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In this study, detailed characteristics and performance assessment of 3&amp / #8722 / 5 &micro / m p-i-n InSb photodetectors on Si substrates are reported. The detector epilayers were grown on GaAs coated Si substrates by molecular beam apitaxy (MBE). Both homojunction and single heterojunction (AlInSb/InSb) detector structures were investigated. Arrays of 33x33 &micro / m2 detectors were fabricated and flip-chip bonded to a test substrate for detailed electrical and optical characterization. A peak detectivity as high as 1x1010 cmHz1/2/W was achieved with InSb homojunction detectors on Si substrate in spite of the large lattice mismatch between InSb and Si (%19). In both homojunction and single heterojunction structures the differential resistance is significantly degraded by trap assisted tunneling (TAT) under moderately large reverse bias and by ohmic leakage near zero-bias. While the heterojunction structures provide a higher 80 K zero bias differential resistance, the responsivity of this structure is significantly lower than that of homojunction InSb photodiodes. In both homojunction and heterojunction photodetectors, 80K 1/f noise is dominated by TAT processes, and the noise current at 1 Hz follows the empirical relation in= &amp / #945 / TAT(ITAT) &amp / #946 / with &amp / #945 / TAT&amp / #8764 / 1.1x10&amp / #8211 / 6 and &amp / #946 / &amp / #8764 / 0.53.

We present studies of the electical detection of spin injection and transport in InSb/CoFe heterostructures. As a narrow gap semiconductor, InSb has a high mobility and strong spin-orbit interaction. Using ferromagnetic CoFe, lateral InSb/CoFe devices are fabricated by semiconductor processing techniques. The saturation magnetizations of various CoFe electrodes with different widths are calculated from Hall measurements in which the fringing fields of the CoFe electrodes are detected. A magnetic model provides reasonable estimation of the saturation magnetization for micrometer scale geometries. The interface magnetoresistance measurements of InSb/CoFe thin film layered structures present a unique peak at low field, having a symmetric behavior in magnetic field with a critical field Hc and a strong temperature dependence. We attribute our signal to a ferromagnetic phase in the InSb induced by spin injection. In a non-local lateral spin valve measurement, we observed the following. Firstly, Hc of the lateral spin valve signals is identical to Hc of interface magnetoresistance signals. Secondly, the non-local lateral spin valve signals are strongly dependent on temperature, which is also a unique characteristic magnetoresistance. Thirdly, the signals are tunable in response to an applied injector bias. Lastly, the signals are dependent on the exact interfaces. Based on these observations, the detected signals may be considered as spin current signals. The Hall and magnetoresistance signals are measured locally and non-locally in InSb/CoFe Hall devices. The non-local magnetoresistance signals exhibit asymmetric behavior in applied magnetic field which are considered as signatures of spin phenomena. The non-local Hall signals present switching behavior with the CoFe magnetization switching at the coercive field. The non-local Hall signals in a perpendicular field show Hc, similarly seen in non-local lateral spin valves. Inverse spin Hall effect measurements with tilted magnetic fields show an in-plane magnetic field dependence in non-local type Hall signal and a perpendicular magnetic field dependence in the local Hall measurement. We have found that the signal can have its origin in a spin current from our observation of Hc and hysteresis in the magnetization traces. As yet, the spin current transport mechanism is unknown. / Ph. D.

The relation between the electrical property and the material microstructure of InSb grown on Si utilizing electron beam evaporation technology has been investigated. The improvement of the InSb electrical property with controlling annealing environment after post annealing is demonstrated. The crystal structure of InSb thin films were characterized with X-ray diffraction (XRD) and the surface morphology was examined by scanning electron microscope (SEM). The composition of InSb films was analyzed by electron probe microscope analysis (EPMA) and the mobility of InSb films were measured by Hall measurement. Finally, the grain size and texture of InSb films microstructure were studied by transmission electron microscope (TEM). The films were grown with different In/Sb flux ratio by controlling electron energy during electron evaporation. The results show that the poly-InSb films were formed due to large lattice difference between Si and InSb . The InSb films which had higher In concentration behave higher mobility. The highest mobility of the as-grown film is around 12000(cm2/Vs). The mobility of InSb can be improved to 26000 (cm2/Vs) by added extra Sb source annealed at 500¢J for 5 hours in an sealed ampoule. The extra Sb which dissolved with the existed In droplet in the film and adjust the composition ratio of In/Sb closing to 1:1. Besides, the post-annealing process provides the InSb film to gain much better texture. Both these two factors contribute to improve the electrical property of InSb films.

