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The electrical properties and the interface abruptness of aluminum silicon oxide (AlSiO) dielectric grown in situ on 0001¯ N-polar and (0001) Ga-polar GaN by metal organic chemical vapor deposition were studied by means of capacitance-voltage (CV) and atom probe tomography (APT) measurements. The growth of AlSiO on N-polar GaN resulted in a positive flatband voltage shift of 2.27 V with respect to that on Ga-polar GaN, which exemplifies the influence of the GaN surface polarization charge on the electrical properties of GaN-based metal oxide semiconductor (MOS) devices. The AlSiO/GaN(N-polar) interface was sharp, which resulted in nondispersive CV characteristics and a relatively low density of interface states (Dit) of 1.48 × 1012 cm−2. An intermixed layer of AlGaSiO was present at the interface between AlSiO and Ga-polar GaN, which contributed to the measured dispersive CV characteristics and resulted in an ∼2× higher Dit than that on N-polar GaN. The superior properties of the N-polar AlSiO MOS devices are promising for further advancement of N-polar GaN-based high electron mobility transistors for high-frequency and power electronics applications.

The impact of post-metallization annealing of N-polar AlSiO metal-oxide semiconductor (MOS) capacitors was investigated. Annealing in air at 320 °C and 370 °C reduced the density of near-interface traps from 5.6 × 10 11 to ~2.8 × 10 11 cm −2 and extended the region of flat-band voltage stability and low-leakage operation from 0-2.6 to 0-4 MV cm −1 in the forward bias accumulation region. Moreover, annealing at 370 °C fully suppressed the instabilities in the flat-band voltage within the test voltage range (−10 to −25 V) of depletion operation. The robust dielectric results demonstrated in this letter are promising for further enhancements of gate-robustness in N-polar GaN-based MOS-based transistors.

The bulk and interfacial properties of aluminum silicon oxide (AlSiO) on N-polar GaN were investigated systematically employing capacitance–voltage (C–V) methods on metal–oxide–semiconductor capacitors using a thickness series of the AlSiO dielectric. The fixed charge density, electron slow trap density, and electron fast trap density located near the interface were extracted to be –1.5 × 1012 cm−2, 3.7 × 1011 cm−2, and 1.9 × 1011 cm−2, respectively. Using ultraviolet (UV) assisted C–V methods, an average interface state density of ∼4.4 × 1011 cm−2 eV−1 and a hole trap concentration in bulk AlSiO of ∼8.4 × 1018 cm−3 were measured. The negative fixed interface charge makes it favorable to achieve a normally off GaN transistor. The analysis presented in this paper provides a systematic and quantitative model to study the properties of oxide dielectrics on wide bandgap (WBG) semiconductors, which can promote the development of metal–oxide–semiconductor-based WBG semiconductor 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.