Heterostructure avalanche photodiodes have beesn successfully fabricated in several III-V alloy systems: GaAIAs/GaAs, GaAISbIGaSb, GaAIAsSb/GaAlSb, and InGaAsP/InP. These diodes cover optical wavelengths from 0.4 to 1.8 m. Early stages of development show very encouraging results. High speed response of <35 ps and high quantum efficiency >95 percent have been obtained. The dark currents and the excess avalanche noise Wiu also be discussed. A direct comparison of GaAISb, GaAlAsSb, and InGaAsF'avalanchep hotodiodes is given. Copyright © 1979 by The Institute of Electrical and Electronics Engineers, Inc.