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

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