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III-V compound semiconductors such as Gallium Arsenide, Indium Phosphide as well as Indium Arsenide have recently demonstrated the capability of applications in high speed semiconductor devices compared to those made from Silicon. As a result, III-V compound semiconductors have drawn attention of material researchers, in particular in understanding the effects that may occur during manufacturing of these devices. Optical and electrical properties of a device may alter when a foreign atom is introduced during the manufacturing of the device. However, the foreign atom may also lead to the formation of lattice disorder (defects). A convenient way of introducing impurity atoms into a substrate and tailoring their functionality for particular applications is by ion implantation. Mössbauer spectroscopy is a useful technique usually utilized for understanding site location of the impurity atoms in a lattice and the formation of defect complexes. The focus of this dissertation is the study of lattice location of ion implanted ⁵⁷Mn/⁵⁷Fe ions in the III-V semiconductors InP, n-type InAs and p type InAs, and the annealing of implantation induced lattice damage in these samples. ⁵⁷Fe Mössbauer spectroscopy studies have been conducted on III-V semiconductors InP, n-type InAs and p-type InAs with the 57Fe Mössbauer state being populated following the implantation of radioactive ⁵⁷Mn⁺ ions which has the advantage that extremely low fluence implantations are sufficient to give data with good statistics. The ⁵⁷Mn⁺ ions were accelerated to 60 keV at the ISOLDE/CERN facility and implanted with fluences of up to 2x10¹² ions/cm² into single crystal samples which were held at 300 –700 K in an implantation chamber. βdecay of the Mn⁺ imparts an average recoil energy of 40 keV to the daughter ⁵⁷*Fe which are then re-distributed onto interstitial and/or substitutional sites, or trapped in defect complexes and damage sites. The Mössbauer spectra were collected with a light-weight parallel plate avalanche counter, with ⁵⁷Fe enriched stainless steel electrodes, mounted on a conventional drive unit outside the implantation chamber. The spectra were analyzed with the Mössbauer fitting code VINDA which allowed for simultaneous fits of the set of spectra for each sample collected at different temperatures. Acceptable fits to the Mössbauer spectra of the InP, n-type InAs and p-type InAs samples required three components: an asymmetric doublet attributed to Fe atoms in implantation induced damaged environments, a single line assigned to Fe on substitutional In sites, and a weak symmetric doublet assigned to impurity-vacancy complexes. In InP there is already an appreciable substitutional Fe (Feѕ) fraction on implantation at room temperature; while in the InAs samples FeS only becomes significant above 400 K. In all samples, the asymmetric doublet dominates the spectra below 400 K. Implantation damage, however, anneals quite rapidly and at high temperatures (above 400 K), the single line due to Feѕ dominates the spectra while the Fe-defect complex dissociates at 500 K. The implantation induced damage is observed to anneal fast in the arsenide samples compared to the phosphide sample. The slow annealing of the damage in InP was supported by the higher Debye temperature (290 K) extracted from the temperature dependence of the site population for the damage site in InP compared with InAs (194 K and 200 K for n-type and p-type, respectively). Variations in the isomer shift and quadrupole splitting for the damage site in InP at high temperatures (above 400 K) suggest structural changes in the neighborhood of the ⁵⁷Fe probe. Furthermore, the isomer shifts of the spectral components were consistent with near trivalent state and fully trivalent state i.e., Fe³⁺ with d⁵ electron configuration for Fe ions in the damage site and at the substitutional (In) site, respectively. The impurity Fe atoms associated with vacancies are identified to be in the Fe²⁺ state with a d⁶ electron configuration. ________________________________________________________________ / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2011.

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This thesis is concerned with the interaction of a finely focussed light beam and a semiconductor. The object of the work is to develop a consistent theory which explains the formation of both the optical beam induced current and photoluminescence signals with a view to using these techniques to characterize semiconductor materials. Here we extend previous theories by considering a light beam which is focussed through a lens of finite numerical aperture. Expressions are derived which give the distribution of excess minority carriers injected into a semi-infinite semiconductor by the focussed light beam. The injected minority carrier distribution is then used to predict the imaging properties of the optical beam induced current and photoluminescence techniques when used to image electrically active defects in semiconductors. High resolution scanning photoluminescence images of indium phosphide are presented showing a resolution which is in good agreement with theory. The form of both the steady state and time dependent optical beam induced current in Schottky barrier diodes, planar junction diodes and devices where the p-n junction is perpendicular to the semiconductor surface is derived. Various methods are suggested for measuring the minority carrier diffusion length and lifetime. An extension to previous analyses is given by considering the effect of scanning the light beam, at some arbitrary velocity, on the form of the optical beam induced current collected by a p-n junction either parrallel or perpendicular to the semiconductor surface. It is also shown how the scan speed can effect the imaging of electrically active defects producing a contrast function which is asymmetric and reduced in magnitude. An analysis of the photoluminescence signal generated from a semi-infinite semiconductor by a finely focussed light beam is given. Various methods based on the photoluminescence technique are suggested for measuring the minority carrier lifetime.

The purpose of this research was to develop a more convenient method to distinguish bacteria using Fourier transform infrared (FT-IR) spectroscopy. The specular reflectance infrared spectra of bacterial colonies were obtained in-situ, without removing them from the agar growth media. The spectra of a variety of bacterial species were obtained by the infrared microscope and then were analyzed by factor analysis. Using this statistical method in conjunction with in-situ sampling we evaluated how well Grampositive species were sorted from Gram-negative species. Also, how the type of agar used and how the age of bacterial colonies affects the results of Gram stain predictions were evaluated; our experiments showed that the influence of those various conditions can be decreased. The suitability of various sets of standard spectra for predicting Gram stain, including sets constructed with and without Kramers-Kronig transformation and those constructed using partial regions verses the complete mid-infrared region, was evaluated.The effect that water on the surface of the colonies has been studied in distinguishing bacteria. Furthermore, the original method was improved and the method's suitability to differentiate a larger number of different bacterial species was examined. / Department of Chemistry