La croissance localisée de SiC dopé p par un mécanisme Vapeur-Liquide-Solide (VLS) a été effectuée sur substrats SiC-4H (0001) 8°off et diamant (100). Pour ce faire, des motifs constitués d'un empilement silicium-aluminium sont fondus puis alimentés en propane. Dans le cas de l'homoépitaxie de SiC-4H, il a été démontré que la quantité limitée de phase liquide initiale entraine une évolution constante des paramètres de croissance en raison de l'appauvrissement graduel en silicium. Il est toutefois possible de trouver des conditions de croissance satisfaisantes (alliage contenant 40 at% Si, 1100 °C) résultant en un dépôt conforme sur l'ensemble des motifs avec une morphologie step-bunchée. A partir de tels dépôts, des contacts ohmiques de très faible résistivité (jusqu'à 1,3.10-6 Ω.cm2) ont été mesurés et des diodes PiN ont été fabriquées et caractérisées. Dans le cas de la croissance de SiC sur diamant, la forte réactivité entre l'alliage Si-Al liquide et le substrat diamant conduit à la formation d'un dépôt dense et polycristallin de SiC-3C par un mécanisme de dissolution-précipitation. Nous avons montré que la formation préalable d'une couche tampon nanométrique de SiC par siliciuration du substrat de diamant (réaction solide-solide entre une couche de Si et le diamant) permet d'obtenir une croissance épitaxiale de SiC-3C en ilots, avec les relations [110] SiC // [110] diamant et (100) SiC // (100) diamant. Il n'a cependant pas été possible de former une couche complète et épitaxiale de SiC sur diamant par VLS localisée. Nous avons toutefois montré que cela est réalisable par dépôt chimique en phase vapeur (CVD) en utilisant la même étape de siliciuration / The localized growth of p-doped SiC by Vapor-Liquid-Solid (VLS) mechanism was made on (0001) 8°off 4H-SiC and (100) diamond substrates. A silicon-aluminium stacking, localized on top of the substrate, is used after melting as the liquid phase for the growth, carbon being brought by the propane of the gas phase. Regarding the homoepitaxial growth of 4H-SiC, the limited amount of liquid phase leads to a significant consumption of silicon during the growth which is responsible for a continuous variation of the growth parameters. Satisfying growth conditions can therefore be found (40 at% Si alloy, 1100 °C) leading to the formation of a step-bunched layer on the initial Si-Al patterns. Very Low resistivity ohmic contacts (as low as 1.3x10-6 Ω.cm2) and PiN diodes were successfully fabricated from these deposits. Regarding the SiC growth on diamond, the high reactivity between the Si-Al liquid alloy and the diamond substrate leads to the polycrystalline growth of 3C-SiC by a dissolution-precipitation mechanism. It is thus necessary to use a SiC buffer layer in order to achieve an epitaxial growth. This buffer layer, grown by a solid-solid reaction between silicon (deposited by CVD) and the diamond called silicidation, favors the epitaxial growth of 3C-SiC ([110] SiC // [110] diamond and (100) SiC // (100) diamond) during the later VLS growth. Considering the 3D growth mechanism that takes place the formation of a single-crystalline layer from these epitaxial islands seems difficult. Such single-crystalline layer can be achieved using chemical vapor deposition (CVD) after the silicidation step of the diamond substrates

Anomalous Hall behavior of HgCdTe refers to a "double cross-over" feature of the Hall coefficient in p-type material, or a peak in the Hall mobility or Hall coefficient in n-type material. A magnetoconductivity tensor approach was utilized to identify presence of two electrons contributing to the conduction as well as transport properties of each electron in the material. The two electron model for the mobility shows that the anomalous Hall behavior results from the competition of two electrons, one in the energy gap graded region near the CdZnTe/HgCdTe interface with large band gap and the other in the bulk of the LPE film with narrow band gap. Hg0.78Cd0.22Te samples grown by LPE on CdZnTe(111B)-oriented substrates were exposed to various doses of thermal neutrons (~1.7 x 1016 - 1.25 x 1017 /cm2) and subsequently annealed at ~220oC for ~24h in Hg saturated vapor to recover damage and reduce the presence of Hg vacancies. Extensive Magnetotransport measurements were performed on these samples. SIMS profile for impurities produced by neutron irradiation was also obtained. The purpose for this study is to investigate the influence of neutron irradiation