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, /spl tau//sub b/, decreases with increasing temperature. The low temperature /spl tau//sub 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. /spl tau//sub b/ increases with In-mole fraction showing a stronger dependence at lower temperatures. Unity gain current cut-off frequency, f/sub T/, is a strong function of temperature and base doping concentration. An f/sub T/ of 20 GHz is obtained for a 0.05 /spl mu/m HBT.