Spin-dependent phenomena in semiconductor nanowires have recently gained a lot of attention, in special because these nanostructures can be a viable setup to study exotic states of matter like the Majorana fermions. One of the key ingredients to accommodate the Majorana zero modes is the spin-orbit coupling in the nanowires, which has been usually treated with two-band Hamiltonians. The spin-orbit coupling in semiconductors arise from two distinct sources being the bulk inversion asymmetry, when the unit cell does not present inversion symmetry, e.g. when the crystal unit cell is composed by two different atoms, and the structural inversion asymmetry, when the whole system does not have a mirror symmetry. To describe the system these effective models take as input, parameters that are dependent on the system configuration and measurement setups. Although these effective models have been successful in determine relevant physical properties, a more realistic description of the interacting energy bands is required, specially in quantum confined systems where the interplay between both sources of spin-orbit coupling can change the systems properties in non-trivial ways. For instance, in quantum wells there is an anisotropy of the g-factor due to the quantum confinement and structural inversion asymmetry. Furthermore, the in-plane g-factor also have an anisotropy which is due to the intrinsic spin-orbit coupling and it is not captured by these effective models. In this study, we use realistic multiband k · p Hamiltonians, including both spin-orbit coupling mechanisms, to determine the band structure of zincblende InSb and wurtzite InAs nanowires under a transverse electric field. We analyze the effects of the lateral quantum confinement for a hexagonal cross-section geometry and of the change in growth directions, extracting the relevant physical parameters for the first conduction subband. We found that the g-factors are heavily dependent on the quantum confinement and nanowire orientation, with in-plane/out-of-plane anisotropies up to 3%. We also found that for zinc-blende nanowires the extrinsic spin-orbit coupling is dominant over the intrinsic one whereas, for wurztize, the opposite behavior holds. In order to assess if the nanowires could host the aforementioned Majorana zero modes we investigate under which circumstances the topological phase transition occurs, using the Bogoliubov-de Gennes formalism to couple the nanowire with a superconductor, and we found that using realistic and experimental feasible parameters, indeed, the phase transition occurs. In conclusion, our systematic investigation of nanowires shows that the spin-orbit coupling energy can be fine tuned by the external electric field in experimentally achievable setups that ultimately could guide the search for the elusive Majorana modes. Moreover, our numerical approach is not restricted to a specific material or dimensionality and can be used to study others systems to provide useful insights into the electronic and spintronic fields. / Recentemente, fenômenos dependentes de spin em nanofios semicondutores se tornaram uma área de pesquisa ativa especialmente porque essas nanoestruturas podem ser viáveis para o estudo de estados exóticos da matéria como, por exemplo, os férmions de Majorana. Um dos ingredientes chave para que esses modos de excitação possam existir em nanofios é o acoplamento spin-órbita, o qual tem sido usualmente tratado com modelos de duas bandas. O acoplamento spin-órbita em semicondutores aparece de duas fontes distintas sendo elas a assimetria de inversão no bulk, quando a célula unitária do cristal não possui simetria de inversão, por exemplo, quando é formada por dois átomos diferentes, e a assimetria de inversão estrutural, quando o sistema como um todo não possui simetria de inversão. Para descrever o sistema, os modelos efetivos de duas bandas usam como entrada parâmetros que dependem tanto do sistema específico quanto da configuração do arranjo experimental. Apesar desses modelos terem sucesso em descrever algumas das propriedades físicas relevantes, uma descrição mais realística da interação entre as bandas de energia se faz necessária, especialmente em sistemas com confinamento quântico onde a ação combinada das duas fontes de acoplamento spin-órbita muda as propriedades do sistema de maneira não-trivial. Por exemplo, o fator giromagnético em poços quânticos é anisotrópico devido aos efeitos