We report on the growth of monoclinic β- and orthorhombic κ-phase Ga2O3 thin films using liquid-injection metal-organic chemical vapor deposition on highly thermally conductive 4H-SiC substrates using gallium (III) acetylacetonate or tris(2,2,6,6-tetramethyl-3,5-heptanedionato) gallium (III). Both gallium precursors produced the β phase, while only the use of the latter led to growth of κ-Ga2O3. Regardless of the used precursor, best results for β-Ga2O3 were achieved at a growth temperature of 700 °C and O2 flows in the range of 600–800 SCCM. A relatively narrow growth window was found for κ-Ga2O3, and best results were achieved for growth temperatures of 600 °C and the O2 flow of 800 SCCM. While phase-pure β-Ga2O3 was prepared, κ-Ga2O3 showed various degrees of parasitic β phase inclusions. X-ray diffraction and transmission electron microscopy confirmed a highly textured structure of β- and κ-Ga2O3 layers resulting from the presence of multiple in-plane domain orientations. Thermal conductivities of 53 nm-thick β-Ga2O3 (2.13 + 0.29/−0.51 W/m K) and 45 nm-thick κ-Ga2O3 (1.23 + 0.22/−0.26 W/m K) were determined by transient thermoreflectance and implications for device applications were assessed. Presented results suggest great potential of heterointegration of Ga2O3 and SiC for improved thermal management and reliability of future Ga2O3-based high power devices.

Ga ₂ O ₃ , a wide-bandgap semiconductor material, offers a great potential for power and high-voltage electronic devices. We report on the growth of undoped α - and β -phase Ga ₂ O ₃ using liquid-injection metal-organic chemical vapor deposition (LI-MOCVD) on sapphire substrates. Using the same precursor (gallium acetylacetonate) and deposition temperature of 700 °C, the phase selection was controlled by the sapphire substrate orientation, where the growth of α - and β -phase Ga ₂ O ₃ was achieved on m - and c -plane surface, respectively. As deduced from x-ray diffraction, α -Ga ₂ O ₃ films show epitaxial character, while β - Ga ₂ O ₃ films exhibit highly textured structure. Oxygen flow was also found to have a strong impact on the phase purity of α -Ga ₂ O ₃ for the flow rates examined. Optical and electrical properties of the layers grown at different oxygen flow rates were also studied systematically. LI-MOCVD growth of α -phase Ga ₂ O ₃ layers at relatively high deposition temperature widens the high-temperature processing of the Ga ₂ O ₃ -based electronic and optoelectronic devices.

We report on crystal structure and thermal stability of epitaxial ε/κ-Ga₂O₃ thin films grown by liquid-injection metal–organic chemical vapor deposition (LI-MOCVD). Si-doped Ga₂O₃ films with a thickness of 120 nm and root mean square surface roughness of ~1 nm were grown using gallium-tetramethylheptanedionate (Ga(thd)₃) and tetraethyl orthosilicate (TEOS) as Ga and Si precursor, respectively, on c-plane sapphire substrates at 600 °C. In particular, the possibility to discriminate between ε and κ-phase Ga₂O₃ using X-ray diffraction (XRD) φ-scan analysis or electron diffraction analysis using conventional TEM was investigated. It is shown that the hexagonal ε-phase can be unambiguously identified by XRD or TEM only in the case that the orthorhombic κ-phase is completely suppressed. Additionally, thermal stability of prepared ε/κ-Ga₂O₃ films was studied by in situ and ex situ XRD analysis and atomic force microscopy. The films were found to preserve their crystal structure at temperatures as high as 1100 °C for 5 min or annealing at 900 °C for 10 min in vacuum ambient (<1 mBar). Prolonged annealing at these temperatures led to partial transformation to β-phase Ga₂O₃ and possible amorphization of the films.