IMPROVEMENT OF DARK CURRENT OF GA(AL)SB MESA DIODES USING (NH4)(2)S TREATMENT

The effects of chemical sulphuration on GaSb mesa photodiodes performa nance were investigated by electrical characterization. (NH4)(2)S trea tment was found to be very effective in reducing the reverse dark curr ents by one module value, leading them down to 1 = 0.2 mu A (V = 1 V) for a Phi = 60 mu m diameter diode. The capacitance variation versus f requency, investigated from 10 kHz to 10 MHz, becomes flat over the wh ole range of frequency, attesting of a volume conduction mechanism. Th ese performances exhibited a remarkable stability during 1 year, witho ut encapsulation. The X-ray photoelectron spectrum of the Sb 3d level shows that after (NH4)(2)S treatment the surface is free of native Sb oxides, Sb-S bonds being created by the adsorption of sulphur atoms on the surface. These surface modifications are responsible for the obse rved improvement in characteristics and their stability.