High voltage implanted-emitter bipolar junction transistors and Darlington transistors in 4-hydrogen-silicon carbide

Silicon carbide (SiC) has recently been considered a good alternative to silicon in high-voltage, high power applications. This research focuses on implanted-emitter bipolar junction transistors and Darlington transistors in 4H-SiC. BJTs and Darlington transistors with breakdown voltage of 400--500V and peak current gain up to 40 (for BJT) and 2000 (for Darlington transistors) have been developed, and these are the first implanted-emitter 4H-SiC BJTs and Darlington transistors reported in the literature.; Analytical expressions derived to calculate the forward drop at saturation predict that SiC BJTs can have a much lower (>100 times) on-resistance than the silicon BJTs for the same blocking voltage. At higher blocking voltages, the achievable current gain is reduced. A two-stage monolithic Darlington transistor was designed to improve the blocking voltage vs. current gain tradeoff.; 4H-SiC implanted-emitter BJTs and Darlington transistors have been fabricated with variations in emitter implantation species and annealing temperature, as well as the emitter trench depth. High-quality implanted emitter layers have been achieved with phosphorus as the implant species and implant activation at 1600°C. Our SiC power BJTs and Darlingtons exhibit promising high temperature performance. The current gain decreases as temperature increases due to increased ionization in the p-base region. The resulting increased on-resistance at higher temperature permits the SiC BJTs and Darlington transistors to be paralleled and also prevents thermal runaway. Typically, current gain decreases to 25% of the room temperature value at 200°C.; The measured current gain and blocking voltage of the Darlington transistors with different isolation trench designs confirm the design rules established with the simulation results. For a trench width of 5mum, the isolation trench needs to be deep enough (>0.2mum over etch from the base-collector junction) to ensure good isolation hence proper operation of Darlington transistors.; While a substantial improvement has been achieved in SiC bipolar transistors in this research, the specific on-resistance is still higher than predicted for SiC. The reasons for the high specific on-resistance have been analyzed and possible solutions have been suggested.