Effects of Chemical Treatments on CdZnTe X-Ray and Gamma-Ray Detectors

Abstract

Room-temperature semiconductor detectors, such as cadmium zinc telluride (CdZnTe), often are subjected to surface damage during fabrication, thus reducing their performance in detecting X-rays and gamma-rays. In this study, we compared two surface-passivation chemical solutions: Ammonium fluoride in hydrogen peroxide ( ${\rm {NH}}_{4}{\rm F}+ {{\rm H}_2}{{\rm O}_2}+ {{\rm H}_2}{\rm O}$ ) and potassium hydroxide in hydrogen peroxide (0.1 g of KOH + 10 ml of 30% ${{\rm H}_2}{{\rm O}_2}$ ). X-ray photoelectron spectroscopic analysis showed that the ${\rm {NH}}_{4} {\rm F}$ -based solution is more effective at converting Te species on the CdZnTe surfaces into a more stable ${\rm {TeO}}_2$ layer, attaining values of 4.90 and 5.34 for the ${\rm {Te}}3{d_{3/2}}{{\rm O}_2}/{\rm {Te}}3{d_{3/2}}$ and ${\rm {Te}}3{d_{5/2}}{{\rm O}_2}/{\rm {Te}}3{d_{5/2}}$ peak-height ratios respectively, compared to the KOH-based solution with 1.25 and 1.19, respectively. The current-voltage measurements showed an increase in the bulk leakage current for freshly passivated samples compared to those of mechanically polished samples. However, within a period of about three to 14 days, their leakage currents reduced to values in the range of the mechanically polished samples. The resistivity of the CdZnTe samples is on the order of ${10^{10}}\;\Omega\hbox{-cm}$ . The ${\rm {NH}}_{4}{\rm F}$ -based chemical contributed less to the leakage current. Its leakage current at 60 V is 6.3 times that of the mechanically polished sample, compared to 30.5 for the sample passivated with the KOH-based solution. Analysis of the 59.5-keV peak of Am-241 showed that the sample passivated with the ${\rm {NH}}_{4}{\rm F}$ -based solution has a better energy resolution compared to the one passivated with the KOH-based solution.