Nanosecond pump-and-probe study of wurtzite GaN

We present a nanosecond pump-and-probe optical study of wurtzite GaN under the excitation condition that the carrier-longitudinal optical phonon scattering does not contribute to the energy relaxation process. The delay time after which the isothermal condition is achieved is found to be ∼50 ns. This comes from both the phonon structure in GaN and the fact that the carrier cooling depends on excess kinetic energies of carriers.