Abstract
We present a direct observation of time-resolved intervalley transitions of electrons between the conduction band Γ and L valleys in GaN single crystals using a two-color (ultraviolet and near-infrared), femtosecond, pump-probe spectroscopic technique. We have found that the threshold for the Γ↔L transition appears at the energy of 4.51±0.05eV and the electron scattering time from the Γ to L valley is comparable to the 170fs width of our pump pulses, while the return process of electrons from L to Γ is measurably slower. The L to Γ scattering time is 1.02ps, while the total depopulation time of the L valley is estimated to be ∼20ps. Our physical model, based on the three-state rate equations, fitted our experimental data very well and allowed us to calculate the optical phonon emission time of 290fs. The deformation potential between the two valleys was also obtained from the intervalley scattering modeling and the value was 0.92×109eV∕cm.
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