a Photoemission Study of the Electronic Structure and Oxidation Properties of Mercury-Cadmium Telluride.

The study of electronic structure and oxidation properties of the random substitutional alloy Mercury Cadmium Telluride is of general interest in relating the electronic structure and surface properties of a semiconductor alloy with a strongly aperiodic potential to these aspects of the binary compounds that represent the composition extremes. It is also of practical value, as study of the electronic structure and oxidation properties provides an underpinning of fundamental knowledge for further technological development. Angle-integrated and polarization dependent angle -resolved photoemission spectroscopy (along the normal) from the (110) cleavage face of the alloy and the binaries Cadmium Telluride and Mercury Telluride were performed to examine the composition dependence of the electronic structure and bonding. Emission from the valence states documents the breakdown of the virtual crystal approximation and the success of the coherent potential approximation in treating the alloy potential. The consequences of this finding for the bonding and materials properties are described. Detailed dispersion relations as a function of composition have been deduced from the angle-resolved data for a portion of the band structure along (110) and are compared to theory. To augment the discussion of the photoemission final states and the polarization dependence of the data, a nonlocal pseudopotential calculation extending to 30 eV above the valence band maximum was executed. In the oxidation studies, core level photoemission spectroscopy was used to characterize the clean surface and monitor the growth of native oxide films a few monolayers thick formed on the semi- conductor at room temperature by exposure to oxygen in the gas phase activated by contact with a hot filament. The cleaved (110) surface of p-type solid state recrystallized alloy samples was found to be stoichiometric, stable against Hg loss over time in vacuum at room temperature, but converted to n-type conductivity. Detectable oxidation occurs only when the process is activated by, for example, the hot filament. The composition of the oxide phases formed, their stability, and preliminary kinetic information regarding their formation are discussed.