The influence of the M-π-n structure on CdTe X-ray detector performance

High energy resolution, good charge collection and low spectral background have been obtained with M-pi-n CdTe xray detectors. The good spectroscopic performance is mainly due to the high quality of the CdTe crystals and the M-pi-n structure (metal/slightly p-type semiconductor/n-type semiconductor). With the M-pi-n structure we were able to achieve leakage current densities below 1 nA/mm(2). Further reduction in the leakage current was achieved by cooling the detectors. Low leakage currents enabled the use of higher bias voltages resulting in better charge collection efficiency, which improved the spectral response. In addition, low leakage currents made possible the use of low noise pulsed feedback preamplifiers which further improved the energy resolution. Energy resolutions of 0.42 keV at 5.9 keV, 0.62 keV at 59.6 keV and 2.4 keV at 662 keV have been measured for a detector of size 2.5 mm x 2.5 mm x 0.6 mm and 1.9 keV at 662 keV for a detector of size 4 mm x 4 mm x 1 mm at -30 degrees C. The application of pulse shape discrimination improved the energy resolution to 1.5 keV at 662 keV. In this work the performances of CdTe detectors before and after processing the M-pi-n structure were compared.