The Study On Optical Absorption Mechanism And Avalanche Breakdown Of Semi-insulating GaAs Photoconductive Semiconductor Switches

Compared with the traditional switch,photo-conductive semiconductor switch(PCSS)have many advantages,such as fast switching speed,low timing jitter,small parasitic inductance,capacitance small,and simple structure,especially its high voltage,large power storage capacity made it occupy a great application dominant position in the field of pulsed power and other technologies.PCSS fabricated with III-V semiconductor compounds,such as: GaAs,InP,due to various phenomena appear in the locked mode,the areas of its application are more open.In this paper,based on the experiments of photoconductive switch in linear mode,the optical absorption mechanism of semiconductor GaAs switches and avalanche breakdown in nonlinear mode have been studied.The conclusions as follows:1.In the linear mode,the output current was all depended on photo-generated carriers.Analysis and calculation of switch output waveform triggered by 1064 nm nanosecond pulsed laser in linear mode have been studied.Combined with the switch trigger beam geometry,carrier concentration got in the bulk switch;we also study the changes between bias voltage(or electric)and carrier concentration,it is shown that photo-excited carriers are almost steady as bias voltage change.However,the density gradually increases as incident energy increasing.2.Based on the propagation of light in the medium laws of physics,the theoretical calculation of the absorption mechanism(two-photon absorption,impurities absorb)light excitation carrier concentration have been gained;by comparing the theoretical and experimental results,it is shown that the impurities or two-photon absorption(TPA)is not main absorption mechanism in the switch which is the order of the pulse energy mJ at a wavelength of 1064 nm,however,two-photon absorption is the main absorption mechanism in the switch which is the order of the pulse energy ?J at a wavelength of 1064 nm,In accordance with the laws of light absorption,we can attribute the absorption mechanism of the switch is the three-photon absorption,and obtained three-photon absorption(3PA)coefficient in the experiments.And the relationship between carrier concentration and light intensity in three-photon absorption process was gained.3.Based on optical excitation avalanche domain model,combined with three-photon absorption mechanism of avalanche breakdown mechanism for nonlinear photo-conductive switches.The relationship between incident light and bias field was obtained,which is in good agreement with the experimental relationship.