Detection of terahertz radiation with low-temperature-grown GaAs-based photoconductive antenna using 1.55 mu m probe

THz radiation is detected by a low-temperature-grown GaAs (LT-GaAs) photoco nductive antenna probed with a 1.55 mu m probe laser. The detection efficie ncy is found to be approximately 10% of that obtained with a 780 nm probe. From the nonquadratic dependence of photoconductivity on laser intensity, t wo-step photoabsorption mediated by midgap states in LT-GaAs is suggested, instead of the two-photon absorption, as the primary process for the photoc onductivity. (C) 2000 American Institute of Physics. [S0003-6951(00)01335-8 ].