Comparison of the X-ray performance of small pixel CdTe and CZT detectors

The Rutherford Appleton Laboratory has built a small pixel detector for spectroscopic measurements of high energy X-rays using CdTe and CdZnTe. The detector has an array of 20×20 pixels on a 250μm pitch with each pixel bonded to a separate channel on an application specific integrated circuit (ASIC). Each channel in the ASIC contains a charge preamplifier, leakage current compensation circuit, shaping amplifier and peak hold circuit. In recent years there has been an increase in the availability of high quality CdTe and CdZnTe material and the contacting technology required for low leakage current small pixel devices. The energy resolution and stability of the X-ray performance of 1mm thick CdTe with Aluminum Schottky contact pixels and 2mm thick CdZnTe grown by travelling heater method (THM) are measured. The CdTe detectors had an energy resolution of 1 to 1.1keV at 75keV. The THM CdZnTe had an energy resolution of 1.3keV at 75keV. The stability of the performance was measured over a 12 hour exposure with the detectors biased to -500V and held at 25°C. The CdZnTe exhibited stable performance whereas the CdTe suffered from bias induced polarization, the onset of which was delayed by cooling the detectors to 12°C.