| Gallium arsenide(GaAs)semiconductors are widely used in pulse power devices because of their high electron mobility and low carrier lifetime.Compared with linear mode,GaAs photoconductive semiconductor switch(PCSS)in nonlinear mode has lower trigger light demand and higher output gain,which makes the construction and use of high-voltage ultra-fast power pulse system more efficient,convenient and flexible.Although the existing nonlinear theory can explain the experimental phenomena in nonlinear mode to a certain extent,but the change of transient characteristics in the device is lack of a certain understanding,so it is particularly important to use a reasonable model to reproduce the nonlinear working mode of PCSS and study its formation process.In this paper,the Sil vaco TCAD software is used to simulate GaAs Gunn diode and GaAs PCSS based on the numerical calculation method.The domain formation conditions of GaAs Gunn diode and the influence of photo-generated carriers on the domain formation of devices are studied.The nonlinear working mode and locking phenomenon of GaAs PCSS are obtained.Specific conclusions are as follows:1.In the simulation of GaAs Gunn diode,we compare the formation and evolution of highfield domains with and without optical trigger.The evolution and development of domains inside the device are simulated by adjusting the doping concentration.It is concluded that only when the product of the doping concentration n and the distance between electrodes L is greater than or equal to 14×1012cm-2(i.e.,nL≥14×1012cm-2),the domain can be formed inside the device.In the case of nL=1.4×1010cm-2,the evolution and development of high field domains in the device is simulated by applying light with different optical power densities to the device.It is found that the peak electric field of the domain in the device increases with the increase of the optical power density.At the peak optical power density of 1×107W/cm2,multiple domains appear inside the device,which are caused by the enhancement of the carrier concentration in the device.2.In the simulation of PCSS,both coplanar and opposed contacts electrode transverse PCSS were studied.The simulation results of transverse PCSS of coplanar electrodes show that when the optical pulse width is 0.5 ns,the peak optical power density is 20000W/cm2,and the electrode gap is 1000μm,the output current at external bias voltages of 3000V,3200V,3400V,3600V,and 3800V is nonlinear,and the peak output current increases with the increase of external bias voltage;When the external bias voltage is 3900V and 4000V,there is a lock-on phenomenon in the output current,and from the output waveform,there is a current delay phenomenon.The current delay phenomenon slows down when the external bias voltage is 4000V.The simulation results of the transverse PCSS with an opposed contacts electrode show that at an external bias voltage of 4000V,the peak optical power density is 20000W/cm2,and the switch is in a nonlinear operating mode,but there is no lockon phenomenon;The lock-on phenomenon occurs when the external bias voltage of 4000V and the trigger light power density are 30000W/cm2.It can be seen from the results of two parts of simulation that the photoelectric threshold required for locking phenomenon in the transverse PCSS with coplanar electrode is lower than that required by the transverse PCSS with opposed contacts electrode.Finally,according to the experimental scheme,the output pulse width control of PCSS is simulated.The domains studied in this paper are the basis for the study of the nonlinear operating mode of PCSS.Current delay and current oscillation occur in the output electrical pulses of the simulated nonlinear operating mode.The length of current delay is related to the external bias and laser intensity,and the current oscillation is related to the motion of the domains in the device.This work plays a certain role in explaining the formation of nonlinear operating mode of PCSS. |
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