PICOSECOND PHOTOLUMINESCENCE STUDIES OF PHOTOCORROSION AND PASSIVATION OF N-GAAS IN NA2S-CONTAINING SOLUTIONS

Passivation of n-GaAs by Na2S in an electrochemical cell has been studied using photoluminescence decays and voltage dependence of photoluminescence;lescence intensity. A significant increase in the degree of passivation of the (100) n-GaAs surface is seen when the concentration of Na2S is increased above similar to 1 M. The observed passivation in higher concentrations of Na2S eventually deteriorates with extended exposure to light. The corrosion that develops when the n-GaAs is in higher concentrations of Na2S leads to traps that can be occupied at all voltages. This behavior is different from corrosion seen in lower concentrations of Na2S in which the traps can only be occupied at voltages greater than V = 0.0 V. Decay measurements at flatband potential and at open circuit indicate no significant changes in surface-trapping velocity as the Na2S concentration is changed from 0.008 to 1 M. This suggests that repinning or removal of surface traps is not responsible for the passivation that is observed upon increasing the Na2S concentration. An increase in the rate of charge transfer across the interface as the Na2S concentration in the electrolyte is increased appears responsible.