First principles studies of semiconductor epitaxial growth

Abstract

This thesis conducts investigations mainly on the structures, energetics, and reactions of semiconductor as well as oxide surfaces using first principles cluster model approach. The first part of the research work addresses the issues in the epitaxial growth of Hg1-xCdxTe (MCT) materials. Hg divalent compounds were studied thoroughly using a variety of quantum chemical methods in order to understand the energetics of Hg precursors for growth. The (001) growth surfaces were then examined in detail using cluster model calculations. Based on these results, a novel metal-organic molecular beam epitaxial (MOMBE) growth strategy with favorable energetics for growing MCT using H2C=CH-CH2-Hg-C=C-CH3 is proposed. It is hoped that with this new growth strategy, the Hg vacancy and p-doping problems that currently exist in growth can be avoided. The second part of the thesis discusses the molecular beam epitaxial (MBE) growth of cubic GaN on the (001) surface using various N sources. Surface reconstructions and the interactions of gas-phase atomic and molecular nitrogens with the surface were elucidated using cluster models. Using these results an energy phase diagram for the growth of GaN has been constructed. It suggests that excited state molecular N2 (3Σu+) is the most favorable of all N species for growth of high quality GaN because it can undergo a dissociative chemisorption process. Ground state atomic N (4S) is also good for growth. The doublet excited states N (2D and 2P) might cause surface N abstraction, leading to N vacancies in the material. Finally, a Fe(OH)3(H20)3 GVB cluster model of crystalline α-Fe203 was developed. This simple model can describe the local geometry and bonding of Fe in the bulk oxide. Using quantum mechanical calculations, the orientation of the oleic imidazoline (OI) molecule bonding to the oxide surface has been determined. OI class of molecules are used extensively for corrosion inhibitor in oil field pipeline applications. It is found in this work that OI can make very strong bonding to the Fe of the iron oxide. In aqueous environments they can replace water on the pipe surface to form a protective layer to prevent corrosion.