Abstract
Strong photoinduced reflectivity change in the midinfrared region in GaN is observed by femtosecond pump–probe measurements. By comparing the results of simultaneous emission and reflectivity measurements, we show that midinfrared reflectivity spectra are governed by coupled phonon-plasmon modes and spatial inhomogeneity of carrier density. Even when the plasma frequency lies in the far infrared region at low carrier density of 1018 cm−3, the strong plasmon–phonon coupling drives the position of upper phonon–plasmon mode to midinfrared region, allowing us to investigate dynamics of photogenerated free carriers in GaN-based materials by midinfrared reflectivity measurements.