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

We report on the dc characteristics of an InGaP/ GaAs_0.57P_0.28Sb_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/cm², 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_0.57P_0.28Sb_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.