This study focuses on the growth and characterization of epitaxial InAs and InAs1-xSbx. Layers are grown on InAs, GaAs and GaSb substrates by metalorganic vapour phase epitaxy, using trimethylindium, trimethylantimony and arsine as precursors. The growth parameters (V/III ratio, Sb vapour phase compositions) are varied in the temperature range from 500 ºC to 700 ºC, in order to study the influence of these parameters on the structural, optical and electrical properties of the materials. The layers were assessed by X-ray diffraction, electron and optical microscopy, photoluminescence and Hall measurements. Furthermore, the influence of hydrogenation and annealing on the electrical and optical properties of GaSb was investigated. It is shown that the growth temperature and the V/III ratio play a vital role in the resulting surface morphology of homoepitaxial and heteroepitaxial InAs layers. Growth at low temperatures is found to promote three-dimensional growth in both cases, with improvements in the surface morphologies observed for higher growth temperatures. All the investigated epilayers are n-type. It is shown that the electrical properties of heteroepitaxial InAs epilayers are complicated by a competition between bulk conduction and conduction due to a surface accumulation and an interface layer. The low temperature photoluminescence spectra of homoepitaxial InAs are dominated by two transitions. These are identified as band-to-band/excitonic and donor-acceptor recombination. The incorporation efficiency of antimony (Sb) into InAs1-xSbx is dependent on the growth temperature and the V/III ratio. Under the growth conditions used in this study, the incorporation efficiency of Sb is controlled by the thermal stability of the two constituent binaries (i.e. InAs and InSb). Changes in the low temperature photoluminescence spectra are detected with increasing x. From temperature and laser power dependent measurements, the highest energy line is attributed to band-to-band/excitonic recombination, while the peak appearing approximately 15 meV below this line is assigned to donor-acceptor recombination. The origin of an additional “moving” peak observed for higher Sb mole fraction x is tentatively attributed to quasi-donor-acceptor-recombination, arising from increased impurity/defect concentrations and a higher compensation ratio in the material. However, the unusual behaviour of this peak may also be ascribed to the presence of some degree of ordering in InAsSb. The exposure of a semiconductor to a hydrogen plasma usually leads to the passivation of shallow and deep centres, thereby removing their electrical and optical activity. In this study, the passivation and thermal stability of the native acceptor in p-type GaSb is also investigated. It is shown that this acceptor can be passivated, where after improvements in the electrical and optical properties of GaSb are observed. Upon annealing the passivated samples above 300 °C, the acceptor is reactivated.

Ce travail de thèse porte sur la croissance et sur la caractérisation optique de nanostructures à base d’antimoine sur substrats InP, en vue d’applications dans le domaine des télécommunications optiques. La transition inter-sous-bande est un processus ultrarapide qui permet la modulation de la lumière dans les réseaux de télécommunication optique. Durant cette thèse, une absorption inter-sous-bande dans le proche-infrarouge provenant de puits quantiques Ga0.47In0.53As/AlAs0.56Sb0.44 a été observée pour la première fois au laboratoire. Les analyses par microscopie électronique à effet tunnel sur la face clivée montrent cependant de nombreux déviations à l’idéalité de nos structures : mélange à l’échelle atomique aux interfaces entre GaInAs et AlAsSb, inhomogénéité de l’alliage GaInAs, incorporation non-intentionnel d’antimoine dans le GaInAs. Les puits quantiques InAs/AlAs0.56Sb0.44 sont potentiellement des objets de choix pour la réalisation de composants intersous- bande travaillant à 1,55 μm. Des puits quantiques InAs/AlAs0.56Sb0.44 contraint, exempt de défauts ont été obtenus par croissance assistée par effet surfactant de Sb. En symétrisant la contrainte induite par le dépôt d’InAs par l’insertion de couches nanométriques de AlAs dans les barrières, des multi-puits InAs/AlAs0.56Sb0.44 sans contrainte macroscopique ont été réalisés. L’effet de l’antimoine en surface sur la croissance de structure InAs/GaAs0.51Sb0.49 a également été étudié. En présence d’antimoine sur substrats InP d’orientation (001), le dépôt d’InAs conduit à la formation de puits quantiques. Par contre sur ceux orientés suivant (113)B des boites quantiques sont formées suivant le mode de croissance Volmer-Weber. Ces résultats sont discutés en termes d’effets cinétiques ou énergétiques de l’antimoine en surface. La modification de l’anisotropie de l’énergie de surface induite par l’antimoine permet d’interpréter nos résultats sur substrats (100) et (113) B. / This PhD work presents molecular beam epitaxy growth and optical studies on several Sb-nanostructures on InP substrate, for their potential use in optical telecommunication. Inter-subband transition in Ga0.47In0.53As/AlAs0.56Sb0.44 quantum well is a useful physical process for implementing ultrafast fulloptical modulations. Near-infrared inter-subband transition in this material was achieved and microscopic studies on this structure has revealed that the intermixing at GaInAs/AlAsSb interface, unintentional Sb incorporation in GaInAs layer and the inhomogeneity within GaInAs layer could prevent Ga0.47In0.53As/ AlAs0.56Sb0.44 multiple quantum wells from achieving intersubband transition in 1.55 μm optical telecommunication band. The strained InAs/AlAs0.56Sb0.44 quantum well is another material that has potential use in 1.55 μm full-optical modulation. 2 nm-thick defect-free InAs/AlAs0.56Sb0.44 was obtained under Sb surfactant-mediated growth, and by using strain compensation techniques, InAs/AlAs0.56Sb0.44 multiple quantum wells with zero net-strain were realized. The study of Sb-mediated growth is also carried on to InAs/GaAs0.51Sb0.49 nanostructures. The growths of such structures on InP (001) substrate has led to the formation of flat InAs layer, while high-density InAs/GaAs0.51Sb0.49 quantum dots were obtained on InP (113)B substrates under Volmer-Weber growth mode. We attribute such phenomena to the surfaceorientation dependent surfactant effect of Sb. Emission wavelength close to 2 μm was achieved with only 5 ML of InAs deposition, which makes these quantum dots attractive to InPbased mid-wave applications.

