Дисертації з теми "Wind band gap Semiconductors"
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1
Dorji, Chencho. "Etude des propriétés des isolants liquides pour l’encapsulation des substrats d’électronique de puissance." Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALT022.
Анотація:
Les modules de puissance basés sur un semi-conducteur à large bande interdite ont le potentiel de résister à des températures élevées (température de jonction >> 200°C) et à des tensions élevées (tension de blocage de 10 kV) contrairement aux modules de puissance à base de silicium. Cependant, le gel de silicone, le matériau d'encapsulation le plus couramment utilisé dans les modules d'alimentation, ne peut pas fonctionner au-dessus de 200°C. De plus, les pannes électriques et les décharges partielles entraînent des dommages permanents au module d'alimentation. Dans ce travail, nous proposons un diélectrique liquide comme agent d'encapsulation potentiel qui pourrait avoir de meilleures performances électriques et thermiques que le gel de silicone. Nous avons effectué la caractérisation diélectrique de plusieurs liquides potentiels et développé un modèle de simulation de champ pour étudier le champ électrique au point triple dans les modules de puissance. Des mesures de décharges partielles ont été effectuées sous courant alternatif et à montée rapide avec différents substrats électroniques de puissance intégrés dans des diélectriques liquides. Nous avons également étudié la possibilité de refroidir des dispositifs de puissance avec une amélioration du transfert de chaleur EHD et réalisé des expériences supplémentaires sur le vieillissement thermique des liquides. Les résultats ont indiqué que les liquides peuvent potentiellement être utilisés comme encapsulants dans les modules de puissancePower modules based on wide band gap semiconductor has the potential to withstand high temperature (junction temperature >>200°C) and high voltage (blocking voltage of 10kV) contary to silicone based power module. However, silicone gel, the most commonly used encapsulant material in power modules cannot operatrate above 200°C. Moreover, electrical breakdown and partial discharge events results in permanent damage of the power module. In this work, we propose liquid dielectric as a potential encapsulant that may have better electrical and thermal performance than silicone gel. We did dielectric characterization of several potential liquids and developed field simulation model to study the electric field at triple point in power modules. Partial discharge measurements were made under AC and fast rise with different power electronic substrates embedded in liquid dielectrics. We also investigated the possibility of cooling power devices with EHD heat transfer enhancement and performed some supplementary experiments on thermal againg of liquids. The results indicated that liquids have potential to be used as encapsulant in power modules
2
Chan, Yung. "Optical functions of wide band gap semiconductors /." View the Table of Contents & Abstract, 2004. http://sunzi.lib.hku.hk/hkuto/record/B32021264.
3
Tirino, Louis. "Transport Properties of Wide Band Gap Semiconductors." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5210.
Анотація:
Transport Properties of Wide Band Gap Semiconductors
Louis Tirino III
155 pages
Directed by Dr. Kevin F. Brennan
The objective of this research has been the study of the transport properties and breakdown characteristics of wide band gap semiconductor materials and their implications on device performance. Though the wide band gap semiconductors have great potential for a host of device applications, many gaps remain in the collective understanding about their properties, frustrating the evaluation of devices made from these materials.
The model chosen for this study is based on semiclassical transport theory as described by the Boltzmann Transport Equation. The calculations are performed using an ensemble Monte Carlo simulation method. The simulator includes realistic, numerical energy band structures derived from an empirical pseudo-potential method. The carrier-phonon scattering rates and impact ionization transition rates are numerically evaluated from the electronic band structure. Several materials systems are discussed and compared. The temperature-dependent, high-field transport properties of electrons in gallium arsenide, zincblende gallium nitride, and cubic-phase silicon carbide are compared.
Since hole transport is important in certain devices, the simulator is designed to simulate electrons and holes simultaneously. The bipolar simulator is demonstrated in the study of the multiplication region of gallium nitride avalanche photodiodes.
4
Chan, Yung, and 陳勇. "Optical functions of wide band gap semiconductors." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B45015338.
5
Saadatkia, Pooneh. "Optoelectronic Properties of Wide Band Gap Semiconductors." Bowling Green State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1562379152593304.
6
Farahmand, Maziar. "Advanced simulation of wide band gap semiconductor devices." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/14777.
7
Kusch, Gunnar. "Characterization of low conductivity wide band gap semiconductors." Thesis, University of Strathclyde, 2016. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27392.
Анотація:
This thesis covers research on low electric conductivity wide band gap semiconductors of the group-III nitride material system. The work presented focussed on using multi-mode scanning electron microscope (SEM) techniques to investigate the luminescence properties and their correlation with surface effects, doping concentration and structure of semiconductor structures. The measurement techniques combined cathodoluminescence (CL) for the characterization of luminescence properties, secondary electron (SE) imaging for imaging of the morphology and wavelength dispersive X-ray (WDX) spectroscopy for compositional analysis. The high spatial resolution of CL and SE-imaging allowed for the investigation of nanometer sized features, whilst environmental SEM allowed the characterisation of low conductivity samples. The investigated AlxGa₁₋xN samples showed a strong dependence on the miscut of the substrate, which was proven to influence the surface morphology and the compositional homogeneity. Studying the influence of the AlxGa₁₋xN sample thickness displayed a reduced strain in the samples with increasing thickness as well as an increasing crystalline quality. The analysis of AlxGa₁₋xN:Si samples showed the incorporation properties of Si in AlxGa₁₋xN, the correlation between defect luminescence, Si concentration and resistivity as well as the influence of threading dislocations on the luminescence properties and incorporation of point defects. The characterization of UV-LED structures demonstrated that a change in the band structure is one of the main reasons for a decreasing output power in AlₓGa₁₋ₓN based UV-LEDs. In addition the dependence of the luminescence properties and crystalline quality of InxAl₁₋xN based UV-LEDs on various growth parameters (e.g. growth temperature, quantum well thickness) was investigated. The study of nanorods revealed the influence of the template on the compositional homogeneity and luminescence of InxAl₁₋xN nanorod LEDs. Furthermore,the influence of optical modes in these structures was studied and found to provide an additional engineering parameter for the design of nanorod LEDs.
8
Mickevičius, Jūras. "Carrier recombination in wide-band-gap nitride semiconductors." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2009~D_20091121_102304-00016.
Анотація:
The thesis is dedicated to carrier recombination investigations in wide-band-gap semiconductors and their structures. The complex experimental studies were performed by combining several different techniques. Carrier dynamics in GaN epilayers were investigated under extremely low and high excitation conditions. A new method for interpreting photoluminescence decay kinetics was suggested by interrelating luminescence and light-induced grating decay transients. The new approach for studies of yellow band in GaN was shown by linking the carrier lifetime with yellow band intensity. Two AlGaN epilayers grown by different novel growth techniques were compared and the factors limiting carrier lifetime were identified. Moreover, more evidence on alloy mixing and band potential fluctuations in AlGaN was provided by our study. Essential knowledge was attained about carrier dynamics in high-Al-content AlGaN/AlGaN multiple quantum well structures: the influence of built-in electric field and carrier localization on carrier dynamics. Most of the samples under study were grown by MEMOCVDTM growth technique, and our study confirmed the high potential of this innovative growth technique for improving material quality.Disertacija skirta krūvininkų rekombinacijos tyrimams plačiatarpiuose nitridiniuose puslaidininkiuose bei jų dariniuose. Kompleksiniai eksperimentiniai tyrimai buvo atlikti naudojant kelias skirtingas metodikas. Atlikti krūvininkų dinamikos GaN sluoksniuose tyrimai labai žemų ir aukštų sužadinimų sąlygomis. Pasiūlytas naujas liuminescencijos gesimo kinetikų interpretavimo metodas, siejant liuminescencijos ir šviesa indukuotų dinaminių gardelių kinetikas. Naujas požiūris į geltonosios liuminescencijos juostą GaN sluoksniuose leido susieti geltonosios liuminescencijos intensyvumą su krūvininkų gyvavimo trukme. Skirtingomis technologijomis augintų AlGaN sluoksnių palyginimas suteikė informacijos apie juostos potencialo fliuktuacijas bei krūvininkų gyvavimo trukmę ribojančius veiksnius AlGaN medžiagose. Atskleista naujų krūvininkų dinamikos daugialakštėse AlGaN/AlGaN kvantinėse duobėse ypatumų – vidinio elektrinio lauko bei kvantinės duobės pločio fliuktuacijų sąlygotos lokalizacijos įtaka krūvininkų dinamikai. Dauguma tirtų bandinių buvo auginti naudojant MEMOCVDTM technologiją ir tyrimai patvirtino šios technologijos potencialą siekiant pagerinti medžiagų kokybę.
9
Bellotti, E. (Enrico). "Advanced modeling of wide band gap semiconductor materials and devices." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/15354.
10
Lajn, Alexander. "Transparent rectifying contacts on wide-band gap oxide semiconductors." Doctoral thesis, Universitätsbibliothek Leipzig, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-102799.
Анотація:
Die vorliegenden Arbeit befasst sich mit der Herstellung und Charakterisierung von transparenten Metall-Halbleiter- Feldeffekttransistoren. Dazu werden im ersten Kapitel
transparente gleichrichtende Kontakte, basierend auf dem Konzept von Metalloxidkontakten, hergestellt und im Hinblick auf chemische Zusammensetzung des Kontaktmaterials, Barriereninhomogenität und Kompatibilität mit amorphen Halbleitern untersucht. Außerdem wird die
Anwendbarkeit der Kontakte als UV-Sensor studiert. Im zweiten Kapitel werden transparente leitfähige Oxide vorgestellt und insbesondere deren optische und elektrische Eigenschaften
in Abhängigkeit von den Herstellungsbedingungen studiert. Das dritte Kapitel beinhaltet Untersuchungen zu transparenten Feldeffektransistoren, die auf den im ersten Kapitel untersuchten transparenten gleichrichtenden Kontakten basieren (TMESFETs). Insbesondere die elektrischen Stabilität der Bauelemente hinsichtlich Beleuchtung, erhöhten Temperaturen und Spannungsstress wird untersucht. Auch die Langzeitstabilität, Reproduzierbarkeit und der
Effekt gepulster Spannungen wird betrachtet. Weiterhin wird die Verwendung amorpher Halbleiter im Kanal und damit auch die Herstellung flexibler Transistoren auf Folie demonstriert.
