ALGAAS/GAAS COLLECTOR-UP HETEROJUNCTION BIPOLAR-TRANSISTORS WITH A CARBON-DOPED BASE LAYER

A carbon-doped base is applied to AlGaAs/GaAs collector-up HBTs for the first time. An HBT structure with a C-doped base with a thickness of 80 nm and a doping of 2.5 x 10(18) cm-3 is grown by solid-source MBE. The extrinsic base is formed by Be+/F+ implantation and rapid thermal annealing. The inherent emitter/base junction remains unaffected during the device fabrication process, even in the region near the extrinsic base. This results in the elimination of h(FE) reduction in small geometry collector-up HBTs. A cutoff frequency f(T) of 23 GHz and a maximum oscillation frequency f(max) of 54 GHz are attained in an HBT with a collector size of 2 x 10-mu-m2 with a high emitter/collector breakdown voltage, BV(CEO), greater than 17 V.