSe and theory for non-parabolic near-mirror bands and non-degenerate statistics were in good agreement. Comparisons with HgCdTe showed a reduction in the Auger coefficient of 1-2 orders of magnitude in the PbSe. Using Landau confinement to model spatial confinement in quantum dots (QDs) "phonon bottlenecking" was studied. The results obtained from pump probe and cyclotron resonance saturation measurements showed a clear suppression in the cooling of carriers when Landau level separation was not resonant with LO phonon energy. When a bulk laser diode was placed in a magnetic field to produce a quasi quantum wire device the resulting enhanced differential gain and reduced Auger recombination lowered Ith by 30%. This result showed many peaks in the light output which occurred when the LO phonon energy was a multiple of the Landau level separation. This showed for the first time evidence of the phonon bottleneck in a working laser device. A new technique called time resolved optically detected cyclotron resonance, was used as a precursor to finding the earner dynamics within a spatially confined quantum dot. By moving to the case of a spatial QD using an optically detected intraband resonance it was possible to measure the energy separation interband levels and conduction and valence sublevels within the dot simultaneously. Furthermore this technique has been shown that the inhomogeneous broadening of the photoluminescence spectrum is not purely affected by just size and composition. We suggest that other processes such as state occupancy, In roughing, and exciton binding energies may account for the extra energy.

Ce mémoire de thèse est consacré à l’étude et au développement des hétérostructures semi-conductrices à base de GaN et ZnO. Ces matériaux sont particulièrement prometteurs pour le développement de composants optoélectroniques inter-sous-bandes infrarouges et notamment pour les dispositifs à cascade quantique. Ces semiconducteurs possèdent en effet plusieurs avantages pour la conception de dispositifs à cascade, tels qu’une grande discontinuité de potentiel en bande de conduction et une énergie du phonon LO très élevée. Ces propriétés se traduisent par la possibilité de développer des dispositifs couvrant une gamme spectrale allant du proche-infrarouge au térahertz et offrent la possibilité de réaliser des lasers à cascade quantique térahertz fonctionnant à température ambiante
This manuscript focuses on the study and on the development of semiconductor heterostructures based on GaN and ZnO material. These materials are particularly promising for the development of infrared optoelectronic intersubband devices in particular for quantum cascade devices. These semiconductors own several advantages to design quantum cascade devices such as a large conduction band offset and a large energy of the LO phonon. These properties predict the possibility to develop devices covering a large spectral range from near-infrared to terahertz and offer the possibility to realize terahertz quantum cascade lasers operating at room temperature

Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2003.
Thesis advisor(s): Gamani Karunasiri, James Luscombe. Includes bibliographical references (p. 59-61). Also available online.

The GaInAsSbP pentanary system has been utilised to grow epilayers on InAs substrates using Liquid Phase Epitaxy, and used to form the basis of. optoelectronic devices in the technologically important Mm spectral range (3-5 μm). The photoluminescence spectra of a single epilayer confirmed that the dominant radiative recombination mechanism was band-to-band in the pentanary layer. XRD analysis indicated the epilayers did not suffer from spinodal decomposition, and SEM and SIMS confirmed the layers were flat and abrupt. Raman spectroscopy was carried out over a wide range of lattice-matched InAsSbP compositions for the first time, before a further study on GaInAsSbP. Binary-like optical phonon signals were identified, and their position was found to directly relate to the composition of the alloy. Phonon signals resulting from alloy disorder were identified in the Raman spectra, which provides a valuable tool for future work on determining crystal quality. Prototype mesa diode devices were fabricated using wet etching with the addition of an InAsSbP window layer. Uncooled photodetectors were found to operate at room temperature, limited by diffusion current. Thermophotovoltaic cells using the same structure, designed for use with comparatively low temperature heat sources, were found to have a 33% fill factor. This is the first report of a pentanary alloy used for such an application. The corresponding photoresponse spectra exhibited two peaks, attributed to recombination in both the window layer and active region. Room temperature LEDs were demonstrated, operating with a 50% duty cycle, with their emission peaking at ~3.75 μm. The analysis of the excitation dependent electroluminescence allowed the electron effective mass of 0.018 mo to be calculated for the GaInAsSbP alloy. The devices were found to be limited by CHCC Auger recombination, even though the CHSH mechanism was suppressed by increasing the spin-orbit split-off band, as confirmed by high pressure measurements. The bandgap dependence of GalnAsSbP on pressure was found to be 10.7 meV/khar, which is believed to be the first such investigation for a III-v pentanary alloy. Multi-ring structures v/ere fabricated and current crowding effects were investigated. It was found that by employing multiple rings, rather than spot contacts, there was an improvement in the current spreading. and hence the output of the device. When only the outer-most contact was energised the current crowding under the contact was sufficient to facilitate whispering gallery modes. Lasing was achieved at 4K with drive currents of >300 mA, peaking at 3.3 μm.

