OBSERVATION OF A CS-INDUCED STATE IN THE BAND-GAP OF GAP(110) - ALKALI-METAL BONDING AND FERMI-LEVEL PINNING

The deposition of submonolayer quantities of Cs onto GaP(110) causes s trong photoemission features in the region of the semiconductor fundam ental band gap. This observation is interpreted in terms of emission f rom a hybrid state caused by the interaction of the Cs 6s level with t he unoccupied dangling-bond state. This hybrid state has long been pos tulated in descriptions of the metal-semiconductor surface bond, and i s responsible for the pinning of the Fermi level. The absence of dispe rsion in the state suggests that Cs/GaP(110) represents a realization of a Mott-Hubbard insulator, by comparison with results from other alk ali-metal/compound-semiconductor systems.