Study of geometry effect on the performance of thin-film transistors fabricated with ZnGa2O4 epilayer grown by metalorganic chemical vapor deposition for high voltage applications

Enhancement mode thin film transistors (TFTs) having different geometries were fabricated on the Zinc gallium oxide (ZnGa2O4) epilayer grown on a c-plane sapphire substrate by metalorganic chemical vapor deposition (MOCVD). A field emission scanning electron microscope, atomic force microscopy, and X-ray diffraction were employed to conduct a detailed analysis of the film composition, morphology, and crystal structure. The distance between the source-to-gate and gate length was kept to be 7 μm and 3 μm in all the devices with varying gate-to-drain lengths of 10, 20, and 30 μm. Moreover, neutral beam etching technology was employed to isolate the individual devices and reduce the defects induced by plasma etching. It was found that the threshold voltage changes from 6 V to 7.6 V with the increase in source to drain length from 20 μm to 40 μm. The On/Off ratio of the devices was found to be 105, with a maximum current around 1 μA/mm. Additionally, the device breakdown voltage increased from 240 V to about 656 V with the increase in the device length. The results demonstrate the fabrication of the high breakdown voltage ZnGa2O4-based TFT and establish the co-relation of the source to drain length with the device characteristics. [Display omitted] •High-quality ZnGa2O4 epilayer with a thickness of 80 nm was grown by MOCVD on the c-plane sapphire substrate.•ZnGa2O4-based enhancement-mode TFTs having source to drain lengths 20 μm, 30 μm, and 40 μm were fabricated.•The threshold voltage changes from 6 V to 7.6 V as the source to drain length increases from 20 μm to 40 μm.•Breakdown voltages of TFTs were 240 ± 20 V for 20 μm, 518 ± 22 V for 30 μm, and 656 ± 9 V for 40 μm.