H2S adsorption on the (110) surfaces of III–V semiconductors

The adsorption of H2S on cleaved (110) surfaces of InP, GaP and GaAs has been studied by core level soft X-ray photoelectron spectroscopy (SXPS) and angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) using synchrotron radiation. H2S adsorption occurs at room temperature on InP and GaP. At low exposures (up to 5 L) the surface component of the cation spectra (In 4d, Ga 3d) is strongly reduced while that of the P 2p core level spectra is replaced by a component at higher binding energy. The S 2p spectrum shows a single component and the valence band spectra show sharp new features. This adsorbate can be removed by gentle annealing. Adsorption on GaAs does not occur at room temperature, but low temperature (200 K) adsorption yields SXPS and ARUPS spectra which indicate that this low exposure adsorption process is essentially the same for all three substrates. A model of dissociative adsorption consistent with these photoelectron data is presented.