THEORETICAL PREDICTION OF THE PERFORMANCE OF SI AND SIC BIPOLAR-TRANSISTORS OPERATING AT HIGH-TEMPERATURES

Silicon carbide (SiC) is a promising material for semiconductor device s operated at high temperatures because of its large energy bandgap, h igh thermal conductivity and silicon compatibility. This paper develop s an analytical model to predict and compare the d.c and a.c performan ce of SiC and conventional Si bipolar junction transistors (BJTs) at h igh temperatures. Based on the device parameters available in the lite rature, our calculations show that the SiC BJT indeed possesses a high er current gain than its silicon counterpart as the temperature is inc reased beyond 500 K. This is primarily because SiC has a larger bandga p than Si. As a result, at high temperatures, the majority carrier con centration in the base of the SiC BJT remains the same value as the do ping concentration, whereas the majority carrier concentration in the base of the Si BJT increases considerably beyond the doping concentrat ion. The cutoff frequency of the SiC BJT, however, decreases and becom es smaller than that of the Si BJT when the temperature increases. We suggest this is caused by a faster decrease in the electron mobility o f SiC than of Si as the temperature is increased. The model compares f avourably with data measured from a typical Si BJT.