Rresearch Progress On Avalanche Multiplication GaAs Photoconductive Terahertz Emitter

The development of high radiation energy and micro terahertz source is always the key technology problem of terahertz technology development.As a terahertz radiation source,GaAs photoconductive switch is widely used to produce terahertz wave.However,at present,the linear mode of GaAs photoconductive switch is used in the world,and the radiation energy is too low.The output power of the GaAs photoconductive switch operating in the avalanche multiplier mode is far larger than the linear working mode,and it can greatly improve the radiation intensity of the electromagnetic wave.In order to develop a strong terahertz electromagnetic wave with a GaAs photoconductive switch with an avalanche multiplier mechanism,a semi insulating GaAs photoconductive switch of a 1mm gap is used in this paper to achieve an avalanche doubling quenching output of a GaAs photoconductive switch under single and heavy frequency triggering,thus obtaining ultra fast and ultra short electrical pulses and improving the life of the switch.In order to compare the electric pulse and electromagnetic wave of the GaAs photoconductive switch,a terahertz time-domain spectrum system is built to test the electric pulse and electromagnetic wave of the photoconductive switch.The analysis shows that the terahertz radiation field strength is directly proportional to the bias voltage.The increase of the terahertz radiation power should be mainly considered from the improvement of bias voltage.However,in practice,the shielding effect of the internal electric field and the voltage resistance of the photoconductive switch electrode should be considered,and the bias voltage can not be increased greatly.The analysis and calculation of the switch structure should be carried out in the specific application.The loss of the optical conductance switch is found in the experiment.The reason may be that the conduction resistance of the photoconductive switch can not be recovered rapidly in the nonlinear mode,which leads to the loss of the output electric pulse.The thermal damage of photoconductive switch under high repetition rate and high voltage is further analyzed.At the same time,the effect of the trigger light energy on the carrier concentration is obtained by solving the photogenerated carrier rate equation,and then the effect on the rise time and the pulse width of the output electric pulse is further compared with the experiment.It is shown that the increase of the light generated carrier concentration increases faster and the rise along the steep along with the increase of the triggered light energy.The response speed of the conductance switch is accelerated at this time.