Academic literature on the topic 'InAs QDs on silicon'

The epitaxy of III-V semiconductors on silicon substrates remains challenging because of lattice parameter and material polarity differences. In this work, we report on the Metal Organic Chemical Vapor Deposition (MOCVD) and characterization of InAs/GaAs Quantum Dots (QDs) epitaxially grown on quasi-nominal 300 mm Ge/Si(001) and GaAs(001) substrates. QD properties were studied by Atomic Force Microscopy (AFM) and Photoluminescence (PL) spectroscopy. A wafer level µPL mapping of the entire 300 mm Ge/Si substrate shows the homogeneity of the three-stacked InAs QDs emitting at 1.30 ± 0.04 µm at room temperature. The correlation between PL spectroscopy and numerical modeling revealed, in accordance with transmission electron microscopy images, that buried QDs had a truncated pyramidal shape with base sides and heights around 29 and 4 nm, respectively. InAs QDs on Ge/Si substrate had the same shape as QDs on GaAs substrates, with a slightly increased size and reduced luminescence intensity. Our results suggest that 1.3 μm emitting InAs QDs quantum dots can be successfully grown on CMOS compatible Ge/Si substrates.

As an ideal single-photon source, quantum dots (QDs) can play a unique role in the field of quantum information. Controlling QD exciton spontaneous emission can be achieved by anti-phase coupling between QD exciton dipole field and Au dipole field after QD film has been transferred onto the Si substrate covered by Au nanoparticles. In experiment, the studied InAs/GaAs QDs are grown by molecular beam epitaxy (MBE) on a (001) semi-insulation substrate. The films containing QDs with different GaAs thickness values are separated from the GaAs substrate by etching away the AlAs sacrificial layer and transferring the QD film to the silicon wafer covered by Au nanoparticles with a diameter of 50 nm. The distance <i>D</i> (thickness of GaAs) from the surface of the Au nanoparticles to the QD layer is 10, 15, 19, 25, and 35 nm, separately. A 640-nm pulsed semiconductor laser with a 40-ps pulse length is used to excite the QD samples for measuring QD exciton photoluminescence and time-resolved photoluminescence spectra at 5 K. It is found that when the distance <i>D</i> is 15–35 nm the spontaneous emission rate of exciton is suppressed. And when <i>D</i> is close to 19 nm, the QD spontaneous emission rate decreases to <inline-formula><tex-math id="M2">\begin{document}$ ~{10}^{-3} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20211863_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20211863_M2.png"/></alternatives></inline-formula>, which is consistent with the theoretical calculations. The physical mechanism of long-lived exciton luminescence observed in experiment lies in the fact that Au nanoparticles scatter the light field of the exciton radiation in the QD wetting layer, and the phase of the scattered field is opposite to the phase of the exciton radiation field. Therefore, the destructive interference between the exciton radiation field and scattering field of Au nanoparticles results in long-lived exciton emission observed in experiment.

Optical communication wavelength emissions from the quantum dots (QDs) structures prepared on (001)-oriented GaAs substrates are discussed. A new growth technique of low-stressed InAs QDs on the AlGaSb layer in a low lattice-mismatched (1.3%) InAs/AlGaSb system is presented. The average height and diameter of the 4-ML InAs QDs on AlGaSb are evaluated to 5.8 nm and 45.2 nm respectively with an average density of 2.18 x 1010 /cm2 using atomic force microscope (AFM) measurements. There is structural selectivity between the QDs layer and the flat hetero-interface under changing growth conditions in the InAs/AlGaSb system. Long-wavelength PL emissions around 1.3 µm and 1.55 µm can be achieved by embedding InAs QDs in AlGaSb layers. Therefore it is expected that low-stressed InAs QDs grown on a AlGaSb layer prepared on a GaAs substrate will be useful in the fabrication of novel QDs devices for optical-communication networks.

InAs QDs were grown by supplying 2.5 mono-layers (MLs) of InAs at 500 °C in a molecular beam epitaxial (MBE) system. The QDs are approximately 4–6 nm height with an areal density of 3×85 ×1010 cm−2 for single layer QDs. Typical diameter was found to be about 15–25 nm. InAs QDs were stacked with the spacer layer thickness of 5, 10, 15, 25 and 35 nm. For 15 nm of spacer layer thickness the QDs density decreased to 2.62×1010 cm−2 and again increased for 35 nm spacer layer and reached to the value of 3.65×1010 cm−2. The 14 K photoluminescence (PL) spectra of single layer InAs QDs covered by GaAs layer centered at 1079 nm. For the stacking of InAs QDs with spacer layer thickness of 5 and 10 nm another peak appeared around 1100 nm due to size broadening of QDs because of strain propagation to next layer due to less thickness of spacer layer. When the thickness of the spacer layer increased to 35 nm the peak position is around 1073 nm and the intensity increased more than 3 fold when compare to single layer QDs.

The influences of a thin InGaAs layer grown on GaAs(100) substrate before deposited InAs self-assembled quantum dots(SAQDs) were experimentally investigated. Scanning electronic microscope (SEM) measurements show that the InGaAs strained layer may release the strain between wetting layer and QDs, and then enlarge size of QDs. When the thickness of InAs layer is small, the QDs are chained. Temperature dependent photoluminescence (TDPL) measurements show that the PL peaks of InAs QDs with In0.1Ga0.9As show much more red shift compared with the QDs directly deposited on GaAs matrix, and PL integral intensity enhances as T rises from 50K to 90K. We attribute this enhancement to the small potential barrier between WL and QDs produced by the InGaAs stained layer.

