High-speed InGaP/GaAs HBTs using a simple collector undercut technique to reduce base-collector capacitance

High-speed InGaP/GaAs HBTs were fabricated using a simple collector undercut (CU) technique to physically remove the collector material underneath the extrinsic base region by selective etching for reducing base-collector capacitance (C/sub BC/). The best HBTs achieved a f/sub T/ of 80 GHz and a f/sub max/ (MSG/MAG) of 171 GHz. To our knowledge, this is the highest f/sub max/ (MSG/MAG) ever reported for the InGaP/GaAs HBTs. Compared to the HBTs without CUs, the CU HBTs showed a factor of 1.38 times improvement in the highest achievable f/sub max/ (MSG/MAG) due to the significant reduction of the C/sub BC/.