The role of polarization in the threshold voltage of field effect transistors based on ZnO/MgO

In this work, we report on fabrication and characterization of a field effect transistor (FET) based on a ZnO/MgO bilayer employing a top-gate configuration. X-ray diffraction patterns show that the resulting ZnO and MgO films grow epitaxially with planes (002) and (111) parallel to the substrate surface, respectively. Typical current–voltage curves for different applied gate voltages are obtained, and the results are well fitted using standard FET equations. From these fittings, an extracted electronic mobility of μ = 0.8 cm2/V s was obtained in close agreement with the value extracted from Hall effect measurements. A threshold voltage of V T H = − 34 ± 3 V was obtained, which is the value that can be explained by the polarization difference of both materials. UV illumination shifts the VTH to V T H = − 43 ± 1 V. These findings show how the intrinsic properties of transparent conducting oxides can determine key parameters of a FET device.