Demonstration of Bixbyite-Structured δ-Ga₂O₃ Thin Films Using β-Fe₂O₃ Buffer Layers by Mist Chemical Vapor Deposition

Abstract

Gallium oxide (Ga 2 O 3 ) possesses five polymorphs: α, β, γ, κ (ε), and δ. Although the first four polymorphs have been well-studied, there are few reports on δ-Ga 2 O 3 . Here, we demonstrate the epitaxial growth of metastable δ-Ga 2 O 3 thin films by mist chemical vapor deposition using β-Fe 2 O 3 buffer layers. X-ray diffraction (XRD) 2θ−ω scan pattern revealed that (004) κ-Ga 2 O 3 grew on (111) yttria-stabilized zirconia (YSZ) without a buffer layer or with a bcc-In 2 O 3 buffer layer, whereas (222) δ-Ga 2 O 3 grew on (222) β-Fe 2 O 3 . The β-Fe 2 O 3 buffer layer led to the epitaxial growth of the δ-Ga 2 O 3 thin film. The lattice mismatch between the equivalent crystal structures of β-Fe 2 O 3 and δ-Ga 2 O 3 triggered this growth. XRD analysis shows that δ-Ga 2 O 3 grew epitaxially on the β-Fe 2 O 3 buffer layer/YSZ substrate in both the out-of-plane and in-plane orientations, and the lattice constant inferred from the diffraction peaks was estimated to be 9.255 Å. Reciprocal space mapping results indicated that the δ-Ga 2 O 3 grown on β-Fe 2 O 3 was fully relaxed. Selected area electron diffraction images confirmed that the δ-Ga 2 O 3 exhibited a cubic bixbyite structure. The optical band gap of δ-Ga 2 O 3 was 4.3 or 4.9 eV, as calculated from reflection electron energy loss spectroscopy. We successfully grew a δ-Ga 2 O 3 epitaxial thin film for the first time. KEYWORDS: δ-Ga 2 O 3 , β-Fe 2 O 3 , bixbyite structure, epitaxial growth, mist CVD

Epitaxial Growth of δ‐Ga2O3 Thin Films Grown on YSZ and Sapphire Substrates Using β‐Fe2O3 Buffer Layers via Mist Chemical Vapor Deposition

“…Recently, our group successfully grew δ-Ga 2 O 3 thin films using a β-Fe 2 O 3 buffer layer with the same bixbyite structure grown on yttria-stabilized zirconia (YSZ) and reported that the experimental lattice constant of δ-Ga 2 O 3 was a = 9.255 Å, and its bandgap was %4.9 eV. [25] Without the buffer layers, the Ga 2 O 3 thin films exhibit a κ-phase on bcc-In 2 O 3 and YSZ. [26,27] Thus, β-Fe 2 O 3 possessing a small lattice mismatch with δ-Ga 2 O 3 (%1.6%) plays an important role in the growth of δ-Ga 2 O 3 thin films.…”