Research On Withstand Voltage Experiment Of GaAs Photoconductive Switch

Photoconductive semiconductor switches(PCSS)as a semiconductor device,due to its small size,light weight,high precision,high speed and high frequency,especially the high gain nonlinear mode,has important applications in the field of military radar,communications,electronics and other transient.Therefore,PCSS has drawn wide attention.According to the characteristics of PCSS application,the characteristics of Photoconductive semiconductor switches can be explored from two aspects,one is in the application of low power,switch’s sensitivity and switching ratio should be further improved;the other is in the application of high power,the withstand voltage of device is actually much smaller than the theoretical value.The device’s voltage resistance limits the development of PCSS,so improving the withstand voltage of device is very critical.In theory,the working mechanism of the linear operation mode and the non-linear working mode of PCSS was explained firstly,and the characteristics of the two working modes were summarized.The high gain characteristics of the non-linear were pointed out.It was because GaAs material has a large band gap,electron mobility,dark state resistivity and breakdown electric field are large,at the same time have a shorter carrier life,GaAs could be used as PCSS’s material perfectly;Then the switch chip’s structure and the characteristics of each layer has been shown.What’s more,we have explained Ohmic heating caused by on state current,when the PCSS was in the conduction state,and finally we have enunciated the breakdown theory of PCSS from the two aspects: thermal breakdown and high voltage breakdown.In the experiment,the relationship between the position of the laser spot and the output power of PCSS has been studied.When the incident spot was perpendicular to the electrode,the output power of PCSS is gradually increased as the voltage increased.When the incident light spot was parallel to the electrode,the output power of PCSS is smaller.In addition,the affecting factors of PCSS’S withstand voltage,such as electrode shape,electrode pitch,ohmic contact,passivation layer,and heat dissipation,were studied.Under the same conditions,a photoconductive switch with a coplanar fillet electrode has a smaller dark current and better resistance to pressure;For spacing,the larger of the electrode spacing,the better the withstand voltage will be,but the excess body resistance will affect the sensitivity of the switch.Under the sensitivity requirement of PCSS,the electrode spacing of 8mm device could withstand high voltage of 5.5kV;As for the passivation layer,the thicker the thickness of silicon nitride,the better the voltage resistance of the device will be.A device that covered by 770 nm silicon nitride as a passivation layer can withstand 6 kV.Finally,the external heat dissipation device could improve the device’s heat dissipation capability,reduce the dark current of the switch by 82% and increase the withstand voltage of the switch by 20%.