on this material as a basis for further study on HgCdTe74Se. The result shows that total mobility is observed to decrease with increased neutron dose and can be fitted by including a mobility inverse proportional to neutron dose. Electron introduction rate of thermal neutron is much smaller than that of fission neutrons. Total recovering of the material is suggested to have longer time annealing. Using Kane's model, we also fitted carrier concentration change at low temperature by introducing a donor level with activation energy changing with temperature. Results on Se diffusion in liquid phase epitaxy (LPE) grown HgCdTe epilayers is reported. The LPE Hg0.78Cd0.22Te samples were implanted with Se of 2.0×1014/cm2 at 100keV and annealed at 350-450oC in mercury saturated vapor. Secondary ions mass spectrometry (SIMS) profiles were obtained for each sample. From a Gaussian fit we find that the Se diffusion coefficient DSe is about one to two orders of magnitude smaller than that of arsenic. The as-implanted Se distribution is taken into account in case of small diffusion length in Gaussian fitting. Assuming a Te vacancy based mechanism, the Arrhenius relationship yields an activation energy 1.84eV. Dislocations introduced in HgCdTe materials result in two energy levels, where one is a donor and one is an acceptor. Hydrogenation treatment can effectively neutralize these dislocation defect levels. Both experimental results and theoretical calculation show that the mobility due to dislocation scattering remains constant in the low temperature range (<77K), and increases with temperature between 77K and 150K. Dislocation scattering has little effect on electrical transport properties of HgCdTe with an EPD lower than 107/cm2. Dislocations may have little effect on carrier concentration for semiconductor material with zinc blende structure due to self compensation.

A TPases do tipo P são proteínas integrais de membrana que usam a energia química contida na molécula de ATP para o transporte de cátions através de membranas. O nosso trabalho apresenta a clonagem e o sequenciamento de um gene (BePAT2) e a caracterização da expressão de dois genes (BePAT1 e BePAT2) codificando isoformas de uma ATPase do tipo P no fungo aquático Blastocladiella emersonii. As proteínas codificadas por estes genes, surpreendentemente se mostraram mais similares às Na+/K+ e H+/K+-ATPases de eucariotos superiores do que a outras ATPases de fungos. Experimentos de \"Northern blot\", imunoprecipitação e \"Western blot\" demonstraram que as ATPases (BePAT1 e BePAT2) são diferencialmente expressas durante o desenvolvimento de B. emersonii. Os resultados obtidos mostraram que o aumento da transcrição dos genes refletiu em um aumento da síntese e do acúmulo das ATPases, sugerindo um controle pré-traducional da expressão de BePAT1/2. Estudos de formação de fosfoenzima na presença de diferentes íons e inibidores, utilizando as enzimas imunopurificadas, sugerem que as proteínas codificadas por estes genes tenham uma atividade semelhante às Na+/K+-ATPases. Os nossos resultados de expressão e atividade mostram pela primeira vez, evidências da funcionalidade de genes codificando uma proteína similar às Na+/K+-ATPases em um eucarioto inferior. / P- type A TPases are integral membrane proteins which use the energy stored in the A TP molecule to drive the transport of cations through biological membranes. In this work we report the cloning and sequencing of the BePAT2 gene and the characterization and expression of two genes (BePAT1 and BePAT2) encoding isoforms of a P-Type ATPase in the aquatic fungus Blastocladiella emersonii. Surprisingly the putative BePAT1 and BePAT2 proteins are more similar to Na+/K+and H+/K+-ATPases from animal cells than to other P-type ATPases from fungi. Northern blot, immunoprecipitation and Western blot experiments demonstrated that these ATPases (BePAT1 and BePAT2) are developmentally regulated in B. emersonii. The results showed that the increase in the BePAT1/2 transcription reflects in an increase in the synthesis and accumulation of the proteins, suggesting a transcriptional control of the BePAT1/2 expression. Studies of phosphoenzyme formation using the immunopurified enzymes in the presence of different ions and inhibitors suggested a Na/K-ATPase like activity. Our results demonstrate for the first time biochemical evidences of functionality of genes encoding a Na+ /K+-ATPase like protein in an eucaryotic microorganism.

