High-speed InGaP/GaAs transistors with a sidewall base contact structure

We have fabricated InGaP/GaAs double heterojunction bipolar transistors with a sidewall base contact structure. These transistors operate in both emitter-up and emitter-down modes. Symmetric characteristics of the cutoff frequency f/sub T/=68 GHz and the maximum oscillation frequency f/sub max/=31 GHz were obtained at a base-collector bias V/sub BC/ of 0 V. For emitter-down operation, f/sub T/ was found to reach a maximum of 78 GHz when the base-collector junction was forward biased at 0.9 V. The product of f/sub T/ for emitter-down operation and f/sub T/ for emitter-up operation was 5.3/spl times/10/sup 3/ GHz/sup 2/, which is about six times that of previously reported SiGe heterojunction bipolar transistors.