Photon Counting with Silicon Avalanche Photodiodes

Within the past few years, avalanche photodiodes (APDs) have been developed with detection efficiencies for single photons as high as 50% and dark count rates in the 10 4 cps range at room temperature. Besides being extremely small and rugged, these devices have rapid recovery from overloads, wide dynamic ranges, very low after-pulsing, relatively low operating voltages (~200-400V) compared to PMTs, and other properties which make them very suitable for use in photon correlation systems. The purpose of this paper is to review their properties when used in the photon counting mode, to summarize recent progress, and to indicate the types of further improvements that should be possible in the future.