Characteristics of Al2O3/native oxide/n-GaN capacitors by post-metallization annealing

Abstract

This work investigated characteristics of Al2O3/native oxide/n-GaN MOS capacitors by post-metallization annealing (PMA). A native oxide interlayer which composed of ε- and γ-Ga2O3 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 Al2O3 deposition using atomic layer deposition. An as-grown capacitor (Native oxide) exhibited a small flatband voltage (Vfb) hysteresis of ∼30 mV and a large frequency dispersion, suggesting that the initial growth of the Al2O3 resulted in the formation of electrical defects on the GaN surface. Both the Vfb hysteresis and frequency dispersion were drastically improved by PMA of the device at 300 °C. The positive fixed charge values (QIL) estimated from the relationships between capacitance equivalent thickness and Vfb were +6.1 × 1012 and +0.4–1.0 × 1012 cm−2 for as-grown and PMA-processed capacitors in the PMA temperature range of 300 °C–600 °C, respectively. The interface state density (Dit) determined using a conductance method was also significantly reduced (by an order of magnitude) after PMA processing at 300 °C. These trends in the QIL and Dit data were observed in both the Native oxide and Reduced capacitors, indicating that this interlayer does not greatly affect fixed charge generation at the Al2O3/native oxide and Al2O3/modified native oxide interfaces. As a result, two types of treatments result in insignificant difference in the electrical properties of the capacitors.