Ultrafast carrier relaxation in radiation-damaged silicon on sapphire studied by optical-pump-terahertz-probe experiments

We investigate the relaxation of photogenerated carriers in radiation-damag ed silicon on sapphire using a collinear optical-pump-terahertz-probe arran gement. Carrier densities greater than 10(20) cm(-3) are injected using 400 nm, 100 fs pump pulses, and the change in transmission of the terahertz-pr obe pulse is measured as a function of pump-probe delay. The time-dependent carrier density is deduced using a thin-film Drude model. A carrier mobili ty of 422 +/- 17 cm(2)/V s is measured, and single-exponential carrier rela xation times of 4 ps at low fluence and 6 ps at high fluence are observed. (C) 2001 American Institute of Physics.