<p></p><p>High mobility 2DEG (two-dimensional electron gas) confined in GaAs is a good platform to understand correlated electron systems and a promising candidate for qubit devices. For example, the non-Abelian feature of Fractional Quantum Hall state enabling topological quantum computation is only found in GaAs with high mobility. Theoretical calculations have shown that the mobility is inversely proportional to impurities in GaAs/AlGaAs heterstructures grown by Molecular Beam Epitaxy (MBE). In recent MBE experiments, the source Ga was found to be more important in the limitation of mobility than Al and As. A high mobility of 35 million cm²/Vs was recently observed when an 8N Ga (total nominal impurity concentration of ~10 ppb) source was used compared to 25 million cm²/Vs for a 7N Ga source. In addition, significant mobility increase was observed after in-situ distillation of the source Ga before growth. In order to clarify the mechanism of how the distillation contributed to the Ga purification, thus resulting in the mobility increase, the MBE in-situ distillation was analyzed by molecular distillation theory. Evaporation behavior of solvent Ga was analyzed including effects of evaporation from a crucible with receding liquid depth. Then impurity removal through molecular distillation was analyzed with molecular evaporation kinetics. The remaining 7N and 8N Ga after in-situ MBE distillation and growth were elementally analyzed by ICP-MS (Inductively Coupled Plasma Mass Spectrometry) and compared with analyses of the starting 7N and 8N Ga from same lots. Due to the increased detection limit of ICP-MS in metal analysis, the concentrations of most impurity elements reached the detection limit of ~1-10 ppb. However, unusual high concentration of 690 ppb Ge was found in the 7N Ga, exceeding the nominal concentration of 7N (100 ppb). Significant decrease in Ge concentration was found in the comparison of initial ultra-pure Ga and remaining Ga for both grades of 7N and 8N. The significant Ge losses cannot be explained by atomic Ge evaporation due to the low vapor pressure of Ge. However, a hypothesis of Ge evaporation as GeO(g) by Ge active oxidation was proposed. In order to test the active oxidation of very dilute Ge in Ga in the MBE conditions with very low P(O₂), the equilibrium P(GeO)-P(O₂) vapor species diagram was calculated from thermodynamics. The analysis shows that even very dilute Ge in Ga of ~ 1 ppm concentration can be <a>actively oxidized in the extremely low P(O₂) of MBE</a>. In order to prove active oxidation of Ge, molecular distillation of 7N Ga was performed in <a>a specially constructed high vacuum chamber. The 7N Ga with unusual high Ge concentration of 440 ppb (by GDMS analysis) was distilled for 16 h at 1360 K under the starting P(O₂) of 3 x 10^-6 torr and the total pressure of 10^-5 torr. The chamber vacuum was monitored by Residual Gas Analyzer (RGA) and the residual Ga after 16 h distillation was analyzed by GDMS. In the GDMS analysis, significant Ge loss was found from 440 ppb to below the detection limit of 10 ppb, confirming Ge active oxidation hypothesis. The oxygen-assisted impurity removal in distillation also may be applicable to other impurities with high vapor pressure gaseous oxide, but low vapor pressure itself, such as Al, Si and Sn. </a></p><br><p></p>

