Raman scattering study of cubic GaN and GaMnN epilayers grown by plasma- assisted molecular beam epitaxy

We perform visible and ultraviolet (UV) Raman-scattering experiments to study a series of undoped and Mn-doped c-GaN thin films grown by plasma-assisted molecular beam epitaxy under Ga-rich and N-rich conditions. The visible, non-resonant experiments confirm that the Ga-rich growth yields the improved crystal quality. New Raman features, most probably related to Mn-induced disorder, show up in the spectra of the c-GaMnN epilayers grown under N-rich conditions. We find that the introduction of an AlN buffer favors the growth of the hexagonal phase. In the UV spectra of the samples with better crystal quality, we detect multiphonon mA1(LO) peaks up to m = 4 together with strong PL signal from c-GaN. In the more disordered samples the PL emission is quenched, and this allows us to detect multiphonons up to m = 6. The intensity of the multiphonon peaks can be used to assess the crystal quality of the c-GaN and c-GaMnN samples.This work was supported by the Spanish Ministry of Science and Innovation under contract MAT2007-63617 and by the FPI and Ramon y Cajal Programs.Peer reviewe