Raman-active modes in wurtzite(GaN)m(AlN)nsuperlattices

Abstract

We have established that the symmetry of wurtzite $(\mathrm{GaN}{)}_{m}(\mathrm{AlN}{)}_{n}$ superlattices grown along the symmetry axis depends on the numbers of monolayers $m$ and $n:$ the appropriate space groups are ${C}_{6v}^{4}$ and ${C}_{3v}^{1}$ for odd and even values of $m+n,$ respectively. The difference in the superlattice point symmetry drastically influences the first-order vibrational spectra: the number of Raman-active modes depends nonmonotonically on $m+n$ whereas the dependence for the IR-active modes is monotonic. A simple Raman test to distinguish the superlattices with even and odd $m+n$ values is proposed.