Low-Temperature Nucleation-Mediated Spontaneous Growth of GaN Nanowires on Sapphire by Plasma-Assisted Molecular Beam Epitaxy

Abstract

The controlled synthesis of GaN nanowires (NWs) on sapphire substrates remains challenging due to the high surface diffusivity of Ga adatoms on the (0001) surface, which favors two-dimensional layer growth. In this work, a low-temperature nucleation-layer-assisted growth strategy was developed. A thin GaN layer deposited at 550 °C provides uniformly distributed nucleation sites across the entire substrate surface, which undergo recrystallization upon annealing at 900 °C to form isolated, defect-free seeds for nanowire growth. Subsequent high-temperature growth yields uniform GaN nanowire arrays. Characterization demonstrates that the NWs exhibit high crystalline quality in the wurtzite structure, low dislocation density, and uniform elemental distribution. Reflection high-energy electron diffraction monitoring and scanning electron microscopy imaging at each growth stage confirm the proposed three-stage nucleation and growth mechanism. This work establishes a reliable, catalyst-free route for GaN nanowire synthesis on sapphire substrates.