Characteristics Study Of 4H-SiC BJT Power Devices

As the third-generation semiconductor, Silicon Carbide (SiC) is suitable for high temperature and high pressure appliations for its wide band-gap, high critical breakdown electric field, and high thermal conductivity. Among the Homogeneous isoforms of SiC,4H-SiC has high electron mobility and low anisotropy, which make it great research and commercial value. As a current-controled device and SiC BJT has lower on-resistance, lower on-state losses, as well as the advantages of no secondary breakdown. But until now, some challenges still remain, including the low cuurent gain and degradation of device under long-term work, so doing research on SiC BJT is significant.In this paper, SiC BJT is studied based on two-dimensional numerical analysis. For more accurate simulation results, the simulation model is built firstly and the parameters is given, including incomplete ionization model, SRH and Auger recombination model, impact ionization model, band-gap narrowing model and mobility model. Secondly, the factors,which have influence device performance parameters, is analysised, such as the influence of emitter area, base area and drift area on the breakdown voltage, conduction resistance and current gain. With 1200V 4H-SiC BJT as the goal, the device parameters are optimized and a devce with common emitter current gain of 39, on-resistance of 3.7Ω·cm2 and ideal breakdown voltage of 1580V is achieved. Considering electric field concentrated on the edge, field limiting ring and junction terminal extension are designed to reduce the peak electric field. The two terminals achieved the high breakdown voltage of 1470V and reachs 93% of ideal value of parallel plane structureFinally, aiming at the surface recombination effect leading to the low current gain, the new device structure and process are discussed. In the aspect of device structure, the structure of emitter metal extension and p-type passivation layer is put forward. In the structure of emitter metal extension, the surface carriers’density can be modulated by controlling the surface potential. According to the simulation results, the surface recombination is suppressed and the common emitter current gain increased by 63% consequently. The structure of p-type passivation layer can lower the exterior base resistence by introducing high concentrations of p-type passivation, and the common emitter current gain increased by 117%. In the aspect of device process, Comparing SiC/SiO2 interface quality under different oxidation and annealing condition, we found that NO annealing can reduce the interface state density, which is consistent with the previously reported literature. Additionally, the quality of the interface can be improved by increasing the annealing temperature properly.