Chemisorption of NH3 on GaN(0001)-(1 x 1)

The chemisorption of MH, on the GaN(0001)-(1 X 1) surface has been studied using ultraviolet photoemission spectroscopy together with semiempirical mo lecular orbital cluster calculations. Adsorption removes surface states nea r the valence band maximum with little or no change in band bending. The da ta indicate a much smaller emission intensity for the N lone-pair orbital t han is expected for an -NH2 species with three-fold coordinated N. Comparis on of observed and calculated spectra suggests that NH3 dissociates into ch emisorbed NH2 and H, with the N atom four-fold coordinated as an asymmetric bridge between two surface Ga atoms. (C) 2000 Elsevier Science B.V. All ri ghts reserved.