Investigation of the occupation behavior for oxygen atoms in AlN films using Raman spectroscopy

We investigated the behavior of Raman modes for AlN thin films fabricated with plasma source molecular beam epitaxy method having high levels of oxygen contamination. Oxygen atoms occupy different lattice sites depending on their at. % value and, thus, strongly influence spectral features of certain Raman modes. We studied the variations in the width of nonpolar E2low and E2high modes which represent mainly the vibrations of Al sublattice and N atoms, respectively, in the AlN lattice. When oxygen occupies a N site, it affects the width of the E2high mode, and at the same time, the charge neutrality constraint creates an Al vacancy and, thus, simultaneously affects the width of the E2low mode. We found that for our films whose oxygen concentration vary from 1to10at.%, the width of both the E2high and E2low modes varies linearly with the oxygen contamination levels suggesting that even at such high levels of oxygen contamination, oxygen atoms still prefer to occupy the N site. This is contrary to previous s...