CARRIER DYNAMICS OF LOW-TEMPERATURE-GROWN GAAS OBSERVED VIA THZ SPECTROSCOPY

Subpicosecond electron lifetimes in low-temperature-grown GaAs are una mbiguously demonstrated via far infrared terahertz spectroscopy. A sys tematic study of low-temperature-grown GaAs, as-grown and annealed, re veal carrier Lifetimes to be directly related to the excess arsenic in corporation 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 infrar ed interaction and the use of dilute photoexcitation densities which e liminate both band-edge resonance and high carrier densities effects. A simple model is developed to determine the relative electron mobilit y and to interpret the results. Additionally, time resolved differenti al spectroscopy reveals Drude-like behavior of the free carrier conduc tivity within 1 ps of excitation. (C) 1997 American Institute of Physi cs.