Fabrication and UV Sensitivity of a ZnO Decorated NiO Thin Film Field Effect Transistor

In this letter we propose a new field effect transistor (FET) with a ZnO nanorod decorated NiO thin film acting as the source-drain channel. The sensor was fabricated by immersing a 40 nm Ni thin film on a p-type Si/SiO2 wafer in a standard hydrothermal ZnO nanorod growth solution. After this step, vertically aligned ZnO nanorods were grown on the Ni layer. We have argued the existence of a thin layer of NiO on the Ni layer, caused by partial oxidization of Ni in this aqueous solution. The resulting ZnO nanorods form p-n junctions with the NiO layer which creates a depletion layer for the separation of photogenerated electron-hole pairs. Gate voltage is applied using the Si layer and the effect of gate voltage on the depletion layer is discussed. High sensitivity UV detection was performed under positive gate voltages where the depletion layer extends over the entire width of the NiO layer. The proposed sensor, with an effective surface area of 0.6 cm $\times \,\,0.6$ cm, can detect UV intensities as low as $30~\mu \text{W}$ /cm
²
. The sensor shows good quantum efficiency, reasonable responsivity and a low field mobility of 50%, $0.16~\frac {A}{W}$ and 59.6 cm
²
/V.s respectively.