Forward transit delay in In0.53Ga0.47As heterojunction bipolar transistors with nonequilibrium electron transport

Summary form only given. The authors have performed a comprehensive study of the high-frequency current gain h₂₁ in InP-In_0.53Ga_0.47As HBTs (heterojunction bipolar transistors) (with an emitter area A_E=3.5 μm×3.5μm and 500 Å base thickness with p-type doping level of 1×10²⁰ cm^-3) over the temperature range 55 K⩽T⩽340 K. Detailed device modeling was used to extract τ_F from the measured data. Results show that the intrinsic emitter-collector forward delay decreases from a value of τ_F=0.5 ps at a temperature T=340 K and saturates at a value of τ_F~0.28 ps for T=150 K and below. This marked decrease in measured forward delay with decreasing temperature arises from the temperature dependence of electron scattering in the device. The extrinsic current gain cutoff frequency, f_T, of these devices at T=55 K is greater than 300 GHz. Such a high value of f_T can only be explained by the existence of extreme nonequilibrium electron transport in the base and collector