Emerging transparent semiconducting oxide (TSO) materials have achieved their initial commercial success in the display industry. Due to the advanced electrical performance, TSOs have been adopted either to improve the performance of traditional displays or to demonstrate the novel transparent and flexible displays. However, due to the lack of feasible p-type TSOs, the applications of TSOs is limited to unipolar (n-type TSOs) based devices. Compared with the prosperous n-type TSOs, the performance of p-type counterparts is lag behind. However, after years of discovery, several p-type TSOs are confirmed with promising performance, for example, tin monoxide (SnO). By using p-type SnO, excellent transistor field-effect mobility of 6.7 cm2 V-1 s-1 has been achieved. Motivated by this encouraging performance, this dissertation is devoted to further evaluate the feasibility of integrating p-type SnO in p-n junctions and complementary metal oxide semiconductor (CMOS) devices. CMOS inverters are fabricated using p-type SnO and in-situ formed n-type tin dioxide (SnO2). The semiconductors are simultaneously sputtered, which simplifies the process of CMOS inverters. The in-situ formation of SnO2 phase is achieved by selectively sputtering additional capping layer, which serves as oxygen source and helps to balance the process temperature for both types of semiconductors. Oxides based p-n junctions are demonstrated between p-type SnO and n-type SnO2 by magnetron sputtering method. Diode operating ideality factor of 3.4 and rectification ratio of 103 are achieved. A large temperature induced knee voltage shift of 20 mV oC-1 is observed, and explained by the large band gap and shallow states in SnO, which allows minor adjustment of band structure in response to the temperature change. Finally, p-type SnO is used to demonstrating the hybrid van der Waals heterojunctions (vdWHs) with two-dimensional molybdenum disulfide (2D MoS2) by mechanical exfoliation. The hybrid vdWHs show excellent rectifying performance. Due to the ultra-thin nature of MoS2, the operation of hybrid vdWHs is gate-tunable, and we further discover such gate-tunability depends on the layer number of MoS2, i.e., the screening effect. The detailed study in such hybrid vdWHs provides valuable information for understanding the switching performance of junctions contain 2D materials.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21772号 / 工博第4589号 / 新制||工||1715(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 木本 恒暢, 教授 藤田 静雄, 准教授 杉山 和彦 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

The study of defects in semiconductors has been on-going for over 50 years. During this time, researchers have been studying the origins and identity of process induced defects, a task which has proved to be very demanding. While defects in silicon, the most widely used semiconductor, have been widely studied, there is more literature on n-type silicon than on p-type silicon. Compared to n-type silicon, p-type silicon is challenging to work with when it comes to making good Schottky diodes. A good rectifying device is essential for the performing of electrical characterisation techniques such as deep-level transient spectroscopy. In spite of this challenge p-silicon cannot be ignored. Many of the electronic devices are a combination of both n- and p-silicon therefore the need to understand the electronic properties of both materials. In this thesis, defects introduced in p-Si by electron beam deposition (EBD) were investigated. In order to understand these defects better, defects introduced by conditions of electron beam deposition (EBD) without metal deposition, were investigated. This process will be referred to as electron beam exposure (EBE). Finally, the defects were compared to defects induced by alpha-particle irradiation. EBD defects, introduced during electron beam deposition (EBD) of titanium (Ti) contacts on p-Si were investigated. The Schottky contacts were annealed within a temperature range of 200–400 oC. Current-voltage (I-V) measurements were conducted to monitor the change in electrical characteristics with every annealing step. Deep-level transient spectroscopy (DLTS) and Laplace-DLTS techniques were employed to identify the defects introduced after EBD and isochronal annealing of the Ti Schottky contacts. DLTS revealed that the main defects introduced during metallisation were hole traps with activation energy of 0.05 eV, 0.23 eV