de ambos, confinamento quântico e a assimetria de inversão estrutural. Ademais, o fator giromagnético ao longo do plano também possui uma anisotropia, a qual tem origem no acoplamento spin-órbita intrínseco do sistema e não é capturada por esses modelos efetivos. Nesse estudo, nós usamos Hamiltonianos k · p multibanda, incluindo ambos os mecanismos de acoplamento spin-órbita, para determinar a estrutura de bandas de nanofios de InSb na fase blenda de zinco e InAs na fase wurtzita sob a ação de um campo elétrico transversal. Nós analisamos os efeitos do confinamento quântico lateral, para fios com seção transversal hexagonal, e diferentes direções de crescimento, extraindo parâmetros físicos relevantes para a primeira sub-banda de condução. Nós encontramos que os fatores giromagnéticos são fortemente influenciados pelo confinamento quântico e orientação dos nanofios, com anisotropias no plano e fora do plano de até 3%. Nós também encontramos que para nanofios de InSb na fase blenda de zinco, o acoplamento spin-órbita extrínseco domina o intrínseco enquanto que, em nanofios de InAs na fase wurtzita, vale o oposto. Para avaliar se os nanofios podem hospedar os modos de Majorana de energia zero nós investigamos sob quais circunstâncias a transição de fase topológica ocorre usando o formalismo de Bogoliubov-de Gennes para acoplar o nanofio a um supercondutor, e encontramos que usando nossos parâmetros e em condições experimentalmente factíveis, de fato, a transição de fase ocorre. Em conclusão, nossa investigação sistemática nos nanofios mostrou que o acoplamento spin-órbita pode ser ajustado por fontes externas, tais como um campo elétrico aplicado, e em configurações experimentais factíveis e que ultimamente pode guiar à busca dos elusivos modos de Majorana. Além do mais, nossa abordagem numérica não é restrita a esses materiais em específico e nem a nanofios, podendo ser usada para estudar outros sistemas provendo intuições úteis nos campos de eletrônica e spintrônica.

Cette thèse, réalisée à l'IES en partenariat avec la société SOFRADIR et le CEA-LETI, avait pour objectif d'évaluer les potentialités du matériau InSb pour la réalisation de photodiodes à avalanche (APD) moyen infrarouge (MWIR). Par l'étude du design (simulations TCAD), de la fabrication technologique en configuration MESA (voie humide, voie sèche, passivation), puis par la caractérisation électrique des dispositifs, ce travail de thèse s'est attaché à explorer l'ensemble des éléments nécessaires au développement de cette filière de photodétecteurs. Les photodiodes InSb fabriquées par épitaxie par jets moléculaires (EJM) ont présenté des densités de courant d'obscurité sur des monoléments de 10 à 30nA/cm² à -50mV et à 77K. Ces performances positionnent ces photodiodes à l'état de l'art pour la filière épi-InSb et souligne ainsi l'excellente qualité cristalline des couches épitaxiées. Les premières APDs InSb ont ensuite été épitaxiées et caractérisées. Avec une pure injection d'électrons nous avons observé une augmentation exponentielle du gain dans l'InSb, signature d'une multiplication initiée exclusivement par les électrons. Un premier gain de 3 à -4V a été mesuré. Cette asymétrie du processus d'ionisation par impact indiquerait la possibilité d'obtenir du gain sans excès de bruit, propriété indispensable pour les applications d'imagerie faible flux visée. A ce stade de l'étude, les performances des APDs InSb sont limitées par un dopage résiduel trop élevé dans les zones de multiplications réalisées, entrainant une forte contribution du courant tunnel bande à bande. Néanmoins, ces travaux fournissent tous les éléments d'orientations nécessaires au développement des APDs InSb dont le point clé est définitivement l'obtention d'un faible dopage résiduel dans la zone de multiplication. / This thesis realized at the IES, with the collaboration of SOFRADIR and the CEA-LETI, had for objective the potential evaluation of the InSb material for the realization of midwave infrared (MWIR) avalanche photodiodes (APD). Studying the design (TCAD modeling), the MESA technological fabrication (wet etching, dry etching, passivation) and analyzing the electrical characterizations of devices fabricated, this work has investigated all the scientific elements necessary for the development of this photodetector technology. The MBE (Molecular Beam Epitaxy) grow InSb photodiodes have shown monopixel dark current density from 10 to 30nA/cm² at -50mV