Photoreflectance has been used to study the electronic properties of (100) GaAs surfaces exposed to aCl2/Arplasma generated by an electron cyclotron resonance source and subsequently passivated byP2S5.The plasma etch shifts the Fermi level ofp-GaAsfrom near the valence band to midgap, but has no effect onn-GaAs.For ion energies below 250 eV, post-etchP2S5chemical passivation removes the surface etch damage and restores the electronic properties to pre-etch conditions. Above 250 eV, the etch produces subsurface defects which cannot be chemically passivated. Auger electron spectroscopy shows that etching increases As at the GaAs/oxide interface, while passivation reduces it. ©1998 American Institute of Physics.