Material Science Forum, Vol. 897, pp. 563-566, 2017 DOI: 10.4028/www.scientific.net/MSF.897.563 Collector conductivity modulation in 1200-V 4H-SiC BJTs(modeling) P.A. Ivanov 1,a* , V.S. Yuferev 1,b , V.E. Levinshtein 1,c , Jon Q. Zhang 2,a , J.W.Palmour 2,b 1 Ioffe Institute, 26 Politekhnicheskaya, 194021 St. Petersburg, Russia 2 Wolfspeed, 3026 East Cornwallis Rd., Research Triangle Park, NC27709, USA a Pavel.Ivanov@mail.ioffe.ru, b valyuf@ammp.ioffe.rssi.ru, c melev@nimis.ioffe.ru, d Jon.Zhang@wolfspeed.com, e John.Palmour@wolfspeed.com Keywords: Silicon carbide, power devices, bipolar junction transistors, fast switching, collector conductivity modulation. Abstract.The resistance of the BJT collector layer can be sharply reduced by the effective injection of minority carriers (holes) from base to collector. As a result, the voltage drop across the BJT becomes substantially lower. The conditions under which this process can occur are the short rise time and the high amplitude of the base pulse. Introduction Owing to the junction voltage cancellation, junction barrier transistors (BJTs) are of considerable interest as high power switching devices. The effect of the junction voltage cancellation is especially important for SiC devices because the built-in potential of SiC p-n junctions is rather high (~2.8 V at appropriate current densities). The specific on-resistance (R ON ) of a SiC BJT in the saturation mode is, as a rule, determined by the resistance of the unmodulated collector layer, which may be rather high in high-voltage BJTs [1-3]. A decrease in R ON in the dc mode due to the modulation of the collector layer by minority carriers was demonstrated in [4]. In the present study, the processes of the collector resistance modulation in high-voltage (1200-Vclass) 4H-SiC BJT in the pulse mode we analyzed by making a one-dimensional simulation. One-dimensional software package used in this study has been successfully employed previously to analyze transient processes in Si and GaAs BJTs [5]. Simulation conditions The parameters of the n + -p-n 0 -n + 4H-SiCstructure under study were typical of 1200-V class 4H- SiC BJTs. The n 0 -collector layer had a thickness W c =15m and a doping level N c = 4×10 15 cm -3 . (With electron mobility μ n = 900 cm 2 /Vs, the specific resistance of the unmodulated collector layer is 2.6 m cm 2 ).The thickness of the p-base layer doped to 2.5×10 17 cm -3 was W b =0.5 μm. The hole lifetime in the collector layer was taken to be  c = 2 μs. The electron lifetime in the base layer was taken to be b = 100 ns. The hole lifetime in the 2-μm n + -emitter layer doped to N e = 210 19 cm -3 was taken to be e = 10 -9 s. The operation area of the structure was S = 0.02 cm 2 . A BJT in the common emitter configuration was turned-on at t =0 by a base current pulse with rise time of 0.1 ns. The base current I b is regarded as generation of an appropriate majority carrier concentration in the base region. The collector load resistor, R l = 50 Ohm. Results and discussion Figure 1 shows the time dependence of the collector current I c during the switch-on process at the rated collector bias U 0 = 1200 V. It is seen that, for all values of I b , the current I at the end of the transient process is nearly equal to the maximum value U 0 /R l =24 A. As expected, the lower the base current I b , the slower the switching. The resistance of the transistor defined as R(t)= U(t)/I(t), decreases monotonically to approach the steady-state value R ON .