Abstract : Photonic Integrated Circuits (PIC) are of tremendous interest for photonics system in order to reduce their power consumption, size, fabrication cost and improve their reliability of fiber optics linked discrete component architecture. However, unlike for microelectronics, in photonics different heterostructures are required depending on the type of device (laser sources, detectors, modulators, passive waveguides…). Therefore photonics integration needs a technology able to produce multiple bandgap energy wafers with a suitable final material quality in a reproducible manner and at a competitive cost: a technological challenge that has not been completely solved yet. Quantum Well Intermixing (QWI) is a post growth bandgap tuning process based on the localized and controlled modification of quantum well composition profile that aims to address these matters. UV laser induced QWI (UV-Laser-QWI) relies on high power excimer laser to introduce point defects near the heterostructure surface. By adjusting the laser beam shape, position, fluence and the number of pulse delivered, the different regions to be intermixed can be defined prior to a rapid thermal annealing step that will activate the point defects diffusion across the heterostructure and generate quantum well intermixing. UV-LaserQWI presents the consequent advantage of allowing the patterning of multiple bandgap regions without relying on photolithographic means, thus offering potentially larger versatility and time efficiency than other QWI processes. UV-Laser-QWI reproducibility was studied by processing samples from an InGaAs/InGaAsP/InP 5 quantum well heterostructure emitting at 1.55 µm. 217 different sites on 12 samples were processed with various laser doses. The quantum well intermixing generated was then characterized by room temperature photoluminescence (PL) mapping. Under those experimental conditions, UV-Laser-QWI was able to deliver heterostructures with a PL peak wavelength blue shift controlled within a +/- 15 % range up to 101.5nm. The annealing temperature proved to be the most critical parameter as the PL peak wavelength in the laser irradiated areas varied at the rate of 1.8 nm per degree Celsius. When processing a single wafer, thus limiting the annealing temperature variations, the bandgap tuned regions proved to be deliverable within ± 7.9%, hence establishing the potential of UV-Laser-QWI as a reproducible bandgap tuning solution. The UV-Laser-QWI was used to produce multiple bandgap wafers for the fabrication of broad spectrum superluminescent diodes (SLD). Multiple bandgap energy profiles were tested and their influence on the SLDs’ performances was measured. The most favorable bandgap modifications for the delivery of a very broadband emitting SLD were analyzed, as well as the ones to be considered for producing devices with a flat top shaped spectrum. The intermixed SLDs spectra reached full width at half maximum values of 100 nm for a relatively flattop spectrum which compare favorably with the ≈ 40nm of reference devices at equal power. The light-intensity characteristics of intermixed material made devices were very close to the ones of reference SLD made from as-grown material which let us think that the alteration of material quality by the intermixing process was extremely limited. These results demonstrated that the suitability of UV-Laser-QWI for concrete application to photonic devices fabrication. Finally, an alternative laser QWI technique was evaluated for SLD fabrication and compared to the UV laser based one. IR-RTA relies on the simultaneous use of two IR laser to anneal local region of a wafer: a 980 nm laser diode coupled to a pigtailed fiber for the wafer background heating and a 500 µm large beam TEM 00 Nd:YAG laser emitting at 1064 nm to anneal up to intermixing temperature a localized region of the wafer. The processed samples exhibited a 33 % spectral width increase of the spectrum compare to reference device at equal power of 1.5 mW. However, the PL intensity was decreased by up to 60 % in the intermixed regions and the experiments proved the difficulty to avoid these material degradations of material quality with IR-RTA.
Résumé : L’intégration de circuit photonique vise à réduire la consommation énergétique, la taille, le coût et les risques de panne des systèmes photoniques traditionnels faits de composants distincts connectés par fibre optique. Cependant, contrairement à la microélectronique, des hétérostructures spécifiques sont requises pour chaque composant : lasers, détecteurs, modulateurs, guides d’ondes… De cette constatation découle le besoin d’une technologie capable de produire des gaufres d’hétérostructures III/V de qualité à plusieurs énergies de gap, et ce de façon reproductible pour un coût compétitif. Aucune des techniques actuelles ne répond pour l’instant pleinement à tous ces impératifs. L’interdiffusion de puits quantique (IPQ) est un procédé post épitaxie basé sur la modification locale de la composition des puits quantiques. L’IPQ induite par laser UV (IPQ-UV) est basée sur l’utilisation de laser excimer (Argon-Fluor émettant à 193 nm ou Krypton-Fluor à 248 nm) pour introduire des défauts ponctuels à la surface de l’hétérostructure. En ajustant la taille du faisceau, sa position, son énergie ainsi que le nombre d’impulsions laser délivrées à la surface du matériau, on peut définir les régions à interdiffuser ainsi que leur futur degré d’interdiffusion. Un recuit de la gaufre active ensuite la diffusion des défauts et par conséquent l’interdiffusion du puits. L’IPQ-UV présente l’avantage considérable de se passer de photolithographie pour définir les zones de différentes énergies de gap, diminuant ainsi la durée et potentiellement le coût du procédé. La reproductibilité de l’IPQ-UV a été étudiée pour l’interdiffusion d’une structure à 5 puits quantiques d’InGaAs/InGaAsP/InP émettant à 1.55 µm. 217 régions sur 12 échantillons ont été irradiés par un laser KrF avec des nombres d’impulsion variables selon les sites et avec une densité d’énergie constante de 155 mJ/cm². Les modifications de la structure générée par ce traitement furent ensuite mesurées par cartographie en photoluminescence (PL) à température ambiante. L’analyse des données montra que l’IPQ-UV permet un contrôle du décalage vers le bleu du pic de PL à +/- 15 % jusqu’à 101.5nm. La température du recuit est apparue comme le paramètre crucial du procédé, puisque la longueur d’onde du pic de PL des zones interdiffusées varie de 1.8 nm par degré Celsius. En considérant les sites irradiés sur une seule gaufre, c’est à dire en s’affranchissant des variations de température entre deux recuits de notre système, la variation du pic de PL est contrôlable dans une plage de ± 7.9%. Ces résultats démontrent le potentiel de l’IPQ-UV en tant que procédé reproductible de production de gaufre à plusieurs énergies de gap. L’IPQ-UV a été utilisé pour la fabrication de diodes superluminescentes (DSLs). Différents type de structure à énergie de gap multiple ont été testés et leurs influences sur les performances spectrales des diodes évalués. Les spectres des DSLs faites de matériau interdiffusé ont atteint des largeurs à mi-hauteur dépassant les 100 nm (jusqu’à 132 nm), ce qui est une amélioration conséquente des ≈ 40nm des DSLs de référence à puissance égale. Les caractéristiques intensité–courant des DSLs interdiffusés furent mesurées comme étant très proches de celle des dispositifs de référence faits de matériau brut, ce qui suggère que l’IPQ-UV n’a pas ou très peu altéré la qualité du matériau initial. Ces résultats prouvent la capacité de l’IPQ-UV à être utilisé pour la fabrication de dispositifs photoniques. Une technique alternative d’IPQ par laser a été évaluée et comparée à l’IPQ-UV pour la fabrication de DSL. Le recuit rapide par laser IR est basé sur l’utilisation simultanée de deux lasers IR pour chauffer localement l’hétérostructure jusqu’à une température suffisante pour provoquer l’interdiffusion: une diode laser haute puissante émettant à 980 nanomètre couplée dans une fibre chauffe la face arrière de la gaufre sur une large surface à une température restant inférieure à celle requise pour provoquer l’interdiffusion et un laser Nd:YAG TEM 00 émettant à 1064 nm un faisceau de 500 µm de large provoque une élévation de température additionnelle localisée à la surface de l’échantillon, permettant ainsi l’interdiffusion de l’hétérostructure. Les dispositifs fabriqués ont montré une augmentation de 33 % de la largeur à mi-hauteur du spectre émis à puissance égale de 1.5 mW. Cependant, l’intensité du pic de PL dans les zones interdiffusées est diminuée de 60 %, suggérant une dégradation du matériau et la difficulté à produire un matériau de qualité satisfaisante.

La région moyen-infrarouge se situe entre les domaines de l’optique et du THz du spectre électromagnétique. Cette région a un intérêt particulier dans les applications spectroscopiques et la communication dans l’espace libre.Grâce à des avancées technologiques sur la fabrication de dispositifs unipolaires basés sur des transitions inter-sous-bandes, la région du moyen-infrarouge est devenue accessible par une nouvelle famille de lasers et détecteurs à base de semi-conducteurs. Ces dispositifs optoélectroniques sont basés sur des transitions optiques entre les états électroniques de la bande de conduction d’une structure composée d’une succession de puits quantiques. Leur temps de vie caractéristique est de l’ordre du picosecondes et ainsi, les dispositifs inter-sous-bandes disposent de propriétés de dynamique ultra rapides intéressantes dans le développement des applications à hautes fréquences.L’objectif de cette thèse est le dessin d’un système prêt à l’emploi pour la communication dans l’espace libre à fort taux de transfert de bit dans le moyen-infrarouge, avec tous les composants qui fonctionnent à température ambiante. Dans ce but, nous avons étudié les performances hautes fréquences d’un système composé de détecteurs et de lasers à cascade quantiques.Dans un premier temps, nous avons caractérisé les propriétés électriques et optiques d’un détecteur à cascade quantique à 4.9 μm à température ambiante. La structure de bande ainsi que la distribution des charges a été étudié en détails dans différentes conditions de température et de tensions appliquées aux bornes du détecteur. Nous avons montré une température limite de détection de 135 K avec une detectivité à cette température de 2 × 1011 Jones, nous situant dans l’état de l’art. Par la suite, nous nous sommes concentrés sur la réponse en modulation à haute fréquence du détecteur à cascade quantique. Nous avons, en premier lieu, optimisé le système électronique afin qu’il soit compatible avec des mesures hautes fréquences. Avec ce système, nous avons mesuré une détection optique jusqu’à 5.4GHz en utilisant un détecteur à cascade quantique de taille 50 × 50 (μm)2 avec son pont suspendu en or adapté en impédance avec tout le reste du montage expérimental. Grâce à des mesures de rectification, nous avons montré que la fréquence de coupure est limitée par la structure de bande du détecteur en soit. Nous avons ensuite développé un système prêt à l’emploi pour les modulations hautes fréquences du laser à cascade quantique, ce dernier étant optimisé grâce une étude sur son contact d’injection. Nous montrons ainsi une fréquence de coupure optique de 10 GHz, limitée par le photo-détecteur. Enfin, comme preuve de concept, nous avons réalisé une communication dans l’espace libre de 4 Gb/s à l’échelle du laboratoire en utilisant un laser à cascade quantique et un photo-détecteur infrarouge à puits quantiques. Pour cela, nous avons utilisé une modulation par changement de phase binaire et nous avons obtenu un taux d’erreur de 10(−5)
Mid infrared (MIR) covers the region of the electromagnetic spectrum between optics and THz ranges. This frequency range is of great interest for applications in spectroscopy and free space optical communications. The progress on unipolar devices based on intersubband transitions, has introduced in the MIR a new family of semiconductor lasers and detectors. These optoelectronic devices are indeed based on optical transitions between electronic states in the conduction band of a complex sequence of quantum wells. Their characteristic lifetime is of the order of picoseconds and therefore intersubband devices have a great potential for wideband ultrafast applications.The aim of this work is the design of a system for high data bit rate free space optical communication in the mid infrared spectral region, with all the components operating at room temperature. To this end, we investigate the high frequency performances of quantum cascade detectors (QCD) and lasers (QCL).Firstly, we carefully explore the electrical and optical characteristics of QCD at 4.9 μm operating at room temperature. A detailed study of the band structure and charge distribution at different operating temperature and under different applied bias is reported. We demonstrate a background limited infrared photodetector (BLIP) temperature of 135 K and a detectivity at this temperature of 2 × 1011 Jones, which is at the state of the art. We then focus on QCD response to high frequency modulation. We engineered and realized an electronic system compatible with high frequency operation. We report an optical response up to 5.4 GHz with a 50 × 50 (μm)2 square mesa using a gold air-bridge technology. Thanks to rectification measurements, we show that the band-pass is limited by the specific detector bandstructure. For the high frequency modulation of QCLs, we develop a plug and play system with an optimization on the injection contact that allows the demonstration of a cut off frequency of 10 GHz, limited by the photodetector. Finally, we present a proof of principle demonstration of a free space optical communication experiment using a QCL and a quantum well infrared photodetector (QWIP) at 4 Gb/s. We use a Binary Phase-Shift Keying (BPSK) modulation technique and we obtain a bit error rate of 10(−5)

