Effect of cleanings on the composition of HgCdTe surfaces

Abstract

The surface chemistry of HgCdTe is investigated with regard to the combined effects of etching, photochemical oxidation, and exposure to acids. The potential of angle-resolved x-ray photoelectron spectroscopy is utilized to characterize the surface region of the processed compound semiconductor with respect to its compositional depth profile. Upon exposure to the acids HNO3, HCl, H2SO4, and lactic acid, the HgCdTe surface does not degrade but becomes chemically passivated by the coverage of up to a monolayer of a native oxide. By such acid treatments, a residue to elemental tellurium, typically present after the Br2/methanol etching process, cannot be removed but becomes partially oxidized. However, the removal of this Te residue is made possible by the employment of a photochemical oxidation step between the etch and the acid treatment. Upon the formation of the photochemical oxide layer, the substrate composition below the interface is not affected. During the oxidation process, HgO segregates to the surface, leaving a Hg deficient oxide region in the bottom part of the layer.