DC and microwave characteristics of In0.3(AlxGa1-x)0.7As/ In0.3Ga0.7As heterojunction bipolar transistors grown on GaAs

The dc and microwave characteristics of In_0.3 (Al_0.5Ga_0.5)_0.7As/In_0.3Ga_0.7As and In_0.29Al_0.71As/In_0.3Ga_0.7As heterojunction bipolar transistors (HBTs) grown on GaAs are investigated. A step-graded In_xGa_1-xAs buffer is employed to effectively suppress the threading dislocations resulting from the lattice mismatch between In_0.3Ga_0.7As and GaAs. These devices exhibit a high collector-emitter breakdown voltage (BV_CEO > 11V) and a collector offset voltage as small as 66 mV, demonstrating the excellent quality of the base-emitter and base-collector junctions. The typical common-emitter current gain at a collector density of 16 kA/cm² is 25 for the In_0.3(Al_0.5 Ga_0.5)_0.7As/In_0.3Ga_0.7As HBTs with a base doping concentration of 1x10¹⁹ cm^-3. The Ft and Fmax for the non-self-aligned device with an emitter size of 4x4 μm² is 33 GHz and 20.5 GHz, respectively.