Time-dependent current-voltage characteristics of Al/p-CdTe/Pt x-ray detectors

Current-voltage (I-V) characteristics of Schottky Al/p-CdTe/Pt detectors were investigated in dark and at different temperatures. CdTe detectors with Al rectifying contacts, very appealing for high resolution x-ray and gamma ray spectroscopy, suffer from bias-induced polarization phenomena which cause current increasing with the time and severe worsening of the spectroscopic performance. In this work, we studied the time-dependence of the I-V characteristics of the detectors, both in reverse and forward bias, taking into account the polarization effects. The I-V measurements, performed at different time intervals between the application of the bias voltage and the measurement of the current, and the measured current transients show as the electrical instability manifests itself even in time intervals shorter (i.e., <1 s) than those are necessary to make evident the degradation of the spectroscopic properties. The results point out as this time interval is a critical parameter for correct investigations on the electrical properties of these devices. Although the detectors are typically classified as Schottky-type detectors, we find that the thermionic emission is not the dominant transport mechanism, except at very low bias voltage values. Finally, the Schottky barrier height of the Al/p-CdTe contact was extracted by measuring the contact resistance at zero bias.