Photoreflectance study of H2S plasma-passivated GaAs surface

Abstract

Photoreflectance is used to study the effect of H2S plasma passivation on the GaAs surface. GaAs samples are treated with a H2S plasma in an electron cyclotron resonance chemical vapor deposition system and in-situ encapsulated with a SiNx film. The surface Fermi level moves towards the conduction band after H2S plasma passivation and a surface state density of 6×1010 cm−2 is achieved under optimal passivation conditions. The surface state density is highly dependent on the sample temperature during passivation. The movement of the surface Fermi level is due to the reduction of the surface state density and not due to a shift of midgap surface states, suggesting that S–Ga bonds play the major role in H2S plasma passivated GaAs surfaces. This work demonstrates the need to measure both the surface Fermi level and the density of surface states.