Experimental results from Al/p-CdTe/Pt X-ray detectors

Abstract

Recently, Al/CdTe/Pt detectors have been proposed for the development of high resolution X-ray spectrometers. Due to the low leakage currents, these detectors allow high electric fields and the pixellization of anodes with the possibility to realize single charge carrier sensing detectors. In this work, we report on the results of electrical and spectroscopic investigations on CdTe diode detectors with Al/CdTe/Pt electrode configuration (4.1×4.1×0.75 and 4.1×4.1×2 mm3). The detectors are characterized by very low leakage currents in the reverse bias operation: 0.3 nA at 25 °C and 2.4 pA at -25 °C under a bias voltage of -1000 V. The spectroscopic performance of the detectors at both low and high photon counting rates were also investigated with a focus on the minimization of time instability, generally termed as polarization, looking for the optimum bias voltage and temperature. Good time stability, during a long-term operation of 10 h, was observed for both detectors at -25 °C and by using an electric field of 5000 V/cm. The 2 mm thick detector exhibited good energy resolution of 6.1%, 2.5% and 2.0% (FWHM) at 22.1 keV, 59.5 and 122.1 keV, respectively. Performance enhancements were obtained by using digital pulse processing techniques, especially at high photon counting rates (300 kcps). The 2 mm thick detector, after a digital pulse shape correction (PSC), is characterized by similar performance to the thin detector ones, opening up to the use of thick CdTe detectors without excessive performance degradations. This work was carried out in the framework of the development of portable X-ray spectrometers for both laboratory research and medical applications.