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 of the order of several nA/mm² are achieved at room temperature which compares well with the leakage current of commercially available CdZnTe detectors. The leakage current can be reduced further by cooling the detector to about -30°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 background and peak tailing. Applying rise time discrimination circuitry to the linear amplifier reduces the tailing effect even further, especially at higher radiation energies. We tested several 4 to 30-mm², 0.6 to 1-mm thick p-i-n structure CdTe detector crystals at -20 to -30°C with a low-noise pulsed-optical feedback preamplifier and rise-time discriminator, and at best obtained energy resolutions of 700 eV at the 59.5-keV line of ²⁴¹Am, 1.2 keV at the 122-keV line of ⁵⁷Co, and 2.5 keV at the 662-keV line of ¹³⁷Cs. A similar p-i-n structure was processed on a 4-mm ² Cd_0.9Zn_0.1Te detector crystal in order to reduce its leakage current, and energy resolutions of 368 eV at the 5.9-keV line of ⁵⁵Fe, 670 eV at the 59.5-keV line of ²⁴¹Am, and 2.6 keV at the 662-keV line of ¹³⁷Cs were obtained. However, the detector suffered from a charge collection problem yielding relatively high background under the peaks