Importance of collector doping in the design of AlInAs/GaInAs/InP double heterojunction bipolar transistors

AlInAs/GaInAs/InP double heterojunction bipolar transistors (DHBTs) have been made with an InP collector thickness of 0.75 μm and collector dopings of 1.4, 2.4, and 3×1016 cm−3. It is shown that because of the conduction band potential barrier between the GaInAs base and the InP collector in DHBTs and particular velocity‐field characteristics of InP, the dc and rf performance of the DHBT is very sensitive to the collector doping level. With a collector doping of 3×1016 cm−3 devices conducted a collector current density of 1×105 A/cm2 without gain compression and had a IC‐VCE saturation voltage of about 2 V. Base‐collector and collector‐emitter breakdown voltages were 22 and 14.5 V, respectively, and fT and fmax were in the range of 65–70 GHz.