Single-Domain and Atomically Flat Surface of κ-Ga₂O₃ Thin Films on FZ-Grown ε-GaFeO₃ Substrates via Step-Flow Growth Mode

Abstract

Herein, single-domain κ-Ga2O3 thin films were grown on FZ-grown ε-GaFeO3 substrates via a step-flow growth mode. The ε-GaFeO3 possessing the same crystal structure and similar lattice parameters as those of the orthorhombic κ-Ga2O3 facilitated the growth of κ-Ga2O3 thin films, as observed by the X-ray diffraction (XRD) analysis. Furthermore, the surface morphologies of the κ-Ga2O3 thin films exhibited a step–terrace and atomically flat structure. XRD φ-scan and transmission electron microscopy with selected area electron diffraction revealed that there is no occurrence of in-plane rotational domains in the κ-Ga2O3 thin films on ε-GaFeO3 substrates and that the κ-Ga2O3 thin film comprised a single domain. TEM analysis revealed that there were no clear dislocations in the observation area. Moreover, high-resolution TEM observation showed that the atomic arrangements of the film and the substrate were continuous without the presence of an intermediate layer along the growth direction and were well-aligned in the in-plane direction.

Unlocking the Single-Domain Heteroepitaxy of Orthorhombic κ-Ga2O3 via Phase Engineering

“…Furthermore, phase segregation starting at a temperature of 575 °C leads to an increased density of screw dislocations, which consequently facilitates the occurrence of three rotational domains by breaking the crystallographic symmetry of the growth front. It is noted that a nonpolar single-terminated surface (such as a -plane sapphire) or symmetry-matched ε-GaFeO 3 could be better choices to ultimately achieve single-domain epitaxy …”

Observing the microstructure of a (001) κ-Ga2O3 thin film grown on a (−201) β-Ga2O3 substrate using automated crystal orientation mapping transmission electron microscopy

“…Twelve κ-Ga 2 O 3 {122} peaks were observed, indicating that κ-Ga 2 O 3 exhibited a domain structure with three 120° rotations. 23,29 These rotations are usually observed when conventional substrates, including α-Al 2 O 3 , 23 GaN, 29 AlN, 36 STO, 29 and MgO, 34 are used. Therefore, there is nothing special about the occurrence of rotational domains using a (−201) β-Ga 2 O 3 substrate.…”

“…For example, (−201) β-Ga 2 O 3 is not observed near the interface when κ-Ga 2 O 3 is grown on cubic (111) NiO 35 and orthorhombic (001) ε-GaFeO 3 substrates. 36 Among these, ε-GaFeO 3 has the same crystal structure as that of κ-Ga 2 O 3 , and a small lattice mismatch allows the growth of single-phase and single-domain κ-Ga 2 O 3 . Although the cause of β-Ga 2 O 3 formation in κ-Ga 2 O 3 thin films has not yet been investigated, it is important to choose an appropriate substrate that can prevent its formation for HEMT applications.…”

“…Therefore, there is nothing special about the occurrence of rotational domains using a (−201) β-Ga 2 O 3 substrate. Recently, it has been demonstrated that almost lattice-matched ε-GaFeO 3 (001) substrates with κ-Ga 2 O 3 36,37 and the lateral overgrowth on c -plane sapphire substrates 38 prevent the occurrence of this rotational domain. However, the origins of the peaks at around −114°, −72°, 68°, and 108° indicated by blue triangles in Fig.…”

Silane‐Mediated Expansion of Domains in Si‐Doped κ‐Ga2O3 Epitaxy and its Impact on the In‐Plane Electronic Conduction

“…[20][21][22] Nonetheless, despite the possibility of depositing high quality (001)-oriented κ-Ga 2 O 3 /Al x Ga 2-x O 3 hetero structures on cheap c-plane sapphire substrates, no 2DEG has been so far experimentally reported. [23] This is probably linked to the real structure of this orthorhombic polymorph [24] and in particular to the presence of rotational domains commonly found in heteroepitaxial films despite different employed substrates, [25] with the exceptions of recently reported single domain layers obtained on an epitaxially matched GaFeO 3 substrate [26] and on an offcut c-plane sapphire. [27] In fact, epitaxial (001)-oriented κ-Ga 2 O 3 thin films are characterized by a peculiar columnar structure with ≈ 10 nm width.…”