and 77K. These performances are at the state of the art for InSb epi-diodes and highlight the excellent crystal quality of the epitaxial layers. The first InSb APDs were grown and characterized. With a pure electron injection, we have observed an exponential increase of the gain, signature of a single carrier multiplication exclusively initiated by the electrons. A gain value of 3 was measured at -4V. This asymmetrical aspect of the impact ionization process would indicate the possibility to obtain a gain without excess noise. This is fundamental for the intended imaging applications. At this stage, InSb APD performances are limited by a too high residual doping level, resulting in a strong band to band tunneling current. Nevertheless, this work provides all the milestones needed for the InSb APD development where the key point is undoubtedly the getting of low residual doping level in the multiplication layer.

Spin-dependent phenomena in semiconductor nanowires have recently gained a lot of attention, in special because these nanostructures can be a viable setup to study exotic states of matter like the Majorana fermions. One of the key ingredients to accommodate the Majorana zero modes is the spin-orbit coupling in the nanowires, which has been usually treated with two-band Hamiltonians. The spin-orbit coupling in semiconductors arise from two distinct sources being the bulk inversion asymmetry, when the unit cell does not present inversion symmetry, e.g. when the crystal unit cell is composed by two different atoms, and the structural inversion asymmetry, when the whole system does not have a mirror symmetry. To describe the system these effective models take as input, parameters that are dependent on the system configuration and measurement setups. Although these effective models have been successful in determine relevant physical properties, a more realistic description of the interacting energy bands is required, specially in quantum confined systems where the interplay between both sources of spin-orbit coupling can change the systems properties in non-trivial ways. For instance, in quantum wells there is an anisotropy of the g-factor due to the quantum confinement and structural inversion asymmetry. Furthermore, the in-plane g-factor also have an anisotropy which is due to the intrinsic spin-orbit coupling and it is not captured by these effective models. In this study, we use realistic multiband k · p Hamiltonians, including both spin-orbit coupling mechanisms, to determine the band structure of zincblende InSb and wurtzite InAs nanowires under a transverse electric field. We analyze the effects of the lateral quantum confinement for a hexagonal cross-section geometry and of the change in growth directions, extracting the relevant physical parameters for the first conduction subband. We found that the g-factors are heavily dependent on the quantum confinement and nanowire orientation, with in-plane/out-of-plane anisotropies up to 3%. We also found that for zinc-blende nanowires the extrinsic spin-orbit coupling is dominant over the intrinsic one whereas, for wurztize, the opposite behavior holds. In order to assess if the nanowires could host the aforementioned Majorana zero modes we investigate under which circumstances the topological phase transition occurs, using the Bogoliubov-de Gennes formalism to couple the nanowire with a superconductor, and we found that using realistic and experimental feasible parameters, indeed, the phase transition occurs. In conclusion, our systematic investigation of nanowires shows that the spin-orbit coupling energy can be fine tuned by the external electric field in experimentally achievable setups that ultimately could guide the search for the elusive Majorana modes. Moreover, our numerical approach is not restricted to a specific material or dimensionality and can be used to study others systems to provide useful insights into the electronic and spintronic fields. / Recentemente, fenômenos dependentes de spin em nanofios semicondutores se tornaram uma área de pesquisa ativa especialmente porque essas nanoestruturas podem ser viáveis para o estudo de estados exóticos da matéria como, por exemplo, os férmions de Majorana. Um dos ingredientes chave para que esses modos de excitação possam existir em nanofios é o acoplamento spin-órbita, o qual tem sido usualmente tratado com modelos de duas bandas. O acoplamento spin-órbita em semicondutores aparece