| Summary: | In this work, the atomic level doping of Sn into Ga<sub>2</sub>O<sub>3</sub> films was successfully deposited by using a plasma-enhanced atomic layer deposition method. Here, we systematically studied the changes in the chemical state, microstructure evolution, optical properties, energy band alignment, and electrical properties for various configurations of the Sn-doped Ga<sub>2</sub>O<sub>3</sub> films. The results indicated that all the films have high transparency with an average transmittance of above 90% over ultraviolet and visible light wavelengths. X-ray reflectivity and spectroscopic ellipsometry measurement indicated that the Sn doping level affects the density, refractive index, and extinction coefficient. In particular, the chemical microstructure and energy band structure for the Sn-doped Ga<sub>2</sub>O<sub>3</sub> films were analyzed and discussed in detail. With an increase in the Sn content, the ratio of Sn–O bonding increases, but by contrast, the proportion of the oxygen vacancies decreases. The reduction in the oxygen vacancy content leads to an increase in the valence band maximum, but the energy bandgap decreases from 4.73 to 4.31 eV. Moreover, with the increase in Sn content, the breakdown mode transformed the hard breakdown into the soft breakdown. The <i>C</i>-<i>V</i> characteristics proved that the Sn-doped Ga<sub>2</sub>O<sub>3</sub> films have large permittivity. These studies offer a foundation and a systematical analysis for assisting the design and application of Ga<sub>2</sub>O<sub>3</sub> film-based transparent devices.
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