$\hbox{InGaP/GaAs}_{0.57}\hbox{P}_{0.28} \hbox{Sb}_{0.15}/\hbox{GaAs}$ Double HBT With Weakly Type-II Base/Collector Junction

We report on the dc characteristics of an InGaP/ GaAs
_0.57
P
_0.28
Sb
_0.15
/GaAs double heterojunction bipolar transistor (DHBT). In comparison with control InGaP/GaAs single heterojunction bipolar transistors (SHBTs), the DHBT shows a lower turn-on voltage (V
_{BE, on}
) by ~ 70 mV, a lower knee voltage up to J
_c
~ 40 kA/cm
²
, and less temperature-sensitive current gain. The validity of reciprocity in the Gummel plot suggests no potential spikes at the emitter/base and base/collector (BC) junctions of the DHBT. By considering the differences, in terms of the built-in voltage of the BC junction, the Fermi level in the base, and the renormalized energy gap of the base, between the GaAsPSb DHBT and the control InGaP/GaAs SHBT, we conclude that the heavily p-doped GaAs
_0.57
P
_0.28
Sb
_0.15
base and the lightly n-doped GaAs collector are in weakly type-II band alignment with a conduction and valence band offset of 44 and 221 meV, respectively. These findings indicate that GaAsPSb is a promising base material for DHBTs operating at high temperature and low V
_{BE, on}
conditions without suffering from the collector current blocking.