HIGH-RESOLUTION P-I-N CDTE AND CDZNTE X-RAY-DETECTORS WITH COOLING AND RISE-TIME DISCRIMINATION

The leakage current of CdTe detectors can be significantly reduced by processing detector crystals with p-i-n structures. Leakage currents o f the order of several nA/mm(2) are achieved at room temperature which compares well with the leakage current of commercially available CdZn Te detectors. The leakage current can be reduced further by cooling th e detector to about -30 degrees C, where values of about pA/mm(2) are achieved. These low values enable the use of low-noise, pulsed-optical feedback preamplifiers and higher bias voltages. High bias voltage is necessary for efficient charge collection which reduces spectrum back ground and peak tailing. Applying rise time discrimination circuitry t o the linear amplifier reduces the tailing effect even further, especi ally at higher radiation energies. We tested several 4 to 30-mm(2), 0. 6 to l-mm thick p-i-n structure CdTe detector crystals at -20 to -30 d egrees C with a loci-noise pulsed-optical feedback preamplifier and ri se-time discriminator, and at best obtained energy resolutions of 700 eV at the 59.5-keV line of Am-241, 1.2 keV at the 122-keV line of Co-5 7, and 2.5 keV at the 662-keV line of Cs-137. A Similar p-i-n structur e was processed on a 4-mm(2) Cd0.9Zn0.1Te detector crystal in order to reduce its leakage current, and energy resolutions of 368 eV at the 5 .9-keV line of Fe-55, 670 eV at the 59.5-keV line of Am-241, and 2.6 k eV at the 662-keV line of Cs-137 were obtained. However, the detector suffered from a charge collection problem yielding relatively high bac kground under the peaks.