XPS analysis of aluminum nitride films deposited by plasma source molecular beam epitaxy

Ten samples of crystalline aluminum nitride (AIN) film were deposited on sapphire and silicon substrates by a plasma source molecular beam method. The samples were analyzed using X-ray photoelectron spectroscopy (XPS) depth profiling and high-resolution X-ray diffraction. Oxygen levels were observed to decrease exponentially from the surface into the bulk film. Aluminum, nitrogen and oxygen peaks were fitted with subpeaks in a consistent manner and the subpeaks were assigned to chemical states. AIN subpeaks were observed at 73.5 eV for Al2p and 396.4 eV for N1s. An N1s subpeak at 395.0 eV was assigned to N-N defects. No direct N-O bonds are assigned; rather it is proposed that an N-Al-O bond sequence is the source of higher binding energy N1s subpeaks. The observations in this study support a model in which oxygen is bound only to aluminum in the form of Al-O octahedral complexes dispersed or clustered throughout the main AIN matrix or as Al-O bonds on the crystal grain boundaries. The data also suggest that the AIN lattice parameters are related to oxygen content, since the c-axis is observed to increase with increasing oxygen content. Copyright (C) 2008 John Wiley & Sons, Ltd.