Le sujet de la thèse a porté sur la mise au point, la caractérisation et l'utilisation de matériaux semi-conducteurs, au sein desquels les porteurs libres ont un temps de vie extrêmement brefs (picoseconde ou sub-picoseconde), pour réaliser des antennes photoconductrices émettrices ou détectrices de rayonnement électromagnétique térahertz (THz). Contrairement au semi-conducteur LTG-GaAs (low temperature grown GaAs) à la technologie bien dominée et aux performances exceptionnelles lorsque photo-excité par des impulsions lasers de longueurs d'onde typiquement inférieures à 0,8 µm, le travail portait ici sur des matériaux permettant l'emploi de lasers dont les longueurs d'onde sont celles des télécommunications optiques, à savoir aux alentours de 1,5 µm. L'intérêt est de bénéficier de la technologie mature de ces lasers, et du coût relativement modique des composants pour les télécommunications optiques. Pour réaliser des antennes THz performantes et efficaces, le matériau semi-conducteur doit présenter plusieurs qualités : vie des porteurs libres très courte, grande mobilité des porteurs, haute résistivité hors éclairement, et bonne structure cristallographique pour éviter les claquages électriques. Pour obtenir une courte durée de vie, on introduit un grand nombre de pièges dans le semi-conducteur, qui capturent efficacement les électrons libres. Pour les matériaux de type InGaAs employés à 1,5 µm, le problème est que le niveau en énergie de ces pièges, par exemple pour les matériaux épitaxiés à basse température, est très proche de la bande de conduction du semi-conducteur. Cela est équivalent à un dopage n du matériau, ce qui en diminue fortement sa résistivité hors éclairement. Plusieurs solutions ont été apportées par différents laboratoires : compensation par dopage p pour les matériaux épitaxiés à basse température, bombardement ionique, implantation ionique, ou même structures à couches alternées où la photo-génération et la recombinaison des porteurs libres se produisent à des endroits différents. Le but du travail de thèse était de fabriquer des matériaux préparés suivant ces différentes techniques, de les caractériser et de comparer leurs performances pour l'optoélectronique THz. Les semi-conducteurs à étudier étaient de type InGaAs comme déjà publiés par la concurrence, l'originalité de thèse portant sur la comparaison de ces différents matériaux et si possible leur optimisation,. Au cours de ce travail de thèse, de nombreuses couches d'InGaAs ont été épitaxiées, en faisant varier les paramètres de dépôt, et des antennes THz ont été fabriquées. Les couches ont été caractérisées du point de vue cristallographique, ainsi que pour la conductivité électrique DC (mesures 4 pointes, mobilité Hall...), les propriétés d'absorption optique (spectroscopie visible et IR), la durée de vie des porteurs par mesure optique pompe-sonde. Pour les couches épitaxiées à basse température, l'influence d'un recuit thermique ainsi que du dopage en béryllium ont été étudiés. Dans le cas de couches bombardées ou implantées, plusieurs ions ont été utilisés, le brome, le fer et l'hydrogène. Les relations entre la cartographie des défauts structuraux et/ou des ions implantés et les propriétés électriques et de dynamique des porteurs ont été examinées en détail. Ces études permettent de comprendre le type de défauts qui piègent les porteurs dans ces matériaux, ainsi que leur formation lors du processus de fabrication et de traitement des couches. Finalement les meilleures couches fabriquées présentent des performances comparables à celles publiées par ailleurs. Les derniers travaux de thèse ont permis d'obtenir les premiers signaux de rayonnement THz générés par une antenne fabriquée avec l'InGaAs optimisé.

This project investigates dilute nitrides such as InAsN and InGaAsN with a view to the fabrication of optoelectronic sources and detectors operating in the mid-infrared (2-5 um) spectral range which has many practical applications. Samples of both bulk epitaxial layers and state-of-the-art nanostructures have been grown by liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE). The effect of N incorporation on the material quantum efficiency has been studied using temperature dependent photo- and electroluminescence spectroscopy, high resolution x-ray diffraction and other techniques. InAsN and InGaAsN bulk epilayers were grown by liquid phase epitaxy under standard and neutral solvent growth techniques to investigate the feasibility of high quality material production. Photoluminescence (PL) showed that the dominant peak in the majority of the material was from a defect related transition which quickly quenched leaving just band - band recombination. Raman spectroscopy was employed to identify the types of defect levels present within the material, the strange behaviour of the PL from InGaAsN material was determined to be from a doubly-ionised defect involving a combination of In vacancies and higher order nitrogen complexes. High quality InAsN layers were grown from neutral solvent growth with an XRD full-width-half-maximum (FWHM) of 17.5 arc-seconds obtained from 0.3% N incorporation; this however was only observed in thin layers of the dilute nitride believed to be due to the rapid depletion of N within the growth melt. High quality InAsN was grown onto GaAs substrates using molecular beam epitaxy; PL from this material persisted up to room temperature with a final emission wavelength of 4 urn and nitrogen incorporation of 1%. The temperature dependence of the material was found to be superior to that of similar material grown onto InAs substrates and shown to have an 'S' shaped behaviour at low temperatures originating from tail states caused by inhomogeneous nitrogen incorporation typical of all nitrogen inclusive materials. A comparison with LPE material was then carried out. PL measurements showed that the LPE material had comparable emission intensities with narrower FWHM for low N content samples but MBE proved more favourable for higher N content material with the maximum N inclusion from LPE being 0.5%. The addition of Sb to InAsN multi quantum wells was then studied with the view to device fabrication. The addition of Sb was found to improve both lattice quality and PL intensities while reducing the overall strain of the material. Interpretation of the 4 K PL was shown to be intense with the observation of recombination originating from both the first heavy hole and light hole consistent with a type I band alignment. A model to determine the band alignment of the InAsSbN multiple quantum wells (MQWs) was derived from a single-band Schrodinger solver and found to be in good agreement with the experimental results. Finally InAsSbN light emitting diodes (LEDs) were fabricated and shown to exhibit strong electroluminescence reaching room temperature with final wavelengths of 3.7 urn and the presence of hydrocarbon absorption in the spectrum reveals that this material has potential for gas detection. Output powers of over 3 μW under 100 mA drive current at 50% quasi- continuous operation were obtained leading to an internal efficiency of 0.63%, an improvement over InAsSb and InSb quantum dot LEDs. These prototype devices show promise for type I dilute nitride materials operating in the mid infrared region.

A cluster expansion method combined with Density Functional Theory is used to derive structural properties of quaternary AlGaInN and binary GeSn alloys. The energy gaps for both systems are calculated including quasiparticle effects within the framework of the computationally inexpensive and parameter free DFT-1/2 method. The model developed is able to treat the complexity of semiconductor alloys, which have important application in heterostructures, band gap engineering and lattice constant matching. The transition energy of the effective electronic bands is calculated including statistical disored and compared to spectroscopic measurements. The range of the tunable energy gap of cubic and hexagonal AlGaInN alloys lattice matched to GaN is calculated, together with the direct-indirect gap transition region in the cubic alloy. We also discuss trends for phase separation of GeSn alloys and do not observe any significant indication of decomposition in the binodal-spinodal composition range. It is shown that the oscillator strength of the optical transition in the alloy is considerably higher than that of pure Ge. Results are contextualized in light of applications of AlGaInN alloys for ultraviolet and GeSn alloys for mid-infrared photoemission. Differences and similarities between our model and other calculations in the existing literature are also elucidated.

