Ulm, Univ., Diss., 1998.

M.Ing. (Electronic and Electrical Engineering) / Please refer to full text to view abstract

III-V compound Gallium Antimonide (GaSb), with a low bandgap of 0.72 eV at room temperature, is an attractive candidate for a variety of potential applications in optoelectronic devices. Ion implantation, among non-epitaxial methods, is a common and reliable doping technique to achieve local doping and obtain high-performance ohmic contacts in order to form a pn junction in such devices. An advantage of this technique over the diffusion method is the ability to perform a low-temperature process leading to accurate control of the dopant profile and avoiding Sb evaporation from GaSb surface occurring at 370 C. In this work, the effect of protons and sulfur ions as two implant species on the electrical behavior of MBE-grown undoped GaSb on semi-insulating (SI) GaAs was investigated via the Hall Effect. Protons and sulfur ions were implanted at room temperature (27 C) and 200 C, respectively, and rapid thermal annealing (RTA) was implemented at various temperatures and durations upon encapsulated GaSb. The damage induced by protons enhanced the hole density of GaSb up to around 10 times, whereas mobilities showed both increase and decrease compared to the un-implanted one, depending on the dose. While the activation of sulfur donors at an elevated temperature was anticipated after annealing sulfur implanted GaSb, instead it led to increase in p-type concentration, as the residual damage originated from sulfur implantation dominated substitutional doping. Furthermore, GaSb p/n photovoltaic devices were fabricated by applying sulfur implantation through silicon nitride layer at RT into an n-GaSb wafer (n-type base, p-type emitter). The device showed a rectifying current and photovoltaic characteristic. The J-V plot under AM1.5G illumination conditions, before and after an etch-back optimizing process, indicated lower short circuit current density J_sc, the same open circuit voltage V_oc, and higher fill factor FF, compared to the photovoltaic device with a p-type base. Also, both normalized series R_s and shunt R_p resistances in p/n diode indicated lower and higher values, respectively, as opposed to a GaSb p++/p diode, indicative of higher quality and lower manufacturing defects. / Master of Science / Generally, the photovoltaic effect is a process by which voltage or electric current is generated in a photovoltaic cell when exposed to light. A solar cell is a photovoltaic device, typically consisting a pn junction, that converts incident photon power into electrical power and delivered to a load to do electrical work for variety of applications. There are variety of methods to form a pn junction and fabricate such devices, among which ion implantation is a reliable doping technique. In this process, dopant ions are accelerated and smashed into a perfect semiconductor lattice, creating a cascade of damage that may displace a thousand atoms for each implanted ion and become activated after an annealing process. The ions themselves can act as either electron donors, make the semiconductor n-type, or electron acceptors, make it p-type. In this work, sulfur ions and protons, as two implant species, were implanted into separate Gallium Antimonide (GaSb) substrates and the effect of each on the electrical behavior of GaSb was investigated by Hall effect experiment. Both species raised hole carrier concentration. This behavior was not expected for sulfur ions as they would be assumed to act as electron donors after activation and convert the GaSb surface to an n-type semiconductor. It was identified that this behavior is due to the domination of created defects during implantation over the number of activated sulfur donors. The same characteristics were predicted and verified for proton implantation as well, the effect of which is just leaving damage in the lattice. Furthermore, to verify this method for converting n-type GaSb to p-type and fabricating a pn junction in GaSb for photovoltaic application, sulfur implantation into an n-type GaSb wafer was performed and optimized by removing the excess surface damage away from the device's metal contacts using wet etching. The device showed a diode-like rectifying current and photovoltaic characteristic. Some parameters such as short circuit current density J_sc, open circuit voltage V_oc, fill factor FF, and resistances (shunt and series) were measured and calculated using J-V plot under dark and illuminated conditions.

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At the onset of this study, the work presented in Chapter 3 of this thesis was the primary focus. The work was motivated by JF Prins where he observed the formation of diamond layers on copper followed by C+ implantation into copper. This initial result suggested that it may be possible to generate single crystal diamond layers on single crystal copper. Subsequent efforts to reproduce this result failed. A unique end station was developed where a number of parameters could be altered during the implantation process. A series of carbon ion implantations were carried out on copper and copper-nickel (FCC) single crystals in this end station. The layers were characterised using initially Auger Electron Spectroscopy (AES), Low Energy Electron Diffraction (LEED) and later Raman Spectroscopy. During the early period of this study, the surface science equipment at the then Wits-Schonland Research Institute for Nuclear Sciences, was constantly giving problems. The time constraints on waiting for funds to be made available to repair the equipment, urged me to pursue alternative research endeavours and the results of this research is presented in chapter 4 and 5. The initial work will be investigated further in the future. Details of the end station are presented and the initial results of carbon layers generated in this end station are presented. In chapter 4, a study of C+ implantation into a type IIa (FCC single crystal) diamond using the cold implantation rapid annealing (CIRA) technique is reported. The Raman spectrum was recorded as a function of annealing temperature and C+ ion dose. De- fect peaks at 1450, 1498 and 1638 cm−1 appear in the Raman spectra, which have been previously considered to be unique to MeV implantation. The maximum energy of implantation used in this study was 170 keV. The peaks were monitored as a function of annealing temperature and ion dose. The annealing behaviour of the peaks were similar to those observed in the MeV implantation experiments. It is thus concluded that the defects that give rise to these peaks are related to the point-defect interac- tions that occur within the implantation regime and not to the implantation energy. 1 Understanding the nature of the defects that arise during the implantation annealing process, allows one to manipulate the implantation-annealing cycle, so as to generate defect structures that are useful in the fabrication of an active device in a diamond substrate. This is shown in chapter 5. A p-type (type IIb, FCC crystal) diamond was implanted with either carbon or phos- phorus ions using the cold implantation rapid annealing (CIRA) process. In each case, the energies and doses were chosen such that upon annealing, the implanted layer would act as an n-type electrode. The electroluminescence (EL) emitted from these carbon and phosphorus junctions, when biased in the forward direction, was compared as functions of annealing and diode temperatures. Typical luminescence bands such as those observed in cathodoluminescence (CL), in particular blue band A (2.90 eV) and green band (2.40 eV) were observed. Two bands centred around 2.06 and 4.0 eV were also observed for both the carbon and phosphorus junctions, while a band at 4.45 eV appeared only in the phosphorus implanted junction. This was the first time that the 4.45 eV band was observed in an electroluminescent junction.