and 0.38 eV. Depth profiles of these defects showed that the formed close to the interface within a depth of 0.4 μm. Defects induced by EBE were studied by exposing samples for 50 minutes after which nickel (Ni) Schottky contacts were fabricated using resistive deposition. Only one defect with an activation energy of 0.55 eV was observed. This activation energy is similar to that of the I-defect. DLTS depth profiling revealed that the defect could be detected up to a depth of 0.8μm below the junction, which is significantly deeper than EBD defects. Defects induced when p-Si was irradiated by alpha particles from a 5.4 MeV americium (Am) 241 foil radioactive source with a fluence rate of 7×106 cm−2 s−1 at room temperature were investigated. After exposure at a fluence of 5.1×1010 cm−2, hole traps with the following activation energies were observed: 0.10 eV, identified as a tri-vacancy related defect, 0.33 eV, the interstitial carbon (Ci), 0.52 eV, a B-related defect and 0.16 eV. Low temperature irradiation experiments were also carried out using alpha- particles with the same fluence rate. Measurements were taken between 35 K and 120 K. The defect levels were at 0.10 eV, 0.14 eV and 0.18 eV. These levels were attributed to the boron-substitutional vacancy complex, the mono-vacancy and a vacancy-related defect, respectively. We conclude that EBD and EBE induced more complex defects than those induced by alpha-particle irradiation. / Thesis (PhD)--University of Pretoria, 2019. / Physics / PhD / Unrestricted

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Recent studies suggest that the performance of dye-sensitised solar cells (DSC) has appeared to have reached a limit, therefore solar cells based on semiconductor materials, such as extremely thin absorber (ETA) solar cells and tandem solar cells are currently the subject of intense research in the framework of low-cost photovoltaic devices as sources of harvesting sunlight to generate electricity. Generally, semiconductor solar cells have been divided into two different types, namely anodic and cathodic type solar cells. Extensive research and development work has been focused on anodic semiconductor sensitised solar cells to date. In contrast, the cathodic semiconductor sensitised solar cells have received no attention which is very surprising. Developing the cathodic semiconductor sensitised solar cell concept is very important in the development of tandem solar cells as well as other new solar cell configurations. The main reason for the lack of research in this area was due to the rarity of p-type semiconductor materials, which made it difficult to find suitable materials to match the energy band edges for cathodic semiconductor sensitised solar cells (CSSC) as well as solid-state cathodic semiconductor solar cells (SS-CSSC). The primary aim of this thesis was to construct cathodic semiconductor sensitised solar cells as well as their solid-state analogues (SS-CSSC). The work conducted within this doctoral study presents state-of-art materials and thin film processing/preparation methods, their characterisation and developing CSSCs and SS-CSSCs employing such films in cascade configurations. No reports have been published in the literature on SS-CSSC to date. The first stage of this thesis is focused on optimising the morphology and the texture (porosity) of the CuI and NiO semiconductor photocathode, by the introduction of new deposition methods namely, pulsed-electrodeposition (PED) and Aerosol-Assisted Deposition (AAD) and Aerosol-Assisted Chemical Vapour Deposition (AACVD). The electrodes prepared by employing the methods mentioned above and controlling the deposition parameters systematically, we have achieved significant improvement in the film morphology and the texture of the deposited films. The resulting electrodes showed excellent improvement in the photoelectrochemical performance which made it suitable for application in construction of both CSSC and SS-CSSC. The photoelectrochemical performance of the electrodes can be seen clearly through the photocurrent density data. For the case of bare CuI, the PEC performance of electrode prepared by the AAD and PED compared against that of continuous-electrodeposition (ED) electrodes. The photocurrent density achieved for the electrodes prepared by AAD and PED was reported around 175 and 75 µAcm-2 respectively which are way higher than the ED case. At the second stage of this study, the