de duas fontes distintas sendo elas a assimetria de inversão no bulk, quando a célula unitária do cristal não possui simetria de inversão, por exemplo, quando é formada por dois átomos diferentes, e a assimetria de inversão estrutural, quando o sistema como um todo não possui simetria de inversão. Para descrever o sistema, os modelos efetivos de duas bandas usam como entrada parâmetros que dependem tanto do sistema específico quanto da configuração do arranjo experimental. Apesar desses modelos terem sucesso em descrever algumas das propriedades físicas relevantes, uma descrição mais realística da interação entre as bandas de energia se faz necessária, especialmente em sistemas com confinamento quântico onde a ação combinada das duas fontes de acoplamento spin-órbita muda as propriedades do sistema de maneira não-trivial. Por exemplo, o fator giromagnético em poços quânticos é anisotrópico devido aos efeitos de ambos, confinamento quântico e a assimetria de inversão estrutural. Ademais, o fator giromagnético ao longo do plano também possui uma anisotropia, a qual tem origem no acoplamento spin-órbita intrínseco do sistema e não é capturada por esses modelos efetivos. Nesse estudo, nós usamos Hamiltonianos k · p multibanda, incluindo ambos os mecanismos de acoplamento spin-órbita, para determinar a estrutura de bandas de nanofios de InSb na fase blenda de zinco e InAs na fase wurtzita sob a ação de um campo elétrico transversal. Nós analisamos os efeitos do confinamento quântico lateral, para fios com seção transversal hexagonal, e diferentes direções de crescimento, extraindo parâmetros físicos relevantes para a primeira sub-banda de condução. Nós encontramos que os fatores giromagnéticos são fortemente influenciados pelo confinamento quântico e orientação dos nanofios, com anisotropias no plano e fora do plano de até 3%. Nós também encontramos que para nanofios de InSb na fase blenda de zinco, o acoplamento spin-órbita extrínseco domina o intrínseco enquanto que, em nanofios de InAs na fase wurtzita, vale o oposto. Para avaliar se os nanofios podem hospedar os modos de Majorana de energia zero nós investigamos sob quais circunstâncias a transição de fase topológica ocorre usando o formalismo de Bogoliubov-de Gennes para acoplar o nanofio a um supercondutor, e encontramos que usando nossos parâmetros e em condições experimentalmente factíveis, de fato, a transição de fase ocorre. Em conclusão, nossa investigação sistemática nos nanofios mostrou que o acoplamento spin-órbita pode ser ajustado por fontes externas, tais como um campo elétrico aplicado, e em configurações experimentais factíveis e que ultimamente pode guiar à busca dos elusivos modos de Majorana. Além do mais, nossa abordagem numérica não é restrita a esses materiais em específico e nem a nanofios, podendo ser usada para estudar outros sistemas provendo intuições úteis nos campos de eletrônica e spintrônica.

Miniaturized stretchable electronic devices that can be bent and strained elastically without breaking, have drawn considerable research interest in recent years for wearable computers and integrated bio-sensor applications. Portable electrical power harvesting remains a critical challenge in flexible electronics materials. One proposed solution has been to convert waste heat from the human body into electricity using thermoelectric materials. Traditionally, however, these materials are brittle ceramic semiconductors with limited fracture resistance under deformation. The primary objective of this thesis is to address this challenge by fabricating and studying the mechanical, thermal and electrical performance of stretchable composites combining natural latex polymer with either metallic (Ni) or thermoelectric (InSb) powders. Ni-based and InSb-based latex specimens were synthesized with different powder concentrations up to 36 vol.%. The effects of the powder concentration on tensile elongation, electrical conductivity, and thermal conductivity of the composites were measured at ambient temperature. Strong dependences of mechanical and electrical properties on powder concentration were found. By contrast, thermal conductivity was observed to remain low at all concentrations, suggesting that the predominant heat transport process is through the low-conductivity latex matrix rather than the conductive particles. This thesis was conducted with the support of a Vermont Space Grant Consortium graduate research assistantship.

