Carrier dynamics of low-temperature-grown GaAs observed via THz spectroscopy

Subpicosecond electron lifetimes in low-temperature-grown GaAs are unambiguously demonstrated via far infrared terahertz spectroscopy. A systematic study of low-temperature-grown GaAs, as-grown and annealed, reveal carrier lifetimes to be directly related to the excess arsenic incorporation and anneal conditions. Contrary to previous observations, electron lifetimes of 600 fs (200 fs) are found in 0.25% (0.5%) excess arsenic GaAs. We attribute the observed differences to the far infrared interaction and the use of dilute photoexcitation densities which eliminate both band-edge resonance and high carrier densities effects. A simple model is developed to determine the relative electron mobility and to interpret the results. Additionally, time resolved differential spectroscopy reveals Drude-like behavior of the free carrier conductivity within 1 ps of excitation.