Adsorption-controlled growth of Ga₂O₃ by suboxide molecular-beam epitaxy

Patrick Vogt, Felix V. E. Hensling, Kathy Azizie, Celesta S. Chang, David Turner, Jisung Park, Jonathan P. McCandless, Hanjong Paik, Brandon J. Bocklund, Georg Hoffman, Oliver Bierwagen, Debdeep Jena, Huili G. Xing, Shin Mou, David A. Muller, Shun-Li Shang, Zi-Kui Liu, Darrell G. Schlom

Abstract
This paper introduces a growth method—suboxide molecular-beam epitaxy (S-MBE)—which enables a drastic enhancement in the growth rates of Ga₂O₃ and related materials to over 1 μm h^-1 in an adsorption-controlled regime, combined with excellent crystallinity. Using a Ga+ Ga₂O₃ mixture with an oxygen mole fraction of x(O) = 0.4 as an MBE source, we overcome kinetic limits that had previously hampered the adsorption-controlled growth of Ga₂O₃ by MBE. We present growth rates up to 1.6 μm h^-1 and 1.5 μm h^-1 for Ga₂O₃/Al₂O₃ and Ga₂O₃/Ga₂O₃ structures, respectively, with very high crystalline quality at unparalleled low growth temperature for this level of perfection. We combine thermodynamic knowledge of how to create molecular beams of targeted suboxides with a kinetic model developed for the S-MBE of III-VI compounds to identify appropriate growth conditions. Using S-MBE, we demonstrate the growth of phase-pure, smooth, and high-purity homoepitaxial Ga₂O₃ films that are thicker than 4.5 μm. With the high growth rate of S-MBE, we anticipate a significant improvement to vertical Ga₂O₃-based devices. We describe and demonstrate how this growth method can be applied to a wide range of oxides. With respect to growth rates and crystalline quality, S-MBE rivals leading synthesis methods currently used for the production of Ga₂O₃-based devices.