Filled and empty surface electronic states observed on GaAs(110)1×1-K

An investigation of the development of the potassium-covered GaAs(110) surface up to a monolayer coverage has been performed. Low-energy electron diffraction shows that a monolayer of K forms an ordered 1×1 structure. Ultraviolet photoelectron spectroscopy reveals the early formation of a filled surface state extending into the fundamental band gap. At full coverage this state relaxes to below the valence-band maximum. Using angle-resolved inverse photoemission the appearance of an empty surface state has been observed at normal incidence. The energy position of the latter is lower than the state found on clean GaAs(110) but is still 0.35 eV above the conduction-band minimum. As a consequence of this the GaAs(110)1×1-K surface is found to be nonmetallic. © 1989 The American Physical Society.