Study Of Fast-electrical Pulse Source Based On PCSS

With the development of science and technology, high power pulse technology inmilitary and civil fields is gradually being applied, ultrafast-electrical pulse technologyis improving, at the moment, the mainstream technology is using switching technique toobtain the electrical pulse. Photoconductive switch has the characteristics of high speed,large dynamic range, no jittering in the picosecond optical conductor, highvoltage-withstanding, simple and compact structure, which is used to replace thetraditional switch. Semi-insulating GaAs material has property of high dark resistance,short carrier life, high carrier mobility, it is a good choice for using the GaAs material todeveloping ultra-high speed photoconductive switch. GaAs photoconductive switch hasa rapid opto-electronic response, which is consistent with optical pulse in the linearmode, utilizing the linear relationship between the photocurrent and the optical pulse, itis can be obtained ultrafast electrical pulse to convert high-speed optical pulse in thefemtosecond laser into photoelectric current. Based on GaAs photoconductive switchwith the characteristics of obtaining ultrafast pulse, it has important research value forGaAs photoconductive switch. It has the vital significance for the electronic switch gate,sampling gate, waveform generation, microwave modulation, optical detection, X ray,particle detection, synchronous streak camera, driving Pockels cell, mixing radio,analog-to-digital conversion, electromagnetic pulse weapon, impulse radar, highcurrent ignition device, ultra wide pulse source, THz electromagnetic wave emissionsource.At present, at home and abroad many colleges and universities and ScientificResearch Institute are studying the principle of GaAs photoconductive switch, butreferences seldom reports that switch characteristics are studied by computeremulational tool. This paper catches up the computer software to simulate thephotoconductive switch.Firstly, after photoconductive switch is triggered by laser, through theestablishment of excess carrier transport equations the relationship is solved for theexcess carrier concentration depended on the various parameters, the dissertationanalyzes clearly that intensity, carrier lifetime, optical pulse width, absorptioncoefficient have a effect on the conductance in the form of the curves. Some importantconclusions are obtained that excess carriers are generated only in the surface of the semiconductor layer, the rising time of excess carrier concentration and conductivity arepicoseconds level, concentration and conductivity pulse width can reach1ns.Considering propagation of the high speed pulse signal, the dissertation analyzesthe function of the transmission line in the pulse propagation and forming, gives thecircuit depended on ideal switch control in single transmission line, gives the electricpulse ideal representation in matching load in the end of load, the electric pulse of pulsewidth at60ns is obtained, and the correctness of the theoretical results is verifiedthrough the simulation. The dissertation solves the telegraph equation of transmissionline through numerical calculation, the electric pulse of pulse width at15ns is obtainedunder the control of the photoconductive switch.According to the rate equation for carrier the dissertation establishes a model ofPspice for photoconductive switch, simulates factors from light energy, pulse width,carrier lifetime on the effects of electric pulse, simulates the electrical pulse after addingtransmission line. The dissertation gives the relationship between the dark statebreakdown field and electrode gap distance using Silvaco TCAD and Sentaurus TCADdevice simulation tool. A short electric current pulse with the pulse width0.2ns and therising time25ps is obtained by simulating transient photoelectric characteristics. Thework simulates the different electrode structure on the effects of the electric field,carrier mobility, the current density.This paper verifies that the theoretical study of photoconductive switch is correctthrough the experimental test and the Pspice model is reasonable. The nanosecond pulseis obtained.