Improved f (T)/f (max) in wide bias range by steam-annealed ultrathin-Al2O3 gate dielectrics for InP-based high-electron-mobility transistors

In this study, we successfully achieved flat cutoff frequency (f (T)) and maximum oscillation frequency (f (max)) across a wide bias range on InP-based high-electron-mobility transistors (HEMTs) using a steam-annealed ultrathin-Al2O3 gate dielectric due to the reduction in gate leakage current and increase in forward breakdown voltage. Fourier transform infrared spectroscopy analysis demonstrated that steam annealing reduced defects in atomic layer deposited-Al2O3 because of the hydrolysis of carbon impurities and that reducing electron traps suppressed the increase in sheet resistance due to dielectric passivation. Consequently, the insulated-gate HEMTs developed show a high f (max) of > 700 GHz across a wide bias range.