Vibrational and electronic excitations at GaN{0001} surfaces

The vibrational properties of clean, H- and D-covered GaN{0001} surfaces as well as electronic excitations were investigated by high-resolution electron energy-loss spectroscopy. Surface cleanliness and structure were monitored by Auger electron spectroscopy and low-energy electron diffraction. At hydrogenated surfaces HGa and HN stretching vibrations were found at 1900 cm−1 (235.6 meV) and 3255 cm−1 (403.6 meV), respectively. After deuteration a DN stretching as well as a DGa bending mode were detected at 2395 cm−1 (297.0 meV) and 390 cm−1 (48.4 meV). From the isotope shift of the stretching vibrations, the periodic displacement of the N atoms is calculated. In the electronic loss regime, a transition from band gap states was found to vanish after H exposure.