Effects of Parasitic Region in SiC Bipolar Junction Transistors on Forced Current Gain
Effects of a parasitic region in SiC BJTs on conductivity modulation and a forced current gain (βF) were investigated by using TCAD simulation with various device structures. By introducing an Al+-implanted region below the base parasitic region, βF can be improved because the implanted region can reduce the base spreading resistance, leading to alleviation of debiasing effect. βF in devices with various parasitic areas, whose base spreading resistances were reduced by the Al+-implantation, were compared. We found that βF can be enhanced by expanding the parasitic area if the base spreading resistance is sufficiently reduced. The higher βF is attributed to an expanded conductivity-modulated region. The collector current spreading in the collector layer and the hole injection from the parasitic region as well as from the intrinsic region can play a role to evoke the conductivity modulation. Thus, the larger parasitic region can expand the conductivity-modulated region, resulting in expansion of an active area and the enhancement of βF.
Robert Stahlbush, Philip Neudeck, Anup Bhalla, Robert P. Devaty, Michael Dudley and Aivars Lelis
S. Asada et al., "Effects of Parasitic Region in SiC Bipolar Junction Transistors on Forced Current Gain", Materials Science Forum, Vol. 924, pp. 629-632, 2018