Research On Characteristics Of 4H-SiC BJT Power Devices

Silicon Carbide(SiC) is the third generation wide gap semiconductor material which has high critical electric field, high saturation drift velocity and high thermal conductivity. Due to these advantageous characteristics, Si C power devices has a very promiss prospect in the application of high power, high temperature and anti radiation areas. Among these SiC power devices, Si C BJT gets a lot of attention as it has low conductive resistance and fast switching speed.In this paper TCAD software Silvaco TCAD is used to research 4H-SiC BJT’s electric characteristics. Firstly, physical models,including incomplete ionization model, mobility model, band gap model, carriers recombination rate model and impact ionization model, is constructed. Based on the existing optimized 4H-SiC BJT structure, the forward and reverse characteristics of the device are studied. Secondly, the breakdown characteristics of BJT 4H-SiC devices are analyzed, and FLR, field plate structures are used to improve device breakdown voltage. After optimization, the ring concentration of FLR structure is 2×1018cm-3, junction depth is 0.4μm, breakvltage is improved to 1470 V. Device with field plate structure has a breakdown voltage about 1475 V.Surface recombination current caused by interface states decreases device current gain seriously. So two new structures are presented in the third part. The first structure has a heavily doping area in the external base area. Concentration difference in external base forms a built-in electric field which will resist electrons diffuse to external base surface and improve current gain up to 55. Another structure is embedded with fluorine ions in SiO2 passivation. The fluorine ions modulate carrier density under the external base surface to restrain the recombination of carriers and current gain is improved to 44.At last device layout and some important experiment is brief introducted. TRIM is used to simulate the implantation experiment and give reference reaults of inplantation energy and implantation dose which would be used in experiment.