A Pi-Shaped Gate Design for Reducing Hot-Electron Generation in GaN HEMTs

The use of a Pi-shaped gate structure is proposed for GaN HEMTs, which effectively reduces the hot-electron generation under all regimes of operation, while preserving device performance well into the lower millimeter-wave frequency range. Simulations under dc and large-signal RF conditions of the proposed Pi-gate device, along with the corresponding electron energy distribution functions, were obtained with a full-band cellular Monte Carlo device simulator self-consistently coupled to a harmonic-balance circuit solver and compared with the simulations of a typical Tgate HEMT whose dc curves were calibrated to experimental data. Our results show that the peak hot-carrier generation obtained with an asymmetric-Pi-gate is up to 41%, 44%, and 75% lower at dc and in Class AB mode at 10 GHz and 40 GHz, respectively, as compared with that observed with the comparable Tgate devices. This new gate structure suggests that significantly higher reliability against hot-electron-induced device damage can be achieved with modest impacts on performance.