Freie Universiẗat, Diss., 2004--Berlin. / Dateiformat: zip, Dateien im PDF-Format.

Thesis (Ph. D.)--Georgia State University, 2006. / Title from title screen. Unil Perera, committee chair; Donald Edwards, Gennady Cymbaluyk, Mark Stockman, Nikolaus Dietz, Paul Wiita, committee members. Electronic text (348, 24-32 p. : ill.) : digital, PDF file. Description based on contents viewed June 8, 2007. Includes bibliographical references (p. 24-30, second sequence).

Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 16-19, 108-110, 157-159, 203-205, 270-272, 315-316, 337).

Th. 3e cycle--Électronique, électrotech., autom.--Toulouse 3, 1979. N°: 2193.

A study has been made of 7, LEC grown, tellurium doped gallium phosphide samples using pulsed nmr, Hall effect, and related measurements. The results have been correlated with nmr, esr, electron susceptibility, and transport measurements in similar systems, and changes which occur in the donor electron system in the intermediate doping region preceding the metallic transition have been discussed. The effects which these changes have on the nuclear relaxation times of the host nuclei have been discussed in terms of the various stages of nuclear relaxation by spin diffusion to paramagnetic impurities. In the lightly doped samples, rapid diffusion and diffusion limited relaxation processes have been identified around the minima in the T1:T curves of the P31 , and two Ga isotopes respectively. The effects on nuclear relaxation of the preferential distribution of the Te donor wavefunction on P31 sites have been discussed. Experimental calculations of the Ga69 and Ga71 spin diffusion coefficients have been made and compared with values derived from spin diffusion theory. T1 results from the more heavily doped samples have been discussed in terms of the various models of the state of the electron system in the intermediate doping region. Evidence of the increasing importance of electron spin-spin interactions and diffusion vanishing relaxation processes have been obtained from the concentration, magnetic field, and temperature dependences of the T1's of all three isotopes at low temperatures. Hall and conductivity measurements reflected the reduction in donor ionisation energy with increasing donor concentration in the intermediate doping region, and the observed movement of the position of the T1 minima to lower temperatures in the same samples have been taken as further evidence of this effect. Calculations of the donor ionisation energy have been made from analysis of the temperature dependence of the Ga69 and Ga71 T1's around the T1 minima and from the variation of the position of the minimum with frequency. The weakening and eventual disappearance of the T1 minima in the most heavily doped samples have been discussed in terms of the reduction in the effectiveness of nuclear relaxation to single paramagnetic impurities as impurity hopping and spin-spin effects increase. The enhanced magnetic field dependence and increase in T1 observed in the most heavily doped samples at low temperatures have been taken as evidence for the incomplete delocalisation of the donor electron system in these samples.

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Since the development of the transistor in the Bell Telephone Laboratories in 1948 [78], the semiconductor industry has transformed the world we live in. It is difficult to picture a world without the modern day cutting edge technology. Imagine performing every day functions without “trivial” devices such as computers, cell phones or microwave ovens. The ability to tailor the band gaps of various binary, ternary and quaternary semiconductor systems has opened up a whole new spectrum of potential purpose designed devices [27]. This thesis focuses on the electronic properties of gallium (III) antimonide (V). The antimonides, in general, have the smallest band gap and highest electron mobility of the III-V compound semiconductors and are well suited for long wavelength emission and detection as well as high frequency switching device applications. Furthermore, III-V ternaries and quaternaries, such as (AlGaIn)(AsSb), lattice matched to gallium antimonide (GaSb) are considered serious competitors for HgCdTe and PbSe in long-wavelength infrared (LWIR) and very long-wavelength infrared (VLWIR) technology [4, 10, 11]. Epitaxial material systems based on GaSb are suitable for a wide range of applications such as missile and surveillance systems and a host of other military and civil applications. In addition, an assortment of devices on InAs, GaSb, and AlSb, including resonant tunnelling devices, infrared detectors and mid-infrared semiconductor lasers have been demonstrated [14, 15]. Furthermore, antimonide based devices could potentially reduce optical fibre power loss by a few orders of magnitude, as their implementation can lead to use of non-silica based optical fibres that minimise Raleigh scatter related power loss [8]. GaSb related technology faces a number of challenges. A significant amount of effort is required to exploit the potential it offers. GaSb oxidises readily in the ambient, resulting in the formation of a native oxide layer as well as deposits of elemental antimony (Sb) at the oxide/substrate interface therefore it has poor surface electronic properties resulting from high surface state densities[4, 17, 18]. As grown GaSb is characterised by a high density of surface states of which many are classified as non-radiative (Auger) recombination centres. The elemental Sb layer constitutes an unwanted conduction path parallel to the active surface region [17]. The potential that GaSb and GaSb-based strained layer superlattices offer as successors to the current generation of LWIR and VLWIR optoelectronic materials has therefore been largely impeded [4]. Furthermore, processing steps in device fabrication leads to an unintentionally damaged GaSb surface exacerbating the situation. Any efforts to engineer devices of superior quality on GaSb have to address these and more material specific problems [19]. This study attempts to contribute towards an improved understanding of the structural and electrical properties of the near surface region of Te-doped bulk (100) and MOVPE grown epitaxial Te doped n- GaSb. The main focus of this study is to develop means to de-oxidise and stabilize the highly reactive GaSb surface and to develop diode structures to demonstrate the improved interface characteristics and use related current–voltage (I-V) measurements to quantify the surface state density before and after treatment. These devices were also used to probe the near surface region for electrically active deep level defects that often act as non-radiative recombination centers. Au, Pd and Al were used as metals to establish a metal semiconductor barrier and subsequent depletion region. Sulphur based chemicals, ([(NH4)2S / (NH4)2SO4] + S), not previously reported for the treatment of (100) n-GaSb surfaces, and the commonly used passivants Na2S:9H2O and (NH4)2S were compared by assessing the electrical and structural properties both before and after treatment. The effect of treatment on the electrical response of the material was determined using current-voltage, capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements, while the surface morphology and composition were studied by SEM, AES and XPS.

