Effects of Tellurium Oxide on Surface Current and Performance of CdZnTe Nuclear Radiation Detectors

Cadmium zinc telluride (CdZnTe) radiation detectors have found applications in medical imaging and in the detection of radiological and nuclear threats. While there has been success in developing CdZnTe detectors with less than 1% FWHM energy resolution at the 662 keV gamma energy, charge collection can be improved through optimization of surface treatment techniques. The dominant surface species on CdZnTe are cadmium, tellurium, and tellurium oxide. The tellurium oxide is expected to produce a more chemically stable surface. This paper presents the quantification of the tellurium oxide species on CdZnTe wafers that are freshly etched in a mixture of hydrogen bromide in hydrogen peroxide and ethylene glycol solution. It also presents the effects of the tellurium oxide on surface current and detector performance. X-ray photoelectron spectroscopy (XPS) was used to quantify the tellurium oxide species on the wafer surface. The formation of tellurium oxide on the CdZnTe wafers immediately after etching contributes to an increase in the surface leakage current. The electron mobility-lifetime product was significantly reduced from 5.94 × 10
^-3
cm
²
/V to 0.60 × 10
^-3
cm
²
/V for a freshly etched wafer. The FWHM for a freshly etched wafer used in this study is 32% for the 59.5-keV gamma-peak of Am-241. The mobility-lifetime product and the energy resolution are expected to improve with time as the wafer surfaces become more stable.