Low Turn-On Voltage and High-Current $\hbox {InP}/ \hbox {In}_{0.37}\hbox {Ga}_{0.63}\hbox {As}_{0.89}\hbox {Sb}_{0.11}/\hbox {In}_{0.53}\hbox {Ga}_{0.47}\hbox {As}$ D

We report on the dc and microwave characteristics of an InP/In_0.37Ga_0.63As_0.89Sb_0.11/In_0.53Ga_0.47As double heterojunction bipolar transistor grown by solid-source molecular beam epitaxy. The pseudomorphic In_0.37Ga_0.63As_0.89Sb_0.11 base reduces the conduction band offset DeltaE_C at the emitter/base junction and the base band gap, which leads to a very low V_BE turn-on voltage of 0.35 V at 1 A/cm². A current gain of 125 and a peak f_T of 238 GHz have been obtained on the devices with an emitter size of 1times10 mum², suggesting that a high collector average velocity and a high current capability are achieved due to the type-II lineup at the InGaAsSb/InGaAs base/collector junction.