In this dissertation the microstructure and hardness of phosphorous implanted SiC and neutron irradiated SiC and GaAs have been investigated. SiC is important due to its application as a barrier coating layer in coated particle fuel used in high temperature gas cooled reactors. The characterisation of neutron irradiated GaAs has been included in this study in order to compare the radiation damage produced by protons and neutrons since proton bombardment of SiC could in principle be used for out-of-reactor simulations of the neutron irradiation damage created in SiC during reactor operation. The following SiC and GaAs compounds were investigated: As-implanted and annealed single crystal 6H-SiC wafers and polycrystalline 3C-SiC bulk material implanted with phosphorous ions. As-irradiated and annealed polycrystalline 3C-SiC bulk material irradiated with fast neutrons. As-irradiated and annealed single crystal GaAs wafers irradiated with fast neutrons. The main techniques used for the analyses were transmission electron microscopy (TEM) and nano-indentation hardness testing. The following results were obtained for the investigation of implanted and irradiated SiC and GaAs: Phosphorous Implanted 6H-SiC and 3C-SiC The depth of the P+ ion damage was found to be in good agreement with predictions by TRIM 2010. Micro-diffraction of the damage region in P+ implanted 6H-SiC (dose 5×1016 ions/cm2) indicates that amorphization occurred and that recrystallisation of this layer occurred during annealing at 1200°C. TEM analysis revealed that the layer recrystallised in the 3C phase of SiC and twin defects also formed within the layer. Micro-diffraction of the damage region in P+ implanted 3C-SiC (dose 1×1015 ions/cm2) indicates that amorphization also occurred for this sample and that recrystallisation of this layer occurred during annealing at 800°C. Nano-hardness testing of the P+ implanted 6H-SiC indicated that the hardness of the implanted SiC was initially much lower than unimplanted SiC due to the formation of an amorphous layer during ion implantation. After annealing the implanted SiC at 800°C and 1200°C, the hardness increased due to re-crystallisation and point defect hardening. Neutron Irradiated 3C-SiC TEM investigations of neutron irradiated 3C-SiC revealed the presence dark spot defects for SiC samples irradiated to a dose of 5.9×1021 n/cm2 and 9.6×1021 n/cm2. Neutron Irradiated GaAs TEM investigation revealed a high density of dislocation loops in the unannealed neutron irradiated GaAs. The loop diameters increased after post-irradiation annealing in the range 600 to 800 °C. The dislocation loops were found to be of interstitial type lying on the {110} cleavage planes of GaAs. This finding is in agreement with earlier studies on 300 keV proton bombarded and 1 MeV electron irradiated GaAs where interstitial loops on {110} planes became visible after annealing at temperatures exceeding 500 °C. The small dislocation loops on the {110} planes of the neutron irradiated GaAs transformed to large loops and dislocations after annealing at 1000 °C.

This investigation is concerned with a study of the properties of scandium-germanium systems, and a study of the properties of selenium and zinc doped gallium arsenide„ In part one the physical properties of scandium and germanium are used to empirically estimate the relative solubility of scandium in germanium. It was shown that scandium and germanium are miscible in the liquid phase and that scandium has a very low solid solubility in germanium. Crystals of scandium-doped germanium were grown and analyzed using Hall constant and resistivity measurements from liquid nitrogen temperature to room temperature. The results show that the crystals grown are p-type, but that this behaviour cannot be completely attributed to scandium. However, it was shown that if scandium does not form compounds on crystal growth, it has a maximum solubility in germanium of less than one part per million. Methods for analysing the results of experimental measurements, to determine the concentration of acceptors, donors and free carriers, and the ionization energies are given. In part two the properties of selenium and zinc doped gallium arsenide were studied, again using resistivity and Hall measurements. Selenium and zinc were determined to be shallow donors and acceptors respectively. The concentration of the impurities present were determined and the properties of the material were discussed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate