Image Number 6 for United States Patent #6830982.
According to one exemplary embodiment, an NPN bipolar transistor comprises a base layer situated over a collector, where the base layer comprises an intrinsic base region and an extrinsic base region. The NPN bipolar transistor may be, for example, an NPN silicon-germanium heterojunction bipolar transistor. The base layer can be, for example, silicon-germanium. According to this exemplary embodiment, the NPN bipolar transistor further comprises a cap layer situated over the base layer, where a portion of the cap layer is situated over the extrinsic base region, and where the portion of the cap layer situated over the extrinsic base region comprises an indium dopant. The cap layer may be, for example, polycrystalline silicon. According to this exemplary embodiment, the NPN bipolar transistor may further comprise an emitter situated over the intrinsic base region. The emitter may be, for example, polycrystalline silicon.