We present the effect of post-implantation annealing conditions on the structural and optical quality of InAs quantum dots (QDs) grown by combination of focused ion beam (FIB) and molecular beam epitaxy (MBE) approach. A FIB of Ga + ion was employed to pattern a homogeneously GaAs buffer layers and then, an in situ annealing step followed by InAs deposition was performed. Three different post-implantation annealing conditions were tested and under well-optimized conditions, a dislocation and defect-free InAs QDs growth on FIB patterned surface was successfully achieved. Furthermore, using photoluminescence (PL) study, we demonstrate that our best sample shows almost similar optical quality as MBE grown QDs on unimplanted GaAs surface. The patterning technique described here can presumably be applied to systems other than InAs / GaAs and highly interesting for site-controlled nucleation of QDs that finds its potential applications in nanooptoelectronic devices.

Photoelectric spectra of heterostructures containing InAs quantum dots (QDs) produced in different technological regimes were studied. A simple nondestructive method to reveal a bimodality of the QDs’ size distribution was described. The method based on the analysis of the shape of InAs/GaAs QDs’ photoelectric spectra and their temperature dependencies. The quantitative analysis of the temperature dependencies of the photoelectrical spectra was performed. All possible emission processes occurring from quantum confined levels to the semiconductor matrix were considered at the simulation. The surface concentration of the QDs was estimated.

We discuss the growth kinetics of InAs/GaAs self-assembled quantum dots (QDs) using two different InAs deposition rates, relatively fast growth rate of 0.22 ML/sec and slow growth rate of 0.054 ML/sec. With increasing InAs deposition amount to 3.0 ML, the QD density was almost constant after 2D to 3D island transition at the slow deposition rate while the QD density kept increasing and the QD size distribution was relatively broad at the fast growth rate. After the 2D to 3D transition, at the slow growth rate, further deposited In adatoms seemed to incorporate primarily into already formed islands, and thus contribute to equalize island size. The photoluminescence (PL) full-width at half maximum (FWHM) of 2.5 ML InAs QDs at 0.054 ML/sec was 23 meV at 78K. The PL characteristics of InAs/GaAs QDs were degraded significantly after thermal annealing at 550 oC for 3 hours.

We investigate the growth of low-density(~4×108cm-2) InAs quantum dots (QDs) on GaAs by molecular beam epitaxy,with emission wavelength up to 1.3 µm at room temperature were achieved. The QDs density are sensitive to growth temperature,growth rate.The optical properties of the QDs annealing temperature used after spacer layer growth that is attributed to the suppressed In segregation from the QDs into the cap layer, reduced the strain in the QDs,significant decrease of integrated PL intensity was observed as the annealing temperature increases.

