HYDROGEN ADSORPTION ON GAAS(110) - A STUDY OF THE SURFACE OPTICAL-PROPERTIES

The linear optical response of the GaAs(110) surface has been investig ated by studying the adsorption of hydrogen on semi-insulating and var iously doped GaAs(110) using both ellipsometry and reflectance differe nce spectroscopy. The surface optical properties were influenced by th e hydrogen-induced change in surface geometry and, hence, the microsco pic surface electronic structure, and by macroscopic band bending effe cts. We detected surface electronic transitions of the clean surface a t 2.75 eV that disappear with hydrogen adsorption, as well as signific ant hydrogen-induced changes of the surface optical properties near th e bulk critical points. Furthermore, it was observed that hydrogen ads orption leads to a significantly lower surface anisotropy, as compared to the clean surface, in the case of semi-insulating GaAs(110), where the band bending effects are negligible; the energy dependence of the surface anisotropy is similar to that reported in the Literature for oxidized GaAs(110), but with a much smaller amplitude. The influence o f doping is discussed in light of the band bending effects-the electri c-held effect and the unscreening of impurities in the depletion layer . We estimate the strength of these two contributions and conclude tha t the unscreening of impurities predominates over the electric-field e ffect.