Ageing of semiconductor single crystals and metal-semiconductor junctions

CdTe radiation detectors resistance were periodically measured during long time interval with an applied voltage in range U=1 V to U=30 V. In 1.5 years of measurements we observed the aging of the homogenous semiconductor and metal-semiconductor junction. The resistance of the semiconductor increased significantly. The metal-semiconductor junction working in forward bias had much higher value of voltage drop than it must have had. Volt-ampere characteristics were not stable and significantly changed in small periods of time. Dependence of the resistance also was unstable.