Relaxation Phenomena in Planar Ge(Li) Detectors

A study has been made of the changes in net impurity concentration which occur when Ge(Li) diodes are allowed to remain unbiased at or near room temperature (termed relaxation), and when subjected to reheat cycles. The changes occur too rapidly to be explained in terms of lithium diffusion at the junction edges. Capacitance measurements have been used to determine impurity concentration profiles, and ¿-ray scanning techniques used to locate junction positions. It has been shown that a reheat at 400°C causes the compensated region to become slightly n-type. On the other hand, a device allowed to remain unbiased at room temperature becomes more or less uniformly p-type. In the samples studied (twelve diodes made from gemanium from four different supliers) ´generation´ rates of acceptors at 23°C varied from approxcimately 4 × 108 to 4 × 1010/cm3/hour. Since a well compensated diode has a net impurity concentration less than 1010 /cm3, this implies that in many diodes the degree of compensation changes substantially in a few hours.