Characteristics of MSM-type CdTe γ-ray detector fabricated from undoped p-type crystals

Metal-semiconductor-metal (Au-p-CdTe-Au) type γ-ray detectors are made of undoped high-resistivity p-type THM crystals grown from Te solution under an appropriate Cd over-pressure. Detector performances concerned mainly with the hole transport in the detectors are investigated by evaluation of the FWHM energy resolution of the main photo peaks of γ-rays. It is found that low-energy tailing becomes prominent in detectors with decrease of the μtau product in the holes. The lineshape of the photo peak is analyzed using a simple model with mobile holes and electrons with a trapping event and then a comparison is made between the observed and the calculated spectra. From the temperature dependence of the energy resolution (FWHM) of the 59.9 keV photo peak from 241Am γ-rays, an activation energy is obtained at approximately 0.13 eV, which is close to those acquired from the temperature dependence of the concentration of holes and thermal detrapping times. The net concentration of acceptors involved in the crystal is estimated to be about 1011 cm-3 at room temperature by evaluation of the counting efficiency of the 59.5 keV photo peak as a function of the detector bias voltage. (author)