Numerical studies of femtosecond laser spectroscopy experiments in gallium arsenide material and quantum well structures
Bailey, Daniel William
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https://hdl.handle.net/2142/23674
Description
Title
Numerical studies of femtosecond laser spectroscopy experiments in gallium arsenide material and quantum well structures
Author(s)
Bailey, Daniel William
Issue Date
1990
Doctoral Committee Chair(s)
Hess, Karl
Department of Study
Engineering, Electronics and Electrical
Discipline
Engineering, Electronics and Electrical
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Language
eng
Abstract
In this thesis the methods and results of numerical simulations of femtosecond laser spectroscopy experiments in Al$\sb{x}$Ga$\sb{1-x}$As quantum well structures and bulk GaAs are presented. Photoexcited carriers are modeled by an ensemble Monte Carlo method including hole bandstructure effects. The time-dependent distributions from the Monte Carlo simulations in turn serve as a basis for interpreting transient differential transmission data, leading to an understanding of relaxation processes and the determination of material parameters in Al$\sb{x}$Ga$\sb{1-x}$As quantum wells and GaAs.
In Chap. 2 the Al$\sb{x}$Ga$\sb{1-x}$As quantum well system is examined by electron ensemble Monte Carlo simulations of 2-eV and near-band edge laser spectroscopy experiments. Results are contrasted, where appropriate, with comparable simulations in bulk GaAs. Simulations show that, unlike bulk experiments, the effects of polar optical phonon scattering are obscured in Al$\sb{x}$Ga$\sb{1-x}$As quantum well measurements because of coupling between hole subbands. Three scattering mechanisms are investigated and discussed: electron-electron, polar optical phonon, and (intervalley) optical deformation potential.
Femtosecond laser spectroscopy experiments in bulk GaAs are studied in Chap. 3. Electron and hole dynamics are modeled simultaneously. The time-dependent distribution functions from the ensemble Monte Carlo simulation are used to obtain the differential transmission directly, thus avoiding problems imposed by extracting time constants from the experimental spectra. By matching experimental results and artificially varying the strength of scattering mechanisms, dominant and sensitive relaxation mechanisms are clearly identified.
These simulations show that for 2-eV femtosecond laser spectroscopy measurements in GaAs at room temperature, for electrons the intervalley scattering rate is the most critical parameter determining the width of the initial transient transmission peak, and that the best fit with experimental results occurs for $D\sb{o}$ = 5 $\times$ 10$\sp8$ eV/cm. Equally important in the analysis, however, is the effect of holes on the differential transmission. It is also shown that carrier-carrier scattering plays a much less important role.
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