Analysis of transit times and minority carrier mobility in n-p-n 4H-SiC bipolar junction transistors

An analysis of the transit times and minority carrier mobility in n-p-n 4H-SiC RF bipolar junction transistors is presented. These parameters were extracted from small signal RF measurements on 4H-SiC RF transistors with three different base thicknesses: 100, 140, and 200 nm. The study shows that the room temperature minority carrier electron mobility is 215 cm²/V·s for a base Al doping of N_B=4×10¹⁸ cm^-3. The analysis reveals that the collector charging time τ_C and the parasitic charging time τ_P from the capacitance between metal pads and the underlying collector region have a significant effect on the transistors RF performance. The calculated RF gain is in good agreement with the measured results.