Observation of longitudinal-optic-phonon-plasmon-coupled mode in n-type AlGaN alloy films

An longitudinal-optic-phonon-plasmon coupled mode (LOPC) has been clearly observed by Raman scattering in n-type AlxGa1−xN films with x ∼ 0.67 and different carrier densities n = 1 × 1017-9 × 1017 cm−3. The A1-LO-phonon mode showed a systematic frequency shift and broadening with increasing n. This is a characteristic behavior of LOPC as previously observed in n-type binary semiconductors. A theoretical line-shape fitting analysis was conducted for the LOPC profile using n and plasmon-damping rate as adjustable parameter. Assuming m*/m0 = 0.28 for the longitudinal effective mass of electron, the analysis well reproduced carrier density and mobility deduced by Hall measurement.