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.