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 Na2S 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 Na2S 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 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 saturation. X-ray photoelectron spectroscopic studies of the three surfaces before and after Na2S 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.