Momentum Space Engineering of GaN HETs for RF Applications Through Full-Band Monte Carlo Simulations

The effect of the structure of the emitter barrier on the performance of GaN hot electron transistors (HETs) is investigated through the description of the hot electrons dynamics in the base region obtained with full-band Monte Carlo simulations. From the momentum distribution of the hot electrons in the base, it is found that the injection of carriers in the satellite valleys is limiting the current gain. A new layout with shorter emitter barrier layer reduces the number of electrons in the satellite valleys and shows an increase of the current gain by a factor of 3. The velocity and energy electron distribution are also calculated for the two devices to show the impact of the satellite valley population on the dynamics of the hot electrons. Several designs of the emitter barrier are proposed based on different AlGaN alloys, yielding cutoff frequencies up to 270 GHz. The design of the collector barrier is found to be related to the power performances highlighting a tradeoff between the maximum output power and the device efficiency. The present analysis provides insight on the operation of these new devices and guidelines to improve the dc and ac small- and large-signal performances of GaN HETs.