High-Gain Low-Noise Photodetectors

摘要

The object was the development and evaluation of wide band p-n junction photodetectors which have the capability of internal modes of amplification. Photodiodes which make use of avalanche multiplication have been fabricated and their behavior studied in detail. The avalanche photodiode compares favorably with the photoparametric diode with regard to both net amplification and attainable signal-to-noise ratio for many applications. Avalanche gain of 45 dB has been observed for modulation frequencies near 1 GHz in silicon photodiodes. The avalanche photodiodes are shot-noise-limited detectors, even for modest values of multiplication (M squared of 5 to 20). The shot-noise available power of the avalanche photodiodes varied approximately as M squared. The reasons for this dependence are not completely clear; they could involve both space-charge-induced 'smoothing' of avalanche noise as well as the fact that the ionization coefficients of holes and electrons are quite different (by an order of magnitude) in silicon. (Author)