THz emission from Be-doped GaAs

Directing ultrashort near-infrared laser pulses between two electrodes on the surface of GaAs:Be may produce THz radiation. We have measured the generated THz signal as a function of the applied bias voltage, the optical excitation energy, and the beam size, for a series of samples of differing doping levels. The variation in THz signal with bias is approximately quadratic, as expected. In contrast, the variation of THz signal with optical excitation power is sub-quadratic. As determined by apertureless z-scans, the THz emission depends strongly on the excitation beam diameter. As the Be concentration is varied, the THz emission varies slightly until the Mott limit is exceeded and the material becomes metallic and THz production ceases.