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Spectroscopic ellipsometry and photoellipsometry studies of n-type gallium arsenide
Abstract
In this dissertation, spectroscopic ellipsometry and photoellipsometry, a newly developed contactless optical method, have been used to study the n-type GaAs sample substrates. Spectroscopic ellipsometry, with its high surface sensitivity when used at near the pseudo-Brewster angle and nondestructive depth profiling capability, has been shown to be a very reliable tool for accurate determination of the bulk optical properties of the given samples, if an appropriate model is employed for data interpretation. Meanwhile, it has been shown that the harmonic oscillator approximation method adopted is very effective for simulating the dielectric function spectra of the given substrates. As a result, not only the sample geometric structure including surface and subsurface conditions but also the doping density dependence of the dielectric function spectra have been determined and analyzed. Photoellipsometry utilizes spectroscopic ellipsometry with the addition of an above-bandgap energy laser pump beam directed at near-normal incidence onto the sample surface. It is highly sensitive to surface and interface built-in electric fields, and has been shown to be a very useful method for accurate and unambiguous measurements of the field-induced changes in the real and imaginary parts of the dielectric functions of the samples under study. Using the proposed modeling methods, namely, the single-layer model and the multilayer model, detailed lineshape analysis has been performed on the measured photoellipsometry spectra, for determination of sample parameters, such as built-in field strength, depletion depth, broadening, critical point energy, etc. While the single-layer model, which includes only the effects of field inhomogeneity and broadening, provides an effective and convenient way of characterizing the measured photoellipsometry spectra from the given samples, it has been shown that the multilayer model, which includes not only the effects of field inhomogeneity and broadening but also the effects of the native oxide overlayer and angular dependence of the probe beam light, gives a more accurate representation for the chosen sample under study. In addition, by analyzing the measured photoellipsometry data as a function of the pump beam power density, surface Fermi energy values for the two chosen samples have been determined. Experimental and theoretical results presented in this dissertation have demonstrated that photoellipsometry, which combines the features of both spectroscopic ellipsometry and photoreflectance, provides a very powerful way of characterizing the GaAs sample substrates. The modeling methods used also represent the first efforts made in this newly created photoellipsometry field.
Subject Area
Condensation
Recommended Citation
Xiong, Yi-Ming, "Spectroscopic ellipsometry and photoellipsometry studies of n-type gallium arsenide" (1993). ETD collection for University of Nebraska-Lincoln. AAI9331435.
https://digitalcommons.unl.edu/dissertations/AAI9331435