<p>With increasing global renewable energy demands, there is a need for new materials with improved performance, lower cost, and less toxicity. One such application is photovoltaics, where halide perovskites (HaPs) represent the fastest growing market of absorbers owing to their impressive optoelectronic properties and excellent tunability from composition engineering and structural manipulation. However, the practically infinite composition-structure space of HaPs when considering cation and/or anion site mixing, octahedral distortion and rotation, and other forms of polymorphism, raise considerable challenges when comprehensively exploring their stability and optoelectronic properties. First principles calculations are powerful tools that can investigate large numbers of compounds and structures in a high-throughput fashion. </p><p>In my thesis, I performed high-throughput density functional theory (DFT) computations to generate a HaP dataset within a wide chemical space covering ~500 unique chemical compositions in the (pseudo-)cubic phase, across a 14-dimensional ionic space. This work explored both pure and alloyed compositions, with the latter simulated using the special quasi-random structures approach. Many critical properties were computed using the semi-local GGA-PBE and hybrid non-local HSE06 functionals, including decomposition and mixing energies, electronic band gap, and spectroscopic limited maximum efficiency (SLME), which is a theoretical surrogate for the likely absorption efficiency of the compound when used in a single-junction solar cell. Property screening over this dataset yielded 32 stable perovskite candidates with attractive optoelectronic properties.</p><p>Polymorphism in HaPs is investigated by simulating larger supercell alloys with different ionic ordering, generating compounds with random octahedral distortions and rotations, and optimizing various compositions in non-cubic phases such as tetragonal and orthorhombic. Linear correlation analysis is performed to gain a critical understanding of how properties are influenced by specific cations and anions, their mixing fractions, the perovskite phase, ionic clustering, and amount of strain or distortion in the lattice. Finally, trends, design rules, and predictive insights achieved from the DFT datasets are applied over a much larger set of thousands of hypothetical compounds, resulting in identification of more promising materials and understanding of the most important A-B-X combinations that yield multiple desired objectives.</p><p>Furthermore, a similar DFT workflow is applied for designing transition metal electrocatalysts. DFT simulations are performed to model Hydrogen adsorption, OH adsorption, and the water splitting reaction on Ni3N/Ni and Co2N/Co hybrid structures, to explore their likelihood in being used for Hydrogen Evolution Reaction (HER). The results reveal the excellent catalytic performance of transition metal and transition metal nitride hybrid structures.</p><p><br></p>

Accurate knowledge of stopping powers is essential for these for quantitative analysis and surface characterization of thin films using ion beam analysis (IBA). These values are also of interest in radiobiology and radiotherapy, and in ion- implantation technology where shrinking feature sizes puts high demands on the accuracy of range calculations. A theory that predicts stopping powers and ranges for all projectile-target combinations is needed. The most important database used to report the stopping powers is the SRIM/TRIM program developed by Ziegler and coworkers. However, other researchers report that at times, these values differ significantly from experimental values. In this study the stopping powers of Si, P and S ions have been measured in Ni, Cu, Ge and GaAs absorbers in the energy range ~ 2-10 MeV. For elemental films of Ni, Cu and Ge, the stopping of heavy ions was measured using a novel ERD (Elastic Recoil Detection) based technique. In which an elastically recoiled lighter atom is used to indirectly measure the energy of the incoming heavy ion using a surface barrier detector. In this way it was possible to reduce the damage and to improve the FWHM of the detector. The results were compared to SRIM-2000 predictions and other experimental measurements. A new technique derived from Molecular Beam Epitaxy (MBE) was developed to prepare stoichiometric GaAs films on thin carbon films for use in transmission ion beam experiments. The GaAs films were characterized using X-ray Photoelectron Spectroscopy (XPS) and Particle Induced X-ray Emission (PIXE). These films were used to investigate the stopping powers of energetic heavy ions in GaAs and to provide data for the calculation of Bethe-Bloch parameters in the framework of the Modified Bethe-Bloch theory. As a result of this study, stopping power data are available for the first time for Si and P ions in the energy range 2-10 MeV stopping in GaAs absorbers.

