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 Al x Ga 1− x N films with x ∼0.67 and different carrier densities n =1 × 10 17 -9 × 10 17 cm −3 . The A 1 -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 * /m 0 =0.28 for the longitudinal effective mass of electron, the analysis well reproduced carrier density and mobility deduced by Hall measurement.