Challenges and solutions in Mist-CVD of Ga2O3 heteroepitaxial films

Abstract

Mist chemical vapor deposition (mist-CVD) has recently attracted interest as a facile, cost-effective, environmentally friendly method for the deposition of Ga₂O₃ films. This paper addresses selected challenges and issues that hinder the fabrication of high-quality Ga₂O₃ epitaxial films. Based on numerical simulations of the gas flow we show that the use of a fan, introducing atmospheric air into the horizontal growth reactor, avoids the formation of vortices and mist velocity fluctuations, which develop when a conventional carrier gas delivery system is employed. We also demonstrate that the presence of organic ligands in Ga acetylacetonate results in undesirable contamination of Ga₂O₃ films by pyrolytic carbon, which strongly affects the optical and morphological properties and can lead to incorrect estimation of the optical band gap. Carbon contamination is shown to be reduced by increasing the growth temperature, by growing under oxygen-rich conditions, or by using carbon-free precursors such as GaCl₃. We further experimentally prove that when the thickness of Ga₂O₃ increases, a multiphase epitaxial film forms, presumably due to enhanced thermal stress. Finally, we experimentally show that nonstoichiometric GaO_xCl_yH_z microparticles form on top of a Ga₂O₃ film in the reactor zone, where the aerosol is completely evaporated and a vapor ambient is formed.