La sonde atomique tomographique est un instrument d’analyse de la matière à trois dimensions avec une résolution atomique. Cet instrument s’appuie sur l’effet de champ électrique généré à l’extrémité d’un échantillon taillé sous la forme d’une aiguille nanométrique pour faire évaporer les atomes de surface qui sont collectés par un détecteur à deux dimensions. La mesure du temps de vol des ions dont l’évaporation est déclenchée par une impulsion électrique ou optique permettent de remonter à la composition chimique en plus de la localisation 3D des atomes. Dans les sondes atomiques actuelles, l’évaporation atomique est déclenchée par un laser ultrarapide émettant dans l’UV. Cependant, l’interaction de la lumière UV avec la matière induit un échauffement thermique qui limite la résolution en masse de l’instrument et empêche son exploitation pour l’analyse de matériaux fragiles comme les composants biocompatibles. Ces travaux de thèse visent à étudier des solutions pour favoriser l’évaporation rapide tout en inhibant les effets thermiques indésirables dans le cadre d’une sonde atomique laser. Notre approche consiste à exploiter des impulsions ultracourtes dans le domaine du moyen infrarouge ou du THz en raison de leur grande énergie pondéromotrice associée à une faible énergie de photon. Ce manuscrit rapporte sur le développementd’un banc de génération et caractérisation d’impulsions THz intenses. Le couplage de ces rayonnements avec une nano-pointe métallique polarisée négativement a permis de caractériser le champ proche induit à la surface de la nano-pointe qui est fortement modifié par l’effet d’antenne de cette dernière. La deuxième partie rapporte sur le développement d’une source laser ultrarapide de haute cadence accordable dans le moyen infrarouge autour de 3 mm en exploitant des fibres en verre fluoré
The atome probe tomography is an instrument for analyzing matter in three dimensions with atomic resolution. This instrument relies on the effect of an electric field generated at the end of a sample cut into the shape of a nanoscale needle to evaporate the surface atoms which are collected by a two-dimensional detector. The measurement of the time of flight of the ions whose evaporation is triggered by an electrical or optical pulse makes it possible to measure the chemical composition in addition to the 3D localization of the atoms. In current atome probes, atomic evaporation is triggered by a high-speed laser emitting in the UV. However, the interaction of UV light with matter induces thermal heating which limits the mass resolution of the instrument and prevents its use for the analysis of fragile materials such as biocompatible components. This thesis work aims to study solutions to promote rapid evaporation while inhibiting unwanted thermal effects of the laser in atome probe. Our approach consists in exploiting ultrashort pulses in the mid-infrared or THz domain due to their high ponderomotive energy associated with low photon energy. This manuscript reports on the development of a bench for the generation and characterization of intense THz pulses. Coupling these radiations with a negatively polarized metallic nanotip has made it possible to characterize the near field induced at the surface of the nanotip, which is strongly modified by the antenna effect. The second part reports on the development of an ultra-fast laser source tunable in the mid-infrared around 3 mm using fluoride glass fibers

Nous avons développé et construit un imageur polarimétrique actif avec une illumination laser à la longueurd'onde 1:55 um. Il peut générer et analyser tous les états de polarisation de la sphère de Poincaré. Il permetde réaliser une optimisation polarimétrique du contraste en analysant la scène à l'aide d'un algorithme desegmentation ultra rapide basé sur des contours actifs. Cet imageur nous permet de comparer plusieursmodalités d'imagerie possédant des nombres de degrés de liberté polarimétrique différents. Nous effectuons ladétection d'objets manufacturés dans différents environnements avec l'imagerie polarimétrique active pourillustrer les capacités de ces modalités. Nous démontrons l'effcacité de l'imagerie polarimétrique active pourdes applications de décamouffage et de détection d'objets dangereux, et mettons en évidence lescaractéristiques qu'un imageur polarimétrique doit posséder pour ce type d'applications. Nous montrons quedans la majorité des scénarios étudiés, les matrices de Mueller sont presque diagonales, et que desperformances de détection satisfaisante peuvent être atteintes avec des imageurs polarimétriques plus simplesqui ont un nombre de degrés de liberté réduit. De plus, la normalisation de l'intensité des images est unecondition nécessaire pour mieux révéler le contraste polarimétrique
We designed and built an active polarimetric imager with laser illumination at 1:55 um wavelength. It cangenerate and analyze any polarization state on the Poincaré sphere. It let us the possibility to perform apolarimetric contrast optimization by analyzing the scene with an ultrafast active-contour-based segmentationalgorithm. This imagins systeme allow to compare several imaging modes having different numbers ofpolarimetric degrees of freedom. We address the detection of manufactured objects in different types ofenvironments with active polarimetric imaging to illustrate the capabilities of the techniques. We demonstratethe effciency of active polarimetric imaging for decamouffage and hazardous object detection, and underlinethe characteristics that a polarimetric imager aimed at this type of application should possess. We show thatin most encountered scenarios the Mueller matrices are nearly diagonal, and suffcient detection performancecan be obtained with simple polarimetric imaging systems having reduced degrees of freedom. Moreover,intensity normalization of images is of paramount importance to better reveal polarimetric contrast

Дисертація на здобуття наукового ступеня кандидата технічних наук (Ph.D) за спеціальністю 05.17.11 – технологія тугоплавких неметалічних матеріалів. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2019. Дисертація присвячена створенню оптичних кольорових стекол зі спектральними параметрами – коефіцієнтом пропускання на довжині хвилі 1060 τ(λ₁₀₆₀) >65 %, поглинанням у спектральному діапазоні до 950 нм та технологіям їх отримання. На цей час існуючі стекла лише частково виконують ці умови, або технології їх отримання є нерентабельними для масового виробництва, тому було поставлена задача про створення стекол, які б могли задовольняти ці умови з фактором технологічності у виробництві. Вирішення досягнуто завдяки дослідженням поглинальної дії системи барвників Cr₂O₃-Mn₂O₃ у системі R₂O-PbO-SiO₂ та додатковому нанесенню оптичного покриття. Завдяки дослідженням було встановлено механізми забарвлення з урахуванням впливу домішок-барвників (Fe₂O₃/FeO), а також знайдені оптимальні концентрації барвників у склі. При розробці технології отримання оптичного кольорового скла були дослідженні основні технічні операції та методи контролю якості скла, що дозволяє отримувати дане скло у виробничому масштабі. Розроблені параметри контролю протікання процесів гомогенізації та освітлення розплаву скла з метою підвищення якості продукції. Також були розроблені методики обробки деталей зі скла та нанесення оптичних покриттів. Для автоматизації виробництва даної продукції та зменшення впливу людського фактору було розроблено програмне забезпечення автоматичної системи керування технологічними процесами (АСК ТП).
Dissertation for the Ph.D. degree in specialty 05.17.11 – "Technology of refractory nonmetallic materials". – National Technical University "Kharkiv Polytechnic Institute", Kharkiv, 2019. The dissertation is devoted to the development of infrared optical glasses with next spectral characteristics, as well as the creation of technologies for their production. The spectral characteristics are transmittance at a wavelength of 1060 nm 1060 τ (λ₁₀₆₀)>65% and absorption in the spectral range up to 950 nm. The solution to this problem was achieved due to the addition of the Cr₂O₃-Mn₂O₃ colorant system to the glass matrix of the R₂O-PbO-SiO₂ system, as well as the additional optical thin-film coatings. For production implementation optical color glass a pot regenerator furnace was used. The ceramic vessel with a volume of 500 liters was chosen. The temperature of the production was 1420 ± 20 °С. To improve the quality of optical glass practical studies were carried out. These studies devote to the modes of batch filling, mixing and temperature parameters. Fundamental researches were conducted on the mode of cooling of colored optical glass. For the first time for such glasses the stage of cooling made by inertia cooling of the furnace construction without gas. Due to introduction of the results and improving of the spectral parameters the volume of quality glass yield has increased. The software was developed to control the technological processes of the furnace in automatic mode.

Дисертація на здобуття наукового ступеня кандидата технічних наук (Ph.D) за спеціальністю 05.17.11 – технологія тугоплавких неметалічних матеріалів. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2019. Дисертація присвячена створенню оптичних кольорових стекол зі спектральними параметрами – коефіцієнтом пропускання на довжині хвилі 1060 τ(λ₁₀₆₀) >65 %, поглинанням у спектральному діапазоні до 950 нм та технологіям їх отримання. На цей час існуючі стекла лише частково виконують ці умови, або технології їх отримання є нерентабельними для масового виробництва, тому було поставлена задача про створення стекол, які б могли задовольняти ці умови з фактором технологічності у виробництві. Вирішення досягнуто завдяки дослідженням поглинальної дії системи барвників Cr₂O₃-Mn₂O₃ у системі R₂O-PbO-SiO₂ та додатковому нанесенню оптичного покриття. Завдяки дослідженням було встановлено механізми забарвлення з урахуванням впливу домішок-барвників (Fe₂O₃/FeO), а також знайдені оптимальні концентрації барвників у склі. При розробці технології отримання оптичного кольорового скла були дослідженні основні технічні операції та методи контролю якості скла, що дозволяє отримувати дане скло у виробничому масштабі. Розроблені параметри контролю протікання процесів гомогенізації та освітлення розплаву скла з метою підвищення якості продукції. Також були розроблені методики обробки деталей зі скла та нанесення оптичних покриттів. Для автоматизації виробництва даної продукції та зменшення впливу людського фактору було розроблено програмне забезпечення автоматичної системи керування технологічними процесами (АСК ТП).
Dissertation for the Ph.D. degree in specialty 05.17.11 – "Technology of refractory nonmetallic materials". – National Technical University "Kharkiv Polytechnic Institute", Kharkiv, 2019. The dissertation is devoted to the development of infrared optical glasses with next spectral characteristics, as well as the creation of technologies for their production. The spectral characteristics are transmittance at a wavelength of 1060 nm 1060 τ (λ₁₀₆₀)>65% and absorption in the spectral range up to 950 nm. The solution to this problem was achieved due to the addition of the Cr₂O₃-Mn₂O₃ colorant system to the glass matrix of the R₂O-PbO-SiO₂ system, as well as the additional optical thin-film coatings. For production implementation optical color glass a pot regenerator furnace was used. The ceramic vessel with a volume of 500 liters was chosen. The temperature of the production was 1420 ± 20 °С. To improve the quality of optical glass practical studies were carried out. These studies devote to the modes of batch filling, mixing and temperature parameters. Fundamental researches were conducted on the mode of cooling of colored optical glass. For the first time for such glasses the stage of cooling made by inertia cooling of the furnace construction without gas. Due to introduction of the results and improving of the spectral parameters the volume of quality glass yield has increased. The software was developed to control the technological processes of the furnace in automatic mode.