by Choy Wing Hong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 95-102). / Text in English; abstract also in Chinese. / by Choy Wing Hong. / ABSTRACT --- p.vi / ACKNOWLEDGEMENTS --- p.x / LIST OF FIGURES --- p.xi / LIST OF TABLES --- p.xiii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- Surface passivation techniques --- p.2 / Chapter 1.2.1 --- Sulfide solution passivation --- p.2 / Chapter 1.2.2 --- Gas-phase sulfide passivation --- p.3 / Chapter 1.2.3 --- Ultra-violet and ozone exposure --- p.4 / Chapter 1.3 --- Surface structure of sulfide-passivated surface --- p.5 / Chapter 1.4 --- Surface structure of ultra-violet/ozone oxidation --- p.8 / Chapter 1.5 --- Objectives of present study --- p.10 / Chapter Chapter 2 --- Instrumentation --- p.12 / Chapter 2.1 --- Introduction --- p.12 / Chapter 2.2 --- Atomic force microscopy (AFM) --- p.12 / Chapter 2.2.1 --- The development of AFM --- p.12 / Chapter 2.2.2 --- Basic principles of AFM --- p.12 / Chapter 2.2.3 --- Forces and their relevance to atomic force microscopy --- p.13 / Chapter 2.2.3.1 --- Van Der Waals forces --- p.15 / Chapter 2.2.3.2 --- Repulsive forces --- p.15 / Chapter 2.2.3.3 --- Capillary forces --- p.15 / Chapter 2.2.4 --- Displacement sensor of AFM --- p.15 / Chapter 2.2.4.1 --- Electron tunneling --- p.16 / Chapter 2.2.4.2 --- Optical interference --- p.16 / Chapter 2.2.4.3 --- Laser beam deflection --- p.16 / Chapter 2.2.5 --- Instrument specification --- p.17 / Chapter 2.2.5.1 --- Contact mode AFM --- p.17 / Chapter 2.3 --- X-ray photoelectron spectroscopy --- p.19 / Chapter 2.3.1 --- The development of XPS --- p.19 / Chapter 2.3.2 --- Basic principles of XPS --- p.19 / Chapter 2.3.3 --- XPS experiments --- p.23 / Chapter 2.3.4 --- Quantitative analysis --- p.26 / Chapter 2.3.4.1 --- Atomic concentration of a homogenous materials --- p.26 / Chapter 2.3.4.2 --- Layer structure --- p.27 / Chapter 2.4 --- Rutherford backscattering spectrometry (RBS) --- p.29 / Chapter 2.4.1 --- Basic principles --- p.29 / Chapter 2.4.2 --- Kinematics --- p.29 / Chapter 2.4.3 --- Channeling --- p.31 / Chapter Chapter 3 --- Surface treatments --- p.32 / Chapter 3.1 --- Semiconductor wafer --- p.32 / Chapter 3.2 --- Cleaning procedures --- p.32 / Chapter 3.3 --- Polysulfide passivation --- p.34 / Chapter 3.4 --- UV/Ozone oxidation --- p.39 / Chapter Chapter 4 --- Surface roughness and oxide contents of sulfide passivation --- p.41 / Chapter 4.1 --- Introduction --- p.41 / Chapter 4.2 --- Experimental methodology --- p.42 / Chapter 4.3 --- Etching --- p.44 / Chapter 4.3.1 --- Etching effect of polysulfide solution --- p.45 / Chapter 4.3.2 --- Possible consequences of the etching effect --- p.45 / Chapter 4.4 --- Oxide contents --- p.47 / Chapter 4.4.1 --- Oxide gained during polysulfide solution treatment --- p.47 / Chapter 4.4.2 --- Oxide gained after polysulfide passivation --- p.47 / Chapter 4.5 --- Surface roughness --- p.49 / Chapter 4.5.1 --- Surface roughness after different passivation methods --- p.49 / Chapter 4.5.2 --- The sticking probability after different passivations --- p.51 / Chapter 4.6 --- The spiral ladder of solution-phase passivation --- p.55 / Chapter 4.7 --- Conclusions --- p.58 / Chapter Chapter 5 --- Sulfide on Ge/GaAs heterojunction --- p.59 / Chapter 5.1 --- Introduction --- p.59 / Chapter 5.1.1 --- Band structure of Ge/GaAs heteroj unction --- p.59 / Chapter 5.1.2 --- Lattice match of Ge/GaAs heteroj unction --- p.60 / Chapter 5.1.3 --- The growth of Ge on GaAs using molecular beam epitaxy --- p.62 / Chapter 5.2 --- The growth of Ge on GaAs using thermal pulse annealing --- p.63 / Chapter 5.3 --- Sulfide as an atomic interdiffusion barrier --- p.65 / Chapter 5.3.1 --- Experimental methodology --- p.65 / Chapter 5.3.2 --- Crystallinity of Ge --- p.67 / Chapter 5.3.3 --- Results and discussions --- p.67 / Chapter 5.3.3.1 --- RBS and XPS results --- p.67 / Chapter 5.3.3.2 --- AFM and I-V results --- p.71 / Chapter 5.4 --- Conclusions --- p.71 / Chapter Chapter 6 --- UV/03 on Ge/GaAs heterojunction --- p.72 / Chapter 6.1 --- Introduction of UV/o3 oxidation --- p.72 / Chapter 6.2 --- UV/o3 oxidation on GaAs --- p.74 / Chapter 6.3 --- Ge on UV/o3 treated GaAs --- p.76 / Chapter 6.3.1 --- Experimental methodology --- p.76 / Chapter 6.3.2 --- Crystallinity of Ge --- p.77 / Chapter 6.3.3 --- AFM results --- p.77 / Chapter 6.3.4 --- RBS results --- p.80 / Chapter 6.4 --- Diodes --- p.82 / Chapter 6.4.1 --- Fabrication of diode --- p.82 / Chapter 6.4.2 --- Diode characteristics --- p.84 / Chapter 6.4.3 --- I-V characteristics --- p.90 / Chapter 6.5 --- Conclusions --- p.90 / Chapter Chapter 7 --- Conclusion and future work --- p.93 / Chapter 7.1 --- Conclusions --- p.93 / Chapter 7.2 --- Future works --- p.94 / Reference --- p.95

