Evaluation of the spectroscopic performance of small pixel, room temperature semiconductor detectors with a digital shaping amplifier

The use of CZT and CdTe as room-temperature detectors for the characterization of X-ray spectra is well known. These wide-bandgap semiconductors are suited for spectroscopic applications because of their high resistivity and fast charge collection properties. In this study, detector performance is characterized using digital data acquisition and processing. Using the raw data, the charge pulses generated by individual-photon absorption events are analyzed. The relationship of rise time, shaping time, and energy resolution is investigated and detector performance is characterized. Using a fast oscilloscope and low-noise charge sensitive preamplifier, the intrinsic charge collection time of the detector is found to approach 27 and 10.5 ns for 1 and 0.5 mm pitch pixels. The impact of system capacitance on the measured rise time is observed. Corrected measured rise time values agree with those obtained from a first-order model. The trade-off between the detector signal-to-noise ratio and pulse shape is studied by applying very short shaping times to the captured charge waveforms to get the energy resolution of possible readout shaping amplifier circuits. As a result of the digital acquisition, there is no additional contribution of electronic noise from a shaping amplifier or analog to digital converter. The maximum energy resolution is found to be 9 keV. Very short dead times are achieved using short shaping times. Mobility and mutau values are calculated to be 940 cm²/V- sec and 5.9 times 10^-3 cm²/V.