Intervalley energy of GaN conduction band measured by femtosecond pump-probe spectroscopy

Time-resolved transmission and reflection measurements were performed for bulk GaN at room temperature to evaluate the energy of the first conduction band satellite valley. The measurements showed clear threshold-like spectra for transmission decay and reflection rise times. The thresholds were associated with the onset of the intervalley electron scattering. Transmission measurements with pump and probe pulses in the near infrared produced an intervalley energy of 0.97±0.02 eV. Ultraviolet pump and infrared probe reflection provided a similar value. Comparison of the threshold energies obtained in these experiments allowed estimating the hole effective mass in the upper valence band to be 1.4m0. Modeling of the reflection transients with rate equations has allowed estimating electron–LO (longitudinal optical) phonon scattering rates and the satellite valley effective mass.