Noise and oscillations in gold-doped germanium photodiodes

Abstract

Considerable noise effects in excess of shot noise and oscillations found in commercially available, gold-doped germanium photodiodes have been investigated. The noise and oscillation effects occur in the photocurrent of reversely biased diodes at temperatures below about 100°K. The dependence of the observed phenomena on external parameters, such as voltage, current, illumination level and temperature has been studied. The excess noise is attributed to a modulation of the voltage across the junction due to generation-recombination fluctuations of the large bulk-resistance. The voltage across the junction modulates the current through the device, since the differential resistance of the junction is not infinite. There is reasonable agreement between the experiments and a simple theoretical model. The oscillations, which are not directly connected with the excess noise, are believed to arise owing to the presence of the gold levels, and might be associated with the recombination instability described by Bonch-Bruevich and Kalashnikov. In order to arrive at more definite conclusions better defined structures should be investigated.