2012/2013
Riassunto (Abstract) La fabbricazione di punti quantici (quantum dots, QD) auto-assemblati è una tematica di particolare rilevanza a causa delle loro possibilità di applicazione in dispositivi optoelettronici. Nel presente lavoro, ci siamo prefissi di ottenere array di QD di semiconduttore altamente uniformi, con lo scopo di raggiungere un controllo completo sulla loro distribuzione spaziale, ed un’uniformità spettrale superiore, rispetto a QD auto-assemblati convenzionali. Il metodo consiste in un approccio combinato top-down ebottom-up: QD auto-assemblati vengono cresciuti tramite Epitassia a Fasci Molecolari (MolecularBeam Epitaxy, MBE) su una superficie pre-patternata con un array regolare di buchi. Nella prima parte di questo lavoro di tesi, abbiamo ottimizzato la crescita di punti di InAs su substrati patternati di GaAs. Nella maggior parte dei lavori precedenti, i substrati vengono patternati tramite litografia elettronica (Electron BeamLitography, EBL), che non è la tecnica ottimale per l’applicazione a dispositivi broad-area, a causa della sua natura seriale e degli alti costi. Il metodo più indicato per superare questa limitazione è la scelta di un approccio litografico alternativo come la litografia a nanostampa (Nanoimprint Lithography,NIL), che ha come vantaggi un alto volume di produzione e dei costi più ridotti. Comunque, esistono soltanto pochi studi sull’uso della NIL per il patterning di superfici di GaAs. Nella maggior parte dei casi, viene usata la variante dell’UV-NIL, che richiede l’uso addizionale di una maschera di SiO2, con conseguente complicazione del processo. In questo lavoro, abbiamo utilizzato la forma di NIL più semplice, che non richiede alcun processo addizionale (quali il trattamento in UV o uno strato di SiO2). L’attacco chimico del GaAs è stato effettuato tramite wetetcìhing, per ottenere superfici prive di difetti, ed è stato ottimizzato per ottenere nanopori con le dimensioni laterali e la profondità desiderate. I substrati patternati di GaAs, dopo un processo di pulizia, vengono usati per la crescita controllata di QD nell’MBE. Abbiamo ottimizzato i protocolli di crescita per migliorare le proprietà strutturali ed ottiche dei QD, con lo scopo di migliorare le prestazioni di dispositivi optoelettronici. Abbiamo esaminato l’effetto del desorbimento dell’ossido superficiale a bassa temperatura tramite fasci di gallio (tecnica già applicata con successo in precedenza)e l’effetto della crescita sul substratodi uno strato di GaAs sulla forma e dimensione dei buchi, per migliorare l’occupazione di QD singoli nei buchi stessi. Abbiamo adottato un approccio alternativo per rimuovere l’ossido superficiale usando fasci di indio. Questo approccio è stato adottato siccome l’eventuale indio in eccesso può essere desorbito facilmente dalla superficie di GaAs scaldando a temperature che non alterino il profilo dei buchi. Inoltre, abbiamo osservato che nei nostri array patternati il desorbimento tramite fasci di indio ha anche l’effetto benefico di preservare meglio la forma dei buchi dopo la deposizione dello strato di GaAs, il che è di grande aiuto per migliorare l’occupazione di QD singoli e l’uniformità dei QD. Abbiamo usato la spettroscopia di fotoluminescenza (photoluminescence, PL) a bassa temperatura per esaminare le proprietà ottiche dei punti di InAs/GaAs. I risultati sono confrontabili o migliori, rispetto ai pochi studi simili effettuati su punti cresciuti su substrati definiti con la NIL, ed hanno il potenziale di raggiungere l’allargamento spettrale non-omogeneo ottenuto su QD controllati ottimizzati realizzati con la tecnica EBL. Nella seconda parte della tesi, abbiamo esteso questa tecnica alla crescita selettiva di punti InAs/GaAs su silicio patternato. Il silicio è il materiale principale per i dispositivi a semiconduttore (90%). Comunque, il gap di energia indiretto del silicio limita la realizzazione di dispositivi optoelettronici efficienti. D’altra parte, a causa del loro gap in molti casi diretto, i semiconduttori III-V hanno proprietà ottiche ed optoelettroniche eccellenti. L’integrazione di semiconduttori composti III-V su Si ha una grande prospettiva per la realizzazione di circuiti fotonici integrati. Tuttavia, l’integrazione GaAs/Si è limitata fortemente dalla loro differenza del 4% nel parametro reticolare, che induce dislocazioni e difetti nel materiale cresciuto sul substrato di silicio e previene l’emissione di luce. Svariati approcci sono stati esplorati per l’integrazione III-V/Si, quali la crescita di nanofili, la fusione dei substrati, l’utilizzo di strati spessi di rilassamento e l’applicazione di composizioni di materiali per accomodare i parametri reticolari. La crescita di strati spessi aumenta la complessità dei processi ed il costo dei materiali. Un’alternativa sarebbe quindi la crescita diretta di nanostrutture III-V su silicio. La crescita di QD III-V su substrati Si patternati dovrebbe aiutare a ridurre i difetti a causa di effetti di taglia e rilassamento della tensione laterale. Tuttavia, ad oggi esistono solo pochi studi su substrati di Si patternati, e la maggior parte includono maschere di SiO2con grosse periodicità dei buchi (1 µm) e piccole aree patternate (1 mm2) definite tramite EBL. In questo lavoro abbiamo cresciuto nanostrutture III-V direttamente su substrati patternati di Si con array di buchi densi (periodo 300 nm) e grandi aree patternate attraverso la tecnica NIL. Abbiamo ottimizzato l’attacco chimico del SI e la passivazione della sua superficie tramite terminazione in idrogeno, allo scopo di facilitare il desorbimento dell’ossido nella camera MBE a temperature relativamente basse. Il desorbimento dell’ossido ed i protocolli di crescita sono stati ottimizzati allo scopo di ottenere array di punti uniformi. Abbiamo usato la spettroscopia EDS (Energy Dispersive X-rayspectroscopy) per verificare la presenza di InAs e GaAs solo in corrispondenza dei buchi. Verranno anche mostrati risultati preliminari di spettroscopia PL per controllare le proprietà ottiche dei punti InAs/GaAs.
Abstract The fabrication of self-assembled quantum dots (QDs) is a topic of high current interest due to their vast applications in optical devices. In this research work, our aim is to obtain highly uniform arrays of semiconductor QDs to reach a complete control on their spatial distribution and a superior spectral uniformity, with respect to conventional self-assembled dots. The method consists of a combined top-down and bottom-up approach: self-assembled QDs are grown by molecular beam epitaxy (MBE) on a pre-patterned surface with a regular array of holes. In the first part of this thesis work, we have optimized the growth of InAs dots on patterned GaAs substrates. In most of the research efforts, GaAs substrates are patterned through electron beam lithography (EBL), which is not the optimal technique for application in broad-area devices, due to its serial nature and high cost. The finest way to overcome this limitation can be through choosing an alternative lithographic approach like nanoimprint lithography (NIL) for patterning of the GaAs surfaces, which has the advantage of high throughput and low cost. However, there are only few studies available that have used NIL for the patterning of GaAs surfaces. In most of the cases, instead of NIL, UV-NIL is being used for patterning, that requires an additional layer of SiO2 for masking, which also complicates the process. In this work, we have tried to use the simplest form of NIL for patterning, which requires no additional processing (like UV treatment or SiO2 layer). Wet etching process is chosen for GaAs etching to get defect-free surfaces, and is optimized to get the nanopores with required lateral dimensions and depth. These patterned GaAs substrates after optimizing all cleaning procedures are used for further growth of site-controlled QDs in MBE. We have optimized the growth protocols to improve the structural and optical properties of the dots, with the aim of improving the performance of optoelectronic devices. We have examined the effect of the low-temperature oxide desorption by means of Ga beams (which was already applied successfully to patterned GaAs surfaces) and the effect of the GaAs buffer layer growth on the hole shape and size, to improve the single-dot occupancy of the patterned holes. We have adopted an alternative approach to remove the oxide layer using In beams. This approach have been adopted because excess In can be easily desorbed from GaAs surface just by heating it to temperatures that do not alter the hole profiles. Furthermore, we have observed that for our patterned arrays In-assisted desorption has also the beneficial effect to better preserve the hole shape after the growth of the GaAs buffer layer, which ultimately helps in improving the single-dot occupancy, as well as the structural uniformity of the dots. We have used low temperature photoluminescence (PL) spectroscopy to assess the optical properties of InAs/GaAs dots. The results compare favourably with the few similar dot arrays previously grown on NIL-defined patterns, and have the potential to match the inhomogeneous broadening reported for optimized site-controlled dots on EBL-defined patterns. In the second part of the thesis, we have extended this technique to the selective growth of InAs/GaAs QDs on patterned silicon. Silicon is the main material for semiconductor devices (90%). However, the indirect bandgap of silicon prevents the realization of efficient light emitting devices. On the other hand, due to their direct bandgap in many cases, III-V semiconductors have excellent optical properties and optoelectronic capabilities. Integration of III-V compound semiconductor with Si has a broad prospective for the realization of photonic integrated circuits. However, GaAs/Si integration is largely limited by their 4% lattice mismatch, which induces dislocations and defects in the grown material on the Si substrate and ultimately prevents light emission. Several approaches are under exploration for III-V/Si integration like nanowire growth, wafer fusion techniques, using thick relaxation layers and applying lattice matched material compositions. Growth of these buffer layers increases the process complexity and material cost. A perfect alternative would thus be the direct epitaxial growth of III-V nanostructures on silicon. Growth of III-V quantum dots on pre-patterned Si substrates should help to reduce defects because of size effect and effective lateral stress relaxation due to the presence of facet edges and side walls. However, there are limited research efforts available on patterned Si substrates including mostly on SiO2 as mask with large periods (1µm) and small patterned areas (1mm2) defined by EBL. In our work, we have grown III-V nanostructures directly on patterned Si substrates with dense hole arrays (period 300nm) and larger patterned areas through nanoimprint lithography. We optimized the dry etching of Si and its surface passivation with H-termination, in order to facilitate oxide desorption in the MBE at relatively low temperatures. Oxide desorption and growth protocols were optimized in order to obtain uniform dot arrays. We used energy-dispersive X-ray spectroscopy (EDS) analysis for the characterization of InAs/GaAs QDs to verify the presence of GaAs and InAs only at the hole location. We will also show preliminary results using photoluminescence spectroscopy to assess the optical properties of InAs/GaAs dots.
XXVI Ciclo
1976

