Investigation of momentum relaxation and time-dependent conductance in radiation-damaged GaAs

We report experimental characterization of a transient capacitative electrical effect in a GaAs photoconductive switch due to initial momentum relaxation of the carriers within the photoexcited plasma. The carrier-momentum-dampening rate (${\mathrm{\tau }}_{\mathit{d}}$) of approximately 1 ps is characterized by optical square-pulse excitation in a radiation-damaged GaAs substrate, which produces asymmetries in the electrical impulse response of the photoconductor. Defect densities in the radiation-damaged samples are measured with use of medium-energy Rutherford backscattering and correlated with the electrical characteristics. Simulations of the electron transport and electrical response under our experimental conditions agree favorably with the observed electrical characteristics of the photoconductor. We discuss the effect of plasma dampening on electrical-switching characteristics and the site-defect capture process.