Dynamics of local photoconductivity in GaAs and InP investigated by THz SNOM

Terahertz scanning near-field optical microscope (THz-SNOM) is employed to measure ultrafast evolution of THz conductivity spectra after photoexcitation of GaAs and InP wafers using ultrashort laser pulses. Unlike in GaAs, the THz photoconductivity decay in InP is controlled mainly by the diffusion of electrons away from the photoexcited area, and also by the drift due to band-bending at the surface of the semiconductor. We propose and discuss several general strategies of the analysis of signals measured using THz-SNOM, and we estimate the accuracy of the obtained near-field photoconductivity spectra.