One of the main electronic noise sources of a room temperature spectroscopy system is the leakage current of a detector. It can be reduced with a pn-junction type detector structure such as a M-i-n configuration, and with cooling. In this work eight CdZnTe detectors with a M-i-n structure were fabricated by indium diffusion. The junction was characterized by a currentvoltage technique. Detector electrical, charge collection and spectroscopic properties were compared to the ones received with the traditional electroless Au contacts, before the junction formation. As a result of the indium diffusion an improved detector leakage current performance was achieved. However, a corresponding improvement in the detector energy resolution was not always observed due to the CdZnTe charge collection properties and process variables.

High energy resolution, good charge collection and low spectral background havc been obtained with M-n-n CdTe xray detectors. The good spectroscopic performance is mainly due to the high quality of the CdTe crystals and the M-n-n structure (metalhlightly p-type semiconductorh-type semiconductor). With the M-n-n structure we were able to achieve leakage current densities below 1 nNmm . 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 "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-n-n structure were compared. 2

The electrical and charge collection properties of a semiconductor detector play an important role in a spectrometer's final performance. However, the studies of these properties often concentrate on only a few samples. In this work over 100 CdZnTe detectors from 12 different growth boules were characterized with one of the following test methods. The composition uniformity was evaluated with low temperature photoluminescence (PL) measurements. From the current-voltage characteristics the differences in CdZnTe detector resistivities were investigated. Charge collection properties, μτ-products, and energy resolutions were characterized with spectroscopic methods using an alpha and isotopic sources. A wide selection of test results are presented indicating the variety of CdZnTe material.