Characterisation of Surface Treated CdZnTe and Thin Film CdTe based Devices

The performance of single crystal CdZnTe radiation detectors is dependent on both the bulk and thesurface properties of the material. After single crystal fabrication and mechanical polishing, modificationof the surface to remove damage and reduce the surface leakage current is generally achieved throughchemical etching followed by a passivation treatment. In this work, CdZnTe single crystals have beenchemically etched using a bromine in methanol (BM) treatment. The BM concentrations employed were0.2 and 2.0 (v/v) % and exposure times varied between 5 and 120 s. Angle resolved XPS and sputterdepth profiling has been employed to characterize the surfaces for the different exposure conditions. ATe rich surface layer was formed for all exposures and the layer thickness was found to be independent ofexposure time. The enriched Te layer thickness was accurately determined by calibrating the sputter rateagainst a CdTe layer of known thickness. For BM concentrations of 0.2 (v/v) % and 2 (v/v) %, the Te layerthickness was determined to be 1.3 ± 0.2 and 1.8 ± 0.2 nm, respectively. The BM etched surfaces havesubsequently been passivated in a 30 wt.% H2O2 solution employing exposure time of 15 s. The oxidelayer thickness has been calculated using two standard XPS methodologies, based on the Beer–Lambertexpression. The TeO2 thickness calculated from ARXPS data are slightly higher than the thickness obtainedby the simplified Beer–Lambert expression. For BM exposures of 30–120 s followed by a passivationtreatment of 30 wt. % H2O2 solution employing an exposure time 15 s, the ARXPS method gave an averageTeO2 thickness value of 1.20 nm and the simplified Beer–Lambert expression gave an average thicknessvalue of 0.99 nm.© 2012 Elsevier B.V. All rights reserved.