High-frequency characteristics of AlGaAs/GaAs heterojunction bipolar transistors

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Abstract
The fabrication and high-frequency performance of MBE-grown AlGaAs/GaAs heterojunction bipolar transistors (HBT's) is described. The achieved gain-bandwidth product fTis 25 GHz for a collector current density Jcof 1 × 104A/cm2and a collector-emitter voltage VCEof 3 V.fTcontinues to increase with the collector current in the high current density region over 1 × 104A/cm2with no emitter crowding effect nor Kirk effect. The limitation on fTin fabricated devices is found to be caused mainly by the emitter series resistance.