Surface passivation of cadmium zinc telluride radiation detectors by potassium hydroxide solution

The spectral resolution of cadmium zinc telluride (CZT) room temperature nu clear radiation detectors is often limited by the presence of conducting su rface species that increase the surface leakage current. Surface passivatio n plays an important role in reducing this surface leakage current and ther eby decreasing the noise of the detectors and improving the spectral energy resolution. Chemical etching with a Br-MeOH solution leaves CZT surfaces r ich in Te and is considered as one of the primary causes of the increased s urface leakage current. Previous studies have shown that hydrogen peroxide (H2O2) forms oxides of tellurium on the CZT surface and thus acts as a good passivating agent. In this study we will present results on the use of pot assium hydroxide (KOH) as an alternative passivating agent. The KOH aqueous solution leaves a more stoichiometric (evaluated from the trends in the su rface Cd:Te ratio) and smoother CZT surface. The passivation effects of KOH solution on the surface of the CZT have been characterized by current-volt age measurements for different KOH concentrations and etching times for bot h parallel strip electrodes as well as a metal-semiconductor-metal configur ation. The surface chemical composition and its morphology were studied by scanning x-ray photoelectron spectroscopy and atomic force microscopy. The comparison and demonstration of improvements in the spectral resolution of the CZT detectors (based on Am-241 spectra) with and without the KOH treatm ent are presented.