PHOTOCORROSION OF N-GAAS AND PASSIVATION BY NA2S - A COMPARISON OF THE (100)B-FACE, (110)B-FACE, AND (111)B-FACE

Photocorrosion of n-GaAs and passivation by Na2S have been studied in a working photoelectrochemical cell as a function of crystal face orie ntation. Time-resolved photoluminescence studies of the (100), (110), and (111)B faces of n-GaAs show that Na2S provides a similar degree of corrosion protection to the (100) and (110) faces, although the corro sion-induced surface states eventually formed at each interface are se parated in energy by similar to 300 meV. Unlike (100) and (110), the ( 111)B surface is not passivated by Na2S. The high density of intrinsic surface states at the (111)B n-GaAs surface, and the lack of removal of these states by Na2S, pins the Fermi level and prevents trap satura tion. X-ray photoelectron spectroscopic studies of the three surfaces before and after Na2S treatment show a significant degree of arsenic s ulfide bonding on (100) and (110). The (111)B face shows very little A s-S bonding, indicating that formation of interfacial sulfides plays a n important role in the reduction of interfacial traps and passivation of the photocorrosion reaction.