Theoretical prediction of the performance of Si and SiC bipolar transistors operating at high temperatures

Silicon carbide (SiC) is a promising material for semiconductor devices operated at high temperatures because of its large energy bandgap, high thermal conductivity and silicon compatibility. The authors develop an analytical model to predict and compare the DC and AC performance of SiC and conventional Si bipolar junction transistors (BJTs) at high temperatures. Based on the device parameters available in the literature, the authors´ calculations show that the SiC BJT indeed possesses a higher current gain than its silicon counterpart as the temperature is increased beyond 500 K. This is primarily because SiC has a larger bandgap than Si. As a result, at high temperatures, the majority carrier concentration in the base of the SiC BJT remains the same value as the doping concentration, whereas the majority carrier concentration in the base of the Si BJT increases considerably beyond the doping concentration. The cutoff frequency of the SiC BJT, however, decreases and becomes smaller than that of the Si BJT when the temperature increases. The authors suggest this is caused by a faster decrease in the electron mobility of SiC than of Si as the temperature is increased. The model compares favourably with data measured from a typical Si BJT