Crystal Phase Control of ε-Ga2O3 Fabricated using by Metal-Organic Chemical Vapor Deposition

Abstract

e-Ga2O3 thin films were grown on (0001) sapphire, (0001) GaN, and a low-temperature buffer layer at different temperatures and flow rates of bubbled H2O (oxygen source) using trimethylgallium and H2O as precursors by using atmospheric-pressure metal-organic chemical vapor deposition. Due to the atmospheric pressure conditions, most of the Ga2O3 thin films were not grown in a pure e-phase, but contain a small portion of the β-phase. The crystal structure, crystal quality, phase ratio, and surface morphology were analyzed by using X-ray diffraction, rocking curve measurements, and field-emission scanning electron microscopy. A certain minimum H2O flow rate was required to form e-Ga2O3 thin films, and the optimal growth temperature for e-Ga2O3 was 650°C. The β-phase fraction of the mixed-phase (e + β) thin films was dominant at temperatures higher than 650 °C. The crystallinities and phase compositions of the thin films changed with the flow rate of H2O. Nearly single-crystalline Ga2O3 thin films were successfully grown on GaN and sapphire, but not on a low-temperature buffer layer. Hexagonally shaped Ga2O3 islands become aligned in an ordered direction that correlated to the substrate’s orientation during the initial stage of the growth and coalesced to complete a two-dimensional layer as the growth went on.