Stduy On The Formation Mechanism Of Uitrafast Filamentary Current In Multiplication Photoconductive Semiconductor Switches

High-gain photoconductive semiconductor switches(PCSS)have many advantages,such as fast response,low trigger jitter,high repetition rate and large power capacity.They have important applications in modern science and technology and national defense construction.When the photoconductive switch operates in high gain mode,the output electric pulse of MW and sub-picosecond rising edge can be triggered by the laser pulse of nJ magnitude.However,the filamentary current and the lock-on phenomenon of tens of microseconds in the high gain mode not only limit the output power and the maximum repetition frequency of the switch,but also greatly reduce the lifetime of the switch.In this paper,a flow model based on avalanche charge domain is proposed to explain the formation mechanism of ultra-fast filamentary current by comparing filamentary discharge phenomena in various media,starting from the physical and chemical properties of GaAs semiconductor materials and the filamentary current experiment in high gain mode.Firstly,the generation of charge domain is analyzed based on the principle of dipole domain theory.Secondly,a flow model suitable for photoelectric semiconductor switches is established by comparing the mature flow theory of gas discharge.The model includes the transition from avalanche charge domain to primary streamer,the development of streamer at all levels,and the lock-on effect.Finally,the super-fast characteristic of filamentary current is theoretically analyzed,and the formula for calculating the speed of filamentary current is deduced.The typical downline of filamentary current velocity is 2.41×108 cm/s.Based on the breakdown experiments of photoconductive switches,the breakdown characteristics of ultrafast filamentary current are studied.according to the mechanism of filamentary current formation.It is pointed out that the filamentary breakdown trace of the switch is caused by the Joule heat effect caused by the high density filamentary current,which leads to the sharp increase of the local temperature of the switch body.The local filamentary breakdown trace of the switch is caused by the enhancement of the local electric field caused by the negative resistance effect.According to the basic principle of Gunn effect electronics and the characteristics of GaAs material,the breakdown voltage of the switch is calculated.The calculated results are basically in agreement with the experimental results.