First principles investigation of water adsorption and charge transfer on III-V(110) semiconductor surfaces

We report a DFT/GGA study of water adsorption and charge transfer at the relaxed (110) surfaces of several III-V binary semiconductors: GaAs, GaSb, and InAs. Our calculations are the first to show that adsorption of dissociated water changes the (110) surface structure. The characteristic III-V bond rotation through an angle of 30 is reversed. The buckled III-V bond at the semiconductor/water interface rotates into the surface through a new angle, which we calculate to be approximately 11 degrees on all three binaries. Only dissociation of water - as opposed to chemisorption or physisorption - leads to this pseudo-unrelaxed configuration. We calculate geometries and reaction energies for several different adsorption mechanisms and find that molecular adsorption is the most favorable. We are able to reproduce binding configurations and energies for known adsorption sites on GaAs(110), but we also show new calculations for water on GaSb(110) and InAs(110). Lastly, we calculate the shift in electronic work function and induced surface dipole moment due to adsorbed water. We show that shifts in work function maximize at 1 ML of water, consistent with previous experimental works. Analysis of the partial charges and electron density reveals that adsorption of water polarizes the (110) surface, leading to local charge transfer across the semiconductor/water interface. Published by Elsevier BM.