Relaxation time in CdTe single crystals

Bulk resistance decay of two cadmium telluride single crystals was investigated. Each CdTe crystal has four golden contacts, two current contacts and two voltage contacts. That allows us to distinguish between bulk resistance and contact area. The bulk resistance of each CdTe single crystal was measured during long time interval with an applied voltage U = 16 V. Detectors were placed into a cryostat. That allowed to hold the temperature constant during the measurements and eliminate the illumination influence. The temperature of the samples was 300 K at first and after some period of time (approximately 1 day) it was sharply raised to 390 K. We observed the resistance slow decreasing with time with temperature T = 300 K and T = 390 K. All the samples have very high value of relaxation time. The presented samples must have not one but four acceptor or donor levels, some of them are deep levels. We have discovered that the interactions between the valence band and deep acceptor levels or between the conductivity band and deep donor levels cause this long value of relaxation time.