Research On Non-linear Characteristics Of GaAs Photoconductive Semiconductor Switches Triggered At Weak Optical Excitation Energy

In recent years,gallium arsenide photoconductive switches(GaAs PCSS)have attracted intensive attention and found a wide range of applications from pulse power,ultra-wideband electronics,and terahertz,owing to their versatile physical properties such as high power capacity,picosecond response and trigger jitter,easy integration etc.As the linear working mode of GaAs PCSS is getting mature,it also becomes a frontier research hotspot in the field of GaAs PCSS to develop ultrafast pulse sources by taking the obvious advantages of such as high gain in the GaAs PCSS nonlinear working mode,superfast rising edge of electric pulse,and lower energy of triggering light.Furthermore,the nonlinear working mode of GaAs PCSS will significantly lower the requirement for the triggering light source,so that the cheap and convenient nanosecond-semiconductor laser device(LD)could be used to replace others lasers.it will greatly improve the ultrafast characteristics and power capacity of GaAs PCSS.However,the intrinsic mechanism of GaAs PCSS's nonlinear working mode is still unclear or controversial so far.This leads to the result that its advantageous characteristics cannot be precisely controlled and practically utilized.In this thesis,we performed careful theoretical and experimental study on the nonlinear operating mode of GaAs PCSS triggered by lower optical energy.The m ain research work consists of the following:Firstly,we have investigated the lowest energy of light triggering the nonlinear operating mode of GaAs PCSS.After a systematically study of the mechanism of the characteristics of GaAs and the working mechanism of the GaAs PCSS,we have fabricated a 0.55 mm gap lateral electrode GaAs PCSS,and an optimal insulation design and packaging has been completed.Then for the first time the nonlinear working mode of GaAs PCSS under a picosecond trigger energy light as low as 24.3 nJ and a bias electric field at 78kV/cm has been observed in our experiment.This implies that our experimental results provide a firm foundation for the realization of the non-linear operating mode of GaAs PCSS triggered by nanosecond LD(NSLD).In addition,the multiplication rate at high multiplication working mode of GaAs PCSS has been quantitatively studied and a multiplication rate as high as 870 has been achievedSecondly,considering the influence of the time jitter of nanosecond LD and the time synchronization of using multiple LDs to trigger multiple GaAs PCSS in parallel on the ultrafast characteristics of GaAs PCSS,we also have studied that the time jitter features of nanosecond pulse LD(including LD drive circuit)and trigger synchronization of 2 LDs.The results show that the time jitter of NSLD(including the LD driving circuits)has to do with the voltage of the driving circuits.After optimalization the minimal time jitter we have achieved is 72ps for a single NSLD and,the time synchronization of two parallel NSLD is about 300ps This paves way for the application of GaAs PCSS triggered by NSLD in the field of ultrafast photoelectric technologyThen,we have fabricated GaAs PCSS with 3mm lateral heterodyne electrodes.To overcome the long pulse lock-on effect of nonlinear GaAs PCSS,a 2ns transmission line structure has been designed.Furthermore,the sub-nanosecond(0.975ns)quenching mode nonlinear electric pulse output has been realized experimentally for the first time,together with its pulse peak value increased by 53 times when the GaAs PCSS triggered by the 25 ns NSLD.When the concentration of the carriers reaches its nonlinear threshold,GaAs PCSS enters its quenching nonlinear working mode and generates the high-voltage narrow electrical pulses due to the modulating action of the way of energy reservation in the 2ns transmission lineFinally,based on the comparative results of the light intensity condition and output characteristics of GaAs PCSSs triggered by picosecond weak light and nanosecond weak light,we concluded that the interaction and scattering of electrons are responsible for the transfer from the main energy valley of GaAs conduction band to the satellite energy valleys under the conditions of high electron concentration and strong electric field.When a GaAs PCSS is triggered by an NSLD,light-excited electrons are first avalanched under the deformed strong electric field.These electrons begin to transfer between energy valleys and results in the formation of photo-excited charge domains when the concentration of electron induced by avalanche multiplication and optical excitation reaches its nonlinear threshold and finally high-voltage ultrafast electrical pulses output of sub-nanosecond nonlinear quenching mode has been obtained.