Research On The Physical Process Of Laser Triggering GaAs Photoconductive Switches Flashover

With the rapid development of pulse power technology,semiconductor switching devices have been widely used,in which GaAs photoconductive semiconductor switches(GaAs PCSS)has been widely concerned with its excellent characteristics.However,under the high working voltage,flashover discharge occurs on the surface of the switch,and along with the damage of the material,the working performance of the switch is greatly limited,which seriously hinders the development of high voltage and high power.Researchers at home and abroad have put forward a large number of theoretical explanations about flashover phenomena,but because of the complexity of this phenomenon,the internal mechanism of flashover is not very clear to date.Therefore,studying the surface flashover phenomenon and mechanism of photoconductive switch is of great significance for its life and reliability improvement.In this paper,the flashover experiment of GaAs PCSS with different electrode structures and different insulation packaging forms is carried out.The physical process of GaAs PCSS flashover is discussed,and its flashover waveform,flashover spectrum,flashover heat channel and other aspects are analyzed in a more comprehensive way.By comparing the flashover voltage and current waveforms of different structure switches,it is found that the flashover must meet two basic conditions:the electric field reaches a certain critical threshold,and the switch operates in a nonlinear mode.The experimental results show that the flashover waveform has a higher peak value of current and voltage,and the larger the flashover current is,the less time it takes to form flashover.At the same time,the flashover spectrum is analyzed.It is found that the flashover spectrum is different from the air discharge spectrum,and it is deduced that there is gas desorption in the process of GaAs PCSS surface flashover of insulated package.Then,the flashover phenomenon of the switch surface was analyzed by infrared,and it was found that the flashover channel started from the cathode,and there was a filamentous current channel between the electrodes,and there were obvious infrared luminescence points.Based on the analysis of the experimental phenomena,the physical mechanism of the flashover phenomenon was discussed,and the electric field at the edge of the electrode was numerically analyzed,indicating that the filament current is an important factor in the distortion of the surface electric field.Finally,the damage of GaAs PCSS is demonstrated and analyzed on the surface flashover.It is pointed out that the high temperature caused by the flashover is the main cause of the electrode dissolving and material damage.It is found that the local flashover near the electrode not only causes the damage of GaAs PCSS,but also accelerates the damage of the region near the electrode.At the same time,it is proved that the flashover voltage of the surface switch is better than the coplanar switch,and the insulation encapsulation technology can effectively suppress the flashover along the surface,and put forward the measures to improve the flashover voltage.