University of Delaware,
Keywords: high power, high speed, transistors, low cost, high cut-off frequency
Summary:Device surface properties are critical for its performance such as channel electron density, leakage current, subthreshold swing, and noise characteristic in gallium nitride high-electron-mobility transistors (HEMTs). In this work, the surface property of InAlN/GaN HEMTs is improved by forming gas (FG, 5% H2 and 95% N2) annealing demonstrated. X-ray photoelectron spectra (XPS) , Transmission line measurement (TLM), capacitance-voltage measurement (CV) were utilized to characterize the material properties. X-ray photoelectron spectra (XPS) shows 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. TLM indicates that N2 annealing offers a lower ohmic contact resistance (RC) while FG annealing features a lower sheet resistance (Rsheet). CV demonstrates an increase of two-dimensional electron gas (2DEG) electron density. FG/N2 two-step ohmic contact annealing is then developed and applied on GaN-on-Si HEMTs to achieve a subthreshold swing (SS) of 113 mV/dec, a transconductance (gm) peak of 415 mS/mm, a record low drain-inducing barrier lowing (DIBL) of 65 mV/V, and a record-high power gain cutoff frequency (fmax) of 270 GHz on a 50-nm InAlN/GaN HEMT on Si.