INITIAL-STAGES OF ATOMIC-HYDROGEN CHEMISORPTION ON GAAS(110) - A HIGH-RESOLUTION PHOTOEMISSION-STUDY

We analyzed atomic hydrogen chemisorption on GaAs(110) surfaces through synchrotron radiation photoemission studies of core level and valence band emission in the 2200-8800 L exposure range. The variation of the surface shifted and hydrogen induced core components as a function of exposure indicates that hydrogen chemisorption involves the formation of both Ga-H and As-H bonds during the early stages of chemisorption, as observed at higher hydrogen exposures, although not all of the dangling bonds are saturated by hydrogen, and there is no evidence of preferential As desorption that takes place at higher hydrogen coverages. The simple electronegativity picture of H-GaAs bonding that would suggest a partially ionic character of the chemisorption bond with charge transfer from surface anions and cations to the hydrogen appears inconsistent with the observed variation in surface work function and electron affinity with hydrogen exposure.