Thesis (M.S.)--Rochester Institute of Technology, 2007. / Typescript. Includes bibliographical references.

For decades, epitaxy is used in nanotechnologies and semiconductor fabrications. So far, it's the only affordable method of high quality crystal growth for many semiconductor materials. Heterostructures developed from these make it possible to solve the considerably more general problem of controlling the fundamental parameters inside the semiconductor crystals and devices. Moreover, as one newly arising study and application branch of epitaxy, selective area growth (SAG) is widely used to fabricate materials of different thicknesses and composition on different regions of a single wafer. All of these new and promising fields have caught the interests and attentions of all the researchers around the world. In this work, we will study the stress and strain analysis of epitaxy in nano-scale materials, in which we seek a methodology to bridge the gap between continuum mechanical models and incorporate surface excess energy effects, which can be obtained by molecular dynamical simulations. We will make a brief description of the elastic behavior of the bulk material, covering the concepts of stress, strain, elastic energy and especially, the elastic constants. After that, we explained in details about the definitions of surface/interface excess energy and their characteristic property tensors. For both elastic constants and surface excess energy, we will use molecular dynamic simulations to calculate them out, which is mainly about curve-fitting the parabola function between the total strain energy density and the strain. After this, we analyzed the stress and strain state in nanoisland during the selective area growth of epitaxy. When the nanoisland is relaxed, the lattice structure becomes equilibrated, which means the total strain energy of system need to be minimized. Compared to other researcher's work, our model is based on continuum mechanics but also adopts the outcome from MD simulations. By combining these microscopic informations and those macroscopic observable properties, such as bulk elastic constants, we can provide a novel way of analyzing the stress and strain profile in epitaxy. The most important idea behind this approach is that, whenever we can obtain the elastic constants and surface property tensors from MD simulations, we can follow the same methodology to analyse the stress and strain in any epitaxy process. This is the power of combining atomistic simulations and continuum method, which can take considerations of both the microscopic and macroscopic factors.

No description available.

Thesis (Ph.D.) -- McMaster University, 1998. / Includes bibliographical references (leaves 185-191). Also available via World Wide Web.