Diffusion and drift in terahertz emission at GaAs surfaces

We study terahertz (THz) emission from GaAs as a function of photon energy and electric field. THz radiation arises from transport of photogenerated charge in an electric field and by hot carrier diffusion (the photo-Dember effect). These mechanisms can be separated by experiments in which either the electric field or the kinetic energy of the carriers is varied. For electric fields Esimilar to4 kV/cm, we find that the electric field controls THz emission for carrier temperatures k(B)T(C)less than or equal to0.1 eV, while hot-carrier diffusion dominates for k(B)T(C)approximate to1 eV. Both mechanisms contribute at intermediate fields and carrier temperatures. Our results are consistent with estimates of the relative magnitudes of these two effects. (C) 2003 American Institute of Physics.