Surface passivation oxide effects on the current gain of 4H-SiC bipolar junction transistors

Effects of surface recombination on the common emitter current gain have been studied in 4H -silicon carbide (SiC) bipolar junction transistors (BJTs) with passivation formed by conventional dry oxidation and with passivation formed by dry oxidation in nitrous oxide (N2 O) ambient. A gradual reduction of the current gain was found after removal of the passivation oxide followed by air exposure. Comparison of the measurement results for two different passivated BJTs indicates that the BJTs with passivation by dry oxidation in nitrous oxide (N2 O) ambient show a half order of magnitude reduction of base current, resulting in a half order of magnitude increase of current gain at low currents. This improvement of current gain is attributed to reduced surface recombination caused by reduced interface trap densities at the base-emitter junction sidewall.