Molecular Beam Epitaxial Growth of Cadmium Telluride and Mercury Cadmium Telluride for New Infrared and Optoelectronic Devices

The objective of the research was to develop growth techniques that would provide a basis for the production of high quality Hg_{rm 1-x} Cd_{rm x}Te epitaxial layers for complex device structures such as focal plane arrays (FPA) and avalanche photodiodes (APD). The research addressed three main issues: (1) the heteroepitaxial growth of HgCdTe, (2) the inherent material problems associated with HgCdTe, and (3) the material requirements of advanced device structures. The heteroepitaxial growth investigation involved the development of solutions to substrate-epilayer interdiffusion. Heteroepitaxial layers grown on GaAs substrates by MBE exhibited localized areas of high gallium concentration which were attributed to enhanced diffusion along defects propagating from the heterointerface. Several gallium diffusion barrier layers were investigated with CdTe/ZnTe strained layer superlattices and MBE grown GaAs buffer layers proving to be the most effective. The research highlights the importance of the quality of the initial growth nucleation surface. The last two issues were addressed by the identification of the problems associated with the HgCdTe material system and the determination of the material requirements of advanced device structures. In this phase of the research, a unique mercury source for the molecular beam epitaxial (MBE) growth of HgCdTe was developed, constructed, and characterized. This source operated on the principle of choked viscous flow and utilized pressure control rather than the conventional thermal control. The source was capable of producing a highly stable and repeatable mercury flux even with mercury reservoir temperature fluctuations of +/- 10^circC. The source also demonstrated a fast response characteristic of 10 seconds and the ability to produce arbitrary flux profiles (as would be required for complex device structures). The source was used to grow MBE Hg_{rm 1-x}Cd_{rm x} Te layers. Finally, chemical beam epitaxy (CBE), which uses gas sources in place of the conventional MBE solid sources, was investigated. Epitaxial layers of HgCdTe were grown using this technique and their electrical and optical properties investigated. These layers typically exhibited lower net background carrier concentrations than currently obtainable by MBE with some layers exhibiting the highest electron mobilities of any Hg_{rm 1-x }Cd_{rm x}Te grown by MBE.