Femtosecond-timescale buildup of electron mobility in GaAs observed via ultrabroadband transient terahertz spectroscopy.

The buildup of photoconductivity in an archetypal polar semiconductor GaAs was monitored on the timescale of carrier-carrier and carrier-lattice correlations, with sub-50 fs temporal resolution provided by ultra-broadband transient terahertz spectroscopy. Two relevant timescales are identified: the transition in photoconductivity from a regime of extremely weak screening to a screened Drude plasma was observed on the ~280 fs timescale, followed by the gradual increase and saturation of electron mobility on a timescale of ~160 fs. The Drude photoconductivity picture following carrier photoinjection was found to stabilize only on the timescale corresponding to several lattice and plasma oscillations. [ABSTRACT FROM AUTHOR]