Raman scattering of cadmium oxide epilayers grown by metal-organic vapor phase epitaxy

We present a lattice-dynamics study of rocksalt cadmium oxide (CdO). We use Raman scattering to investigate a series of high-quality CdO epilayers grown on sapphire substrates by means of metal-organic vapor phase epitaxy. Two main features are found to dominate the Raman spectra of CdO: a sharp peak at $∼265cm−1$ and a broad feature at $∼390cm−1$⁠. To assign these and other weaker second-order features that appear in the Raman spectra, we have carried out an ab initio calculation of the phonon dispersion in CdO. From the calculated two-phonon density of states (PDOS) we tentatively assign the peak at $265cm−1$ to a $2TA(L)$ mode. The broadband centered at $∼390cm−1$ seems to reflect the high two-PDOS in the $300–450cm−1$ spectral region.