A novel two-step chemical passivation process for CdZnTe detectors

The spectrum resolution of cadmium zinc telluride (CZT) room temperature nuclear radiation detectors is often limited by the presence of conducting surface species that increase the surface leakage current. Surface passivation plays a dominant role in reducing the surface leakage current and therefore decreasing the noise and improving the spectral energy resolution of the detectors. In this paper, a novel two-step chemical passivation process for CZT detectors, in which the mixed solution of bromine-methanol and lactic acid in ethylene glycol (BMLB) treated CZT wafer was first etched by using a KOH aqueous solution, and then by using a NH4F/H2O2 mixed solution, is presented. The Auger electron spectroscopy (AES) and atomic force microscopy (AFM) results show that the first-step KOH process consumed the Te-rich layer caused by BMLB and left a more stoichiometric surface and the second-step NH4F/H2O2 process oxidized the elemental constituents of the CZT surface obtained by the KOH etching and formed an oxide layer on the surface. The I-V characteristics show that the novel process leads to a lower surface leakage current compared to the processing by using either a KOH or NH4F/H2O2 agent. The results indicate that this two-step passivation process has a promising potential in the fabrication of CZT detectors.