Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 113-118). Available also in a digital version from Dissertation Abstracts.

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"January 1998." / Thesis (Ph.D.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstract in Chinese.

Thesis (Ph. D.)--Michigan State University. Physics, 2008. / Title from PDF t.p. (Proquest, viewed on Aug. 25, 2009) Includes bibliographical references (p. 153-158). Also issued in print.

Thesis (M.S.)--Oregon Graduate Center, 1987.

Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry, March 2001. / Includes bibliographical references. Also available on the Internet.

Measurement of the differential capacitance (C) of a Schottky diode as a function of voltage (V) is widely used to probe dopant profiles in semiconductors. However, the theory of the dopant profiling method is based on an approximation, and does not work well when the dopant concentration changes rapidly with distance. The region beyond the maximum of an implanted Gaussian profile is of particular interest in connection with ingot qualification tests for GaAs, and it is just there that the problem is the most serious. In this thesis, an investigation was made by numerical simulation on problems associated with the profiling method. Programs were written to calculate the differential capacitance-voltage relation for GaAs Schottky diodes with and without deep energy levels, and with a specified dopant distribution. The programs predict what the approximation method would indicate for the dopant profiles according to a set of canonical equations used in the profiling method. The predicted and the specified dopant profiles were then compared. Mainly ion-implanted dopant profiles in semiconductors were studied although doped epitaxial layers were also considered. For ion-implanted GaAs, the predicted dopant profiles were found to be about 10% lower near the peak region than the true dopant profiles, and the predicted profiles were confirmed to be too high in the tail region. For doped epitaxial layers, the predicted profile was found, in some cases, to give good estimates for the dopant concentrations on the high and low sides of the true step profile, but in some others, the predicted profiles were found to be totally misleading. For GaAs with deep levels, a method of calculating the differential capacitance was developed to take into account the fact that the deep levels do not respond to the 1 MHz a.c. signal normally used in the C(V) measurements. It is believed to simulate the experimental C(V) measurements more realistically. The tail sections of the predicted profiles were found to increase with the concentration of background shallow donor atoms in the deep-level-free semiconductor before ion-implantation, and with the number of impurity atoms which are channelled or diffused to the region during or after ion-implantation. This implies that although the profiling method is erroneous in the tail section, it can nevertheless be used on a comparative basis to indicate the level of background shallow dopant concentration, and the degree of channelling or diffusion. The effects of the substrate parameters in liquid encapsulated Czochralski (LEC) GaAs, which include the concentrations of EL2, net shallow acceptors, and sometimes Cr, have been investigated on the predicted dopant profiles for ion-implanted samples. Increases in Cr and net shallow acceptor concentrations were found to increase the steepness of the predicted dopant profile, while an increase in EL2 concentration has little effect. A method of estimating dopant activation efficiency in GaAs has been proposed. This method uses the author's second program to avoid underestimations of the activation efficiency in GaAs caused by the peak lowering in the predicted dopant profiles. The concept of Debye length in semi-insulating LEC GaAs was also discussed. The Debye length given by the standard formula for semiconductors with shallow donors and acceptors can become inapplicable when deep levels are present. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy

The following is a comprehensive study of transient and steady-state nonlinear optical properties of semiconductor microcrystals embedded in a glass matrix (semiconductor doped glass). Transient thermal effects which give rise to longitudinal excitation discontinuities (i.e., kinks) that arise from partial sample switching in increasing absorption optical bistability are observed in a doped glass. The transient thermal effects occur on time scales of a few hundred milliseconds. Femtosecond and nanosecond laser pulses are employed to measure time-resolved and steady-state transmission and differential transmission spectra. The measured spectra reveal several beautiful effects which are attributed to the many-particle effects of electron-hole plasma. The spectra reveal: bandgap renormalization, broadening of the tail states and screening of the continuum states, state filling (spectral hole burning), thermalization of nonthermal carrier population distributions, band filling due to carrier relaxation of the thermal and nonthermal distributions, direct electron-hole recombination and long lived (>>100 ps) tail states which are attributed to electron trapping. Absorption edge dynamics discussed in this dissertation span 15 orders of magnitude.