Raman spectroscopy as a depth sensor in cubic phase n-GaN

In this work, we investigate the elementary excitations of epitaxial n-doped GaN grown in its meta-stable cubic phase on GaAs substrate. The Raman spectra were obtained in backscattering geometry with the incoming and outgoing light polarizations parallel. We covered the whole spectrum of wavelengths of an argon laser (457-514.5 nm) in a wide range of Raman energy shift, with a minimum temperature of 10 K. We focused our attention on the nature of the Raman structures, in particular, the ones which Stokes shifts are between 550 and 4000 cm−1 whose natures were identified. The control of laser light penetration in the GaN samples together with electronic Raman cross-sections calculations lead us to assign the structures as plasmon-LO phonon coupled modes and density of states of phonons resulting from structural disorder.