Thin films of spinel cubic ZnGa 2 O 4 have been widely investigated as a deep ultraviolet (UV) excited phosphor for potential applications in low-voltage field emission displays, electroluminescent devices, and vacuum fluorescent displays since the 1990s. [1][2][3][4][5][6][7][8][9][10][11][12][13] Recently, ZnGa 2 O 4 thin films have attracted intensive interest for potential wide-bandgap oxides device applications in luminescence, transistors, and sensors. [14][15][16][17][18][19][20][21][22][23][24][25] High-quality stoichiometric or near-stoichiometric ZnGa 2 O 4 epitaxial thin films, with low average density of crystalline defects, would be a preferable platform to study the fundamentals of physical and chemical properties of this material in view of potential device applications. The heteroepitaxial growth of ZnGa 2 O 4 thin films was first achieved along the (100) crystallographic direction on cubic (100) MgO substrates (about 1% lattice mismatch) using the solvent evaporation epitaxy method and pulsed laser deposition (PLD). [5,26] The full-width at half maximum (FWHM) of the (400) rocking curve for (100) ZnGa 2 O 4 epitaxial thin film grown on (100) MgO substrate deposited at 600 C by PLD is about 0.48 . [5] The epitaxial (111) ZnGa 2 O 4 thin films have been grown on (111) MgAl 2 O 4 (about 3% lattice mismatch) and (00.1) LiNbO 3 (about 0.8% lattice mismatch) substrates through the hydrothermal method. [27] While epitaxial (100) ZnGa 2 O 4 thin films have been also grown on (100) MgAl 2 O 4 substrates by mist chemical vapor deposition, the lattice mismatch is about 3% and FWHM of the ω-scan rocking curve for the (400) peak is 0.28 . [28] Sapphire (hexagonal single crystal a-Al 2 O 3 ) substrates are one of the most affordable single-crystal substrates, and ideal for optical, electronic, and optoelectronic device applications due to its optimal physical and chemical properties such as highly optical transparent from deep-UV (150 nm) to near-infrared (5500 nm), excellent electrical insulating properties, and extremely unreactive and resistant to alkaline and acidic fluids, including hydrofluoric acid. These unique properties make it especially useful for UV and deep-UV optical and optoelectronic applications as well as highpower radio frequency (RF) applications. Recently, (111)-oriented ZnGa 2 O 4 epitaxial thin films have been grown on (00.1) sapphire substrates through metal-organic chemical vapor deposition (MOCVD), [14,15,17] however, no information regarding in-plane structural order, average crystalline quality and misalignment was reported. The obtained (111) ZnGa 2 O 3 epitaxial thin films grown on (00.1) sapphire by MOCVD exhibited an apparent strain release as the film thickness increased and contained dislocations as well as an impurity phase of Ga 2 O 3 . [14,15,17] Typically, epitaxial interfaces can easily form between cubic (111) and hexagonal (00.1) crystal planes due to the crystal symmetry. [29][30][31][32] The lattice mismatch between (111) ZnGa 2 O 4 (Ga─Ga distance is 0.299 nm, where...