Study on Instability Phenomena in CdTe Diode-like Detectors

Diode-like In/CdTe/Pt detectors are widely used thanks to their excellent spectroscopic performance. However, when operated at room temperature they are not stable, and their performance degrades with time. The aim of this paper is to investigate in detail the physical mechanisms underlying this effect, by studying the evolution of the space charge inside the detector. Our approach makes use of the Pockels effect, by looking at the evolution of the electric field distribution inside the detector at different temperatures. The results show that a negative space charge accumulation occurs at the anode and that the process is thermally activated. The effect is attributed to a mid-gap acceptor which, under reverse bias, increases its ionization because of hole detrapping. Moreover, we compare the results with those obtained on stable detectors realized from nominally same crystals but having ‘standard’, i.e. not rectifying contacts. Consistently with the detection performance stability of this kind of detectors, the electric field is relatively stable. Furthermore, it decreases from cathode and it shows peculiar features which will be discussed in conjunction with charge transport properties.