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Author

Archana Gupta

Date of Award

5-1997

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Materials Science and Engineering

Supervisor

George C. Weatherly

Abstract

Growth of superlattices on V-grooved substrates has become a popular method of producing quantum wires. The success of this technique to date has been limited to the lattice-matched AlGaAs/GaAs system. The unpredictability of the morphology and defects found in lattice-mismatched systems has been a major hindrance in their development. Additionally, the misfit stresses in lattice mismatched systems may play an important role in determining the properties of the laser. In V-grooves, the singular points at the corners of the groove produce a stress distribution completely different from the case of layers grown on a planar substrate. Accurate knowledge of the stress distribution is hence necessary because a stress can affect the optoelectronic properties and lead to defects, limiting the life of the laser. The aim of the project was two fold: first to characterize the InGaAs/InP growth on (211)A and (111)B grooves using molecular beam epitaxy in terms of faceting, thickness variation, and composition variation; second to obtain an analytical and numerical stress distribution for the case of a layer with uniform composition and thickness grown on a sharp V-groove. The characterization was performed using transmission electron microscope and degree of polarization methods. Composition analysis was done with a high resolution scanning transmission electron microscope. Numerical simulation was done using a commercial finite element program, 'ABAQUS'. The results showed a clearly distinct morphology for layers grown on faceted (211)A and (111)B substrates. The differences observed in faceting, thickness variations, and composition variations in the (211)A and (111)B grooves suggest that the lower incorporation rate of group III atoms on (111)B surfaces leads to increased interfacet diffusion compared to (211)A grooves, where a higher incorporation rate produces layers with uniform composition and thickness. Furthermore, the 46.5% increase in In content found at the bottom of (111)B grooves indicates that the mean diffusion length of In is much higher than Ga for the growth conditions used in this study. The large variation in composition in (111)B grooves produced extensive defects at the bottom of the groove and at certain locations of the sidewall where the misfit exceeds the critical limit. The analytical and numerical solution of the stress distribution were in good agreement with experimental results. The stress fields obtained by these methods would be useful in helping to predict the optoelectronic properties of the quantum wire. Furthermore these models are useful in determining the composition and thickness of the layers which need to be grown to obtain specific optical properties.

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