Band-gap shifts in silicon-germanium heterojunction bipolar transistors

Abstract
The band gap of the base of Si1−xGex strained-layer base heterojunction bipolar transistors has been investigated using minority-carrier transport measurements. We have found a band-gap reduction of 131 meV for a base of Si0.82Ge0.18, which is in reasonable agreement with theoretical calculations. Our measurements for a base of Si0.85Ge0.15 show a band-gap reduction less than predicted, suggesting a reduction of strain in the structure.