The trade-off between common-emitter current gain β and Early voltage VA in heterojunction bipolar transistors (HBT's) where the bandgap varies across the base has been studied. The Early voltage depends exponentially on the difference between the bandgap at the collector side of the base and the largest bandgap in the base, allowing very high Early voltages with only very thin narrow bandgap regions. Using Si/Si1-xGex/Si HBT's with a two-layer stepped base, βVA products of over 100 000 V have been achieved for devices with a cutoff frequency expected to be about 30 GHz.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Electrical and Electronic Engineering