Effects of electron cyclotron resonance etching on the ambient (100) GaAs surface

Photoreflectance has been used to study the electronic behavior of the ambient ~100! GaAs surface and its modification by etching in a Cl2 /Ar plasma generated by an electron-cyclotron resonance ~ECR! source. We observed two pinning positions for ambient ~100! GaAs, with n-GaAs pinning near midgap and p-GaAs pinning near the valance band. ECR etching shifts the Fermi level of p-GaAs toward midgap, but has little effect on n-GaAs. The surface modification is most influenced by the rf power. Auger electron spectroscopy indicates that the etching increases As at the GaAs/ oxide interface. We suggest that the Ga/As ratio controls the position of the Fermi level. © 1995 American Institute of Physics.