by Cheung-Yin Tang. / Title also in Chinese. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1991. / Bibliography: leaves 83-84. / ACKNOWLEDGEMENTS --- p.i / TABLE OF CONTENTS --- p.ii / ABSTRACT --- p.iv / Chapter Chapter 1 - --- Introduction --- p.1 / Chapter 1.1 --- Structure --- p.2 / Chapter 1.1.1 --- Physical Structure --- p.2 / Chapter 1.1.2 --- Electronic Structure --- p.3 / Chapter 1.2 --- Hydrogenation --- p.9 / Chapter 1.2.1 --- Hydrogenation during film formation --- p.10 / Chapter 1.2.2 --- Posthydrogenation --- p.10 / Chapter 1.3 --- Doping of a-Si --- p.11 / Chapter 1.4 --- Previous Results and Applications --- p.13 / Chapter 1.4.1 --- Results --- p.13 / Chapter 1.4.2 --- Applications --- p.24 / Chapter Chapter 2 - --- Experimental Set-up and Techniques --- p.25 / Chapter 2.1 --- Sample Preparation --- p.25 / Chapter 2.1.1 --- Substrate cleaning procedure --- p.25 / Chapter 2.1.2 --- Deposition Method --- p.26 / Chapter 2.1.3 --- Annealing Method --- p.30 / Chapter 2.1.4 --- Hydrogenation Method --- p.31 / Chapter 2.1.5 --- Doping Method --- p.33 / Chapter 2.2 --- Measurements --- p.34 / Chapter 2.2.1 --- Dark Conductivity --- p.34 / Chapter 2.2.2 --- Room Temperature Photo-conductivity --- p.39 / Chapter 2.2.3 --- ESR (Electron Spin Resonance) --- p.39 / Chapter Chapter 3 - --- Results and Discussions --- p.41 / Chapter 3.1 --- Doping effect and posthydrogenation --- p.42 / Chapter 3.2 --- Annealing of the doped films --- p.44 / Chapter 3.3 --- Implantation at different dose levels --- p.46 / Chapter Chapter 4 - --- Conclusions --- p.82 / REFERENCES --- p.83 / APPENDIX --- p.85

Progesterone is unequivocally required for the establishment and maintenance of pregnancy in all mammals studied. Its known functions are complex and encompass global changes in gene expression. Therefore, studies were conducted to characterize the effects of progesterone on expression of genes for endometrial factors having roles in conceptus growth, implantation and establishment of pregnancy. The first study characterized the effect of an artificially induced early increase in circulating progesterone on conceptus growth and development and regulation of expression of galectin-15 (LGALS15), a recently identified protein secreted by the ovine uterine luminal epithelium (LE). Exogenous progesterone beginning on Day 1.5 post-mating accelerated conceptus development on Days 9 and 12. On Day 12 the conceptus was functionally and morphologically advanced to produce greater quantities of interferon tau (IFNT) than blastocysts from control ewes. Further, the endometrium responded to early progesterone and IFNT with early expression of cathepsin L (CTSL), radical S-adenosyl methionine domain containing 2 (RSAD2), and LGALS15 within the endometrium. The second study identifed structural changes within the luminal epithelium which could alter the flux of factors into and out of the uterine lumen to maintain appropriate fetal/maternal communication. In this study, progesterone reduced quantities of proteins associated with both tight and adherens junctions during the elongation period. IFNT subsequently increased these proteins after conceptus elongation. The third and fourth studies identified progesterone-regulated genes which have been implicated as having importance to implantation in sheep, mouse, and human. WNT signaling was transiently downregulated by progesterone, while members of several growth factor families are upregulated including insulin-like growth factor binding proteins (IGFBPs) 1 and 3, hepatocyte growth factor (HGF) and fibroblast growth factor 7 (FGF7), which may enhance conceptus growth. Collectively, these studies assess the role of progesterone in altering gene uterine expression to establish a favorable environment for conceptus development. The long-term goals of these studies are to establish biomarkers of receptivity to conceptus development and implantation, enhance our understanding of gene and pathway regulation in early pregnancy loss, and identify genes which may be targeted in therapeutic strategies to improve reproductive success in humans and animals.