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 $L_g$ have been studied. The maximum values of current and power gaincutoff frequencies ($f_{\mathrm{T}}$ and $f_{\mathrm{max}}$, respectively) amounted to 88 and 155 GHz for HEMTs with $L_g$ = 125 nm, while those for the transistors with $L_g$ = 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 $v_{inj}$ on the gate–drain voltage was determined. The influence of $L_g$ and the drain–source voltage on $v_{inj}$ has been studied.