Zuletzt werden die TMESFETs integriert und als Inverterschaltkreise aufgebaut und untersucht. Außerdem wird die Eignung der Transistoren zur Messung von Aktionspotentialen von Nervenzellen studiert.
11
Harrison, Daniel. "Impact ionisation rate calculations in wide band gap semiconductors." Thesis, Durham University, 1998. http://etheses.dur.ac.uk/4651/.
Анотація:
Calculations of band-to-band impact ionisation rates performed in the semi-classical Fermi’s Golden Rule approximation are presented here for the semiconductors GaAs, In(_0.53)Ga(_0.47)As and Si(_0.5)Ge(_0.5) at 300K. The crystal band structure is calculated using the empirical pseudopotential method. To increase the speed with which band structure data at arbitrary k-vectors can be obtained, an interpolation scheme has been developed. Energies are quadratically interpolated on adapted meshes designed to ensure accuracy is uniform throughout the Brillouin zone, and pseudowavefunctions are quadratically interpolated on a regular mesh. Matrix elements are calculated from the pseudowavefunctions, and include the terms commonly neglected in calculations for narrow band gap materials and an isotropic approximation to the full wavevector and frequency dependent dielectric function. The numerical integration of the rate over all distinct energy and wavevector conserving transitions is performed using two different algorithms. Results from each are compared and found to be in good agreement, indicating that the algorithms are reliable. The rates for electrons and holes in each material are calculated as functions of the k-vector of the impacting carriers, and found to be highly anisotropic. Average rates for impacting carriers at a given energy are calculated and fitted to Keldysh-type expressions with higher than quadratic dependence of the rate on energy above threshold being obtained in all cases. The average rates calculated here are compared to results obtained by other workers, with reasonable agreement being obtained for GaAs, and poorer agreement obtained for InGaAs and SiGe. Possible reasons for the disagreement are investigated. The impact ionisation thresholds are examined and k-space and energy distributions of generated carriers are determined. The role of threshold anisotropy, variation in the matrix elements and the shape of the bands in determining characteristics of the rate, particularly the softness of the rate's threshold behaviour are investigated.
12
Kahn, Kevin. "Two-dimensional wide band gap semiconductors for deep UV photonics." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/48013.
Анотація:
Light emitters and detectors in the deep ultraviolet range (DUV) are of great current interest, with applications in water purification, solar-blind photodetectors and communication, biohazard detection, and phosphor-assisted white light emitters. However, DUV optoelectronics based on solid-state heterostructures suffer from low internal and external quantum efficiencies, due to issues relating to their fundamental material properties. These limitations motivate the exploration of new classes of materials for these applications. The recent emergence of two-dimensional (2D) materials has opened up new possibilities in this area, however 2D materials also bring new experimental challenges: particularly the deposition and characterisation of atomic layers, as well as scientific challenges, especially understanding how interactions between the 2D layer and the substrates and/or the environment may affect the properties of the 2D layer. In this thesis, the optical properties of promising materials for deep UV photonics are assessed using a combination of techniques, and the mathematical links between the resulting data are demonstrated. The first part of this work discusses the optical and structural properties of gallium nitride and its alloys, which are the foundation of current optoelectronics, and addresses the optical processes of freestanding and supported 2D hexagonal boron nitride (h-BN) as a potential candidate for high-efficiency deep UV optoelectronic devices. The objectives are to (i) confirm the validity of the models on well-known materials, (ii) determine whether h-BN is a good candidate for deep UV optoelectronics and (iii) whether and how interactions between 2D h-BN with substrates must be taken into consideration. The second part discusses the optical properties of barium zirconate titanate with changes in composition and dimensionality. The objectives are (i) to apply models developed for the nitrides to extract the bulk properties of these oxides, and (ii) to determine whether they are good candidates for deep UV optoelectronics in their 2D form.
13
Zhang, Shaolin. "Wide band gap nanomaterials and their applications." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B41758225.
14
Zhang, Shaolin, and 張少林. "Wide band gap nanomaterials and their applications." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B41758225.
15
Chen, Xinyi, and 陈辛夷. "Wide band-gap nanostructure based devices." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B49799290.
Анотація:
Wide band gap based nanostructures have being attracting much research interest because of their promise for application in optoelectronic devices. Among those wide band gap semiconductors, gallium nitride (GaN) and zinc oxide (ZnO) are the most commonly studied and optoelectronic devices based on GaN and ZnO have been widely investigated. This thesis concentrates on the growth, optical and electrical properties of GaN and ZnO nanostructures, plus their application in solar cells and light emitting diodes (LEDs).
GaN-nanowire based dye sensitized solar cells were studied. Different post-growth treatments such as annealing and coating with a TiOx shell were applied to enhance dye absorption. It was found that TiOx increased the dye absorption and the performance of the dye sensitized solar cell.
ZnO nanorods were synthesized by vapor deposition and electrodeposition. Post-growth treatments such as annealing and hydrothermal processing were used to modify the defect chemistry and optical properties. LEDs based on GaN/ZnO heterojunctions were studied. The influence of ZnO seed layers on GaN/ZnO LEDs was investigated. GaN/ZnO LEDs based on ZnO nanorods with MgO and TiOx shells were also prepared in order to modify the LED performance. The coating condition of the shell was found to influence the current-voltage (I-V) characteristics and device performance. Moreover, high brightness LEDs based on GaN with InGaN multiple quantum wells were also fabricated.
The origin of the emission from GaN/ZnO LEDs was studied using different kinds of GaN substrates. Direct metal contacts on bare GaN substrates were also employed to investigate the optical emission and electrical properties. It is found that the emission from the GaN/ZnO LEDs probably originated from the GaN substrate.
GaN/ZnO LEDs with MgO as an interlayer were also fabricated. The MgO layer was expected to modify the band alignment between the GaN and the ZnO. It was shown that GaN/MgO/ZnO heterojunctions (using both ZnO nanorods and ZnO films) have quite different emission performance under forward bias compared to those that have no MgO interlayer. An emission peak was around 400 nm could originate from ZnO.
Nitrogen doped ZnO nanorods on n-type GaN have been prepared by
electrodeposition. Zinc nitrate and zinc acetate were used as ZnO precursors and NH4NO3 was used as a nitrogen precursor. Only the ZnO nanorods made using zinc nitrate showed obvious evidence of doping and coherent I-V characteristics. Cerium doped ZnO based LEDs were fabricated and showed an emission that depended on the cerium precursor that was employed. This indicates that the choice of precursor influences the growth, the materials properties and the optical properties of ZnO.published_or_final_version
Physics
Doctoral
Doctor of Philosophy
16
Villeneuve, Alain. "Optical nonlinearities and applications of semiconductors near half the band gap." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/186035.
Анотація:
The nonlinear optical properties of bulk and quantum well semiconductor waveguides were measured as well as their time response near half the band gap. Experiments were performed on different semiconductors including the following bulk semiconductors GaAs, AlGaAs, InGaAlAs, and on GaAs/AlGaAs quantum well samples, to measure the two and three photon absorption, the free carrier cross section, and the nonlinear index of refraction. Also all-optical switching was demonstrated in a nonlinear directional coupler, and for the first time in a nonlinear X-switch. The switching exhibited high throughput, and the switching time is shorter than the 400 femtosecond pulses used in the experiment. A three photon figure of merit including the influence of nonlinear index, waveguide parameters, and three photon absorption was developed for a nonlinear directional coupler. This new figure of merit as well as the other figures of merit developed for all-optical switching are shown to be satisfied in AlGaAs when used below half the band gap.
17
Zacharias, Marios. "Optical properties of semiconductors at finite temperatures from first principles." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:4fad686d-c675-44e6-85c7-2725e6598ca5.
Анотація:
In this thesis we develop a new first-principles method for the calculation of optical absorption spectra and band structures in semiconductors and insulators at finite tem- peratures. The theoretical framework of our methodology originates back to 1950s in two pivotal research papers by F. Williams and M. Lax. Here, we expand the scope of the pioneering works by Williams and Lax, and we present a new theory of phonon- assisted optical absorption and temperature-dependent band structures. We demon- strate that our technique is highly efficient and simple to the point that a single calcu- lation is sufficient to capture temperature-dependent absorption coefficients including the effect of quantum zero-point motion. We report calculations of optical absorption spectra and of direct and indirect band gaps of Si, C, GaAs and MAPbI3 . We obtain good agreement with experiment and with previous calculations. The approach pro- posed in this thesis is highly versatile, and can straightforwardly be combined with improved descriptions of the dielectric function by including electron-hole effects via the Bethe-Salpeter and GW equations. In this thesis we also investigate the underly- ing mechanisms leading to the "inverse Varshni effect" in materials that belong to the family of metal halide perovskites. We show, using the example of MAPbI 3 , that the vibrational modes with metal-halide-metal bending or rocking character are the major cause of the band gap opening with increasing temperature. To this aim we present an approach for elucidating the physics underpinning the changes of the band gap with vibrational motion. Our methodologies developed in this thesis are simple to imple- ment in any electronic structure package as a post-processing step, having the potential to find broad applications in the ab-initio community. We anticipate that our work will open the way to predictive calculations, as well as will contribute to the better under- standing of the optoelectronic properties of solids at finite temperatures.
