Simulation And New Structure Design Of Vanadium-compensated 6H-SiC Photoconductive Semiconductor Switches

Semi-insulating silicon carbide(Si C),with high dark resistance,high breakdown field,large thermal conductivity and stability,and a reasonable electron saturation velocity,is considered as an attractive photoconductive semiconductor switches(PCSS)material Si C-PCSS operated linear-mode is in circuits for solid state pulsed power system application.In this dissertation,the physical mechanisms in Si C-PCSS have been explored.This research has given emphasis to the breakdown of V-doped semi-insulated 6H-Si C photoconductive switches.The main contents in this thesis are as followsV-doped 6H-SiC vertical structure PCSS device model was built based on the Drift-diffusion Model by TCAD tools.Comparing the dark state and transient characteristics,the electric field near the anode is higher than the cathode,and the local peak electric field is present,which leads to an increase in the rate of local impact ionization,which eventually leads to device failure.Simulating different temperature breakdowns,the temperature increases,the fault voltage drops,and the higher the carrier concentration,the easier the collision ionization is.Comparing to the simulation results of the energy balance and the drift-diffusion model under transient conditions,the local thermal effect is also the main cause of the fault.The local peak electric field and local thermal effect together cause the fault of the device.Designing the trench structure can reduce the peak electric field of the electrode edge by 50%,giving the optimal size of the trench.The impact ionization rate and breakdown characteristics of different size switches are proposed,and an idealized model of the new structure is proposed.The simulation results are given based on the drift-diffusion model.The new structure can reduce the peak electric field at the edge of the electrode by an order of magnitude and increase the peak current by a factor of two.It is concluded that the new structural design can achieve low triggering and the high pressure resistance.