1-eicosanethiolate molecules form relatively weak bonds with the surface of InSb(100) limiting the order of the self-assembled monolayer despite the long length of the alkyl chain. Heating to only 225 °C in vacuum completely desorbed the eicosanethiolate layer from the surface based on x-ray photoelectron spectroscopy. Even after deposition times as long as 20 h in ethanol, the asymmetric methylene stretch was at 2925 cm-1 in the attenuated total reflection Fourier transform infrared spectrum, which is indicative of alkane chains that are incompletely ordered. Atomic force microscopy images combined with ellipsometry showed that the eicosanethiolate layer conformed to the rough InSb(100) starting surface (2.3±0.2 nm RMS). The reoxidation kinetics in air of InSb(100) and InSb(111)B covered with eicosanethiolate layers was the same despite the lower surface roughness of the latter (0.64±0.14 nm). The bond that the S head group makes with the substrate is the primary factor that determines the cohesiveness of the molecules on the surface. Although interactions between the alkane chains in the layer are sufficient to form a self-assembled layer, the fluidity of the molecules in the layer compromised the chemical passivation of the surface resulting in reoxidation in air after 20 minutes.

Systems with strong spin-orbit coupling are of particular interest in solid state physics as an avenue for observing and manipulating spin physics using standard electrical techniques. This dissertation focuses on the characteristics of elemental bismuth (Bi), which exhibits some of the strongest intrinsic spin-orbit coupling of all elements, and InSb, which exhibits some of the strongest intrinsic spin-orbit coupling of all compound semiconductors. The experiments performed study the quantum transport signatures of nano- and micron-scale lithographically defined devices as well as spin-orbit coupled material/ferromagnet interfaces. All Bi structures are fabricated from Bi thin "films, and hence a detailed analysis of<br />the characteristics of Bi "film growth by thermal evaporation is provided. Morphologically and electrically high quality "films are grown using a two stage deposition procedure. The phase and spin coherence of Bi geometries constrained in one, two, and three dimensions are systematically studied by analysis of the weak antilocalization transport signature, a quantum interference phenomenon sensitive to spin-orbit coupling. The "findings indicate that the phase coherence scales proportionally to the limiting dimension of the structure for sizes less than 500 nm. Specifically, in Bi wires, the phase coherence length is approximately as long as the wire width. Dephasing due to quantum confinement e"ffects limit the phase coherence in small Bi structures, impairing the observation of controlled interference phenomena in nano-scale Bi rings. The spin coherence length is independent of dimensional constraint by the film thickness, but increases significantly as the lateral dimensions, such as wire width, are constrained. This is a consequence of the quantum transport contribution from the strongly spin-orbit coupled Bi(001) surface state. To probe the Bi surface state further, Bi/CoFe junctions are fabricated. The anisotropic magnetoresistance of the CoFe is modifi"ed when carriers tunnel into the CoFe from Bi, possibly due to a spin dependent tunneling process or an interaction between the spin polarized density of states in CoFe and the anisotropic spin-orbit coupled density of states in Bi. InSb/CoFe junctions are studied as InSb "films are a simpler spin-orbit coupled system compared to Bi "films. For temperatures below 3.5 K, a large, symmetric, and abrupt negative magnetoresistance is observed. The low-"field high resistance state has similar temperature and magnetic "field dependences as the superconducting phase, but a superconducting component in the device measurements seems absent. A differential conductance measurement of the InSb/CoFe interface during spin injection indicates a quasiparticle gap present at the Fermi energy, coinciding with the large magnetoresistance. / Ph. D.