18
Okayama, Taizo. "Performance of devices made of large band-gap semiconductors, SiC and GaN." Fairfax, VA : George Mason University, 2007. http://hdl.handle.net/1920/2935.
Анотація:
Thesis (Ph. D.)--George Mason University, 2007.Title from PDF t.p. (viewed Jan. 21, 2008). Thesis director: Mulpuri V. Rao. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical and Computer Engineering. Vita: p. 128. Includes bibliographical references (p. 122-127). Also available in print.
19
Chakrapani, Vidhya. "Electrochemically Mediated Charge Transfer to Diamond and Other Wide Band Gap Semiconductors." Case Western Reserve University School of Graduate Studies / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=case1175795419.
20
Lim, Sang-Hyun. "Characterization of p-type wide band gap transparent oxide for heterojunction devices." Amherst, Mass. : University of Massachusetts Amherst, 2009. http://scholarworks.umass.edu/dissertations/AAI3359903/.
21
Shakya, Jagat B. "Micro/nano-photonic structures and devices of III-nitride wide band-gap semiconductors /." Search for this dissertation online, 2004. http://wwwlib.umi.com/cr/ksu/main.
22
NICHETTI, CAMILLA. "Development of avalanche photodiodes with engineered band gap based upon III-V semiconductors." Doctoral thesis, Università degli Studi di Trieste, 2021. http://hdl.handle.net/11368/2982139.
Анотація:
This thesis is striving in the development and performance assessment
of GaAs/AlGaAs avalanche photodiodes (APDs) with separated
absorption and multiplication regions, which complement existing
silicon detectors providing higher efficiency for X-ray detection. During
the course of this thesis several APDs were fabricated utilizing
molecular beam epitaxy and lithography and subsequently have been
thoroughly characterized. This thesis is subdivided into six chapters.
It sets in with a general description of APD structures and their functionalities
prescinding the advantages of the developed APDs, which
are fabricated on mesas with a diameter of 200μm and consists of
an absorption and multiplication region separated by a thin p-doped
layer of carbon. In particular the benefits on impact ionization and
charge multiplication when using a superlattice of some (6, 12, 24)
nanometric layers of GaAs/AlGaAs hetero-junctions are described,
which enhances the charge amplification of electrons while reducing
the multiplication of holes thus lowering the overall detector noise.
The second chapter deals with device simulation and points out the
limitations of the established local model to describe impact ionization
in thick multiplication regions. In order to simulate APDs with narrow
intrinsic areas a new and improved nonlocal history-dependent model
for gain and noise based on the energy balance equation has been
developed and is thoroughly described at the end of this chapter. The
materials and method section provides in the third chapter a comprehensive
description of the techniques and machinery employed during
the device manufacturing, while in the fourth chapter the experimental
setups, which were involved to test the devices are outlined. Both, the
used readout and acquisition electronics and the light/particle sources
are thoroughly described. In chapter 5 the different measurements
and associated datamining are presented and discussed. In particular
the role of different doping levels in the p-doped layers has been
deeply investigated revealing that a planar doping with the maximum
effective acceptor density is favored as it maximized the potential drop
in the multiplication region thus enhancing the impact ionization. Furthermore,
measurements and associated results of the time resolution
of the APDs utilizing visible table-top lasers and X-rays are described
in this section, revealing a rise time of 80 ps for the 24-step device.
A study of the noise versus gain behavior is present as well and is
compared to the results of the simulation. Moreover, utilizing a charge
sensitive amplifier both the spectroscopic capabilities and the charge
collection efficiency of the APDs could be determined by means of a
pulsed table-top laser and an Americium source. The thesis finishes
with the conclusions in chapter 6.
23
Sheridan, Liam A. "Alternative cadmium source precursors for the growth of cadmium sulphide and cadmium selenide by metal-organic chemical vapour deposition." Thesis, University of Reading, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339511.
24
Tirpak, Olena. "INFLUENCE OF ELECTRON TRAPPING ON MINORITY CARRIER TRANSPORT PROPERTIES OF WIDE BAND GAP SEMICONDUCTORS." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3278.
Анотація:
Minority carrier transport properties and the effects of electron irradiation/injection were studied in GaN and ZnO containing dopants known to form acceptor states deep within the materials' bandgap. Minority carrier diffusion length and lifetime changes were investigated using Electron Beam Induced Current (EBIC) method, cathodoluminescence spectroscopy, spectral photoresponse and persistent photoconductivity measurements. It is shown that electron irradiation by the beam of a scanning electron microscope results in a significant increase of minority carrier diffusion length. These findings are supported by the cathodoluminescence measurements that demonstrate the decay of near-band-edge intensity as a consequence of increasing carrier lifetime under continuous irradiation by the electron beam. Temperature-dependent measurements were used to determine the activation energies for the electron irradiation-induced effects. The latter energies were found to be consistent with the involvement of deep acceptor states. Based on these findings, the effects of electron irradiation are explained via the mechanism involving carrier trapping on these levels. Solid-state electron injection was also shown to result in a similar increase of minority carrier lifetime and diffusion length. Solid-state injection was carried out by applying the forward bias to a ZnO homojunction and resulted in a significant improvement of the peak photoresponse of the junction. This improvement was unambiguously correlated with the increase of the minority carrier diffusion length due to electron injection.Ph.D.
Department of Physics
Sciences
Physics PhD
25
McGlynn, Andrew G. "Optical and X-ray spectroscopy of wide band gap semiconductors and organic thin films." Thesis, Aberystwyth University, 2010. http://hdl.handle.net/2160/04bbda69-25aa-4feb-90e4-564dc66b3043.
Анотація:
This thesis reports upon synchrotron based luminescence studies of wide band gap semi-conductors and organic thin films. The optical and structural electronic properties of cubic and hexagonal boron nitride have been studied using X-ray Excited Optical Luminescence (XEOL) and Optically Detected X-ray Absorption Spectroscopy (OD-XAS). UV/visible emission was identified in both h-BN and c-BN with additional exciton related deep UV emission for the former. UV excited luminescence measurements were used to determine the band gap energies of h-BN and c-BN, these were found to be 5.96eV ± 0.04eV and 6.36eV ± 0.03eV respectively. Spatially resolved XEOL and OD-XAS was used to investigate c-BN microcrystals revealing lateral differences in luminescence and local structure. Synchrotron/laser pump probe spectroscopy was applied to investigate defect states in h-BN and c-BN. Subsequent correlation to the XEOL emission was made proving these defects states to be responsible for the lowest energy emission bands in both materials. Angular resolved NEXAFS, photo-luminescence (PL) and OD-XAS was used to characterise spin coated thin organic films of poly(phenylamine). The material was shown to exhibit preferred orientation within the film, but spatially resolved imaging OD-XAS revealed lateral variation in the molecular orientation. Electrospray deposition was developed for the growth of thin organic semiconducting films in ultra high vacuum. PL and OD-XAS studies were carried out on pure and mixed films of tetra sulfonated copper phthalocyanine (tsCuPc) and poly(ethyleneoxide) (PEO). Only the mixed complexes displayed infrared emission resulting from disstacking of the tsCuPc by the PEO within the film.
26
Schwarz, Casey Minna. "Radiation Effects on Wide Band Gap Semiconductor Transport Properties." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5488.
Анотація:
In this research, the transport properties of ZnO were studied through the use of electron and neutron beam irradiation. Acceptor states are known to form deep in the bandgap of doped ZnO material. By subjecting doped ZnO materials to electron and neutron beams we are able to probe, identify and modify transport characteristics relating to these deep accepter states. The impact of irradiation and temperature on minority carrier diffusion length and lifetime were monitored through the use of the Electron Beam Induced Current (EBIC) method and Cathodoluminescence (CL) spectroscopy. The minority carrier diffusion length, L, was shown to increase as it was subjected to increasing temperature as well as continuous electron irradiation. The near-band-edge (NBE) intensity in CL measurements was found to decay as a function of temperature and electron irradiation due to an increase in carrier lifetime. Electron injection through application of a forward bias also resulted in a similar increase of minority carrier diffusion length. Thermal and electron irradiation dependences were used to determine activation energies for the irradiation induced effects. This helps to further our understanding of the electron injection mechanism as well as to identify possible defects responsible for the observed effects. Thermal activation energies likely represent carrier delocalization energy and are related to the increase of diffusion length due to the reduction in recombination efficiency. The effect of electron irradiation on the minority carrier diffusion length and lifetime can be attributed to the trapping of non-equilibrium electrons on neutral acceptor levels. The effect of neutron irradiation on CL intensity can be attributed to an increase in shallow donor concentration. Thermal activation energies resulting from an increase in L or decay of CL intensity monitored through EBIC and CL measurements for p-type Sb doped ZnO were found to be the range of Ea = 112 to 145 meV. P-type Sb doped ZnO nanowires under the influence of temperature and electron injection either through continuous beam impacting or through forward bias, displayed an increase in L and corresponding decay of CL intensity when observed by EBIC or CL measurements. These measurements led to activation energies for the effect ranging from Ea = 217 to 233 meV. These values indicate the possible involvement of a SbZn-2VZn acceptor complex. For N-type unintentionally doped ZnO, CL measurements under the influence of temperature and electron irradiation by continuous beam impacting led to a decrease in CL intensity which resulted in an electron irradiation activation energy of approximately Ea = 259 meV. This value came close to the defect energy level of the zinc interstitial. CL measurements of neutron irradiated ZnO nanostructures revealed that intensity is redistributed in favor of the NBE transition indicating an increase of shallow donor concentration. With annealing contributing to the improvement of crystallinity, a decrease can be seen in the CL intensity due to the increase in majority carrier lifetime. Low energy emission seen from CL spectra can be due to oxygen vacancies and as an indicator of radiation defects.ID: 031001520; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Advisers: Elena Flitsiyan, Leonid Chernyak.; Title from PDF title page (viewed August 19, 2013).; Thesis (Ph.D.)--University of Central Florida, 2012.; Includes bibliographical references (p. 104-109).
