The authors present results of research and development of mid-infrared photodiodes based on antimonide solid solutions operating at room temperature in the spectral range of 1.5-4.8 mum. A new physical approach to the design of long-wavelength photodiodes is proposed by using type II broken-gap heterostructures grown by liquid-phase epitaxy on GaSb substrates. The choice of sequence of the narrow-gap and wide-gap layers in the GaSb/InGaAsSb/GaInAsSb and GaSb/InGaAsSb/AlGaAsSb heterostructures allows one to vary the band energy diagram and barrier heights on the interface. Electrical and photoelectrical parameters of three kinds of devices were studied. A detectivity of D-lambda* = 4.1 x 10(8) cm Hz(1/2)/W was found at lambda = 4.7 mum, T = 300 K.