A novel double heterojunction bipolar transistor for power amplifiers

Novel AlGaAs-GaAs double heterojunction bipolar transistors (DHBTs) with composite collector have been proposed and simulated to replace the conventional AlGaAs-GaAs DHBT. The composite collector combines both wide-bandgap (AlGaAs or InGaP) and narrow-bandgap (GaAs) materials. In the composite collector, AlGaAs (or InGaP) provides high breakdown field and thus is able to be employed to reduce collector thickness while keeping the same breakdown voltage; GaAs provides high electron mobility and thus is able to be employed to reduce on-resistance and transit time. The simulation results demonstrate that novel AlGaAs-GaAs DHBTs have higher f_T than conventional DHBTs, higher BV_CBO than HBTs, and lower knee voltage (on-resistance) than DHBTs. The results also show the current gains of all (D)HBTs with difference in the collector are almost identical. Three InGaP-GaAs (D)HBTs with different structures in collector have also been fabricated to confirm the idea of the proposed structures