Increase in response time of low-temperature-grown GaAs photoconductive switches at high voltage bias

The response time of photoconductive submillimeter-wave emitters based on l ow-temperature-grown (LTG) GaAs is known to increase at high applied bias, which limits the output power of these devices at frequencies near 1 THz. W e performed measurements of an LTG GaAs photoconductor embedded in a coplan ar waveguide with both static and dynamic illumination to investigate the i ncrease in response time and an increase in direct-current photoconductance that occurs at the same bias voltages. We attribute both phenomena to a re duction of the electron capture cross section of donor states due to electr on heating and Coulomb-barrier lowering. We discuss why the phenomena canno t be explained by space-charge-limited current or other injection-limited c urrents, or by impact ionization. (C) 1999 American Institute of Physics. [ S0003-6951(99)02041-0].