P-i-n diodes of GaSb InGaAsSb were treated in atomic hydrogen and atomic nitrogen flows in a microwave plasma crossed beams machine and in direct H2 and N2 plasma. The first type of treatment led to degradation of reverse currents of the diodes. Direct plasma treatments in H2 alone also led to a deterioration of the surface properties. However, combined treatment at 450°C in direct H2 and N2 plasmas improved the reverse currents and photoluminescence (PL) intensity by more than an order of magnitude. Formation of a passivating GaN layer at the surface of GaSb depleted of Sb by preliminary intense H2 treatment is thought to be responsible for the effect. © 1995.