work focused on fabrication and characterisation of the CSSCs. Cathodic sensitised PEC solar cells (CuI/Cu2S/(Eu2+/Eu3+) and NiO/Cu2S/(I3-/I-)) were fabricated by deposition of p-Cu2S on the texture controlled CuI and NiO photocathodes. The morphological properties of the photocathode, in particular layer thickness, particle size and film porosity, play an important role in the PEC performance of CSSCs. Optimisation of these parameters led to increased adsorption of the Cu2S light harvester on the photocathode s surface. As a result, the charge injection from Cu2S to the wide band gap photocathode material (CuI and NiO) was significantly improved. Due to this, the CSSC performance showed significant improvement as semiconductor sensitised cathodic solar cells (CSSC). The IPCE and photocurrent density of the CSSC achieved in this study was around (19 and 7 %) and (1 and 0.5 mAcm-2) for the CuI/Cu2S and NiO/Cu2S electrodes respectively. Finally, the SS-CSSC has been fabricated by employing n-Fe2O3 electron transport layer. The construction of SS-CSSC for the first time using the n-Fe2O3 electron transport layer (CuI/Cu2S/Fe2O3 and NiO/Cu2S/Fe2O3) allowed us to study the materials, optical and photoelectrochemical properties of this device. Under AM 1.5 illumination, the SS-CSSC shows a photocurrent density of 6 and 9 µAcm-2 for CuI/Cu2S/Fe2O3 and NiO/Cu2S/Fe2O3 solar cells, respectively. The results of this work indicated low performance for both SS-CSSC compared to CSSC results, due to the lack of adsorption between the absorber and Fe2O3 electrode. However, this study proved the concept of SS-CSSC based on semiconductor material, which is valuable for the future work of cathodic semiconductor sensitised solar cells as well as solid-state tandem solar cells.

This dissertation presents an investigation of the properties, especially the electrical properties, of doped ZnO films grown by plasma-assisted molecular beam epitaxy (MBE) under different conditions. The interest in investigating ZnO films is motivated by the potential of ZnO to replace the currently dominant ITO in industries as n-type transparent electrodes and the difficulty in achieving reliable and reproducible p-type ZnO. On the one hand, n-type ZnO heavily doped with Al or Ga (AZO or GZO) is the most promising to replace ITO due to the low cost, abundant material resources, non-toxicity , high conductivity, and high transparency. On the other hand, ZnO doped with a large-size-mismatched element of Sb (SZO) or co-doped with N and Te exhibits the possibility of achieving p-type ZnO. In this dissertation, the effects of MBE growth parameters on the properties of GZO have been investigated in detail. The ratio of oxygen to metal (Zn+Ga) was found to be critical in affecting the structural, electrical, and optical properties of GZO layers as revealed by x-ray diffraction (XRD), transmission electron microscopy (TEM), Hall measurement, photoluminescence (PL), and transmittance measurements. Highly conductive (~2×10-4 Ω-cm) and transparent GZO films (> 90% in the visible spectral range) were achieved by MBE under metal-rich conditions (reactive oxygen to incorporated Zn ratio < 1). The highly conductive and transparent GZO layers grown under optimized conditions were applied as p-side transparent electrodes in InGaN-LEDs, which exhibited many advantages over the traditional thin semi-transparent Ni/Au electrodes. The surface morphologies of GaN templates were demonstrated to be important in affecting the structural and electrical properties of GZO layers. In those highly conductive and transparent GZO layers with high-quality crystalline structures, studies revealed ionized impurity scattering being the dominant mechanism limiting the mobility in the temperature range of 15-330 K, while polar optical phonon scattering being the mechanism responsible for the temperature-dependence for T>150 K. The majority Sb ions were found to reside on Zn sites instead of O sites for lower Sb concentrations (~0.1 at.%), which can lead to a high electron concentration of above 1019 cm-3 along with a high electron mobility of 110 cm2/V-s at room temperature. The reduction in electron concentration and mobility for higher Sb concentrations (~1 at.%) was caused by the deterioration of the crystalline quality. ZnO co-doped with N and Te was also studied and the advantages of the co-doping technique and problems in achieving p-type conductivity are discussed.