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

The linear optical response of the GaAs(110) surface has been investigated by studying the adsorption of hydrogen on semi-insulating and variously doped GaAs(110) using both ellipsometry and reflectance difference spectroscopy. The surface optical properties were influenced by the hydrogen-induced change in surface geometry and, hence, the microscopic surface electronic structure, and by macroscopic band bending effects. We detected surface electronic transitions of the clean surface at 2.75 eV that disappear with hydrogen adsorption, as well as significant hydrogen-induced changes of the surface optical properties near the bulk critical points. Furthermore, it was observed that hydrogen adsorption 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 of doping is discussed in light of the band bending effects-the electric-field effect and the unscreening of impurities in the depletion layer. We estimate the strength of these two contributions and conclude that the unscreening of impurities predominates over the electric-field effect.