Transient Current Response for ZnO Nanorod-Based Doubly Transparent UV Sensor Fabricated on Flexible Substrate

Abstract

We present the transient current response for a ZnO nanorod-based doubly transparent UV sensor. ZnO nanorods (ZNRs) are sandwiched between indium tin oxide (ITO) electrodes to make the device doubly transparent on a flexible polyethylene terephthalate (PET) substrate. The average ZNR length and diameter are 1.7m and 62nm, respectively, and the ITO is perfectly sputtered upon ZNR surface. All the ZNRs are c-axis oriented perpendicular to the substrate with a typical hexagonal wurtzite ZnO structure. Photoluminescence spectra show a typical high-intensity peak near 375nm and a broad peak in the visible region. UV sensing is confirmed by testing ZNR current-voltage characteristics and transient current response under UV on-off conditions for straight and inflexed ZNRs. The sensor shows a 2.3 times increase in current intensity under UV illumination at 4V. The transient current shows a typical sinusoidal wave-like response with three prominent regions under constant voltage supply. The recovery time is almost five-times of the response time, which confirms the five-times faster boundary hole trapping in the sensor than their release on the flexible substrate. Also, the current intensity decreases for an unilluminated flexed device and increases for an UV-illuminated flexed device because of strain-induced ZNR piezotronic effects under flexible deformation.