Growth of GaN on sapphire substrates using novel buffer layers of ECR-plasma-sputtered Al₂O₃/graded-AlON/AlN/Al₂O₃

We proposed and demonstrated GaN growth on sapphire substrates by metalorganic vapor phase epitaxy using novel buffer layers of Al₂O₃/graded-AlON/AlN/Al₂O₃. The buffer layers were deposited by electron cyclotron resonance plasma sputtering at room temperature. The total thickness of the buffer layers was around 20 nm. The cross-sectional bright-field transmission electron microscope observation showed that the dislocations were bent at the initial stage of the growth, indicating the enhancement of lateral growth. Typical dislocation density in the GaN layer was 6.5×10⁸ cm^-2. We obtained high electron mobility of 640 cm²/Vs at the electron concentration of 2.0×10¹⁷ cm^-3 for Si-doped GaN. We also obtained high electron mobility of 1760 cm²/Vs at a sheet electron concentration of 8.3×10¹² cm^-2 for an AlGaN/GaN heterostructure. These results indicate that the quality of the epitaxial layer grown on sapphire substrates using the electron cyclotron resonance plasma sputtered buffer is comparable or superior to that of GaN layers using the conventional low-temperature buffer layer.