Structural and optical properties of as-synthesized, Ga₂O ₃-coated, and Al₂O₃-coated GaN nanowires

Structural and optical properties of as-synthesized, Ga₂O ₃-coated, and Al₂O₃-coated GaN nanowires are examined in this paper. GaN nanowires were synthesized by thermal evaporation of ball-milled GaN powders in an NH₃ atmosphere. The thermal annealing of the as-synthesized GaN nanowires in an argon atmosphere allows their surfaces to be oxidized, leading to the formation of 2 nm-thick Ga₂O ₃ layers. For the oxidized GaN nanowires, the distances between the neighboring lattice planes are shortened, and an excitonic emission band is remarkably enhanced in intensity, compared with the as-synthesized GaN nanowires. In addition, the as-synthesized GaN nanowires were coated cylindrically with Al₂O₃ by atomic layer deposition technique. Our study suggests that the Al₂O₃-coating passivates some of surface states in the GaN nanowires.