Electronic structure of H/GaN(0001): An EELS study of Ga-H formation

Bare and hydrogenated GaN(0001) were characterized using electron-energy-loss spectroscopy (EELS), Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED). AES and LEED show that the GaN surface is clean but faceted. EELS following hydrogen atom exposure shows a decrease in the intensity of the band-gap transition at 3.5 eV as well as the development of a previously unreported loss peak at 11.7 eV and quenching of a peak at 6.6 eV. We suggest that the peaks at 6.6 and 11.7 eV correspond to occupied states observed in photoemission lying near 1 and 6 eV below the valence-band maximum, respectively. These loss peaks indicate the participation of an unfilled electronic state {~}2 eV above the conduction-band minimum. Hydrogen atom exposure also results in an increase in EELS intensity at 18 eV. Molecular hydrogen does not react with Ga-terminated GaN(0001). These changes in the electronic structure of GaN(0001) may be useful indicators of surface Ga-H.