Optoelectronic devices operating in the mid-infrared spectral region are attracting increasing attention due to potential applications in a wide range of disciplines. For example, mid-infrared photodetectors play a key role in thermophotovoltaic (TPV) energy conversion, whereby a photovoltaic device is used to extract electrical power from heat radiation. This technology is attractive for waste heat harvesting and clean energy production in several different environments. Similarly, mid-infrared light sources are particularly useful for biochemical sensing and spectroscopy, where the distinctive absorption features of many molecular species of interest can be exploited for their sensitive identification and detection. Both devices are investigated in this thesis work. In the area of TPV energy conversion, I have studied the use of intersubband transitions in semiconductor quantum cascade structures as a means to overcome the fundamental limitations of existing TPV devices using mature InP-based technology. Very efficient coverage of the incident radiation spectrum and optimal current matching can be achieved using multiple quantum-cascade structures monolithically integrated with a p-n junction, by taking advantage of their intrinsic cascading scheme, spectral agility, and design flexibility. Numerical simulations indicate that this approach can effectively double the present state-of-the-art in TPV output electrical power. In the area of mid-infrared light sources, my work has focused on developing efficient light emitters based on tensilely strained Germanium nanomembranes (Ge NMs). These ultrathin (a few ten nanometers) single-crystal membranes are good candidates for the development of CMOS-compatible Group-IV light sources, by virtue of their ability to sustain large strain levels and in the process become direct-bandgap materials. My research efforts have concentrated on the development of optical cavities based on Ge NMs that can satisfy the mechanical flexibility requirement of this materials platform. In particular, photonic-crystal (PhC) cavities in the form of disconnected dielectric-column arrays have been designed and fabricated based on a novel membrane assembly method, producing clear cavity-mode features in NM photoluminescence spectra.
2016-08-17T00:00:00Z

abstract: The molecular beam epitaxy growth of the III-V semiconductor alloy indium arsenide antimonide bismide (InAsSbBi) is investigated over a range of growth temperatures and V/III flux ratios. Bulk and quantum well structures grown on gallium antimonide (GaSb) substrates are examined. The relationships between Bi incorporation, surface morphology, growth temperature, and group-V flux are explored. A growth model is developed based on the kinetics of atomic desorption, incorporation, surface accumulation, and droplet formation. The model is applied to InAsSbBi, where the various process are fit to the Bi, Sb, and As mole fractions. The model predicts a Bi incorporation limit for lattice matched InAsSbBi grown on GaSb.The optical performance and bandgap energy of InAsSbBi is examined using photoluminescence spectroscopy. Emission is observed from low to room temperature with peaks ranging from 3.7 to 4.6 μm. The bandgap as function of temperature is determined from the first derivative maxima of the spectra fit to an Einstein single oscillator model. The photoluminescence spectra is observed to significantly broaden with Bi content as a result of lateral composition variations and the highly mismatched nature of Bi atoms, pairs, and clusters in the group-V sublattice. A bowing model is developed for the bandgap and band offsets of the quinary alloy GaInAsSbBi and its quaternary constituents InAsSbBi and GaAsSbBi. The band anticrossing interaction due to the highly mismatched Bi atoms is incorporated into the relevant bowing terms. An algorithm is developed for the design of mid infrared GaInAsSbBi quantum wells, with three degrees freedom to independently tune transition energy, in plane strain, and band edge offsets for desired electron and hole confinement. The physical characteristics of the fundamental absorption edge of the relevant III-V binaries GaAs, GaSb, InAs, and InSb are examined using spectroscopic ellipsometry. A five parameter model is developed that describes the key physical characteristics of the absorption edge, including the bandgap energy, the Urbach tail, and the absorption coefficient at the bandgap. The quantum efficiency and recombination lifetimes of bulk InAs0.911Sb0.089 grown by molecular beam epitaxy is investigated using excitation and temperature dependent steady state photoluminescence. The Shockley-Read-Hall, radiative, and Auger recombination lifetimes are determined.
Dissertation/Thesis
Doctoral Dissertation Electrical Engineering 2020

Copper iron chalcogenides constitute a promising class of optoelectronic materials courtesy of their narrow bandgaps and earth abundant constitution. However, they are yet to receive the attention they deserve due to the lack of easy synthetic protocols and poorly understood material properties. Discordant narratives in the literature regarding their optoelectronic properties has also prevented them from being used for device-based applications. This thesis is aimed at rectifying a few of these issues. The objective of this thesis is to synthesize and study the properties of copper iron chalcogenide nanocrystals viz., CuFeS2 and CuFeSe2, and to explore their utility in the context of optoelectronic devices. Chapter 1 provides a brief introduction to the fundamental concepts related to the work described in this thesis. The chapter further discusses the scope and motivation behind the work carried out in this thesis. Chapter 2 describes our efforts to assign the nature of a feature in the optical absorption spectrum of CuFeS2 nanocrystals occurring at ~500 nm. Using a combination of steady-state and time-resolved optical spectroscopy as well as transport measurements we assign the feature to be a localized surface plasmon resonance and attribute the peculiar properties exhibited by CuFeS2 nanocrystals to this feature. Further, the transport measurements revealed that films of these nanocrystals can support a photoresponse. Chapter 3 describes the fabrication and characterization of a broadband photodetector based on CuFeS2 nanocrystals. Briefly, we fabricated heterojunctions of CuFeS2 nanocrystals with bulk n type silicon and demonstrated a broadband photoresponse from 460 nm-2200 nm with response time of the order of microseconds. The photodetector was further found to possess a photothermal response that is bolometric in nature, which allows the device to sense hot objects at room temperature. Chapter 4 describes our efforts to synthesize and study the optoelectronic properties of CuFeSe2 and CuFeSe2-CdS core-shell nanocrystals. We synthesized CuFeSe2 nanocrystals and studied their properties using structural, optical and electrical characterization techniques. The nanocrystals were found to have a very narrow bandgap of 0.11 eV and were also found to exhibit a plasmon resonance at ~410 nm. We further found that the films of these nanocrystals exhibited a photoresponse in the MIR, thus making them a promising candidate for infrared photodetection. We further synthesized highly luminescent CuFeSe2-CdS core-shell nanocrystals and found that the energetic position of their emission is greatly dependent on the sequence in which the shell growth precursors are added to the reaction mixture. Using optical and structural characterization techniques, we find that there are two different core-shell variants that result from the synthesis and their formation is determined by which one of the shell growth precursors is added to the reaction mixture first. The key difference between the two variants were found to be the presence of an interfacial CdSe layer which occurs whenever the cation precursor is added to the reaction mixture first. Chapter 5 describes the synthesis of CuFexGa1-xS2 nanocrystals, a hitherto unknown composition of nanocrystals. Using alloying as a strategy, we synthesized CuFexGa1-xS2 nanocrystals corresponding to different Fe:Ga ratios. The properties of the resulting nanocrystals were found to be greatly dependent on their composition.

