Characterization of AlSiO dielectrics with varying silicon composition for N-polar GaN-based devices

The properties of aluminum-silicon-oxide (AlSiO) dielectric with varying silicon composition, grown on (000-1) N-polar GaN, were investigated in this paper. The refractive index, dielectric constant, and film density of AlSiO decreased with the increase of the silicon composition as indicated by ellipsometry, low-frequency capacitance-voltage (CV), and x-ray reflectivity (XRR) measurements, respectively. Negligible frequency dispersion in CV measurements and high-intensity XRR oscillations peaks were measured for all AlSiO samples with different silicon compositions, suggesting a high-quality N-polar GaN-AlSiO interface. The leakage current characteristics and flat-band voltage stability improved with the increase of the silicon composition from 20% to 46% and degraded for the sample that had a silicon composition of 73%. This study contributes to understanding the AlSiO dielectric performance for future use in the gate stack of N-polar GaN-based transistors.