M.S. Onder, K. Teker
Istanbul Sehir University,
Keywords: powerless sensors, flexible nanowire sensors, ultraviolet photodetectors
Summary:Flexible and transparent devices are expected to meet increasing consumer demands for upgrades in wearable devices, smart electronics and photonics. In the benchmark of semiconductors, Silicon carbide (SiC) nanowires have great properties such as chemical inertness, high radiation resistance, and high hardness and ductility. Therefore, SiC nanowires are great candidates for the fabrication of reliable and flexible electronic and photonic devices. In this work, we report a cost-effective fabrication of SiC nanowire network based flexible ultraviolet photodetector (UVPD) device capable of operating powerless. Furthermore, the reliability test results are also reported after significant number of bending cycles. Synthesis of SiC nanowires on a SiO2/Si at 1100°C is realized by chemical vapor deposition (CVD) process. The SiC nanowires are quite long reaching to100 µm. SiC nanowire-nanowire (NW-NW) networks in IPA solvent dropped onto a flexible polyvinylchloride (PVC) substrate via a direct transfer method. A pre-patterned stainless-steel mask with multiple gaps was used to deposit gold electrodes by sputtering. The spacing between the Au electrodes is about 30 μm. Figure 1(a) shows a scanning electron microscopy (SEM) image of high-density CVD-synthesized network of SiC nanowires on SiO2/Si substrate. Figure 1(b) is the actual image of the fabricated flexible SiC NW-NW junction device. The fabricated flexible device has been tested under UV light (254 nm) with an intensity of 13.5 W/m2. Figure 1(c) shows the photocurrent - time characteristics of the device without any bias voltage application for a single pulse. The pulse shows a good response of the device to the UV light exposure. Following the opto-electrical measurements, some key parameters including response time and sensitivity were calculated. The rise and decay times of the device were 1.7 s and 2.2 s, respectively, at 0 V bias. Sensitivity of the device was calculated to be 1500, which is very promising in comparison to the other reported similar devices in literature. Figure 2 shows the results of repeatability and stability investigations of the foldable device after good number of bending cycles of 10, 50, and 75. In fact, the sensitivity of the device was still very good (around 96 % of the rest state) even after 75 challenging bending cycles (about 90º bending relative to the rest state).