In situ photoreflectance study of the effects of sputter/annealing on the Fermi level at (001)n- and p-type GaAs surfaces

We report a photoreflectance study of the effects of Ar⁺ sputtering and thermal annealing on the Fermi level (V) on (001) n- and p-type GaAs with large, uniform electric fields. The measurements were performed in situ in an ultrahigh vacuum (UHV) chamber. The effect of the sputtering was to move V from midgap to near the conduction band for both types of material. Subsequent UHV annealing (350°C) and air exposure restored V its original midgap value. The implication of these observations for various models of Schottky barrier formation will be discussed. Our work also demonstrates the need to simultaneously measure both n- and p-type material in order to obtain unambiguous results.