A back-illuminated InGaAs photodiode is described in which a double layer of silicon nitride on the front surface serves several functions; both layers passivate the surface; an opening in the lower layer provides a diffusion mask for forming the p-n junction; and a narrower opening in the upper silicon nitride layer provides a deposition mask for forming a restricted area contact. In order to reduce strain near the junction, and hence reduce leakage currents and enhance reliability, the contact geometry has a narrow pedestal portion which contacts the surface in a zone remote from the junction edges and has a wider cap portion which is formed on the pedestal portion to seal the surface from the introduction of contaminants.