Effects of base doping and carrier lifetime on differential current gain and temperature coefficient of 4H-SiC power bipolar junction transistors

4H-SiC NPN bipolar junction transistor (BJT) is studied systematically by performing two-dimensional numerical simulations. Several design issues are discussed. Depending on the doping concentration of the base and the carrier lifetimes, both positive and negative temperature coefficients in the common emitter current gain could exist in 4H-SiC NPN BJTs with aluminium-doped base. The temperature coefficients of the current gain at different base doping concentrations and different carrier lifetimes have been determined. A high base doping concentration can reduce the requirement for the carrier lifetime in order to obtain negative temperature coefficient in current gain. Device simulations are performed to evaluate the carrier lifetimes by fitting the measured output I-C-V-CE curves. An excellent fitting is obtained and the base electron lifetime and the emitter hole lifetime are extracted to be about 22 and 5.7 ns, respectively.