Ph.D.
Doctorate
Physics
Sciences
Physics
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Ng, Beng Koon. "Impact ionization in wide band gap semiconductors : Alâ†xGaâ‚â†-â†xAs and 4H-SiC." Thesis, University of Sheffield, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251522.
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Jani, Omkar Kujadkumar. "Development of wide-band gap InGaN solar cells for high-efficiency photovoltaics." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/29627.
Анотація:
Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008.Committee Chair: Honsberg, Christiana; Committee Co-Chair: Ferguson, Ian; Committee Member: Citrin, David; Committee Member: Klein, Benjamin; Committee Member: Rohatgi, Ajeet; Committee Member: Snyder, Robert. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Gilzad, Kohan Mojtaba. "Plasmonic Effect of Metal Nanoparticles Deposited on Wide-Band Gap Metal Oxide Nanowire Substrate." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-64762.
Анотація:
The application of nanowires (NWs) in solar cells (SCs) is of great interest due to their new promising aspects established in nanoelectronics. Semiconductors associated with plasmonic metal nanoparticles (NPs) such as Silver (Ag), Gold (Au) and Copper (Cu), show enhanced performance in solid state light absorbing SCs owing to plasmonic characteristic of noble metal NPs. Plasmonic NPs presented a significant role in development of visible light harvesting for many applications such as photocatalytic materials, photodynamic in Surface Enhanced Raman Spectroscopy (SERS) and photovoltaics (PVs). Integration of plasmonic NPs in semiconductor materials have opened the routes to expand new PV systems with high efficiency light absorption. In this project, we introduce the synthesis ZnO and TiO2 NWs used as N-type semiconducting substrates and various methods for isolating plasmonic metal NPs, which are later deposited on the semiconducting substrates. Vertically aligned ZnO and TiO2 NWs arrays were grown on the fluorine-doped tin oxide (FTO) conductive glass substrates via hydrothermal method at low temperature and the plasmonic NPs were synthesized by wet chemistry procedures and finally decorated on the NW films by using electrophoretic deposition. The impact of metal NPs loaded on the ZnO and TiO2 NWs substrates was studied by means of UV-vis spectroscopy and Photoluminescence (PL) spectroscopy. The absorbance spectra of individual NPs were recorded. Remarkably, the reflectance spectra of produced samples presented an enhancement in light absorption of the substrates after uptake of NPs on the ZnO and TiO2 NWs. The optical properties of the as grown ZnO NWs films decorated with Ag NPs (I) in direct contact with substrate and (II) in presence of an Al2O3 insulating spacer layer have been investigated. Both systems exhibited an enhancement in the UV band-edge emission from the ZnO when excited at 325 nm. In contrast, the broad bend defect emission of the samples did not have a significant change compare to bare ZnO substrates. The observed results suggested that the ZnO and TiO2 NWs decorated with plasmonic nanoparticles can boost the optical properties of MOs NWs substrates and hence effectively enhance the separation of photoexcited electron-hole pairs and photo-conversion applications.
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Wang, Dake Park Minseo. "Optical spectroscopy of wide-band-gap semiconductors raman and photoluminescence of gallium nitride, zinc oxide and their nanostructures /." Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Fall/Dissertations/WANG_DAKE_24.pdf.
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Almoussawi, Batoul. "Semi-conducteurs innovants par ingénierie du band gap et manipulation anionique." Electronic Thesis or Diss., Université de Lille (2018-2021), 2021. https://pepite-depot.univ-lille.fr/LIBRE/EDSMRE/2021/2021LILUR043.pdf.
Анотація:
Les composés à anions mixtes peuvent permettre d'atteindre des structures et des propriétés inaccessibles dans le cas de phases mono-anionique, ce qui offre de nombreuses opportunités pour la recherche exploratoire de composés à anions mixtes fonctionnels. Un intérêt majeur de la présence d’anions multiples au sein d’une phase est l'ingénierie du band gap via les contributions des orbitales anioniques en haut de la bande de valence, permettant ainsi le contrôle de la structure électronique et des propriétés. De plus, les environnement hétéroleptiques autour d'un cation (entouré d'au moins deux types d'anions) permettent d'accentuer le caractère acentrique d'une entité structurale, et donc la polarité dans le cas d'un arrangement polaire par rapport à un analogue mono-anionique. Ces deux aspects combinés, c'est-à-dire l'ingénierie du band gap et le caractère acentrique local tous deux modulables avec plusieurs anions, sont puissants pour contrôler et exacerber diverses propriétés. Dans le but d'atteindre de tels environnements dans des phases innovantes à anions mixtes et d'étudier leurs propriétés physiques et chimiques, plusieurs séries de composés ont été formulées sur la base d’unités structurales à anions mixtes intéressantes et leurs synthèses ont été tentées. Dans ce travail, une grande variété de nouveaux systèmes sont présentés, y compris certains environnements peu répandus et propriétés remarquables : propriétés d’optique non linéaire, propriétés magnétiques et propriétés photoélectriques. Parmi ces composés, une grande série de nouveaux composés, dont Ba5(VO2S2)2(S2)2, caractérisés par des thiovanadates hétéroleptiques (VO2S2, VO3S, VOS3) et la présence de paires dichalcogénures sont décrits. À partir de ces éléments constitutifs, notre stratégie pour atteindre les phases polaires a été couronnée de succès avec l'un de ces composés présentant des propriétés d’optique non linéaires (SHG) intéressantes. Aussi, une série de phases polyvalentes halogénure-thiovanadates (halogénure = F, Cl et I) a également pu être développée et montre l'apparition d'un courant photoélectrique sous lumière visible. De plus, l’alignement des bandes calculées par rapport aux réactions d'évolution de H2 et O2 en fait des candidats potentiels pour la photocatalyse de l'eau sous lumière visible. D'autre part, le premier oxysulfure de type Fresnoite (polaire) aux propriétés SHG est également présenté. Enfin, des phases magnétiques ont également été développées comme le composé Ba10Fe7.75Zn5.25S18Si3O12 non centrosymétrique, avec des tétraèdres à anions mixtes (Fe/Zn)3O impliqués dans un cluster magnétique original qui forme l’unité structurale élémentaire. Ces séries de composés sont discutées en s’appuyant également sur des calculs DFT afin de fournir une compréhension de leurs relations structure-propriétés pour aider à concevoir davantage de matériaux à anions mixtes fonctionnelsMixed anions compounds may allow to reach structures and properties inaccessible in the case of single anion phases, which provide great opportunities for exploratory research of functional mixed anions compounds. One major interest of mixing anions in a phase is the band gap engineering by controlling the contribution of anionic orbitals at the top of the valence band, hence controlling the electronic structure and the properties. In addition, heteroleptic environments around a cation (directly surrounded by at least two types of anions) makes it possible to accentuate the acentric character of a structural entity, and therefore the polarity in the case of a polar arrangement comparing to a mono-anionic analogue. These two aspects combined, i.e. band gap engineering and local acentric character both reached with multiple anions, are powerful to control and exacerbate various properties. With the aim to reach such environments in innovative mixed anion phases and study their physical and chemical properties, several series of potential materials were formulated based on interesting mixed anion building blocks and their synthesis attempted. In this work, a wide variety of new systems are presented, including some unusual environments and properties: Non-linear optical properties, magnetic properties and photoelectric properties . Among these compounds, a large series of new compounds, including Ba5(VO2S2)2(S2)2, characterized by heteroleptic thiovanadates (VO2S2, VO3S, VOS3) and the presence of dichalcogenide pairs are described. From those building blocks, our strategy to reach polar phases was successful with one of those compounds showing interesting non-linear optical properties (SHG). Also, a series of versatile halide-thiovanadates phases (halide= F, Cl and I) could also be developed and proves the appearance of a photoelectric current under visible light. In addition, their calculated bands alignment with respect to H2 and O2 evolution reactions makes them potential candidates for photocatalysis of water-splitting under visible light. On another hand, the first Fresnoite oxysulfide (polar) with SHG properties is also presented. Finally, magnetic phases were also developed like the non-centrosymmetric Ba10Fe7.75Zn5.25S18Si3O12, with (Fe/Zn)3O mixed anion tetrahedra involved in an original large magnetic cluster as elementary block. Those series of compounds are discussed with combination of DFT calculations in order to deliver a comprehension of their structure-properties relationships to help further design functional mixed anion materials
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Lajn, Alexander [Verfasser], Marius [Akademischer Betreuer] Grundmann, Marius [Gutachter] Grundmann, and Thomas [Gutachter] Riedl. "Transparent rectifying contacts on wide-band gap oxide semiconductors / Alexander Lajn ; Gutachter: Marius Grundmann, Thomas Riedl ; Betreuer: Marius Grundmann." Leipzig : Universitätsbibliothek Leipzig, 2013. http://d-nb.info/1238242154/34.
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Colmenares, Juan. "Extreme Implementations of Wide-Bandgap Semiconductors in Power Electronics." Doctoral thesis, KTH, Elkraftteknik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-192626.
