An XPS study of bromine in methanol etching and hydrogen peroxide passivation treatments for cadmium zinc telluride radiation detectors

Abstract

The performance of single crystal CdZnTe radiation detectors is dependent on both the bulk and the surface properties of the material. After single crystal fabrication and mechanical polishing, modification of the surface to remove damage and reduce the surface leakage current is generally achieved through chemical etching followed by a passivation treatment. In this work, CdZnTe single crystals have been chemically etched using a bromine in methanol (BM) treatment. The BM concentrations employed were 0.2 and 2.0 (v/v) % and exposure times varied between 5 and 120s. Angle resolved XPS and sputter depth profiling has been employed to characterize the surfaces for the different exposure conditions. A Te rich surface layer was formed for all exposures and the layer thickness was found to be independent of exposure time. The enriched Te layer thickness was accurately determined by calibrating the sputter rate against a CdTe layer of known thickness. For BM concentrations of 0.2 (v/v) % and 2 (v/v) %, the Te layer thickness was determined to be 1.3±0.2 and 1.8±0.2nm, respectively. The BM etched surfaces have subsequently been passivated in a 30wt.% H2O2 solution employing exposure time of 15s. The oxide layer thickness has been calculated using two standard XPS methodologies, based on the Beer–Lambert expression. The TeO2 thickness calculated from ARXPS data are slightly higher than the thickness obtained by the simplified Beer–Lambert expression. For BM exposures of 30–120s followed by a passivation treatment of 30wt. % H2O2 solution employing an exposure time 15s, the ARXPS method gave an average TeO2 thickness value of 1.20nm and the simplified Beer–Lambert expression gave an average thickness value of 0.99nm.