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

We report on the dc and microwave characteristics of an InP/In
_0.37
Ga
_0.63
As
_0.89
Sb
_0.11
/In
_0.53
Ga
_0.47
As double heterojunction bipolar transistor grown by solid-source molecular beam epitaxy. The pseudomorphic In
_0.37
Ga
_0.63
As
_0.89
Sb
_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/cm
²
. 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 mum
²
, 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.