The main focus of this master thesis work has been to image InAs emph{quantum dots} (QDs) using emph{atomic force microscopy} (AFM), to identify and evaluate various image processing methods used to estimate the volume of the InAs QDs. The InAs QDs studied in this thesis work, had been deposited on GaAs substrates, using solid-source emph{molecular beam epitaxy} (MBE) before the thesis work started. The total QD volume was determined for all samples, using eight different estimation methods. The purpose of estimating the total QD volume, was to compare the total volume to the deposited volume.Previous studies on similar samples, have indicated that the total volume can be larger than the deposited volume during MBE growth. This discrepancy is explained by incorporation of Ga from the substrate during growth. This was not observed in this thesis work. One possible explanation is that the samples have oxidized; resulting in a lower measured height.In addition, the relationship between atomic steps, defects and the appearance of large QDs were studied. parTwo series of samples were studied: one in which the QD growth temperature was varied and one in which the amount of deposited InAs was varied. The total QD volumes were found to increase with the QD growth temperature and the deposited InAs thickness. Square-shaped defects and contours of 2D islands were observed in nearly all samples. Higher/multiple terraces seem to be related to regions of higher QD density.

This diploma project has been focused on optimization of the D2B IR detector fabrication process using different mesa sidewall treatments and passivation methods. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscope (AFM) measurements have been carried out on samples treated by different wet etching methods, to analyze their surface chemical composition and roughness. The surface roughness has been improved by critic etching, annealing and NaClO sequential treatment steps. Then these results have been utilized to improve the process of the D2B IR detectors. The dark current of the fabricated detectors passivated with various techniques have been characterized by I-V measurements at low (77 K) and room temperatures. The dark current mechanisms owing to surface shunt or bulk leakage are investigated by dark current temperature dependence analysis. By photoresist passivation devices with least leakage current are achieved.

