A novel double heterojunction bipolar with composite collector

A novel double heterojunction bipolar transistor (DHBT) with a composite collector has been proposed and fabricated to obtain suitable heterojunction bipolar transistor (HBT) performance for power amplifiers in wireless communication. The composite collector combines both wide-bandgap (AlGaAs or GaInP) and narrow-bandgap (GaAs) materials. In the composite collector, wide-bandgap material provides high breakdown field and thus is able to be employed to reduce the thickness of the whole collector while keeping the same breakdown voltage; narrow-bandgap material provides high electron mobility and thus is able to be used to reduce on-resistance and transit time. The simulated and experimental results show that in a DHBT with a composite collector the on-resistance is improved and other characteristics of a conventional DHBT are changed negligibly. The Gummel plots for the proposed DHBTs and HBT show the negligible difference in current gains, which is due to the identical structures in the base/emitter regions and effectively reduced conduction spike in the base-collector junction. Overall, the novel DHBT remains the advantages of DHBT with improved performance in on-resistance and knee voltage. Three GaInP/GaAs (D)HBTs with different structures in the collector have been grown, fabricated and characterized. The experimental results demonstrate the benefit of combining GaInP and GaAs in the collector.