Resonant Raman scattering in GaN/(AlGa)N single quantum wells

Resonant Raman scattering has been used to study longitudinal optical (LO) phonon modes in 2–4-nm-wide ${\mathrm{GaN/Al}}_{\mathrm{0.15}}{\mathrm{Ga}}_{\mathrm{0.85}}\mathrm{N}$ single quantum wells (QW). Raman spectra recorded using subband gap excitation were found to be completely dominated by the phonon modes of the (AlGa)N barriers. In contrast, for excitation close to resonance with the lowest transition between confined electron and hole states in the GaN QW scattering by the $A_1$ (LO) phonon in the QW became dominant in spite of the narrow width of the QW. For well widths of 3 and 4 nm, the frequency of the $A_1$ (LO) phonon in the QW was found to be close to that in bulk GaN, whereas for a well width of 2 nm the QW phonon was broadened and shifted towards the frequency of the (AlGa)N $A_1$ (LO) phonon mode. This broadening and frequency shift indicate some cation intermixing for the narrowest QW with the widths of the interface regions being comparable to the well width of 2 nm, demonstrating the usefulness of resonant Raman scattering for quality assessment of GaN/(AlGa)N QWs and interfaces.