Optoelectronic devices based on III-V materials operating in infrared wavelength range have been attracting intensive research effort due to their applications in optical communication, remote sensing, spectroscopy, and environmental monitoring. The novel semiconductor lasers and photodetectors structures and materials investigated in this thesis cover the spectral range from 1.3µm to 12µm. This spectral region includes near-infrared (NIR), mid-infrared (MIR) and long wavelength infrared. This thesis demonstrated infrared optoelectronic devices, based on III-V compound semiconductors grown by Molecular Beam Epitaxy (MBE,) utilizing various combinations of novel III-V materials, device structures and substrate orientations. This thesis will be presented in two parts; the first part focuses on two types of photodetectors; type-II InAs/GaSb superlattice IR detector and AlGaAsSb/InGaAsSb mid-infrared heterojunction p-i-n photodetector. The second part of this thesis focuses on the three types of quantum well (QW) lasers; phosphor-free1.3µm InAlGaAs strain-compensated multiple-quantum-well (SCMQW) lasers on InP (100), InGaAsNSb/GaAs quantum wells (QWs) grown on GaAs (411)A substrates and mid-infrared InGaAsSb lasers with digitally grown tensile-strained AlGaAsSb barriers. Type-II InAs/GaSb superlattice IR detectors with various spectral ranges were grown by MBE. Two superlattice structures with 15 monolayers (ML) of InAs/12ML GaSb and 17ML InAs/7ML GaSb are discussed. Based on X-ray diffraction (XRD) measurements both InAs/GaSb superlattices exhibit excellent material qualities with the full width at half maximum (FWHM) of the 0th-order peak about 20arcsec, which is among the narrowest ever reported. The 50% cutoff wavelengths at 80K of the two photodiodes with 15ML InAs/12ML GaSb and 17ML InAs/7ML GaSb superlattices are measured to be 10.2 µm and 6.6 µm, respectively. Mid-infrared heterojunction p-i-n photodetector, AlGaAsSb/InGaAsSb lattice-matched to GaSb grown by solid source molecular beam epitaxy using As and Sb valved crackers greatly facilitated the lattice-matching of the quaternary InGaAsSb absorbing layer to the GaSb substrates, as characterized by X-ray diffraction. The resulting device exhibited low dark current and a breakdown voltage of 32V at room temperature. A record Johnson-noise-limited detectivity of 9.0 × [10]^10 cm Hz^(1/2)/W was achieved at 290K. The 50% cutoff wavelength of the device was 2.57 µm. Thus, our result has clearly demonstrated the potential of very high-performance lattice-matched InGaAsSb p-i-n photodetectors for mid-infrared wavelengths. For phosphor-free1.3 µm InAlGaAs multiple-quantum-well (MQW) lasers, the substrate temperature has been found to be a critical growth parameter for lattice-matched InAl(Ga)As layers in the laser structures. As shown by X-ray diffraction measurements, in the temperature range of 485-520° C, spontaneously ordered superlattices (SLs) with periods around 7-10 nm were formed in the bulk InAl(Ga)As layers. Based on photoluminescence (PL) measurements, a large band gap reduction of 300 meV and a broadened PL peak were observed for the In_0.52 Al_0.48 As layers with SL, as compared to those without SL. The undesirable, spontaneously-ordered SL can be avoided by using MBE growth temperatures higher than 530 °C. This results in a high laser performance. Threshold-current density as low as 690 A/cm² and T_0 as high as 80 K were achieved for InAlGaAs laser bars emitting at 1310 nm. InGaAsNSb/GaAs QWs on GaAs (411)A exhibited remarkably enhanced photoluminescence efficiency compared with the same structures on conventional GaAs (100) substrates. It was further observed that the optimum growth temperature for (411)A was 30 °C higher than that for (100). To explain this phenomenon, a model based on the self-assembling of local rough surface domains into a unique global smooth surface at the lowest energy state of the system is proposed. Lastly, the digital-growth approach for tensile-strained AlGaAsSb barriers improved the reliability and controllability of MBE growth for the MQW active region in the mid-infrared InGaAsSb quantum well lasers. The optical and structural qualities of InGaAsSb MQW were improved significantly, as compared to those with random-alloy barriers due to the removal of growth interruption at the barrier/well interfaces in digital growth. As a result, high-performance devices were achieved in the InGaAsSb lasers with digital AlGaAsSb barriers. A low threshold current density of 163 A/cm² at room temperature was achieved for 1000-µm-long lasers emitting at 2.38 µm. An external differential quantum efficiency as high as 61% was achieved for the 880-µm-long lasers, the highest ever reported for any lasers in this wavelength range.

Colloidally produced nanocrystals (NCs) arranged in thin films hold promise for next-generation semiconductors. These NCs offer tunability in semiconductor properties due to their size, shape, composition, and surface characteristics. However, the performance of NC-based optoelectronic devices still lags behind theoretical predictions. This is primarily attributed to electronic deep-level trap states, which act as recombination centres and limit effective mobility. The large surface area, hybrid nature, and disordered structure of NCs contribute to the abundance of trap states. To improve device performance, it is crucial to identify these defects and understand their impact on electrical characteristics. This work employs Deep Level Transient Spectroscopy (DLTS) to identify deep-level defects in NCs and NC-based photovoltaic devices. DLTS allows for determining defect level energy, concentration, capture cross-section, and differentiation between minority and majority carrier traps. This technique is highly sensitive, capable of detecting low defect concentrations, and resolves signals from various traps. The conventional DLTS system suffers from drawbacks, including the need for multiple temperature cycles, which can lead to poor device contact and thin film adhesion. Additionally, maintaining a consistent temperature environment for each measurement is challenging, resulting in low-quality data. To address these issues, we develop a microcontroller-based DLTS system. This system utilizes a capacitance meter and electronic circuits controlled by an Arduino-Due microcontroller. We have used Arduino-Due to generate the filling pulse, monitor the capacitance, temperature, data acquisition, timing control and signal processing. By conducting measurements within a single temperature scan, our system saves time, improves accuracy, and reduces experimental failures. We validate the innovative instrumentation using a gold-doped silicon p-n junction sample. Furthermore, we apply this microcontroller-based DLTS system to study deep-level defects in Mercury Telluride (HgTe) nanocrystal-based photovoltaic devices. We fabricate photovoltaic devices based on HgTe NCs/TiO2 and employ capacitance-voltage (C-V) and DLTS techniques to investigate and collect quantitative data on deep-level trap states. DLTS confirms the presence of interface trap states, while frequency-dependent capacitance measurements support the influence of charge storage in these nanocrystal-based heterostructures, offering insights for advanced device development. Using DLTS, we measure trap energy, capture cross-section, and concentration. These traps in the photovoltaic devices can act as recombination centres and effectively interact with valence and conduction bands. Poor device responsiveness is observed in the ITO/TiO2/HgTe/Au configuration due to inefficient photo charge extraction. To enhance device performance, we optimize hole and electron extractions by introducing a Molybdenum Oxide (MoO3) hole extraction layer. We investigate the effect of this contact layer on trap level formation in the FTO/TiO2/HgTe/MoO3/Au photovoltaic device using low-temperature I-V, C-V, C-F, and microcontroller-based DLTS measurements. The obtained trap energy levels are comparable to those of the ITO/TiO2/HgTe/Au device, indicating the presence of trap levels at the TiO2/HgTe interface and no significant impact of the MoO3 contact layer on trap formation. Our microcontroller-based DLTS system proves to be an efficient tool for determining defect levels in heterojunctions based on nanocrystals. Surface states at the HgTe nanocrystals and oxygen vacancies in TiO2 are identified as the main contributors to trap levels, primarily located at the TiO2/HgTe interface. To further confirm the origin of trap states, we fabricate an ITO/HgTe/Al Schottky junction and measure the defect level energy using low-temperature I-V and C-F measurements. The obtained energy values support trap levels resulting from surface reconstruction at the TiO2/HgTe heterojunction interface. Passivating these trap states is crucial for improving device effectiveness.

abstract: High-performance III-V semiconductors based on ternary alloys and superlattice systems are fabricated, studied, and compared for infrared optoelectronic applications. InAsBi is a ternary alloy near the GaSb lattice constant that is not as thoroughly investigated as other III-V alloys and that is challenging to produce as Bi has a tendency to surface segregate and form droplets during growth rather than incorporate. A growth window is identified within which high-quality droplet-free bulk InAsBi is produced and Bi mole fractions up to 6.4% are obtained. Photoluminescence with high internal quantum efficiency is observed from InAs/InAsBi quantum wells. The high structural and optical quality of the InAsBi materials examined demonstrates that bulk, quantum well, and superlattice structures utilizing InAsBi are an important design option for efficient infrared coverage. Another important infrared material system is InAsSb and the strain-balanced InAs/InAsSb superlattice on GaSb. Detailed examination of X-ray diffraction, photoluminescence, and spectroscopic ellipsometry data provides the temperature and composition dependent bandgap of bulk InAsSb. The unintentional incorporation of approximately 1% Sb into the InAs layers of the superlattice is measured and found to significantly impact the analysis of the InAs/InAsSb band alignment. In the analysis of the absorption spectra, the ground state absorption coefficient and transition strength of the superlattice are proportional to the square of the electron-hole wavefunction overlap; wavefunction overlap is therefore a major design parameter in terms of optimizing absorption in these materials. Furthermore in addition to improvements through design optimization, the optical quality of the materials studied is found to be positively enhanced with the use of Bi as a surfactant during molecular beam epitaxy growth. A software tool is developed that calculates and optimizes the miniband structure of semiconductor superlattices, including bismide-based designs. The software has the capability to limit results to designs that can be produced with high structural and optical quality, and optimized designs in terms of maximizing absorption are identified for several infrared superlattice systems at the GaSb lattice constant. The accuracy of the software predictions are tested with the design and growth of an optimized mid-wave infrared InAs/InAsSb superlattice which exhibits superior optical and absorption properties.
Dissertation/Thesis
Doctoral Dissertation Electrical Engineering 2016

