Reduction of p+-n+ Junction Tunneling Current for Base Current Improvement in Si/SiGe/Si Heterojunction Bipolar Transistors

ABSTRACTA reduction of parasitic tunneling current by three orders of magnitude in epitaxial p+-n+ junctions grown by Rapid Thermal Chemical Vapor Deposition (RTCVD) compared to previously published ion implantation results is reported. These results are very important for the reduction of base current in scaled homojunction and Si/SiGe/Si heterojunction bipolar transistors. High reduction in tunneling currents allows higher limits to transistor base and emitter dopings. Significant tunneling was observed when the doping levels at the lighter doped side of the junction were of the order of 1×1019cm−3 for both Si/Si and SiGe/Si devices. These results were confirmed by I-V measurements performed at different temperatures. Since the tunneling current is mediated by midgap states at the junction, these results demonstrate the high quality of the epitaxial interface.