P-terminated InP(001) surfaces: Surface band bending and reactivity to water

Stable InP(001) surfaces are characterized by fully occupied and empty surface states close to the bulk valence and conduction band edges, respectively. The present photoemission data show, however, a surface Fermi level pinning only slightly below the mid-gap energy that gives rise to an appreciable surface band bending. By means of density-functional theory calculations, it is shown that this apparent discrepancy is due to surface defects that form at finite temperature. In particular, the desorption of hydrogen from metalorganic vapor phase epitaxy grown P-rich InP(001) surfaces exposes partially filled P dangling bonds that give rise to band gap states. These defects are investigated with respect to surface reactivity in contact with molecular water by low-temperature water adsorption experiments using photoemission spectroscopy and are compared to our computational results. Interestingly, these hydrogen related gap-states are robust with respect to water adsorption, provided that water does not dissociate, due to missing adsorption sites in close neighborhood.