TEMPERATURE SENSITIVITY OF SURFACE CHANNEL EFFECTS ON HIGH-PURITY GERMANIUM DETECTORS

The temperature sensitivity of surface channel effects on planar high- purity germanium detectors was measured using 60-keV gamma-ray scannin g techniques, as part of a radiation damage study. When measured in th is manner, the surface effects on most detectors showed extreme temper ature sensitivity in the 72-95 It region. The effect of the surface ch annel increased with increasing temperature to such an extent that the efficiency, as measured by the count rate in the 1332-keV peak from a Co-60 source, decreased by a factor of over two in some cases. Since the peak efficiency for the 1332-keV gamma ray decreased as the temper ature increased throughout the operating range (72-120 K) the effect o f the surface channel must continue to increase beyond the temperature (95 K) at which the 60-keV scan loses its sensitivity because of the strong attenuation of these much lower energy gamma rays. Radiation da mage had no measurable effect on the surface characteristics. No corre lation between the surface effects and the resolution changes of the 1 332-keV peak was observed.