EFFECTS OF HYDROGEN ON THE PHOTOCHEMICAL UNPINNING OF GALLIUM-ARSENIDE

Recent studies have shown that, after a preparative photowashing step, water, oxygen, and light must all be present in order to produce Fermi level unpinning of gallium arsenide surfaces. The in situ photoluminescence (PL) investigations in an optical flow cell reported here confirm this finding and show that the unpinning and subsequent repinning processes speed up with an increase in oxygen concentration in the water during photoluminescence measurements. When the water is saturated with hydrogen the surface unpins, although more slowly than if the water were saturated with oxygen, air, or nitrogen. In addition the surface remains unpinned for longer periods. The PL transient response data suggest that hydrogen is an active participant in surface photochemical reactions. A conceptual model is advanced that is consistent with the experimental data on pinning/unpinning processes on the GaAs surface.