ε-Ga₂O₃Grown onc-Plane Sapphire by MOCVD with a Multistep Growth Process

Abstract

Gallium oxide (Ga2O3) has especially become popular because of its established applications in semiconductors. Of five polymorphs, monoclinic β-Ga2O3 is the most thermodynamically stable phase. However, orthorhombic Ga2O3 (also known as ε-Ga2O3 or κ-Ga2O3) is gaining increasing interest due to its high lattice symmetry and peculiar ferroelectricity. Although the structural approach for estimating Ga2O3 has been studied both theoretically and experimentally, ε-Ga2O3 and κ-Ga2O3 are still confused. In this study, ε-Ga2O3 epilayers are grown on c-plane sapphire by metal–organic chemical vapor deposition with a multistep growth process. A thin annealed ε-Ga2O3 buffer layer is grown in the first step. The sequent growth steps with slow, fast, or combination of slow then fast growth rate significantly influence the quality of epilayers compared with that of directly grown Ga2O3. Through a detailed transmission electron microscopy (TEM) characterization of these Ga2O3 epilayers, the structural relationship between orthorhombic κ-Ga2O3 and hexagonal ε-Ga2O3 is elucidated. A series of first-principles density functional theory calculations are also carried out to confirm the argument.

Flexible gallium oxide electronics

“…Hence, it is a promising conducting channel material in heterostructure field-effect transistors because it can produce high-density two-dimensional electron gas [53]. ε-Ga 2 O 3 thin films have been grown using HVPE, plasma-assisted MBE, and metal-organic CVD (MOCVD) [54][55][56]. Notably, although k-Ga 2 O 3 has an orthorhombic phase, it has been widely confused with ε-Ga 2 O 3 [1].…”

Two-step growth of κ-Ga2O3 thin films on 4H-SiC substrates with temperature-varied buffer layers using mist chemical vapor deposition

“…control of growth temperature and gas flow, adoption of lattice-matched substrates, three-dimensional nucleation, two-step growth, etc. 28,30,[33][34][35][36] In particular, there has been remarkable progress in the epitaxial growth of single-domain κ-Ga 2 O 3 thin films using floating-zone-grown ε-GaFeO 3 substrates having lattice parameters almost similar to those of κ-Ga 2 O 3 . 36) In-plane orientation control of (001) κ-Ga 2 O 3 was also demonstrated by epitaxial lateral overgrowth.…”

Stress Relaxation Due to Dislocation Formation in Orthorhombic Ga2O3 Films Grown on Al2O3 Substrates

“…The pseudohexagonal structure of ε-phase consists of 120° rotational orthorhombic κ-Ga2O3 domains. However, until now, some works indicate the possibility of the existence of pure ε-phase [12]. Despite the ongoing debate about the real structure of the considered phase, most scientific groups tend to consider the phase as composed of 3-fold rotational orthorhombic domains with disordered domain boundaries [10,11,13,14]; the single-domain orthorhombic structure of this phase has been recently demonstrated [3,15].…”