Temperature dependence of the current gain in power 4H-SiC NPN BJTs

For 1-kV 30-A 4H-SiC epitaxial emitter n-p-n bipolar junction transistors, the dependences of the common-emitter current gain /spl beta//sub CE/ on the collector current I/sub C/ were measured at elevated temperatures. The collector-emitter voltage was fixed (at 100 V) to provide an active operation mode at all collector currents varying in a wide range from 150 mA to 40 A (current densities of 24-6350 A/cm/sup 2/). The maximum current gain was measured to be /spl beta//sub CEmax/=40(I/sub C/=7 A) at room temperature and /spl beta//sub CEmax/=32(I/sub C/=10 A) at 250/spl deg/C. The /spl beta//sub CE/-I/sub C/ dependences were simulated in terms of a model that takes into account the main processes affecting the current gain: 1) recombination in the emitter-base space charge region; 2) surface recombination; 3) crowding of the emitter current; 4) decrease in the emitter-injection coefficient at high-level injection; and 5) ionization of deep acceptors. The minority carrier lifetimes and surface recombination velocity were obtained by means of this simulation.