InAlN/GaN HEMT on Si With fmax = 270 GHz

Device surface properties are critical for its performance such as channel electron density, leakage current, subthreshold swing (SS), and noise in gallium nitride high-electron-mobility transistors (HEMTs). In this article, the improved surface property of InAlN/GaN HEMTs with forming gas (FG, 5% H
₂
, and 95% N
₂
) annealing is demonstrated. X-ray photoelectron spectra (XPS) show that the number of Ga–O bonds decreases while that of the Ga–N bonds increases, an indication of the surface native oxide removal after FG annealing. Compared with N
₂
annealing, an increase of two-dimensional electron gas (2DEG) electron density with FG annealing is determined by both energy band simulation and capacitance–voltage measurement. Transmission line measurement (TLM) shows that N
₂
annealing offers a lower ohmic contact resistance (
${R}_{\text {C}}$
) while FG annealing features a lower sheet resistance (
${R}_{\text {sheet}}$
). Herein, a FG/N
₂
two-step ohmic contact annealing is developed to achieve a SS of 110 mV/dec, a transconductance (
${g}_{\text {m}}$
) peak of 415 mS/mm, a record low drain-induced barrier lowing (DIBL) of 65 mV/V, and a record high power gain cutoff frequency (
${f}_{\text {max}}$
) of 270 GHz on a 50-nm InAlN/GaN HEMT on Si.