Анотація:
Wide-bandgap (WBG) semiconductor materials such as silicon carbide (SiC) and gallium-nitride (GaN) allow higher voltage ratings, lower on-state voltage drops, higher switching frequencies, and higher maximum temperatures. All these advantages make them an attractive choice when high-power density and high-efficiency converters are targeted. Two different gate-driver designs for SiC power devices are presented. First, a dual-function gate-driver for a power module populated with SiC junction field-effect transistors that finds a trade-off between fast switching speeds and a low oscillative performance has been presented and experimentally verified. Second, a gate-driver for SiC metal-oxide semiconductor field-effect transistors with a short-circuit protection scheme that is able to protect the converter against short-circuit conditions without compromising the switching performance during normal operation is presented and experimentally validated. The benefits and issues of using parallel-connection as the design strategy for high-efficiency and high-power converters have been presented. In order to evaluate parallel connection, a 312 kVA three-phase SiC inverter with an efficiency of 99.3 % has been designed, built, and experimentally verified. If parallel connection is chosen as design direction, an undesired trade-off between reliability and efficiency is introduced. A reliability analysis has been performed, which has shown that the gate-source voltage stress determines the reliability of the entire system. Decreasing the positive gate-source voltage could increase the reliability without significantly affecting the efficiency. If high-temperature applications are considered, relatively little attention has been paid to passive components for harsh environments. This thesis also addresses high-temperature operation. The high-temperature performance of two different designs of inductors have been tested up to 600_C. Finally, a GaN power field-effect transistor was characterized down to cryogenic temperatures. An 85 % reduction of the on-state resistance was measured at −195_C. Finally, an experimental evaluation of a 1 kW singlephase inverter at low temperatures was performed. A 33 % reduction in losses compared to room temperature was achieved at rated power.QC 20160922
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Ibraikulov, Olzhas. "Bulk heterojunction solar cells based on low band-gap copolymers and soluble fullerene derivatives." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAD046/document.
Анотація:
La structure chimique des semiconducteurs organiques utilisés dans les cellules photovoltaïques à base d’hétérojonction en volume peut fortement influencer les performances du dispositif final. Pour cette raison, une meilleure compréhension des relations structure-propriétés demeure cruciale pour l’amélioration des performances. Dans ce contexte, cette thèse fait état d'études approfondies du transport des charges, de la morphologie et des propriétés photovoltaïques sur de nouveaux copolymères à faible bande interdite. En premier lieu, l'impact de la position des chaînes alkyles sur les propriétés opto-électroniques et morphologiques a été étudié sur une famille de polymères. Les mesures du transport de charges ont montré que la planéité du squelette du copolymère influe sur l’évolution de la mobilité des charges avec la concentration de porteurs libres. Ce comportement suggère que le désordre énergétique électronique est fortement impacté par les angles de torsion intramoléculaire le long de la chaîne conjuguée. Un second copolymère à base d'unités accepteur de [2,1,3] thiadiazole pyridique, dont les niveaux d’énergie des orbitales frontières sont optimales pour l’application photovoltaïque, a ensuite été étudié. Les performances obtenues en cellule photovoltaïque sont très inférieures aux attentes. Des analyses de la morphologie et du transport de charge ont révélé que l’orientation des lamelles cristallines est défavorable au transport perpendiculaire au film organique et empêche ainsi une bonne extraction des charges photo-générées. Enfin, les propriétés opto-électroniques et photovoltaïques de copolymères fluorés ont été étudiées. Dans ce cas, les atomes de fluor favorisent la formation de lamelles orientées favorablement pour le transport. Ces bonnes propriétés nous ont permis d'atteindre un rendement de conversion de puissance de 9,8% avec une simple hétérojonction polymère:fullerèneThe chemical structure of organic semiconductors that are utilized in bulk heterojunction photovoltaic cells may strongly influence the final device performances. Thus, better understanding the structure-property relationships still remains a major task towards high efficiency. Within this framework, this thesis reports in-depth material investigations including charge transport, morphology and photovoltaic studies on various novel low band-gap copolymers. First, the impact of alkyl side chains on the opto-electronic and morphological properties has been studied on a series of polymers. Detailed charge transport investigations showed that a planar conjugated polymer backbone leads to a weak dependence of the charge carrier mobility on the carrier concentration. This observation points out that the intra-molecular torsion angle contributes significantly to the electronic energy disorder. Solar cells using another novel copolymer based on pyridal[2,1,3]thiadiazole acceptor unit have been studied in detail next. Despite the almost ideal frontier molecular orbital energy levels, this copolymer did not perform in solar cells as good as expected. A combined investigation of the thin film microstructure and transport properties showed that the polymers self-assemble into a lamellar structure with polymer chains being oriented preferentially “edge-on”, thus hindering the out-of-plane hole transport and leading to poor charge extraction. Finally, the impact of fluorine atoms in fluorinated polymers on the opto-electronic and photovoltaic properties has been investigated. In this case, the presence of both flat-lying and standing lamellae enabled efficient charge transport in all three directions. As a consequence, good charge extraction was possible and allowed us to achieve a maximum power conversion efficiency of 9.8%
35
Kakanakova-Georgieva, Anelia, Daniel Nilsson, Xuan Thang Trinh, Urban Forsberg, Son Tien Nguyen, and Erik Janzén. "The complex impact of silicon and oxygen on the n-type conductivity of high-Al-content AlGaN." Linköpings universitet, Halvledarmaterial, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-91731.
Анотація:
Issues of major relevance to the n-type conductivity of Al0.77Ga0.23N associated with Si and O incorporation, their shallow donor or deep donor level behavior, and carrier compensation are elucidated by allying (i) study of Si and O incorporation kinetics at high process temperature and low growth rate, and (ii) electron paramagnetic resonance measurements. The Al0.77Ga0.23N composition correlates to that Al content for which a drastic reduction of the conductivity of AlxGa1−xN is commonly reported. We note the incorporation of carbon, the role of which for the transport properties of AlxGa1−xN has not been widely discussed.
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Oyetunde, Temidayo Timothy. "Novel precursors for chalcogenide materials." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/novel-precursors-for-chalcogenide-materials(db26161b-217b-4ee1-9767-d8fb82dc608b).html.
Анотація:
Metal chalcogenides (sulfides, selenides and tellurides) are materials of current interest due to their peculiar properties such as optoelectronic, magnetooptic, thermoelectric and piezoelectric displays. These semiconducting materials have potential applications in solar cell devices, infrared detectors and ambient thermoelectric generators. Previously, these materials have been deposited by multiple-source precursor route with several problems associated with this technique. This work describes the synthesis of metal complexes (Zn, Cd, Fe, Ni, Pd, Pt) using the imidodichalcogenodiphosphinate ligand (Woollins ligand). Their thermal decomposition together with structural and spectroscopy analysis was carried out. The complexes were used as single source precursors for the deposition of cadmium selenide, cadmium phosphide, cadmium sulfide, zinc selenide, iron selenide and the tellurides of nickel, palladium, platinum and iron as thin films and powders. These were deposited by AACVD and pyrolysis. The deposited thin films and powders were characterised by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX), X-ray photoelectron spectroscopy (XPS) and superconducting quantum interference device (SQUID). The cadmium complexes [Cd{iPr2P(Se)NP(Se)iPr2}2] and [Cd{iPr2P(S)NP(Se)iPr2}2] deposited the mixture of hexagonal CdSe and monoclinic Cd2P3 films at the flow rate of 160 sccm at 475 and 500 °C. At the flow rate of 240 sccm, only hexagonal CdSe was deposited from [Cd{iPr2P(Se)NP(Se)iPr2}2] at all temperatures. Hexagonal CdS and the mixture of orthorhombic Cd6P7/cubic Cd7P10 were deposited from [Cd{iPr2P(S)NP(S)iPr2}2]. The zinc complexes [Zn{iPr2P(Se)NP(Se)iPr2}2] and [Zn{iPr2P(S)NP(Se)iPr2}2] both deposited cubic ZnSe at all temperatures with the flow rates of 160 and 240 sccm. The iron complexes [Fe{(SePPh2)2N}2] and [Fe{(SePPh2NPPh2S)2N}2] deposited orthorhombic FeSe2 mixed with monoclinic Fe3Se4 by pyrolysis at 500 and 550 °C. An unresolved pattern was observed from the complex [Fe{(SePPh2NPPh2S)2N}2] at 550 °C. XPS analysis of the deposited FeSe2 showed the surface oxidation of the material, while the magnetic measurements on the sample using SQUID confirmed its ferromagnetic properties. The telluride complexes of nickel, palladium, platinum and iron deposited the metal telluride respectively as: hexagonal NiTe, hexagonal PdTe, hexagonal PtTe2 (mixed with rhombohedral PtTe) and hexagonal FeTe2. Conductivity studies on NiTe and PdTe revealed them to be insulators, while the magnetic measurements on FeTe2 indicated its antiferromagnetic behaviour.
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Le, Thi mai hoa. "Microscopie de biréfringence et caractérisation de matériaux à grand gap." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI102.
