Structure and Thermal Stability of ε/κ-Ga 2 O 3 Films Deposited by Liquid-Injection MOCVD.

We report on crystal structure and thermal stability of epitaxial ε/κ-Ga 2 O 3 thin films grown by liquid-injection metal-organic chemical vapor deposition (LI-MOCVD). Si-doped Ga 2 O 3 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 Ga 2 O 3 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-Ga 2 O 3 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 Ga 2 O 3 and possible amorphization of the films.