Date of Award

Spring 2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Applied Physics - (Ph.D.)

Department

Physics

First Advisor

N. M. Ravindra

Second Advisor

Ken Keunhyuk Ahn

Third Advisor

Anthony Fiory

Fourth Advisor

Martin Schaden

Fifth Advisor

Vitaly A. Shneidman

Abstract

The ability to obtain tunable properties with composition makes multi-ternary alloys extremely useful for a variety of applications in semiconductor devices and is of significant interest in experimental and theoretical research. This dissertation investigates the mechanical, electronic and optical properties of multi-ternary, i.e., binary, ternary and quaternary, semiconductor alloys using analytical methods and first-principles calculations.

For the calculations of mechanical properties, existing models on the average shear modulus of III-V & II-VI binary semiconductors are revised. New expressions are developed for the average Young’s modulus as well as the shear modulus and Young’s modulus on (111) plane for these compounds. It is found that the proposed models provide a simple and accurate means for predicting the elastic constants of ternary semiconductors.

The crystal structures, formation enthalpies and electronic properties of alloys, GaPXSb1-X, InPXSb1-X and CdSXTe1-X, are then investigated using first-principles calculations. These alloys are studied for various structures and compositions. Comparisons between GaPXSb1-X and InPXSb1-X are made. In the study of CdSXTe1-X system, negative bowing parameter of spin-orbit splitting is found in the ordered structure while positive value is found in disordered structure.

This work also gives a recipe to calculate the properties of Y2 alloys in any degree of crystal ordering. For the partially ordered samples, the trends of the Y2 ordering induced changes in the crystal field splitting and band gap narrowing are explored and explained in terms of the lattice mismatch and band offset between the binary constituents. The Y2 ordering induced change in the spin-orbit splitting is found to be positive and small.

Additionally, a model for the pressure dependence of the energy gap of group III-­V & II-VI ternary semiconductor alloys is proposed. The trends in the pressure coefficients with respect to nearest neighbor distance and ionicity are discussed.

Finally, the electronic and optical properties of Cu2ZnGeS4, Cu2ZnGeSe4 and Cu2ZnGeTe4 in KS and ST structures are studied. Band structure and optical spectra including the dielectric function, refractive index, absorption coefficient and reflectivity are determined. The critical points in the optical spectra are assigned to the interband transitions in accord with the calculated band structures. The trends of these properties with respect to crystal structures and VI (S, Se and Te) anion atoms are explored qualitatively.

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