Characteristics And Junction Termination Technique Study Of 4H-SiC BJT Power Devices

Silicon Carbide (SiC),for its outstanding characteristics such as wide bandgap,high thermal conductivity,high critical breakdown field and high electron saturation drift velocity, plays a more and more important role in the field of high power devices, and it has great potential application in power electronic system. Meanwhile,people draw more and more attention to 4H-SiC BJT because it could eliminate the drawbacks of Si based power BJT and the gate-oxide quality problem of MOSEFT based on 4H-SiC.Therefore, it is of vital significance to conduct research on 4H-SiC BJT power devices.For the purpose of 4H-SiC power BJT characteristics study,this thesis mainly contains the following work:Firstly,from the basic work principle of 4H-SiC BJT,the physical model of device is established,the main material parameters are given and the characteristics of 4H-SiC BJT power devices are investigated by using the semiconductor device simulation tool Sentaurus TCAD 2010. The influence of the interface state density of the SiC/SiO2 passivation layer and the emitter doping concentration on device is studied The influence of emitter width and emitter-base distance on the current gain in 4H-SiC BJT is investigated and the main mechanisms are analyzed.The optimization schemes:increase the doping concentration below the emitter to base,adopt double epitaxial base and Gaussian-doping base to attenuate the influence of WP on current gain are put forward as well. Secondly,the influence of temperature on vertical 4H-SiC BJT are investigated,and the influence of the high injection effect in normal (300K) and high(473K) temperature is analyzed.Meanwhile,the high injection effect of vertical BJT and lateral BJT is compared.The research results indicate that the influence of collector electron high injection on lateral BJT is more significant than vertial BJT.With the the increase of the forward voltage,the current gain of the lateral BJT drops faster,and the output current is lower under the same base driving currentlncreasing the collector doping concentration can attenuate the influence of the collector electron high injection on current gain effectively.The breakdown characteristics and the junction termination structure of vertical and lateral 4H-SiC BJT are studied and the breakdown characteristics of vertical and lateral 4H-SiC BJT are compared.The influence of collector doping concentration and base width on breakdown voltage is investigated and the device parameters are optimized.The device breakdown characteristics of two basic junction termination structure:JTE and FFLRs are analyzed.The main parameters of junction termination structure,such as doping concentration, the depth of ion implantation, JTE width,ring width,ring spacing and ring number are designed by optimization. On the basis of the above research,two novel junction termination structure:stair JTE and JTE+ FFLRs structure on lateral 4H-SiC BJT are proposed.The research results indicate that the optimized novel junction termination structure can modulate surface electric field more effectively,and can obtain higher breakdown voltage,which can reach more than 3700V. Meanwhile,compared with vertial BJT, drift doping concentration of lateral BJT can be higher and base width can be thinner under the comparable breakdown voltage and the doping concentration of the junction termination structure can be greatly reduced,this proved that lateral 4H-SiC BJT has a good application prospect in high voltage and high power field.