Photocorrosion of n-GaAs and Passivation by Na2S: A Comparison of the (100), (110), and (111)B Faces

Photocorrosion of n-GaAs and passivation by Na 2 S have been studied in a working photoelectrochemical cell as a function of crystal face orientation. Time-resolved photoluminescence studies of the (100), (110), and (111)B faces of n-GaAs show that Na 2 S provides a similar degree of corrosion protection to the (100) and (110) faces, although the corrosion-induced surface states eventually formed at each interface are separated in energy by ∼300 meV. Unlike (100) and (110), the (111)B surface is not passivated by Na 2 S. The high density of intrinsic surface states at the (111)B n-GaAs surface, and the lack of removal of these states by Na 2 S, pins the Fermi level and prevents trap saturation. X-ray photoelectron spectroscopic studies of the three surfaces before and after Na 2 S treatment show a significant degree of arsenic sulfide bonding on (100) and (110). The (111)B face shows very little As−S bonding, indicating that formation of interfacial sulfides plays an important role in the reduction of interfacial traps and passivation of the photocorrosion reaction.