Strained-Layer INDIUM(X)GALLIUM(1-X)ARSENIDE - Gallium-Arsenide Heterojunctions, Quantum Wells, and Superlattices: Electronic Structure and Optical Properties.
Abstract
The electronic structure and light-emission properties of strained-layer In_{rm x} Ga_{rm 1-x}As -GaAs heterojunctions, quantum wells, and superlattices are investigated through photoluminescence experiments and theoretical models. Spontaneous and stimulated emission from a variety of structures (layers as thin as a few monolayers and alloy compositions up to x = 1), grown by molecular -beam epitaxy and atomic-layer epitaxy, is studied over a range of experimental conditions. Results concerning the strain effects in biaxially strained {rm In_{x}Ga _{1-x}As} are presented first. Critical thicknesses for dislocation formation and strain-induced band-gap shifts are measured for a number of structures and shown to agree well with results from theoretical models. A perturbation-theoretic model is used to study optical transition probabilities, and is shown to predict that electron-to -light-hole emission and absorption characteristics should be highly strain dependent. The electronic structure of strained {rm In_{x}Ga_{1 -x}As}-GaAs heterojunctions is considered next. General considerations relevant to the modeling and measurement of band offsets at strained heterojunctions are discussed, and perturbation-theoretic and tight-binding models for strained zincblende junctions are developed and evaluated. The two models predict that the heavy-hole (m_{rm J} = 3/2) valence-band offset for biaxially strained In_ {rm x}Ga_{rm 1-x}As grown on unstrained (100) GaAs is 20 -30% of the difference between the unstrained gaps for the two materials, and that the m_{rm J} = 3/2 and m_{rm J} = 1/2 valence-band offsets are of opposite sign. These predictions are consistent with the most reliable experimental data currently available. Pseudomorphic single- and multiple-quantum-well heterostructures and strained-layer superlattices are then investigated. Quantum-well structures with strains as high as ~7% are shown to exhibit excellent luminescence characteristics (spectral halfwidths of 7-11 meV at 20K for wells thinner than 50A) provided that layer thicknesses are below critical values, and the observed transition energies are found to agree well with predictions from quantum-mechanical finite-square-well and Kronig-Penney models which incorporate strain effects perturbatively. Spontaneous and stimulated emission from quantum-well structures is concentrated in a single emission band attributable to n = 1 electron-to-heavy-hole quantum -well transitions. Experimental and theoretical evidence is presented which suggests that, in contrast, electron -to-light-hole transitions can be the dominant transitions in some types of In_{rm x} Ga_{rm 1-x}As -GaAs strained-layer superlattices.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1988
- Bibcode:
- 1988PhDT........43A
- Keywords:
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- Engineering: Electronics and Electrical; Physics: Condensed Matter