Long-wavelength photodiodes based on LPE-grown type-II heterostructures in lattice-matched GaSb/InGaAsSb/GaInAsSb and GaSb/InGaAsSb/AlGaAsSb systems were fabricated and studied. Band energy diagram engineering for heterostructures with wide- and narrow-gap layers allows the photodiode parameters to be controlled by varying the conditions at heterointerfaces. Electrical and photoelectric characteristics and the dark current mechanisms in the heterostructures were investigated. The optimal photodiode structure was selected that consists of two type-II broken-gap heterojunctions and one p-n-junction in the narrow-gap active layer. Room-temperature detectivity D-lambda* = 4.1 x 10(8) cm Hz(1/2)/W at lambda = 4.7 mum was obtained. Type-II heterostructures may help develop high-efficiency uncooled photodiodes for the 1.6-4.8 mum range for gas analysis, environmental monitoring, and also the diagnostics of combustion and explosion products. (C) 2001 MAIK "Nauka/Interperiodica".