Анотація:
Les matériaux semi-conducteurs à large bande interdite (WBG) tels que le carbure de silicium (SiC) et le diamant ont des propriétés matérielles exceptionnelles. De nombreuses applications peuvent bénéficier des semi-conducteurs WBG. Afin d'améliorer la qualité de ces matériaux, ainsi que pour augmenter leur gamme d'applications technologiques, il est nécessaire de diminuer ou réduire au minimum le nombre de défauts étendus.Ce travail de recherche a porté sur l'évaluation, la modélisation et le développement de techniques d'analyse s'appuyant sur l'utilisation de la microscopie optique. La thèse s'est focalisée sur l'identification des défauts structurels dans le carbure de silicium (SiC) et le diamant. Les défauts étendus dans des substrats 6H-SiC et du diamant ont été caractérisés par microscopie de biréfringence et les figures de biréfringence des différentes dislocations mesurées ont été modélisées.Dans le cas du SiC, un bon accord est obtenu entre théorie et expérience ce qui a amené à la détermination valide des vecteurs de Burgers et contraintes résiduelles d'arrière-plan. Presque toutes les dislocations observées étaient des dislocations verticales à caractère mixte. Parfois, leur orientation change résultant dans l'observation d'un motif de faible biréfringence. Nous avons comparé les données de biréfringence avec les gravures formées après attaque KOH. La combinaison des deux techniques est une façon de discriminer entre les dislocations vis pures et les dislocations mixtes ou coins.Les dislocations typiques dans du diamant monocristallin CVD ont été déterminées par mesure de biréfringence et quantitativement modélisées. Bien que les images simulées soient des approximations des observations expérimentales, les dislocations individuelles apparaissent comme étant des dislocations coins ou mixtes avec un possible vecteur de Burgers a/2 (011) ou a/2 (110). Parfois, les dislocations verticales peuvent se transformer en ligne horizontale ou inclinée, puis revenir à nouveau à la verticale résultant dans l'observation de deux figures de biréfringence séparées. La propagation de dislocations à partir du substrat HPHT dans la couche CVD a aussi été étudiée en analysant simultanément le substrat HPHT et la couche CVD dans la même région de l'échantillonWide band gap (WBG) semiconductor materials such as Silicon Carbide (SiC) and Diamond have outstanding material properties. Many applications can benefit from WBG semiconductors. In order to improve material quality as well as to increase the range of technological applications of the WBG semiconductor materials, it is necessary to decrease or minimize the number of extended defects.This research work deals with the assessment, modelling and development of analytical techniques based upon the use of optical microscopy. The thesis dedicated to the identification of structural defects in Silicon Carbide (SiC) and diamond materials. Extended defects in 6H-SiC wafer and diamond materials were characterized by birefringence microscopy. The measured birefringence patterns of individual dislocations modelled.In the case of SiC, a good agreement is obtained between theory and experiment, which led to the proper determination of the Burgers vector values and background residual stress. All observed dislocations were almost vertical dislocations with a mixed character. Sometimes, their orientation changes resulting in the observation of a faint birefringence pattern. We compared birefringence data with etch pits formed after KOH etching. Combining both techniques is a method to discriminate between pure screw dislocations and mixed or pure edge dislocations.Typical dislocations in single crystal CVD diamond were determined by birefringence measurement and quantitatively modelled. Although the simulated images only approximate the experimental ones, the individual dislocations are determined to be threading edge dislocations with a possible Burgers vector a/2(011) or a/2(110). Sometimes, the vertical dislocations can convert to a horizontal or slightly tilted line and then turn vertical again resulting in the observation of two separated birefringence patterns. The dislocation propagation from the HPHT substrate into the CVD layer has been investigated by simultaneously analysing the HPHT substrate and the CVD layer in the same sample region
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Huh, Suzanne Lynn. "Design of power delivery networks for noise suppression and isolation using power transmission lines." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42842.
Анотація:
In conventional design of power delivery networks (PDNs), the PDN impedance is required to be less than the target impedance over the frequency range of interest to minimize the IR drop and to suppress the inductive noise during data transitions. As a result, most PDNs in high-speed systems consist of power and ground planes to provide a low-impedance path between the voltage regulator module (VRM) and the integrated circuit (IC) on the printed circuit board (PCB).
For off-chip signaling, charging and discharging signal transmission lines induce return currents on the power and ground planes. The return current always follows the path of least impedance on the reference plane closest to the signal transmission line. The return current path plays a critical role in maintaining the signal integrity of the bits propagating on the signal transmission lines. The problem is that the disruption between the power and ground planes induces return path discontinuities (RPDs), which create displacement current sources between the power and ground planes. The current sources excite the plane cavity and cause voltage fluctuations. These fluctuations are proportional to the plane impedance since the current is drawn through the PDN by the driver. Therefore, low PDN impedance is required for power supply noise reduction.
Alternatively, methods of preventing RPDs can be used to suppress power supply noise. Using a power transmission line (PTL) eliminates the discontinuity between the power and ground planes, thereby preventing the RPD effects. In this approach, transmission lines replace the power plane for conveying power from the VRM to each IC on the PCB. The PTL-based PDN enables both power and signal transmission lines to be referenced to the same ground plane so that a continuous current path can be formed, unlike the power-plane-based PDN. As a result, a closed current loop is achieved, and the voltage fluctuation caused by RPDs is removed in idealistic situations. Without the RPD-related voltage fluctuation, reducing the PDN impedance is not as critical as in the power-plane-based approach. Instead, the impedance of the PTL is determined by the impedance of the signaling circuits.
To use the PTL-based PDN in a practical signaling environment, several issues need to be solved. First, the dc drop coming from the source termination of the PTL needs to be addressed. The driver being turned on and off dictates the current flow through the PTL, causing the dc drop to be dynamic, which depends on the data pattern. Second, impedance mismatch between the PTL and termination can occur due to manufacturing variations. Third, an increase in the number of PCB traces should be addressed by devising a method to feed more than one driver with one PTL. Lastly, the power required to transmit 1 bit of data should be optimized for the PTL by using a new signaling scheme and adjusting the impedance of the signaling circuit.
Constant flow of current through the PDN is one solution proposed to address the first two issues. Constant current removes the dynamic characteristics of the dc drop by inducing a fixed amount of dc drop over the PTL. Moreover, constant current keeps the PTL fully charged at all times, and thereby eliminates the process of repeatedly charging and discharging the power transmission line. The constant current PTL (CCPTL) scheme maintains constant current flow regardless of the input data pattern. Early results on the CCPTL scheme have been discussed along with the measurements. The CCPTL scheme severs the link between the current flowing through the PTL and the output data of the I/O driver connected to it. Also, it eliminates the charging and discharging process of the PTL, thereby completely eliminating power supply noise in idealistic situations.
To reduce any associated power penalty, a pseudo-balanced PTL (PBPTL) scheme is also proposed using the PTL concept. A pseudo-balanced (PB) signaling scheme, which uses an encoding technique to map N-bit data onto M-bit encoded data with fixed number of 1s and 0s, is applied. When the PB signaling scheme is combined with the PTL, the jitter performance improves significantly as compared to currently practiced design approach.
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Опанасюк, Анатолій Сергійович, Анатолий Сергеевич Опанасюк, Anatolii Serhiiovych Opanasiuk, Павло Вікторович Коваль, Павел Викторович Коваль, Pavlo Viktorovych Koval, Володимир Володимирович Косяк, et al. "Structural and optical-properties of CdTe and CdMnTe films." Thesis, Brookhaven National Laboratory, 2012. http://essuir.sumdu.edu.ua/handle/123456789/30130.
Анотація:
We undertook a detailed investigation of the structural- and optical-properties of CdTe- and Cd1-xMnxTe-semiconductor films deposited by close-spaced vacuum sublimation using thermal evaporation on non-oriented substrates. From our structural- and phase-analysis of the layers, we obtained information on their structure, deformations, grain size, and content of dislocations for films deposited at different substrate temperatures. We considered that despite the presence of defects in the crystals, the films offer promise for fabrication into x-ray detectors.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/30130
40
Kenyon, Eleazar Walter. "Low-noise circuitry for extreme environment detection systems implemented in SiGe BiCMOS technology." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44873.
Анотація:
This work evaluates two SiGe BiCMOS technology platforms as candidates for implementing extreme environment capable circuitry, with an emphasis on applications requiring high sensitivity and low noise.
In Chapter 1, applications requiring extreme environment sensing circuitry are briefly reviewed and the motivation for undertaking this study is outlined. A case is then presented for the use of SiGe BiCMOS technology to meet this need, documenting the benefits of operating SiGe HBTs at cryogenic temperatures. Chapter 1 concludes with a brief description of device radiation effects in bipolar and CMOS devices, and a basic overview of noise in semiconductor devices and electronic components.
Chapter 2 further elaborates on a specific application requiring low-noise circuitry capable of operating at cryogenic temperatures and proposes a number of variants of band-gap reference circuits for use in said system. Detailed simulation and theoretical analysis of the proposed circuits are presented and compared with measurements, validating the techniques used in the proposed designs and emphasizing the need for further understanding of device level low-temperature noise phenomena.
Chapter 3 evaluates the feasibility of using a SiGe BiCMOS process, whose response to ionizing radiation was previously uncharacterized, for use in unshielded electronic systems needed for exploration of deep space planets or moons, specifically targeting Europa mission requirements. Measured total ionizing dose (TID) responses for both CMOS and bipolar SiGe devices are presented and compared to similar technologies. The mechanisms responsible for device degradation are outlined, and an explanation of unexpected results is proposed.
Finally, Chapter 4 summarizes the work presented and understanding provided by this thesis, concluding by outlining future research needed to build upon this study and fully realize SiGe based extreme environment capable precision electronic systems.
41
Widmer, Johannes. "Charge transport and energy levels in organic semiconductors." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-154918.
