Driving intervalley scattering and impact ionization in InAs with intense terahertz pulses

We report intense terahertz (THz) pulses inducing intervalley scattering and impact ionization mechanisms in doped InAs crystals by THz pump-THz probe measurements. Two competing mechanisms are observed by varying the impurity doping type of the semiconductors and the strength of the THz field. For p-doped InAs, a cascaded carrier generation dominates while for n-doped InAs, both mechanisms have to be considered. Electron fractional occupancy between the Gamma and L valleys is estimated at different field strengths. (C) 2011 American Institute of Physics. [doi:10.1063/1.3600791]