Raman characterization of passivated GaAs surfaces

The technique of Raman scattering at room temperature, is used to investigate the effect of H 2 S passivation of the surface of n-type GaAs. Well-defined LO, L - and L + features are distinguished in spectra which have been recorded in z ( x, y )[ovbar|zovbar] scatte ring orientation. It is observed that the ratio of the LO to L - peak is reduced by the effects of the passivation process and that the shift of the L + feature from the laser line is decreased. This latter effect, it is suggested, is caused by a decrease in free-carrier concentration due to donor neutralization by hydrogen during passivation. This neutralization effect will also affect the LO to L - ratio and so complicate a quantitative analysis of the influence of passivation on the surface barrier potential.