Анотація:
Organic semiconductors are a new key technology for large-area and flexible thin-film electronics. They are deposited as thin films (sub-nanometer to micrometer) on large-area substrates. The technologically most advanced applications are organic light emitting diodes (OLEDs) and organic photovoltaics (OPV). For the improvement of performance and efficiency, correct modeling of the electronic processes in the devices is essential. Reliable characterization and validation of the electronic properties of the materials is simultaneously required for the successful optimization of devices. Furthermore, understanding the relations between material structures and their key characteristics opens the path for innovative material and device design. In this thesis, two material characterization methods are developed, respectively refined and applied: a novel technique for measuring the charge carrier mobility μ and a way to determine the ionization energy IE or the electron affinity EA of an organic semiconductor. For the mobility measurements, a new evaluation approach for space-charge limited current (SCLC) measurements in single carrier devices is developed. It is based on a layer thickness variation of the material under investigation. In the \"potential mapping\" (POEM) approach, the voltage as a function of the device thickness V(d) at a given current density is shown to coincide with the spatial distribution of the electric potential V(x) in the thickest device. On this basis, the mobility is directly obtained as function of the electric field F and the charge carrier density n. The evaluation is model-free, i.e. a model for μ(F, n) to fit the measurement data is not required, and the measurement is independent of a possible injection barrier or potential drop at non-optimal contacts. The obtained μ(F, n) function describes the effective average mobility of free and trapped charge carriers. This approach realistically describes charge transport in energetically disordered materials, where a clear differentiation between trapped and free charges is impossible or arbitrary. The measurement of IE and EA is performed by characterizing solar cells at varying temperature T. In suitably designed devices based on a bulk heterojunction (BHJ), the open-circuit voltage Voc is a linear function of T with negative slope in the whole measured range down to 180K. The extrapolation to temperature zero V0 = Voc(T → 0K) is confirmed to equal the effective gap Egeff, i.e. the difference between the EA of the acceptor and the IE of the donor. The successive variation of different components of the devices and testing their influence on V0 verifies the relation V0 = Egeff. On this basis, the IE or EA of a material can be determined in a BHJ with a material where the complementary value is known. The measurement is applied to a number of material combinations, confirming, refining, and complementing previously reported values from ultraviolet photo electron spectroscopy (UPS) and inverse photo electron spectroscopy (IPES). These measurements are applied to small molecule organic semiconductors, including mixed layers. In blends of zinc-phthalocyanine (ZnPc) and C60, the hole mobility is found to be thermally and field activated, as well as increasing with charge density. Varying the mixing ratio, the hole mobility is found to increase with increasing ZnPc content, while the effective gap stays unchanged. A number of further materials and material blends are characterized with respect to hole and electron mobility and the effective gap, including highly diluted donor blends, which have been little investigated before. In all materials, a pronounced field activation of the mobility is observed. The results enable an improved detailed description of the working principle of organic solar cells and support the future design of highly efficient and optimized devicesOrganische Halbleiter sind eine neue Schlüsseltechnologie für großflächige und flexible Dünnschichtelektronik. Sie werden als dünne Materialschichten (Sub-Nanometer bis Mikrometer) auf großflächige Substrate aufgebracht. Die technologisch am weitesten fortgeschrittenen Anwendungen sind organische Leuchtdioden (OLEDs) und organische Photovoltaik (OPV). Zur weiteren Steigerung von Leistungsfähigkeit und Effizienz ist die genaue Modellierung elektronischer Prozesse in den Bauteilen von grundlegender Bedeutung. Für die erfolgreiche Optimierung von Bauteilen ist eine zuverlässige Charakterisierung und Validierung der elektronischen Materialeigenschaften gleichermaßen erforderlich. Außerdem eröffnet das Verständnis der Zusammenhänge zwischen Materialstruktur und -eigenschaften einen Weg für innovative Material- und Bauteilentwicklung. Im Rahmen dieser Dissertation werden zwei Methoden für die Materialcharakterisierung entwickelt, verfeinert und angewandt: eine neuartige Methode zur Messung der Ladungsträgerbeweglichkeit μ und eine Möglichkeit zur Bestimmung der Ionisierungsenergie IE oder der Elektronenaffinität EA eines organischen Halbleiters. Für die Beweglichkeitsmessungen wird eine neue Auswertungsmethode für raumladungsbegrenzte Ströme (SCLC) in unipolaren Bauteilen entwickelt. Sie basiert auf einer Schichtdickenvariation des zu charakterisierenden Materials. In einem Ansatz zur räumlichen Abbildung des elektrischen Potentials (\"potential mapping\", POEM) wird gezeigt, dass das elektrische Potential als Funktion der Schichtdicke V(d) bei einer gegebenen Stromdichte dem räumlichen Verlauf des elektrischen Potentials V(x) im dicksten Bauteil entspricht. Daraus kann die Beweglichkeit als Funktion des elektrischen Felds F und der Ladungsträgerdichte n berechnet werden. Die Auswertung ist modellfrei, d.h. ein Modell zum Angleichen der Messdaten ist für die Berechnung von μ(F, n) nicht erforderlich. Die Messung ist außerdem unabhängig von einer möglichen Injektionsbarriere oder einer Potentialstufe an nicht-idealen Kontakten. Die gemessene Funktion μ(F, n) beschreibt die effektive durchschnittliche Beweglichkeit aller freien und in Fallenzuständen gefangenen Ladungsträger. Dieser Zugang beschreibt den Ladungstransport in energetisch ungeordneten Materialien realistisch, wo eine klare Unterscheidung zwischen freien und Fallenzuständen nicht möglich oder willkürlich ist. Die Messung von IE und EA wird mithilfe temperaturabhängiger Messungen an Solarzellen durchgeführt. In geeigneten Bauteilen mit einem Mischschicht-Heteroübergang (\"bulk heterojunction\" BHJ) ist die Leerlaufspannung Voc im gesamten Messbereich oberhalb 180K eine linear fallende Funktion der Temperatur T. Es kann bestätigt werden, dass die Extrapolation zum Temperaturnullpunkt V0 = Voc(T → 0K) mit der effektiven Energielücke Egeff , d.h. der Differenz zwischen EA des Akzeptor-Materials und IE des Donator-Materials, übereinstimmt. Die systematische schrittweise Variation einzelner Bestandteile der Solarzellen und die Überprüfung des Einflusses auf V0 bestätigen die Beziehung V0 = Egeff. Damit kann die IE oder EA eines Materials bestimmt werden, indem man es in einem BHJ mit einem Material kombiniert, dessen komplementärer Wert bekannt ist. Messungen per Ultraviolett-Photoelektronenspektroskopie (UPS) und inverser Photoelektronenspektroskopie (IPES) werden damit bestätigt, präzisiert und ergänzt. Die beiden entwickelten Messmethoden werden auf organische Halbleiter aus kleinen Molekülen einschließlich Mischschichten angewandt. In Mischschichten aus Zink-Phthalocyanin (ZnPc) und C60 wird eine Löcherbeweglichkeit gemessen, die sowohl thermisch als auch feld- und ladungsträgerdichteaktiviert ist. Wenn das Mischverhältnis variiert wird, steigt die Löcherbeweglichkeit mit zunehmendem ZnPc-Anteil, während die effektive Energielücke unverändert bleibt. Verschiedene weitere Materialien und Materialmischungen werden hinsichtlich Löcher- und Elektronenbeweglichkeit sowie ihrer Energielücke charakterisiert, einschließlich bisher wenig untersuchter hochverdünnter Donator-Systeme. In allen Materialien wird eine deutliche Feldaktivierung der Beweglichkeit beobachtet. Die Ergebnisse ermöglichen eine verbesserte Beschreibung der detaillierten Funktionsweise organischer Solarzellen und unterstützen die künftige Entwicklung hocheffizienter und optimierter Bauteile
42
Filsecker, Felipe. "Characterization and evaluation of a 6.5-kV silicon carbide bipolar diode module." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-217848.
Анотація:
This work presents a 6.5-kV 1-kA SiC bipolar diode module for megawatt-range medium voltage converters. The study comprises a review of SiC devices and bipolar diodes, a description of the die and module technology, device characterization and modelling and benchmark of the device at converter level. The effects of current change rate, temperature variation, and different insulated-gate bipolar transistor (IGBT) modules for the switching cell, as well as parasitic oscillations are discussed. A comparison of the results with a commercial Si diode (6.5 kV and 1.2 kA) is included. The benchmark consists of an estimation of maximum converter output power, maximum switching frequency, losses and efficiency in a three level (3L) neutral point clamped (NPC) voltage-source converter (VSC) operating with SiC and Si diodes. The use of a model predictive control (MPC) algorithm to achieve higher efficiency levels is also discussed. The analysed diode module exhibits a very good performance regarding switching loss reduction, which allows an increase of at least 10 % in the output power of a 6-MVA converter. Alternatively, the switching frequency can be increased by 41 %.
43
Goksen, Kadir. "Optical Properties Of Some Quaternary Thallium Chalcogenides." Phd thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609442/index.pdf.
Анотація:
Optical properties of Tl4In3GaSe8, Tl4InGa3Se8, Tl4In3GaS8, Tl2InGaS4 and Tl4InGa3S8 chain and layered crystals were studied by means of photoluminescence (PL) and transmission-reflection experiments. Several emission bands were observed in the PL spectra within the 475-800 nm wavelength region. The results of the temperature- and excitation intensity-dependent PL measurements in 15-300 K and 0.13×10-3-110.34 W cm-2 ranges, respectively, suggested that the observed bands were originated from the recombination of electrons with the holes by realization of donor-acceptor or free-to-bound type transitions. Transmission-reflection measurements in the wavelength range of 400-1100 nm revealed the values of indirect and direct band gap energies of the crystals studied. By the temperature-dependent transmission measurements in 10-300 K range, the rates of change of the indirect band gap of the samples with temperature were found to be negative. The oscillator and dispersion energies, and zero-frequency refractive indices were determined by the analysis of the refractive index dispersion data using the Wemple&ndash
DiDomenico single-effective-oscillator model. Furthermore, the structural parameters of all crystals were defined by the analysis of X-ray powder diffraction data. The determination of the compositional parameters of the studied crystals was done by energy dispersive spectral analysis experiments.
44
Ebenhoch, Bernd. "Organic solar cells : novel materials, charge transport and plasmonic studies." Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/7814.
