Abstract
Coherent A1 (LO) phonon and its coupling with photoexcited plasmon in wurtzite InN were generated and detected with time-resolved second-harmonic generation. The experimental results directly reveal that the plasma damping time constant is about 60∼120 fs, which depends on the photoexcited plasma density in InN. The frequency of the upper-branch A1 (LO) phonon-plasmon coupling mode shifts as a function of the photoexcited plasma density. This frequency shift can be fitted consistently with different InN films by solving the InN dielectric response function and leads to the determination of the electron effective mass m∥* = (0.033±0.003) me, parallel to the c axis of wurtzite InN. © 2007 American Institute of Physics.