Adsorption of germanium and of oxygen on cleaved InP(110) surfaces: Auger electron spectroscopy and measurements of work function and of surface photovoltage

Abstract

The deposition of germanium as well as the chemisorption of molecular oxygen cause the formation of depletion layers on cleave InP(110) surfaces initially exhibiting flat bands, and on p- as well as on n-type doped samples the Fermi level is finally pinned (1.11±0.02) eV above the valence-band top Evs. From the surface band bending vs Ge coverage curves the energies of the chemisorption-induced surface states, i.e., their effective occupation levels, were evaluated as Evs +1.08 eV for the surface donors and Evs +1.15 eV for the surface acceptors. Chemisorbed oxygen, in contrast to germanium, introduces no surface dipoles on InP(110) and is thus incorporated rather than adsorbed. Both the unstimulated and the photon-stimulated interactions of unexcited molecular oxygen with InP(110) surfaces result in a phosphorous loss. After exposures of 1013 L of oxygen in the dark and when simultaneously illuminated by the light of a xenon-arc lamp the phosphorous loss is equivalent to a depletion of one and 1.65 InP layers, respectively, while the oxygen uptake amounts to 0.6 and 1.35 monolayers, respectively. Thus, an indium-oxide layer forms on InP(110) which finding is in agreement with the nonexistent chemisorption dipoles.