Supersaturation-Dependent Competition between β and κ Phases in the MOVPE Growth of Ga2O3 on Al2O3 (0001) and GaN (0001) Substrates

We present an analysis of the phase stabilization of β-Ga2O3 and κ-Ga2O3 grown by metal-organic vapor-phase epitaxy with varying supersaturation of the gas-phase precursors on c-sapphire and GaN substrates. We compare in-depth structural analyses of the bulk and interface layers, also through the measurement of strain relaxation across the structure, with a comprehensive nucleation model, based on multiscale simulations. A coherent and quantitative interpretation of different stages of the nucleation of Ga2O3 phases on sapphire is elaborated on, highlighting the crucial role of the supersaturation of gas precursors and of the residual misfit strain within the initial layers in the stabilization of competing Ga2O3 polymorphs.