Study on the structure and properties of gallium bismuth oxide alloy thin films prepared by sol-gel method

(BixGa1-x)2O3 films were prepared at 820 °C by sol-gel method, an ethylene glycol solution of hydrated gallium nitrate and bismuth nitrate stabilized by monoethanolamine, of which crystallization, surface morphology and electronic structure as well as optical properties were studied in detail by X-ray diffraction, Scanning electron microscope-energy dispersive spectrometer, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Ultraviolet-visible spectroscopy. XRD showed Ga2O3 film prepared from solutions consisted of two crystal structures, β and γ, increasing Bi atoms into Ga2O3 that enable the inhibition of γ phase formation and (BixGa1-x)2O3 and Ga2O3 capable of holding the same monoclinic crystal structure. EDS displayed (BixGa1-x)2O3 films of varied compositions were obtained with content of different Bi atoms into the solution, which kept same monoclinic crystal as β-Ga2O3 when Bi ranged from 0 < x < 0.056. FTIR revealed that the absorption band below 480 cm−1 corresponded to the octahedral position of Ga2O3 and the Bi atoms in the (BixGa1-x)2O3 films substituted the Ga in the [GaO6] octahedron. XPS exhibited increasing Bi content raised Ga3+/Ga ratio. UV-VIS provided evidence that optical band gap of (BixGa1-x)2O3 down to 3.2 eV indicating Bi-doping achieved Ga2O3 band gap tunable, concurrently, the bowing parameter c = 1.83 eV was obtained on the basis of the fitting curve of band gap. Combination monoclinic gallium oxide which has ultra wide band gap and a small amount of Bi3+ by sol-gel method can form (BixGa1-x)2O3 alloy. Bi3+ mainly replaces gallium at the octahedral position of gallium oxide, which lifts the valence band position and reduces the band gap of gallium oxide, and can transfer the optical absorption spectrum of gallium oxide from deep ultraviolet region to blue ultraviolet region.