A mode for the periodicity and weakening surge in semi-insulating GaAs photoconductive semiconductor switches is proposed based on the transferred-electron effect. It is shown that the periodicity and weakening surge is caused by the interaction between the self-excitation of the resonant circuit and transferred electron oscillation of the switch. The bias electric field （larger than Gunn threshold） across the switch is modulated by the AC elec-tric field,when the instantaneous bias electric field E is swinging below Gunn electric field threshold ET but grea-ter than the sustaining field Es （the minimum electric field required to support the domain） at the time of the do-main reaching the anode, and then the delayed-dipole domain mode of switch is obtained. It is the photon-activated carriers that satisfy the requirement of charge domain formation on carrier concentration and device length prod-uct of 10^12 cm^-2,and the semi-insulating GaAs photoconductive semiconductor switch is essentially a type of pho-ton-activated charge domain device.
The experiment results of ultrawide band electromagnetic radiation with DC biased GaAs photoconductive semiconductor switch combining double ridge horn antenna triggered by high repeat frequency femto-second laser pulse are reported.The GaAs switches are insulated by solid multi-layer transparent dielectrics and the distance of two electrodes is 3mm.The electrode material of the switch is ohmic contact through alloy technics with definite proportion of Au/Ge/Ni.This switch and double ridge horn antenna are integrated and the receive antenna is connected with the test instrument.From receiving antenna,ultra fast electrical pulse of 200ps rise time and 500ps pulse width is obtained,the repetition rate of the pulse is about 82MHz and the frequency spectrum is in the range of 4.7MHz～14GHz.The radiation characteristic of the ultrafast electrical pulse is analyzed.
