Ga0.72Al0.28As/Ga0.99Be0.01As heterojunction bipolar transistor grown by molecular beam epitaxy

We report the first heterojunction bipolar transistor (HBT) with base doping level as high as 2 × 10²⁰cm^-3. The device is grown by molecular beam epitaxy (MBE) with growth conditions adjusted to keep perfect surface morphology and to avoid dopant diffusion even at ultra-high doping levels. Maximum dc current gain of 10 is observed, for a base thickness of 40 nm. This is a new step in the optimization of HBT´s structures for high-speed logic and microwave applications.