N-p-n abrupt AlGaAs/GaAs heterojunction bipolar transistors (HBTs) with a 500 Å-thick GaAs base, and regrown thick extrinsic base layers of p+ AlGaAs/GaAs have been fabricated. The regrown extrinsic base layers allow easy contact to the base with low base resistance to achieve high fmax. fmax; was improved by a factor of ∼ 2 with regrown base compared to conventional processing, up to a value of 45 GHz in these non-self-aligned devices. The extrinsic base regrowth was done at 500°C by MOMBE, which employed low-temperature in situ etch using tris-dimethylaminoarsenic to remove residual oxide from the surface before regrowth.
- In situ etch