Photoemission study of Cd loss and its effect on the electronic structure of etched Hg1-xCdxTe surfaces

Abstract

Quantitative measurements using x-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy have been made of the Cd loss and surface Fermi-level position (Ef,s) on Hg1 - x Cdx Te substrates that have undergone chemical surface preparation. The surface cleaning techniques employed were representative of those used in Hg1 - x Cdx Te device fabrication: a bromine in dimethyl formamide polish, a bromine in ethylene glycol spray, and/or an ozone ash etch. For over 20 samples studied of bnlk x = 0.30, an average 30% of the original Cd was found to be removed from within the sampling depth of the surface (25 A). In addition, Ef,s was found to be located 0.15 ± 0.05 eV above the valence-band maximum (VBM) at room temperature for a predominate number of samples, independent of the bulk doping. Some of these samples were also studied at ~ 150 K, and Ef,s was seen to rise an additional -0.05 eV to a location of 0.20 ± 0.05 eV above the VBM at the lower temperature, again independent of bulk doping. Implications of these findings for device modeling are discussed and first-order surface band diagrams introduced. © 1987, American Vacuum Society. All rights reserved.