Si-based light emitting sources are highly demanded for applications in optoelectronic integration circuits. Unfortunately, Si has an indirect bandgap and thus a low efficiency in photon emission. On the other hand, III–V semiconductors have superior optical properties and are considered as strong candidates to achieve efficient light emitting sources on Si platforms via wafer bonding or monolithically epitaxy growth. III–V materials monolithically grown on Si substrate could introduce various types of defects including antiphase domain, threading dislocation, misfit dislocation. These defects must be dealt with satisfactorily in order to fulfill the potential of III–V/Si integration. In this thesis, buffer layers for InAs/GaAs quantum dots (QDs) monolithically grown Si substrate have been investigated. The buffer layer study is mainly focused on the different types of defect filter layers (DFLs). The measurements of atomic force microscopy, photoluminescence and transmission electron microscopy are carried out to investigate the effectiveness of each type of DFLs. The results of lasers and superluminescent diodes (SLDs) have been presented based on the studies of DFLs. In order to improve the performance of InAs/GaAs QDs grown on Si substrates, a GaAs buffer layer and DFLs have been used to reduce the defect density from ~1010 to 106 cm-2 after three sets of DFLs, which consists of strained layer superlattices (SLSs). In the thesis, the optimisation of DFLs has been carried out. Different types of DFLs are investigated in the Chapter 3, including InAs/GaAs QDs, InGaAs submonolayer QDs, InGaAs/GaAs SLSs and InAlAs/GaAs SLSs. DFLs made of InAlAs/GaAs SLSs show the strongest performance, based on the measurements of atomic force microscopy, photoluminescence and transmission electron microscopy. The high performance InAs/GaAs QDs lasers with low threshold current density (194 A/cm2 ) and high operating temperature (85 ̊C) has been obtained for the samples with optimised DFLs. In addition to III–V/Si lasers, III–V SLDs monolithically grown on silicon substrates would further enrich the silicon photonics toolbox, enabling low-cost, highly scalable, high-functional, and streamlined on-chip light sources. In this thesis, the first InAs/GaAs QD SLDs monolithically grown on a Si substrate have been demonstrated based on the similar growth structure of laser devices. The fabricated two-section InAs/GaAs QD SLD produces a close- 4 to-Gaussian emission spectrum of 114 nm centred at ∼1255 nm wavelength, with a maximum output power of 2.6 mW at room temperature. The optimisation of InGaAs/GaAs SLSs DFLs has been carried out in the Chapter 5. The optimisation includes introducing different growth methods into GaAs spacer layer between each set of DFL, indium composition and GaAs thickness in InGaAs/GaAs SLSs. The optimisation is examined by atomic force microscopy, photoluminescence and transmission electron microscopy. The laser device with optimised InGaAs/GaAs SLSs DFLs has a lower threshold current density, higher operating temperature and characteristic temperature. In conclusion, InAs/GaAs QDs lasers with low threshold current density and the first QDs SLDs monolithically grown on Si substrates have been demonstrated. InAlAs/GaAs SLSs DFLs have been proved that as considerable solution to reduce the threading dislocation density significantly. The optimisations of InGaAs/GaAs SLSs DFLs successfully improve the QDs laser performance which could also be used in III–V/Si monolithically integration. The III–V QDs lasers and SLDs monolithically grown on Si substrate are essential steps for Si photonics integration, which will fill the “holy grail” of opto-electronic integration circuits.

To imitate the way electrical components evolved from discrete devices to devices integrated on Si platform, the next stage for integrated circuits is to integrate photonic components with electrical components on one chip, with active devices known as optoelectronic integrated circuits (OEIC). An ideal solution for this would be to have an all-Si laser. However due to the indirect bandgap of Si this is difficult to achieve. Therefore attention has been focused on trying to integrate the existing and mature III-V laser technology with Si. The difference in lattice constant between GaAs and Si makes direct, monolithic growth of GaAs on Si difficult due to the generation of high defect densities. But the advances in quantum dot (QD) technology and in III-V buffer layer techniques have led to the improvements of direct growth integration. In this thesis an AlAs nucleation layer (NL) in the place of a GaAs nucleation layer was found to increase the photoluminescence intensity and reduce defect density in active layers. Lasers were fabricated with lower threshold current densities than similar devices with GaAs NL. Lasing operation at 1.28 μm was achieved up to 63 °C with a threshold current density of 675 A/cm2 at room temperature. In addition, Ge-on-Si substrates have been used to demonstrate the lasers on Si substrates with a very low pulsed threshold current density of 64 A/cm2, which is significantly lower than any other laser integrated with Si substrates. Also this was the first demonstration of a CW laser on Si with a threshold current density of 163 A/cm2. Lasers were operated up to 30 °C for CW devices and 84 °C for pulsed devices. The difference in threshold currents and temperature performance between CW and pulsed operation is due to high device resistances caused by a combination of poor contact resistance and the introduction of defects from the Si/Ge interface. In conclusion, lasers on Si substrates have been fabricated with low threshold current densities. A very low threshold current density of 64 A/cm2 has been achieved with a Ge-on-Si device and is the lowest result for any type of Si laser at the time of writing, which shows good potential for future integration with Si electronics.

