Sheet carrier density enhancement by Si₃N₄ passivation on nonpolar a-plane (1120) sapphire grown AlGaN/GaN heterostructures

The AlGaN/GaN heterostructures (HSs) with high two dimensional electron gas mobility (1070 cm²/V s) were grown on nonpolar a-plane (1120) sapphire substrate by metal organic chemical vapor deposition. High crystalline quality (reduced screw, edge, and mixed dislocations) with small root mean square surface roughness and small peak-valley distance values were observed in a-plane sapphire grown AlGaN/GaN HSs. Hexagonal-GaN phase was also observed on a-plane sapphire grown AlGaN/GaN HSs. An average increase of n_s up to 22% for a plane and 26% for c plane were found after Si₃N₄ passivation. The product of n_s and μ_H also increases for both a-plane (19%) and c-plane (28%) sapphire grown AlGaN/GaN HSs in a wide range of measurement temperature (87–400 K). The enhancement of sheet carrier density by Si₃N₄ passivation for nonpolar (1120) sapphire grown AlGaN/GaN HSs is a useful result for the design of future GaN high-electron-mobil- - ity transistors.