Dark current and trailing-edge suppression in ultrafast photoconductive switches and terahertz spiral antennas fabricated on multienergy arsenic-ion-implanted GaAs

We report ultrafast (∼2.7ps, instrument limited) switching responses of a multienergy-implanted GaAs:As+ photoconductive switches (PCSs) with suppressed trailing edge and reduced dark current. This material is highly resistive with dark current as low as 0.94μA at a bias of 40V. The carrier mobility of the former is ∼590cm2∕Vs, resulting in a small-signal optical responsivity of ∼2mA∕W. Pumped at 100mW and biased at 80V, the multienergy-implanted GaAs:As+ PCS exhibits peak response (0.35V) comparable to the best result of single-energy-implanted ones. The improvement on photoconductive response is crucial for the generation of shorter terahertz emission pulses from spiral antennas fabricated on multienergy-implanted GaAs:As+ (0.8ps) than single-energy-implanted GaAs (1.2ps), with the central frequency blueshifted to 0.2THz (from 0.15THz) and the spectral bandwidth broadened to 0.18THz (from 0.11THz).