Grâce à leur propriétés uniques, les nanofils d'InAs et de Bi1-xSbx sont important pour les domaines de la nanoélectronique et de l'informatique quantique. Alors que la mobilité électronique de l'InAs est intéressante pour les nanoélectroniques; l'aspect isolant topologique du Bi1-xSbx peut être utilisé pour la réalisation de Qubits basés sur les fermions de Majorana. Dans les deux cas, l'amélioration de la qualité du matériau est obligatoire et ceci est l'objectif principal cette thèse ou` nous étudions l'intégration des nanofils InAs sur silicium (compatibles CMOS) et où nous développons un nouvel isolant topologique nanométrique: le Bi1-xSbx. Pour une compatibilité CMOS complète, la croissance d'InAs sur Silicium nécessite d'être auto- catalysée, entièrement verticale et uniforme sans dépasser la limite thermique de 450 ° C. Ces normes CMOS, combineés à la différence de paramètre de maille entre l'InAs et le silicium, ont empêché l'intégration de nanofils InAs pour les dispositifs nanoélectroniques. Dans cette thèse, deux nouvelles préparations de surface du Si ont été étudiées impliquant des traitements Hydrogène in situ et conduisant à la croissance verticale et auto-catalysée de nanofils InAs compatible avec les limitations CMOS. Les différents mécanismes de croissance résultant de ces préparations de surface sont discutés en détail et un passage du mécanisme Vapor-Solid (VS) au mécanisme Vapor- Liquid-Solid (VLS) est rapporté. Les rapports d'aspect très élevé des nanofils d'InAs sont obtenus en condition VLS: jusqu'à 50 nm de diamètre et 3 microns de longueur. D'autre part, le Bi1-xSbx est le premier isolant topologique 3D confirmé expérimentalement. Dans ces nouveaux matériaux, la présence d'états surfacique conducteurs, entourant le coeur isolant, peut héberger les fermions de Majorana utilisés comme Qubits. Cependant, la composition du Bi1-xSbx doit être comprise entre 0,08 et 0,24 pour que le matériau se comporte comme un isolant topologique. Nous rapportons pour la première fois la croissance de nanofils Bi1-xSbx sans défaut et à composition contrôlée sur Si. Différentes morphologies sont obtenues, y compris des nanofils, des nanorubans et des nanoflakes. Leur diamètre peut être de 20 nm pour plus de 10 microns de long, ce qui en fait des candidats idéaux pour des dispositifs quantiques. Le rôle clé du flux Bi, du flux de Sb et de la température de croissance sur la densité, la composition et la géométrie des structures à l'échelle nanométrique est étudié et discuté en détail
InAs and Bi1-xSbx nanowires with their distinct material properites hold promises for nanoelec- tronics and quantum computing. While the high electron mobility of InAs is interesting for na- noelectronics applications, the 3D topological insulator behaviour of Bi1-xSbx can be used for the realization of Majorana Fermions based qubit devices. In both the cases improving the quality of the nanoscale material is mandatory and is the primary goal of the thesis, where we study CMOS compatible InAs nanowire integration on Silicon and where we develop a new nanoscale topological insulator. For a full CMOS compatiblity, the growth of InAs on Silicon requires to be self-catalyzed, fully vertical and uniform without crossing the thermal budge of 450 °C. These CMOS standards, combined with the high lattice mismatch of InAs with Silicon, prevented the integration of InAs nanowires for nanoelectronics devices. In this thesis, two new surface preparations of the Silicon were studied involving in-situ Hydrogen gas and in-situ Hydrogen plasma treatments and leading to the growth of fully vertical and self-catalyzed InAs nanowires compatible with the CMOS limitations. The different growth mechanisms resulting from these surface preparations are discussed in detail and a switch from Vapor-Solid (VS) to Vapor- Liquid-Solid (VLS) mechanism is reported. Very high aspect ratio InAs nanowires are obtained in VLS condition: upto 50 nm in diameter and 3 microns in length. On the other hand, Bi1-xSbx is the first experimentally confirmed 3D topololgical insulator. In this new material, the presence of robust 2D conducting states, surrounding the 3D insulating bulk can be engineered to host Majorana fermions used as Qubits. However, the compostion of Bi1-xSbx should be in the range of 0.08 to 0.24 for the material to behave as a topological insula- tor. We report growth of defect free and composition controlled Bi1-xSbx nanowires on Si for the first time. Different nanoscale morphologies are obtained including nanowires, nanoribbons and nanoflakes. Their diameter can be 20 nm thick for more than 10 microns in length, making them ideal candidates for quantum devices. The key role of the Bi flux, the Sb flux and the growth tem- perature on the density, the composition and the geometry of nanoscale structures is investigated and discussed in detail

We reported the structure peculiarities of nanocrystals formed in Si by means of high-fluence implantation at 25 and 500 °С followed by rapid thermal annealing (RTA). The structure of implanted samples has been investigated by means of transmission electron microscopy (TEM). The crystalline nature of the precipitates is proved by the Moiré fringe patterns presence in the TEM images. The Moiré fringe distance (Moiré period) is equal of 1.8 nm for small precipitates. This experimental value coincides with the calculated one for crystalline InAs. It is noted a Moiré period increasing in the case of large precipitates. We suppose that this feature is a result of surplus As or In atoms embedded in precipitates. One can see an interesting effect – “glowng” of nanocrystal/Si interfaces at the dark-field images of implanted and annealed samples. We ascribe this effect to a presence of misfit dislocation networks at the InAs/Si interfaces generated as a result of strain relaxation in highly mismatched InAs/Si system. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35436

