A raised extrinsic base, silicon germanium (SiGe) heterojunction bipolar transistor
(HBT), and a method of making the same is disclosed herein. The heterojunction
bipolar transistor includes a substrate, a silicon germanium layer formed on the
substrate, a collector layer formed on the substrate, a raised extrinsic base layer
formed on the silicon germanium layer, and an emitter layer formed on the silicon
germanium layer. The silicon germanium layer forms a heterojunction between the
emitter layer and the raised extrinsic base layer. The bipolar transistor further
includes a base electrode formed on a portion of the raised extrinsic base layer,
a collector electrode formed on a portion of the collector layer, and an emitter
electrode formed on a portion of the emitter layer. Thus, the heterojunction bipolar
transistor includes a self-aligned raised extrinsic base, a minimal junction depth,
and minimal interstitial defects influencing the base width, all being formed with
minimal thermal processing. The heterojunction bipolar transistor simultaneously
improves three factors that affect the speed and performance of bipolar transistors:
base width, base resistance, and base-collector capacitance.