Анотація:
Organic solar cells have great potential for cost-effective and large area electricity production, but their applicability is limited by the relatively low efficiency. In this dissertation I report investigations of novel materials and the underlying principles of organic solar cells, carried out at the University of St Andrews between 2011 and 2015. Key results of this investigation: • The charge carrier mobility of organic semiconductors in the active layer of polymer solar cells has a rather small influence on the power conversion efficiency. Cooling solar cells of the polymer:fullerene blend PTB7:PC₇₁BM from room temperature to 77 K decreased the hole mobility by a factor of thousand but the device efficiency only halved. • Subphthalocyanine molecules, which are commonly used as electron donor materials in vacuum-deposited active layers of organic solar cells, can, by a slight structural modification, also be used as efficient electron acceptor materials in solution-deposited active layers. Additionally these acceptors offer, compared to standard fullerene acceptors,advantages of a stronger light absorption at the peak of the solar spectrum. • A low band-gap polymer donor material requires a careful selection of the acceptor material in order to achieve efficient charge separation and a maximum open circuit voltage. • Metal structures in nanometer-size can efficiently enhance the electric field and light absorption in organic semiconductors by plasmonic resonance. The fluorescence of a P3HT polymer film above silver nanowires, separated by PEDOT:PSS, increased by factor of two. This could be clearly assigned to an enhanced absorption as the radiative transition of P3HT was identical beside the nanowires. • The use of a processing additive in the casting solution for the active layer of organic solar cells of PTB7:PC₇₁BM strongly influences the morphology, which leads not only to an optimum of charge separation but also to optimal charge collection.
45
Lajn, Alexander. "Transparent rectifying contacts on wide-band gap oxide semiconductors." Doctoral thesis, 2012. https://ul.qucosa.de/id/qucosa%3A11820.
Анотація:
Die vorliegenden Arbeit befasst sich mit der Herstellung und Charakterisierung von transparenten Metall-Halbleiter- Feldeffekttransistoren. Dazu werden im ersten Kapitel
transparente gleichrichtende Kontakte, basierend auf dem Konzept von Metalloxidkontakten, hergestellt und im Hinblick auf chemische Zusammensetzung des Kontaktmaterials, Barriereninhomogenität und Kompatibilität mit amorphen Halbleitern untersucht. Außerdem wird die
Anwendbarkeit der Kontakte als UV-Sensor studiert. Im zweiten Kapitel werden transparente leitfähige Oxide vorgestellt und insbesondere deren optische und elektrische Eigenschaften
in Abhängigkeit von den Herstellungsbedingungen studiert. Das dritte Kapitel beinhaltet Untersuchungen zu transparenten Feldeffektransistoren, die auf den im ersten Kapitel untersuchten transparenten gleichrichtenden Kontakten basieren (TMESFETs). Insbesondere die elektrischen Stabilität der Bauelemente hinsichtlich Beleuchtung, erhöhten Temperaturen und Spannungsstress wird untersucht. Auch die Langzeitstabilität, Reproduzierbarkeit und der
Effekt gepulster Spannungen wird betrachtet. Weiterhin wird die Verwendung amorpher Halbleiter im Kanal und damit auch die Herstellung flexibler Transistoren auf Folie demonstriert.
Zuletzt werden die TMESFETs integriert und als Inverterschaltkreise aufgebaut und untersucht. Außerdem wird die Eignung der Transistoren zur Messung von Aktionspotentialen von Nervenzellen studiert.
46
Liang, Yi-Hsiang, and 梁逸翔. "Optical properties of wide band gap semiconductors SiNx and ZnO." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/53362155734262519468.
Анотація:
碩士國立東華大學
材料科學與工程學系
94
Optical properties of the gap states in amorphous silicon nitride film deposited on GaAs (a-SiNx/GaAs) are characterized using piezoreflectance (PzR) and photoreflectance (PR) measurements at 15 and 300 K. The defect-state transitions of a-SiNx in both PR and PzR are temperature insensitive with respect to the direct band gaps of GaAs and silicon nitride. The temperature-insensitive behavior is an intrinsic character of an imperfection state existed in the middle gap of a semiconductor. Transition energies of all the gap-state transitions of a-SiNx/GaAs are analyzed by detailed line-shape fits to the PzR spectra. The origins of the gap-state transitions are properly assigned. Based on the experimental results together with previous density-of-states (DOS) calculations, an experimental band scheme including the transition assignments of the experimental gap states for a-SiNx/GaAs is constructed. Optical properties of the band-edge transitions of a ZnO film deposited on silicon substrate (ZnO/Si) are characterized using thermoreflectance (TR) measurements in the temperature range between 35 and 340 K. The TR spectrum of the zinc oxide film clearly shows a lot of transition features present at energies near 3.4 eV at 35 K. The observed TR features correspond to the A, B, and C excitonic series in the wurtzite ZnO. Transition energies of the A, B, C excitonic series are analyzed. The Rydberg constant and threshold energy for each A, B, and C excitonic series are determined. Temperature dependences of the transition energies of the A, B, and C series are analyzed. The parameters that describe the temperature variations of the excitonic transitions in the ZnO film are evaluated and discussed.
47
"Transition Metal Impurities in Semiconductors: Induced Magnetism and Band Gap Engineering." Thesis, 2013. http://hdl.handle.net/10388/ETD-2013-08-1158.
Анотація:
The main subject of this thesis is the study of electronic and magnetic properties of materials containing 3d transition metal atoms. Our motivation stems mainly from the modern fields of spintronic computing and solar energy conversion. The two primary goals of this work are to determine (i) why certain transition metal impurities in certain semiconductors can induce magnetic properties suitable for spintronic computing applications, and (ii) how transition metal impurities can be used to modify the electronic band gaps of semiconductors and insulators in ways useful for harnessing solar energy and for other applications.
To accomplish these goals, we have applied both experimental and theoretical tools. We studied high quality materials prepared by advanced synthesis techniques using x-ray spectroscopy methods at synchrotron light sources. The results of these experiments were interpreted using a variety of theoretical techniques, primarily using computational software developed as part of this thesis and discussed herein.
Regarding the study of introducing transition metal impurities into semiconductors to induce magnetic properties, we first developed and demonstrated a method to determine the location of impurity atoms within the host semiconductor lattice. This allowed to us explain the presence and absence of ferromagnetism in samples prepared under only slightly different synthesis conditions, which helped to address some long--standing issues in the spintronics field. We then studied an advanced and promising material -- indium (III) oxide with iron impurities -- to determine how magnetic ordering was maintained up to room temperatures. Our techniques unveiled that a portion of the iron atoms were coupled to oxygen vacancies in the material to create conditions which propelled the observed magnetism. This finding confirmed some earlier theoretical predictions by others in the field.
For the study of electronic band gap modifications in semiconductors and insulators via the incorporation of transition metal atoms, we investigated a wide range of materials synthesized using different techniques. Again, we used experimental techniques to determine the location of impurity atoms within the materials, and used this to understand how band gaps were modified upon the introduction of the impurities. For Ti implantation into SiO2, Ni substitution into ZnO, and a new material, MnNCN, we have determined the electronic band gaps and used our techniques to explain how the values for the gaps arise.
Finally, an additional outcome of this thesis work is a software program capable of simulating x-ray spectra using various advanced quantum models. We rewrote and built upon powerful existing programs and applied the result to the above studies. Our software was further applied in a collaborative effort with other researchers at the Canadian Light Source to study the differences in two experimental techniques for measuring x-ray absorption: partial and inverse partial fluorescence yields. By using the proper absorption and scattering formalisms to simulate each technique, we were able to explain the differences between the experimental spectra obtained from each. We explain fluorescence yield deviations using an analysis based on the spin configuration of different states, suggesting that the technique can be further extended as a quantitative spin state probe. These results could have significant implications for the field of soft x-ray absorption spectroscopy.
48
Hsun, Hsieh Chang, and 謝昌勳. "Surface Photovoltage and Modulation Spectroscopic Characterization of Wide Band Gap Semiconductors." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/35091270087394515880.
Анотація:
博士國立臺灣科技大學
電子工程系
91
In this thesis, the wide band-gap materials of IV-IV-V SiCN, III-V GaN, and II-VI ZnCdSe thin films are studied using the techniques of piezoreflectance (PzR), contactless electroreflectance (CER), and surface photovoltage spectroscopy (SPS). SiCN thin films deposited on the Si substrate were grown by the electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) method. The experimental PzR spectra of the SiCN films show the energy blue-shift behavior with the increase of the carbon/silicon composition ratio. Temperature dependence of the transition features in SiCN is analyzed using Varshni and Bose-Einstein relations. The fitting parameters are evaluated and discussed. GaN thin films were grown on various substrates of Al2O3 and Si by MOCVD. The thin films were characterized using CER and SPS measurements in temperature range between 15 and 500 K. The SPS experiments are implemented to facilitate the identification of energy positions of transition features in CER spectra. Temperature dependence of the transition features of the GaN films is analyzed. The parameters that describe the temperature variation of the transition energies and broadening function are evaluated and discussed. The temperature dependent spectral analyses indicate that compressive-type stress existed in our GaN film grown on sapphire substrate while the tensile-type strain will occur in the epilayer which deposited on silicon substrate. Temperature dependence of the band-edge transitions of three (Zn0.38Cd0.62)1-xBexSe II-VI films with different Be compositions x is studied using contactless electroreflectance (CER) in the temperature range of 15 to 450 K. The CER spectra of Be incorporated samples present an energy blue-shift behavior and a broadened line-shape character with respect to the ZnCdSe specimen. The identification of light-hole (LH) and heavy-hole (HH) characters of the excitonic transitions of the samples has been accomplished using strain modulated piezoreflectance (PzR) measurements. The temperature dependence analysis yields information on the parameters that describe the temperature variations of energy (including thermal expansion effects) and broadening function of the band-edge transitions of ZnCdBeSe. The study shows that Be incorporation can effectively reduce the rate of temperature variation of the energy gap.
49
Lien, Siou-Cheng. "Raman Studies of Wide Band Gap Semiconductors: GaN, InGaN and SiC." 2007. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-3007200720531800.
50
Vetter, Ulrich. "Lanthanide Doped Wide Band Gap Semiconductors: Intra-4f Luminescence and Lattice Location Studies." Doctoral thesis, 2003. http://hdl.handle.net/11858/00-1735-0000-0006-B555-B.