Two problems have been investigated in connection with this thesis. The first was a search for crystals which detect alpha particles by the transient conductivity produced. The second involved the measurement of Hall voltages and conductivity to determine properties of lead sulphide. A few crystals have been made to count alpha particles, some.at room temperature, and others at liquid air temperatures. As it is inconvenient to cool crystals, an attempt was made to find a suitable room temperature counter. A few crystals were tried, but most of the time was spent investigating periclase. It was thought that periclase, being transparent in the ultraviolet, visible and infra red, should be trap-free and thus might possess good counting properties. Some time was spent investigating associated effects in germanium. In the second problem it was hoped to derive a method of producing lead sulphide in non-stoichiometric, proportions so that reproducible samples could be made. If the properties of one sample were determined by using Hall voltage and conductivity measurements, then the properties of all samples would be known. At present, as there are no methods of making lead sulphide with given properties, this would be advantageous. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Supervisor; Professor Robert Barrie The question to what extent the poles of the temperature dependent Green's functions have physical significance as temperature dependent energy levels Is considered. Our contention is that such levels should not be thought of in terms of internal energy or free energy. They have no physical significance other than perhaps to say how the statistical mechanical averaging was divided into its two steps. It is shown that the knowledge of the energy and life time of quasi particles is not very helpful in studying the Hall Constant. To study the Hall Constant one would have to use the appropriate two particle Green's Function and a number of approximations have to be made before one has a simple relation "between the Hall Constant and the average occupation numbers for the quasi-particles. (We have discussed the Hall Constant since this is usually the technique discussed in the literature.) In the literature on the energy gap in semiconductors, the single particle excitation energies (mechanical quantities) were found. They were made temperature dependent by replacing phonon occupation numbers by their thermal averages, and it was assumed then that the gap could be simply written down as a difference of two of these energies. It was not clear whether this should be interpreted as the optical or the thermal gap. We have shown that the question, many times raised in the literature, whether the two gaps are the same or not, is not the relevant question at all. Due to the completely different physical nature of the Hall and absorption phenomena, the definitions of the gaps in both cases are entirely different. We have shown that certain approximations involved in our calculation of the Hall constant and optical absorption coefficient lead to the thermal and optical gaps being the same. The optical gap is the same as the thermal one because our calculation of optical absorption involved only the zero-phonon process, neglect of the vertex part of the corresponding two particle Green's Function, neglect of the damping and neglect of the frequency dependence of the level shift. In summary, it appears that the picture in which one thinks of temperature-dependent energy levels and transitions between these is often too misleading and that it is safer to carry out the calculation of macroscopic behaviour in the correct fashion. One may by the latter method, obtain the result one would have obtained using one's physical Intuition, but the approximations for this are now spelled out. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The onset of concentration broadening of the impurity energy band, in silicon doped with an acceptor and the increase of bandwidth with increasing impurity concentration found experimentally (White 1967) are in disagreement with Baltensperger’s theory (1953). There are two reasons to account for this discrepancy. What was compared previously was actually two different quantities: the experimental half-width of the impurity band and the theoretical full-width of the band. Besides,, the assumptions on which Baltensperger's theory is based, that the impurities are hydrogen-like and arranged on a regular array is not justified in the present problem. The comparison of experimental and theoretical half-widths does not make the discrepancy vanish. We suggest a new way to tackle this problem theoretically by combining the impurity wave functions found by Schechter (1962) and the Green’s function technique and the graphical method presented by Matsubara and Toyozawa (1962). / Science, Faculty of / Physics and Astronomy, Department of / Graduate

For a monovalent donor impurity in a semiconductor, the number of electrons that can be bound to an impurity site is either zero or one. The one bound electron can have either direction of spin. For the discussion of the occupancy of such bound states, one does not apply the usual Fermi-Dirac statistics. A new derivation of the electron distribution function is presented in terms of creation and annihilation operators and the appropriate projection operators for the case of no interaction with the phonons. With the use of double-time temperature-dependent Green's Functions, the electron and phonon distribution functions are derived when there is interaction between the bound electron and phonons. Under certain circumstances, one can speak of a quasi-particle spectrum and the distribution functions have the same form as the interaction-free case but with renormalized energies, which are temperature dependent. The temperature dependence of the distribution functions is then two-fold; one, the usual, statistical, dependence, the other due to the temperature dependence of the energies themselves. The latter quantity requires detailed knowledge of the wave-function, the interaction potential, and energy spectrum of the donor impurity. An application is made to phosphorus donors in silicon. The shifts in the energy levels are found to be small. The agreement with experiment is not completely satisfactory. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This thesis is concerned with (i) the theory of anisotype hetero-junctions and (ii) the fabrication and study of heterojunctions of wide band, gap II-VI compounds with other semiconductors. The theory of anisotype heterojunctions without interface states is discussed on the basis of minority carrier injection. Expressions for the built-in voltage and current voltage relations are derived. The recombination- generation of the carriers in heterojunctions with interface states is considered, using Sah-Shockley-Noyce. theory. The expressions for the recombination-generation rate of the carriers for nine different cases are derived considering three carrier transport mechanisms. ZnSe films were deposited on Ge, GaAs and mica by sublimation under near-equilibrium conditions in an ultra high vacuum. The crystallite size in the films deposited on mica at 500°c was about 15μ. Epitaxy of ZnSe on GaAs was observed around 380°C. The conductivity and Hall mobility of the films on mica were measured under illumination and the results are explained on the basis of a mosaic film model. The photoconductivity of the films was barrier limited at low intensities but carrier limited at high intensities. The nInAs-pZnTe heterojunctions were fabricated by the interface alloying technique. The current voltage and capacitance-voltage characteristics of the devices were studied, and their theoretical relations are derived. Light emission was observed in these heterojunctions under reverse bias conditions. The spectrum of the emitted light was in the energy range of 1.69 eV to 3.5 eV. A number, of peaks were observed in the spectrum at low currents while at high currents only one peak at 2.04 eV was observed. An energy band diagram of ZnTe with different impurity centers is developed to explain the electroluminescence characteristics. The pGe-CdS (photosensitive) heterojunctions were made by a simple alloying technique. The current-voltage and capacitance-voltage characteristics of the heterojunctions were studied under different illumination intensities. The I-V characteristics were non-rectifying at low intensities but rectifying at high intensities. Energy band diagrams, equivalent circuits and the theory of the prepared devices are discussed. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

M.Ing. (Electrical & Electronic Engineering) / Measurement techniques and software were developed for the automation of IV (Current-voltage), CV (Capacitance-voltage), Ct (Capacitance-time), and QC (Charge-capacitance) measurements of semiconductor devices. Apparatus used are a computer and programmable peripheral measurement instruments such as a pico-ammeter, capacitance-voltage meter and voltmeter. The theory concerning the device characteristics was adapted for compatibility with the equipment and the software. Various electrical parameters of diodes, bipolar and field effect transistors can be obtained with the IV measurements. Various characteristics of MOS capacitors are obtained for example to evaluate the oxidation process during semi conductor production. A probe station was developed for obtaining device characteristics at wafer stage.

Thesis (Ph.D.)--George Mason University, 2008. / Vita: p. 104. Thesis director: Mulpuri V. Rao. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical and Computer Engineering. Title from PDF t.p. (viewed Mar. 17, 2009). Includes bibliographical references (p. 99-103). Also issued in print.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1983. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 111-116).

Thesis (M.S.E.E.)--University of Puerto Rico, Mayagüez Campus, 2004. / Tables. Printout. Abstract in English and Spanish. Includes bibliographical references (leaves 82-85).

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.