碩士
臺灣大學
電子工程學研究所
98
We study the fabrication and the properties of InAsPSb/InAs heterojunction p-i-n (p-InAsPSb/i-InAs/n-InAs) photodetectors. Three structures with different i layer thickness of 0.75 μm (C2759), 1.5 μm (C2758), 2 μm (C2866) were grown by gas source molecular beam epitaxy, and fabricated in devices with four different areas. The responsivity at a wavelength of 3 μm at room temperature increases obviously when the i layer thickness is increased from 0.75 μm to 1.5 μm. But the devices with 2 μm i layer thickness have much lower responsivities because of the large lattice mismatch of the InAsPSb layer. 　　The best performance in our devices is the device with an i layer thickness of 1.5 μm and an area of 500 × 500 μm2. Responsivities at room temperature in the 0.7-1.64 A/W range were obtained in the 2-3.5 μm wavelength range, corresponding to external quantum efficiencies within 50-67 %. If the 65 % transmittance of the surface of the devices is considered, the internal quantum efficiency can be as high as 100 %. And a peak of detectivity of 5.4 × 109 cm-Hz1/2/W was obtained at the wavelength of 3.05 μm. The ideal R0A of our 1.5-um-i-layer samples is 0.77 Ω-cm2. The best detectivity is expected to be 1.67 × 1010 cmHz1/2/W at 3.05 μm with a 100 % quantum efficiency.

碩士
國防大學理工學院
電子工程碩士班
99
In this study, we have investigated the selective wet etching technology applied on quantum well infrared photodetector (QWIP) for optical property analysis. The study focused on two major issues: one is the accuracy improvement of the etching process for optical grating pattern and the other is the calculation for absolute responsivity. In addition, we also used the proposed high selectivity etching recipe to remove the FPA substrate to achieve the better thermal imaging. Because the etching depth of optical grating pattern is an important factor for the responsivity of quantum well infrared photodetector, we used selective wet-etching process with etching stop layer to make the etching depth of optical grating pattern more precise. The proposed method not only solves the problem that previous recipe doesn’t work because the depth of our design couldn’t be approached precisely by normal etching solutions but also enhances the spectral response for the QWIP device. Furthermore, we proposed the modified method to achieve the correction factor that converts the relative responsivity measured from Fourier Transform Infrared Spectrometer (FTIR) into the absolute responsivity because the absolute responsivity is an important parameter to assess the QWIP performance. Finally, we used the high selectivity etching recipe to remove the FPA substrate. It solves the problem that the thicker substrate would cause distortion of the optical crosstalk and the delamination between the FPA and ROIC due to thermal stress generated under cooling cycles to result in dead pixels and worse imaging.

博士
國立臺灣大學
電機工程學研究所
93
The growth mechanisms of the InAs QDs were investigated by using AFM, SEM, TEM and PL. Phase separation growth of InGaAs cap layer on InAs QDs was also observed. GaAs tends to fill up the valley between InAs QDs whereas InAs is forced to remain on the dots, which leads to longer emission wavelength. The effective quantum well model including strain was developed to calculate the energy levels inside the InAs QD and successfully interpreted the PL spectra. The stress mainly comes from the upper GaAs cap layer rather than the lower GaAs matrix. A QDIP with AlGaAs or InAlGaAs blocking layers was fabricated and analyzed. By introducing a 2 nm Al0.3Ga0.7As cap layer on 3 (2.2) ML InAs QDs, the high-performance narrow-bandwidth multicolor InAs/AlGaAs/GaAs QDIPs were successfully fabricated. The origins of the responses were explained. The negative differential conductance, temperature-dependent and TE-mode-enhanced responses were observed. The negative differential conductance is due to intervalley scatterings. The temperature-dependent response originates from the electronic mobility as a function of temperature. The enhanced TE-mode responses could be engineered by RTA and explained by the transition from the S-like ground state to the strain-induced splitting of P-like first excited states, and the RTA process changes the stress inside InAs QDs due to the bond breaking.

abstract: Photodetectors in the 1.7 to 4.0 μm range are being commercially developed on InP substrates to meet the needs of longer wavelength applications such as thermal and medical sensing. Currently, these devices utilize high indium content metamorphic Ga1-xInxAs (x > 0.53) layers to extend the wavelength range beyond the 1.7 μm achievable using lattice matched GaInAs. The large lattice mismatch required to reach the extended wavelengths results in photodetector materials that contain a large number of misfit dislocations. The low quality of these materials results in a large nonradiative Shockley Read Hall generation/recombination rate that is manifested as an undesirable large thermal noise level in these photodetectors. This work focuses on utilizing the different band structure engineering methods to design more efficient devices on InP substrates. One prospective way to improve photodetector performance at the extended wavelengths is to utilize lattice matched GaInAs/GaAsSb structures that have a type-II band alignment, where the ground state transition energy of the superlattice is smaller than the bandgap of either constituent material. Over the extended wavelength range of 2 to 3 μm this superlattice structure has an optimal period thickness of 3.4 to 5.2 nm and a wavefunction overlap of 0.8 to 0.4, respectively. In using a type-II superlattice to extend the cutoff wavelength there is a tradeoff between the wavelength reached and the electron-hole wavefunction overlap realized, and hence absorption coefficient achieved. This tradeoff and the subsequent reduction in performance can be overcome by two methods: adding bismuth to this type-II material system; applying strain on both layers in the system to attain strain-balanced condition. These allow the valance band alignment and hence the wavefunction overlap to be tuned independently of the wavelength cutoff. Adding 3% bismuth to the GaInAs constituent material, the resulting lattice matched Ga0.516In0.484As0.970Bi0.030/GaAs0.511Sb0.489superlattice realizes a 50% larger absorption coefficient. While as, similar results can be achieved with strain-balanced condition with strain limited to 1.9% on either layer. The optimal design rules derived from the different possibilities make it feasible to extract superlattice period thickness with the best absorption coefficient for any cutoff wavelength in the range.  
Dissertation/Thesis
M.S. Electrical Engineering 2013

博士
國立臺灣大學
電子工程學研究所
101
The Growth mechanism of the In(Ga)As quantum dots (QDs) and rings (QRs) are investigated by the atomic force microscopy, scanning electron microscopy and photoluminescence (PL). Different growth conditions are studied to obtain homogenous QDs and QRs. The uniformity is important especially for quantum dot (QDIPs) and quantum ring infrared photodetectors (QRIPs). For infrared photodetectors, two-color or multi-color, high temperature operation and long wavelength (Terahertz) detection must be achieved to have high performance in responsivity and detectivity. In order to achieve the goals, the surface plasmon combined with QDIP, NH3 plasma treatment passivation, the well in quantum dot stack (WD) structure and QR structures are adopted. The two-color QDIPs are fabricated successfully by the use of top metal contact perforated with the cross metal hole arrays. The periodic contact metal hole arrays play double roles, i.e., the top contact and the optical filter. Patterning with lattice constants a = 1.6 μm and a= 2.8 μm, the 4-6 μm and 8-12 μm wavelength ranges can be detected. Its detectivity can be increased up to 1.85 × 1011 cmHz1/2/W at 20 K and the background limited temperature (BLIP) is between 60-70 K. It can be applied to fabricate the focal plane array (FPA) To achieve high-temperature operation, the performance of AlGaAs/GaAs QWIP and InAs/GaAs QDIP with and without NH3 plasma treatment are investigated. It is demonstrated that the NH3 plasma treatment not only gets rid of the oxide defects such as Ga2O3, As2O3 and As2O5, but also prevents the formation of oxides on the GaAs surface when exposed to atmosphere for one month. It lowers the dark current of QWIP and QDIP. The peak responsivity of the QWIPs without NH3 plasma treatment is 0.48 A/W, and the detectivity is 3.13 × 109 cm-Hz1/2/ W at 1.5 V, and 60 K. However, the QWIP after the 10 minute NH3 plasma treatment exhibits a better performance. The highest operation temperature can be increased from 60 to 90 K. At 90 K, the peak responsivity of the NH3 treated QWIP is 1.25 A/W and the detectivity is 3.54 × 109 cm-Hz1/2/ W at 1.5 V. Similarly, the responsivity of the NH3 plasma treated QDIP enhances from 0.8 to 1.5 A/W at 10 K and from 0.06 to 0.09 A/W at 90 K under the bias of ± 1.5 V and 0.8 V, respectively. The operation temperature also increases from 90 to 140 K. It states the importance of passivation to enhance the device performance. Instead of lowering the dark current, a simple structure of WD-QDIP is proposed which can be operated at a high temperature (~230 K) easily. In traditional QDIPs, the carriers (electrons) are supplied from the top and bottom contacts. In order to achieve high temperature operation, various methods are applied to reduce the dark current. This new design adopts the opposite concept, a QW layer doped with Si to 1017/cm3 is inserted in the middle of a stack of 10 QDs layers to serves as a carrier injection layer to supply carriers to QDs layers quickly and sufficiently. The dark current is increased significantly, however, the photo current (PC) is increased even more. Therefore, the operation temperature can be raised to 230 K. This WD-QDIP achieves a responsivity of 0.046 A/W and the detectivity of 1.26 x 107 cmHz1/2/W under the bias of 0.4 V at 230 K. In addition, the carrier transportation mechanism in this WD-QDIP is studied to reveal the existence of two-channel system, the photovoltaic effect and the presence of the scattered electrons. These phenomena describe and prove how a WD-QDIP can be operated at high temperatures. In these discussion, the scattered QDs and the density of QDs are regarded as the key factors to high-temperature operations. For terahertz detection, an InAs/GaAs quantum ring infrared photodetector (QRIP) has been fabricated successfully. This photodetector demonstrates a cutoff wavelength at 175 μm (1.7 THz) and the detectivity of 1.3×107 cmHz1/2/W at 80 K under the bias of 80 mV. The precise control of the In(Ga)As ring height by capping GaAs layer thickness is responsible for extension of the detector response to terahertz range.

