Base transit time in abrupt GaN/InGaN/GaN HBT's

Base transit time in an abrupt GaN/InGaN/GaN HBT is reported. Temperature and doping concentration dependence of low field mobility is obtained from an ensemble Monte Carlo simulation. Base transit time, tau(b), decreases with increasing temperature. The low temperature tau(b) is dominated by the diffusion constant or, in other words, transport within the neutral base region. However, at elevated temperatures base transit time is dependent more upon the base-collector junction velocity or, in other words, by the transport across the heterointerface. tau(b) increases with In-mole fraction showing a stronger dependence at lower temperatures. Unity gain current cut-off frequency, f(T), is a strong function of temperature and base doping concentration, An f(T) of 20 GHz is obtained for a 0.05 mu m HBT.