Evaluation of High-Purity Germanium by Pulse Measurements on Detectors

Evaluation of high-purity germanium exhibiting acceptor concentrations in the 109 to 1010/cm3 range taxes normal methods of measuring semiconductor material parameters. It has proven difficult to obtain unambiguous measurements by the Hall Effect or conductivity methods. We show that pulse measurements on guard-ring radiation detectors fabricated from high-purity germanium, when properly interpreted, can provide data on acceptor and hole concentrations as a function of temperature that supplement data obtained by Hall Effect and conductivity methods. The method, which is an extension of the technique used for detector capacity measurements, employs injection of electrical pulses via the detector into a charge-sensitive preamplifier. The shape and size of the output pulse permits determination of the characteristics of the depleted and undepleted regions of the detector; variation of the applied detector voltage allows choice of the relative thickness of the two regions. Results of measurements on two germanium crystals, over a broad temperature range, will be presented.