Les boîtes quantiques sous formes de nanocristaux semi-conducteurs permettent de réaliser des matériaux à énergie de gap variable, propriété très intéressante pour les composants optoélectroniques. Ce travail est dédié à la création de nanocristaux de silicium dopés enfouis dans SiO2 et de nanocistaux binaires (InAs et GaAs) et ternaires d’InxGa1-xAs enfouis dans Si et à leurs caractérisations structurales, électriques et optiques. La synthèse par faisceaux d’ions permet d’avoir un contrôle de la quantité et de la taille des nanocristaux synthétisés. Des caractérisations structurales ont pu démontrer le dopage des nanocristaux de silicium avec le phosphore et l’arsenic à une concentration atomique moyenne de 8 %. Nous avons également montré la possibilité de moduler la taille et la composition chimique des nanocristaux d’InxGa1-xAs sur une large gamme à l’aide de la dose d’implantation et de la température de recuit
Semiconductor nanocrystals can be used as quantum dots to produce band gap engineering by varying the nanocrystals size, which is a very interesting property for optoelectronic components. This work is dedicated to the creation of doped silicon nanocrystals embedded in SiO2 and binary (InAs and GaAs) and ternary nanocrystals of InxGa1-xAs embedded in Si and also to investigate their structural, electrical and optical properties. Ion beam synthesis allows a control of the nanocrystals amount and size. Structural characterizations were able to demonstrate the doping of silicon nanocrystals with phosphorus and arsenic at an average atomic concentration of 8 %. We have also shown the ability to modulate the size and the chemical composition of InxGa1-xAs nanocrystals in a large range by varying the implantation dose and the annealing temperature

Near-field optical microscopy has attracted remarkable attention, as it is the only technique that allows the investigation of local optical properties with a resolution far below the diffraction limit. Especially, the scattering-type near-field optical microscopy allows the nondestructive examination of surfaces without restrictions to the applicable wavelengths. However, its usability is limited by the availability of appropriate light sources. In the context of this work, this limit was overcome by the development of a scattering-type near-field microscope that uses a widely tunable free-electron laser as primary light source. In the theoretical part, it is shown that an optical near-field contrast can be expected when materials with different dielectric functions are combined. It is derived that these differences yield different scattering cross-sections for the coupled system of the probe and the sample. Those cross-sections define the strength of the near-field signal that can be measured for different materials. Hence, an optical contrast can be expected, when different scattering cross-sections are probed. This principle also applies to vertically stacked or even buried materials, as shown in this thesis experimentally for two sample systems. In the first example, the different dielectric functions were obtained by locally changing the carrier concentration in silicon by the implantation of boron. It is shown that the concentration of free charge-carriers can be deduced from the near-field contrast between implanted and pure silicon. For this purpose, two different experimental approaches were used, a non-interferometric one by using variable wavelengths and an interferometric one with a fixed wavelength. As those techniques yield complementary information, they can be used to quantitatively determine the effective carrier concentration. Both approaches yield consistent results for the carrier concentration, which excellently agrees with predictions from literature. While the structures of the first system were in the micrometer regime, the capability to probe buried nanostructures is demonstrated at a sample of indium arsenide quantum dots. Those dots are covered by a thick layer of gallium arsenide. For the first time ever, it is shown experimentally that transitions between electron states in single quantum dots can be investigated by near-field microscopy. By monitoring the near-field response of these quantum dots while scanning the wavelength of the incident light beam, it was possible to obtain characteristic near-field signatures of single dots. Near-field contrasts up to 30 % could be measured for resonant excitation of electrons in the conduction band of the indium arsenide dots
Die optische Nahfeldmikroskopie hat viel Beachtung auf sich gezogen, da sie die einzige Technologie ist, welche die Untersuchung lokaler optischer Eigenschaften mit Auflösungen unterhalb der Beugungsgrenze ermöglicht. Speziell die streuende Nahfeldmikroskopie erlaubt die zerstörungsfreie Untersuchung von Oberflächen ohne Einschränkung der verwendbaren Wellenlängen. Die Nutzung ist jedoch durch das Vorhandensein entsprechender Lichtquellen beschränkt. Im Rahmen dieser Arbeit wurde diese Beschränkung durch Entwicklung eines streuenden Nahfeldmikroskops überwunden, das einen weit stimmbaren Freie-Elektronen-Laser als primäre Lichtquelle benutzt. Im theoretischen Teil wird gezeigt, dass ein optischer Kontrast erwartet werden kann, wenn Materialien mit unterschiedlichen Dielektrizitätskonstanten kombiniert werden. Es wird hergeleitet, dass diese Unterschiede in unterschiedlichen Streuquerschnitten für das gekoppelte System aus Messkopf und Probe resultieren. Diese Streuquerschnitte definieren die Stärke des Nahfeldsignals, welches auf unterschiedlichen Materialien gemessen werden kann. Ein optischer Kontrast kann also erwartet werden, wenn unterschiedliche Streuquerschnitte untersucht werden. Dass dieses Prinzip auch auf übereinander geschichtete oder sogar verborgene Strukturen angewendet werden kann, wird in dieser Doktorarbeit an zwei Probensystemen experimentell gezeigt. Im ersten Beispiel wurden die unterschiedlichen Dielektrizitätskonstanten durch örtliches Ändern der Ladungsträgerdichte in Silizium durch Bor-Implantation erreicht. Es wird gezeigt, dass die Dichte der freien Ladungsträger an Hand des optischen Kontrastes zwischen implantiertem und reinem Silizium ermittelt werden kann. Zu diesem Zweck wurden zwei unterschiedliche Ansätze verwendet, ein nicht-interferometrischer mittels variabler Wellenlängen und ein interferometrischer mit einer konstanten Wellenlänge. Weil diese Techniken gegensätzliche Informationen liefern, können sie genutzt werden, um die effektive Ladungsträgerdichte quantitativ zu bestimmen. Beide Ansätze lieferten konsistente Resultate für die Trägerdichte, welche sehr gut mit den Vorhersagen der Literatur übereinstimmt. Während die Strukturen im ersten Beispiel im Mikrometer-Bereich lagen, wird die Möglichkeit, verborgene Nanostrukturen zu untersuchen, an Hand einer Probe mit Indiumarsenid Quantenpunkten demonstriert. Diese sind von einer dicken Schicht Galliumarsenid bedeckt. Zum ersten Mal wird experimentell gezeigt, dass Übergänge zwischen Elektronenzuständen in einzelnen Quantenpunkten mit Nahfeldmikroskopie untersucht werden können. Durch die Messung der Nahfeld-Antwort der Quantenpunkte unter Änderung der Wellenlänge des eingestrahlten Lichtes war es möglich, charakteristische Nahfeld-Signaturen der einzelnen Quantenpunkte zu erhalten. Nahfeld-Kontraste bis zu 30 Prozent konnten für die resonante Anregung der Elektronen im Leitungsband der Indiumarsenid Punkte beobachtet werden

