Characteristics of Al ₂ O ₃ /native oxide/n-GaN capacitors by post-metallization annealing

This work investigated characteristics of Al ₂ O ₃ /native oxide/n-GaN MOS capacitors by post-metallization annealing (PMA). A native oxide interlayer which composed of ϵ- and γ-Ga ₂ O ₃ phases (Native oxide) and the reduced amount of one (Reduced) on n-GaN were prepared by cleaning only a sulfuric acid peroxide mixture (SPM) and both SPM and buffered hydrofluoric acid, respectively. The effect of trimethylaluminum precursor on removal of a native oxide layer was not observed during Al ₂ O ₃ deposition using atomic layer deposition. An as-grown capacitor (Native oxide) exhibited a small flatband voltage (V _fb ) hysteresis of ∼30 mV and a large frequency dispersion, suggesting that the initial growth of the Al ₂ O ₃ resulted in the formation of electrical defects on the GaN surface. Both the V _fb hysteresis and frequency dispersion were drastically improved by PMA of the device at 300 °C. The positive fixed charge values (Q _IL ) estimated from the relationships between capacitance equivalent thickness and V _fb were +6.1 -10 ¹² and +0.4-1.0 -10 ¹² cm ^-2 for as-grown and PMA-processed capacitors in the PMA temperature range of 300 °C-600 °C, respectively. The interface state density (D _it ) determined using a conductance method was also significantly reduced (by an order of magnitude) after PMA processing at 300 °C. These trends in the Q _IL and D _it data were observed in both the Native oxide and Reduced capacitors, indicating that this interlayer does not greatly affect fixed charge generation at the Al ₂ O ₃ /native oxide and Al ₂ O ₃ /modified native oxide interfaces. As a result, two types of treatments result in insignificant difference in the electrical properties of the capacitors.