Investigation of Electron Delay in the Base on Noise Performance in InGaP Heterojunction Bipolar Transistors

Modern InGaP/GaAs heterojunction bipolar transistors (HBT) demonstrate excellent microwave and high-speed performance due to high carrier mobility and bandgap engineering. They have found a niche in wireless and optical electronics in spite of higher wafer fabrication costs and lower integration level compared to Si/SiGe technology. State of the art III–V HBTs have a cut-off frequency (fT) exceeding 600 GHz [3]. In a thin base (wB < 90 nm) HBT, the signal delay takes place mainly in the base and the base/collector (B/C) region where the electron transport is also quasi-ballistic . Thus fT is expected to be higher for a thinner base width HBT. However, the base resistance (RB) increases as wB shrinks resulting in compromised power gain and noise performance. Therefore a higher base doping is required to maintain low sheet resistance.