III-V semiconductors present interesting properties and are already used in electronics, lightening and photonic devices. Integration of III-V devices onto a Si CMOS platform is already in production using III-V devices transfer. A promising way consists in using hetero-epitaxy processes to grow the III-V materials directly on Si and at the right place. To reach this objective, some challenges still needed to be overcome. In this contribution, we will show how to overcome the different challenges associated to the heteroepitaxy and integration of III-As onto a silicon platform. We present solutions to get rid of antiphase domains for GaAs grown on exact Si(100). To reduce the threading dislocations density, efficient ways based on either insertion of InGaAs/GaAs multilayers defect filter layers or selective epitaxy in cavities are implemented. All these solutions allows fabricating electrically pumped laser structures based on InAs quantum dots active region, required for photonic and sensing applications.

III-V semiconductors present interesting properties and are already used in electronics, lightening and photonic devices. Integration of III-V devices onto a Si CMOS platform is already in production using III-V devices transfer. A promising way consists in using hetero-epitaxy processes to grow the III-V materials directly on Si and at the right place. To reach this objective, some challenges still needed to be overcome. In this contribution, we will show how to overcome the different challenges associated to the heteroepitaxy and integration of III-As onto a silicon platform. We present solutions to get rid of antiphase domains for GaAs grown on exact Si(100). To reduce the threading dislocations density, efficient ways based on either insertion of InGaAs/GaAs multilayers defect filter layers or selective epitaxy in cavities are implemented. All these solutions allows fabricating electrically pumped laser structures based on InAs quantum dots active region, required for photonic and sensing applications.

This chapter aims at introducing structures where the electron is confined in two or three dimensions, the so-called quantum wires and quantum dots. The basics of the density-of-states are explained, as its strong structure distinguishes these systems from higher-dimensional ones, in addition of the large interface/volume ratio. Fabrication routes of different nature are presented, either self-organised or epitaxial, and the tunability of photonic properties that result from variable size and shape is underlined. The semiconductor families and the applications of each route are presented. The emblematic case of InAs growth on III-V substrates provides the key phenomena of interest. The II-VI colloidal quantum dots are the other emblematic case, leading to the evolving uses of quantum dots, e.g. in displays or as nanoprobes. The description of porous silicon as a lower-dimensional version of silicon is used to introduce the reader to more subtle interplays of electronic and photonic properties.

Quantum dots (QDs) are very small nanoparticles and are composed of hundreds to thousands of atoms. These semiconducting materials can be made from an element, such as silicon or germanium, or compounds such as cadmium sulphide (CdS) or cadmium selenide (CdSe). The colour of these small particles does not depend on the type of semiconducting material from which the dots are made, but rather on its diameter. Besides, ODs attract the most attention because of their unique visual properties. Therefore, these are used in all kinds of applications where precise control of coloured light is important. As these dots are of great importance in chemical, biological and medical applications, they can be designed to deliver anti-cancer drugs and direct them to specific areas of the body. Therefore, with this technique, the harmful side effects of chemical treatments can be reduced. It is possible to examine and study the properties of these nanomaterials and make sure they are analyzed using some scientific devices and techniques, the most important of which are: transmittance electron microscopy (TEM), scanning electron microscopy (SEM), atomic forces microscopy (AFM) with dielectrics, and X-ray diffraction (XRD). This chapter opens horizons towards knowing what quantum dots are and their unique properties, as well as methods of preparation and then placing our hands on the chemical, and biological applications of these dots.