The influence of gate length on the electron injection of velocity in an AlGaN/AlN/GaN НЕМТ channel

Field-effect high-electron-mobility transistors (HEMTs) based on AlGaN/AlN/GaN heterostructures with various gate lengths Lg have been studied. The maximum values of current and power gaincutoff frequencies (fT and fmax, respectively) amounted to 88 and 155 GHz for HEMTs with Lg = 125 nm, while those for the transistors with Lg = 360 nm were 26 and 82 GHz, respectively. Based on the measured S-parameters, the values of elements in small-signal equivalent schemes of AlGaN/AlN/GaN HEMTs were extracted and the dependence of electron-injection velocity vinj on the gate–drain voltage was determined. The influence of Lg and the drain–source voltage on vinj has been studied.