The development of lasers has stimulated the appearance of new technical fields such as optical communications, laser location, optoelectronic computers, and information systems. For all these fields the primary problem is detecting short (tens of nanoseconds and shorter) weak (hundreds, tens of photons) light pulses. Today this problem is being solved by photodetectors such as photomultipliers and avalanche photodiodes with the fast-response mechanism of internal gain: multiplication of carrier numbers by impact ionization.