Ga0.77In0.23As0.20Sb0.80/GaSb pn heterojunction photodiodes have been prepared by liquid phase epitaxy. They exhibit a long-wavelength threshold of 2.4 μm. The room-temperature dark current at V = −0.5 V is 3 μA (10mA/cm2) and the external quantum efficiency is around 40% in the wavelength range 1.75–2.25 μm. The estimated detectivity D* at 2.2 μm is 8.8 × 109 cm Hz½W−1.