Preliminary Study Of Silicon Carbide Photoconductive Semiconductor Switch

Semi-insulating silicon carbide(SiC) with high breakdown field, large thermal conductivity and stability, and a reasonable electron saturation velocity is considered as an attractive photoconductive semiconductor switches(PCSS) material. SiC-PCSS operated linear-mode is in circuits for solid state pulsed power system application. In this dissertation,the physical mechanisms in SiC-PCSS have been explored. This research has given emphasis to the physical mechanisms of V-doped semi-insulated 6H-SiC photoconductive switches. The main contents in this thesis are as follows:1. In V-doped semi-insulated 6H-SiC photoconductive material, the two dominant impurities are showed that the vanadium is compensating the 6H-SiC material by capturing the net excess electrons donated by nitrogen levels, and the material resisitivity increase more than eight orders of magnitude as the compensation ratio(vanadium to nitrogen) inceases from slightly less than one to a value of two. Meanwhile, as the compensation ratio inceases, the material will have a short carriers lifetime, which results in increasing of the switch on-state resistance.2. A V-doped 6H-SiC PCSS device model was built based on the Drift-diffusion Model by TCAD tools, and then the I-V characteristics in the darkroom and transient characteristics excited by 532 nm laser of the SiC-PCSS are simulated respectively under different conditions. The simulation result under different density of two dominant impurities, V level and N level, is successfully used to validate the physical mechanisms. Besides, TCAD is used to simulate the time-resolved electric field current distribution and volt-ampere characteristics of different light power in V-doped semi-insulated 6H-SiC photoconductive switches excited by 532 nm laser.The simulation shows that, the carriers drift velocity with increasing field saturates at a constant velocity, and the time-resolved electric field current is uniformly distributed along the major electric field current direction that is perpendicular to laser incidence direction.3. With the simplification of semiconductor equations based on the TCAD simulations, a SiC-PCSS circuit model has been developed in consideration of carrier field dependent mobility. With the help of the validation in reported experiment, the influence of exterior electric parameters is discussed by using the SiC-PCSS circuit model.4. The test platform for SiC PCSS is built with the help of the PCSS PSpice model, which SiC-PCSS test circuit is anasysed by the model and a suited load is choosed. Triggered by laser pulses with different incident optical energies at a wavelength of 532 nm, photoconductivity tests of the lateral geometry V-doped semi-insulated 6H-Si C SiC-PCSS were performed at different bias voltages. The results of photoconductivity tests were compared and discussed, which show that the PCSS voltage pulse is similar in temporal to the 532 nm optical trigger pulse, and the minimum resistance of PCSS is 720 ? achieved at 124 mJ incident laser pulse with a bias of 5.5 kV. The repetitive tests are under development with 30 pulse at 1 Hz, and initial experimental results are presented that the switch performed well at a low jitter of sub nanosecond. The test of a vertical geometry SiC-PCSS is also explored, and the image of this PCSS breakdown point is showed and analysed.