Competing terahertz radiation mechanisms in semi-insulating InP at high-density excitation

The excitation density dependence of the terahertz radiation from a semi-insulating InP surface was investigated in detail. By changing the excitation density, substantial changes were observed in the wave form with a reversal of the polarity of the radiation field. Different azimuthal angle dependence was also observed for low- and high-density excitations. These facts indicate that three different radiation mechanisms coexist and that the dominant radiation mechanism changes with increasing the excitation density from the drift current, for low-excitation density, to the diffusion current and the optical rectification, for high-excitation density. (C) 2004 American Institute of Physics.