The Anomaly in the Response of Semiconductor Detectors

Preliminary investigation of the response to beta and alpha particles of silicon radiation detectors cooled to temperatures below 77/s=deg/ K has led to the discovery of an anomaly in the pulse height distribution which is a function of detector temperature. The pulse height and resolution of a P-I-N lithium-drift silicon detector shows a rapid decrease in the temperature interval of 40 - 35/s=deg/ K for electric fields up to the maximum of 4200 volts/cm used in this experiment. Lithium-drift detectors of the P+-I-N surface barrier configuration exhibit similar characteristics. Surface barrier detectors of resistivities in the range of 3000 ohm-cm exposed to beta particles exhibit a decrease in pulse height and resolution in the temperature interval of 30 - 15/s=deg/ K. With increasing bias voltage the pulse height tends towards the high temperature values but with degraded resolution. A detailed investigation of the response of a surface barrier detector to alpha particles shows an anomaly of the, same characteristics as the beta particle anomaly. In addition, the pulse height decreases at reduced bias voltages below approximately 14/s=deg/ K. A plausible explanation of the primary anomaly based on the analysis of Walter is discussed.