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 mu = 0.8 cm(2)/V s was obtained in close agreement with the value extracted from Hall effect measurements. A threshold voltage of V T H = - 34 & PLUSMN; 3 V was obtained, which is the value that can be explained by the polarization difference of both materials. UV illumination shifts the V-TH to V T H = - 43 & PLUSMN; 1 V. These findings show how the intrinsic properties of transparent conducting oxides can determine key parameters of a FET device.