VIBRATIONAL PROPERTIES OF GAN(0001) SURFACES

Differently treated hexagonal GaN(0001) epilayers on Al2O3 substrates were investigated by high-resolution electron energy-loss spectroscopy (HREELS) to determine their vibrational properties. X-ray photoemissi on spectroscopy (XPS), Auger electron spectroscopy (AES), and low-ener gy electron diffraction (LEED) were utilized to monitor the surface co mposition and structure, respectively. A comparison was made between s amples which were cleaned solely by a wet chemical etch prior to inser tion into the vacuum system and such which were additionally heated in situ to 800 degrees C first in a Ga-beam and subsequently in UHV. LEE D investigations exhibited 1 X 1 patterns for both of the preparation procedures, whereas only for the latter no oxygen contamination was de tected by XPS and AES. The AES spectra revealed the presence of C whic h cannot be traced back to hydrocarbon contamination, since the HREEL spectra showed no such loss features. Electron energy-loss structures at 700 cm(-1) (86.8 meV) which are attributed to optical Fuchs-Kliewer phonons were found for both preparation methods. Spectra recorded fro m heat-treated samples exhibited additional loss features at 565 cm(-1 ) (70 meV). These may be attributed to vibrations between Ga and resid ual C atoms. (C) 1998 Elsevier Science B.V.