Abstract
LiNbO3 and LiTaO3 substrates are used in wide-bandwidth applications such as surface acoustic wave filter and show structural similarity to α-Ga2O3. In this study, we demonstrated the phase control of Ga2O3 epitaxial thin films, grown by mist chemical vapor deposition, on the (0001) planes of LiNbO3 and LiTaO3 substrates using α-Fe2O3 buffer layers. κ-Ga2O3 thin films were grown epitaxially on bare LiNbO3 and LiTaO3 substrates. Conversely, the insertion of the α-Fe2O3 buffer layer led to the preferential growth of the α-Ga2O3 epitaxial thin films. X-ray diffraction (XRD) φ-scan results revealed that the α-Ga2O3 thin films were grown along the same in-plane direction as that of the substrates. Besides, the XRD φ-scan results indicated that twin-free α-Ga2O3 was grown on the LiNbO3 and LiTaO3 substrates with the α-Fe2O3 buffer layers. The x-ray rocking curve scans of the asymmetric plane of α-Ga2O3 showed that the full width at half maximum values of α-Ga2O3 on the LiNbO3 and LiTaO3 substrates with the buffer layers were smaller than that of the c-plane α-Al2O3 substrate with and without the buffer layer. In addition, we grew the (11-20) and (1-100) planes of the α-Ga2O3 epitaxial thin films on the (11-20) and (1-100) planes of LiNbO3 substrates with the α-Fe2O3 buffer layer, respectively. This study showed that LiTaO3 and LiNbO3 are promising substrates for the epitaxial growth of α-Ga2O3 and κ-Ga2O3.
Highlights
Gallium oxide (Ga2O3) is a wide bandgap semiconductor possessing a bandgap of 4.4–5.3 eV.1,2 Ga2O3 has attracted considerable interest from many researchers to investigate device applications for power-switching devices and deep-ultraviolet region optoelectronic devices.3–6 In addition, Ga2O3 is chemically stable in air because it is composed of oxygen, which is an active and major component of air
It is worth noting that the κ-Ga2O3 thin films preferentially grown on the bare LiNbO3 and LiTaO3 substrates had an orthorhombic structure these substrates exhibit the near-corundum structure
No significant difference was observed in the thickness of the κ- and α-Ga2O3 thin films and all growth conditions were the same except for the buffer layers. These results suggest that the crystal phase of Ga2O3 on the LiNbO3 and LiTaO3 substrates can be controlled by using the α-Fe2O3 buffer layers
Summary
Gallium oxide (Ga2O3) is a wide bandgap semiconductor possessing a bandgap of 4.4–5.3 eV. Ga2O3 has attracted considerable interest from many researchers to investigate device applications for power-switching devices and deep-ultraviolet region optoelectronic devices. In addition, Ga2O3 is chemically stable in air because it is composed of oxygen, which is an active and major component of air. Gallium oxide (Ga2O3) is a wide bandgap semiconductor possessing a bandgap of 4.4–5.3 eV.. It is possible to synthesize Ga2O3 with a bandgap higher than typical wide bandgap materials (SiC and GaN) by various techniques, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), chemical solution technique, and sol–gel process.. Ga2O3 exhibits five polymorphs, namely, α, β, γ, δ, and κ (or ε) phases.. The metastable α-Ga2O3 phase has the largest bandgap (5.3 eV) among the five polymorphs of Ga2O3. Α-Ga2O3 possesses a corundum structure, which is the same structure as sapphire (α-Al2O3) substrates. The same structure permitted the growth of high quality α-Ga2O3 epitaxial thin films on a cplane α-Al2O3 substrate and enabled excellent device performance.. The metastable κ-Ga2O3 phase, which is referred to as ε-Ga2O3, exhibits ferroelectric properties unlike other polymorphs of Ga2O3 due to spontaneous polarization.. The same structure permitted the growth of high quality α-Ga2O3 epitaxial thin films on a cplane α-Al2O3 substrate and enabled excellent device performance. Besides, the metastable κ-Ga2O3 phase, which is referred to as ε-Ga2O3, exhibits ferroelectric properties unlike other polymorphs of Ga2O3 due to spontaneous polarization. The ferroelectricity of κ-Ga2O3 is predicted to enable the formation of a two-dimensional electron gas in a hetero-field effect transistor by the spontaneous polarization of κ-Ga2O3
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