abstract: Optoelectronic and microelectronic applications of germanium-based materials have received considerable research interest in recent years. A novel method for Ge on Si heteroepitaxy required for such applications was developed via molecular epitaxy of Ge5H12. Next, As(GeH3)3, As(SiH3)3, SbD3, S(GeH3)2 and S(SiH3)2 molecular sources were utilized in degenerate n-type doping of Ge. The epitaxial Ge films produced in this work incorporate donor atoms at concentrations above the thermodynamic equilibrium limits. The donors are nearly fully activated, and led to films with lowest resistivity values thus far reported. Band engineering of Ge was achieved by alloying with Sn. Epitaxy of the alloy layers was conducted on virtual Ge substrates, and made use of the germanium hydrides Ge2H6 and Ge3H8, and the Sn source SnD4. These films exhibit stronger emission than equivalent material deposited directly on Si, and the contributions from the direct and indirect edges can be separated. The indirect-direct crossover composition for Ge1-ySny alloys was determined by photoluminescence (PL). By n-type doping of the Ge1-ySny alloys via P(GeH3)3, P(SiH3)3 and As(SiH3)3, it was possible to enhance photoexcited emission by more than an order-of-magnitude. The above techniques for deposition of direct gap Ge1-ySny alloys and doping of Ge were combined with p-type doping methods for Ge1-ySny using B2H6 to fabricate pin heterostructure diodes with active layer compositions up to y=0.137. These represent the first direct gap light emitting diodes made from group IV materials. The effect of the single defected n-i¬ interface in a n-Ge/i-Ge1-ySny/p-Ge1-zSnz architecture on electroluminescence (EL) was studied. This led to lattice engineering of the n-type contact layer to produce diodes of n-Ge1-xSnx/i-Ge1-ySny/p-Ge1-zSnz architecture which are devoid of interface defects and therefore exhibit more efficient EL than the previous design. Finally, n-Ge1-ySny/p-Ge1-zSnz pn junction devices were synthesized with varying composition and doping parameters to investigate the effect of these properties on EL.
Dissertation/Thesis
Doctoral Dissertation Chemistry 2016

Semiconductor devices based on III-V materials have been the focus of intense research due to their superior electron mobility and favorable energy direct bandgap which are applicable in infrared wavelength range optoelectronics and high speed electronic systems. The thesis presented here consists of two thrusts; the first focusing on infrared applications, and the second focusing on InP-based heterojunction bipolar transistors (HBTs). In the first thrust, we investigate type-II InAs/GaSb superlattice IR detector devices and the effect of substrate orientation on InSb and InAs nanostructure morphology. In the second thrust, we study InP-based high frequency HBTs. A low resistance InAs ohmic contact is demonstrated, and we presented along with a study of the crystalline qualities in GaAs0.5Sb0.5 films grown on tilted- axis InP substrates. Chapter 2 presents fabrication and characterization of two type-II superlattice structures with 15 monolayer (ML) InAs/12ML GaSb and 17ML InAs/7ML GaSb grown on GaSb (100) substrates by solid-source molecular beam epitaxy (MBE). The X-ray diffraction (XRD) measurements of both the 15ML InAs/12ML GaSb and 17MLInAs/7ML GaSb superlattices indicated excellent material and interface qualities. The cutoff wavelengths of 15ML InAs/12ML GaSb and 17ML InAs/7ML GaSb superlattices photodetectors were measured to be 6.6μm and 10.2μm, respectively. These different spectral ranges were achieved by growing alternating layers of varying thicknesses which allowed for bandgap engineering of the superlattices of InAs and GaSb. Lastly, a mid-IR type-II superlattice photodiode was demonstrated at 80K with a cutoff wavelength at 6.6µm. The device exhibited a near background limited performance (BLIP) detectivity at 80K and higher temperature operation up to 280K. In Chapter 3, we show that the (411) orientation, though not a naturally occurring surface, is a favorable orientation to develop a buffer layer into a super flat surface at a certain high growth temperature. The (411) surface is a combination of localized (311) and (511) surfaces but at a high growth temperature, adatoms can obtain enough energy to overcome the energy barrier between these localized (311) and (511) surfaces and form a uniform (411) surface with potential minima. This results in a super flat surface which is promising for high-density nanostructure growth. In this work, this is the first time that the highest InSb and InAs nanostructures density can be achieved on the (411) surface which is in comparison with the (100), (311), and (511) surfaces. Chapter 4 of this thesis addresses the use of an InAs layer as a low-resistance ohmic contact to InP-based heterostructure devices. Selective area crystal growth of InAs on a dielectric (Benzocyclobutene, BCB polymer) covered InP (100) substrate and direct growth of InAs on InP substrate were performed by MBE. Heavy doping of InAs using Te was carried out to determine the lowest sheet resistance. Based on scanning electron microscope (SEM) and XRD measurements, increasing substrate temperature from 210 ℃ to 350 ℃, led to an improvement in crystallinity from a polycrystalline layer to a single crystal layer with a corresponding improvement of surface morphology. Moreover, a narrow X-ray diffraction peak indicated full-relaxation of the inherent 3.3% lattice-mismatch in InAs/InP layers. Furthermore, around 290 ℃ a tradeoff was reached between crystallinity and optimized dopant incorporation of Te into InAs for the lowest sheet resistance. Lastly, Chapter 5 discusses the effect of substrate tilting on the material properties of MBE grown GaAsSb alloys closely lattice-matched to an InP substrate. InP(100) substrates tilted 0°off-(on-axis), 2°off-, 3°off-, and 4°off-axis were used for MBE growth; then the material qualities of GaAsSb epitaxial layers were compared using various techniques, including high resolution XRD, photoluminescence (PL) and transmission-line measurements (TLM). Substrate tilting improved the crystalline quality of the GaAsSb alloys, as shown by a narrower XRD linewidth and enhanced optical quality as evidenced by a strong PL peak. The results of TLM show that the lowest sheet resistance was achieved at a 2° off-axis tilt.

博士
臺灣大學
電子工程學研究所
96
The growth mechanisms of the In(Ga)As quantum rings (QRs) and its precursors InAs quantum dots (QDs) were investigated by using atomic force microscopy (AFM), transmission electron microscope (TEM) and photoluminescence (PL). The substrate cooling methods on the morphology of surface QDs were studied, it was discovered that turning off power immediately after growth could avoid variation in surface morphology of QDs significantly. Ripening and In adatoms migration results in size redistribution during the QD annealing time, and the elastic relaxation of QDs was also observed. Strain induced In adatoms aggregation to 3D InAs island by annealing was found when the InAs coverage is below critical thickness. The QDIPs with various size QDs were fabricated and analyzed. The detection peak of QDIPs was tailorable from 5 to 10 um. It is because the QD size influences the absorption band of QDIPs. During the growth of QR, dewetting phenomenon occurs when the GaAs capped on InAs QDs are annealed, the thickness of thin GaAs capped layer was sequentially increased to study the strain effect on the transformation of small to large InAs islands to ring structure, and the relationship between the optical properties and morphology was observed. The aspect ratio of InAs QD will affect the shape of In(Ga)As QR. Finally the In(Ga)As/GaAs quantum ring infrared photodetector are analyzed in detail. By employed a thin GaAs layer to tailor the cutoff wavelength of QRIP to 100 um, the terahertz QRIP was fabricated successfully. The mechanism responsible for the far infrared response was explained.