Band structure of high O/Ga ratio a-GaOx and its electron transport mechanism at the MS interface

Amorphous gallium oxide (a-GaO_x) exhibits excellent electrical conductivity, a wide bandgap, high breakdown field strength, high visible light transmittance, sensitivity to specific ultraviolet wavelengths, low preparation temperatures, relatively simple processing, wide substrate applicability, and ease of obtaining high-quality thin films. These attributes make it a suitable candidate for applications in transparent electronic devices, ultraviolet detectors, high-power devices, and gas sensors. Presently, research on a-GaO_x remains limited, focusing primarily on films with an O/Ga ratio less than or equal to 1.5. Increasing the concentration of oxygen vacancies to enhance the conductivity of the material often leads to a reduction in its bandgap, which is undesirable for high-power applications. Variations in O/Ga in the films can impact the formation of chemical bonds and significantly influence the band structure. In this study, five groups of a-GaO_x thin films with a high oxygen-to-gallium ratio were successfully fabricated by increasing the gas flow rate at low sputtering power. The elemental composition of the films was analyzed using Energy Dispersive Spectroscopy (EDS), revealing a gradual decrease in the O/Ga ratio from 3.89 to 3.39. Phase analysis using X-ray Diffraction (XRD) confirmed the amorphous nature of the films. Optical properties were characterized using an Ultraviolet-Visible Spectrophotometer (UV-Vis), indicating a gradual increase in the optical bandgap and the density of localized states. X-ray Photoelectron Spectroscopy (XPS) was employed to analyze the elemental composition, chemical states, and valence band structure of the films, showing a gradual decrease in the valence band maximum and an increasing content of Ga₂O within the material. Subsequently, Au/a-Ga₂O_x/Ti/Au Schottky devices were fabricated under the same processing conditions. The I-V characteristics of these devices were measured using a Keithley 4200, revealing changes in the electron transport mechanism at the MS interface, with a gradual increase in electron affinity calculated. C-V characteristics were measured using a Keithley 590, and the donor concentration (density of localized states) at the interface was calculated to gradually increase. In summary, by controlling appropriate process parameters, it is possible to improve the conductivity of electronic devices while increasing the bandgap of a-GaO_x, which holds significance for high-power applications.