2:45 PM - 3:00 PM
▼ [6p-C16-4] High Performance Flexible Single-Layer WS2 Optoelectronics Devices Integrated with Multi-Layer Graphene Electrodes and Parylene-C Substrate
Keywords:WS2, graphene, flexible devices
Single-layer WS2, a semiconducting two-dimensional (2D) material, has large potential for various applications due to its exceptional electrical, optical, and mechanical properties. However, its contact with conventional metal electrodes, such as Ti/Au, limits the device performances because of the presence of Fermi level pinning and/or structural deformation. Here, we present the improvement of chemical vapor deposition (CVD)-grown WS2 field-effect transistors (FETs) by changing the electrodes from conventional Ti/Au to CVD-grown multi-layer graphene (MLG). Moreover, we fabricated flexible devices with unique configuration (Figure 1a) by introducing a thin (1 µm) flexible parylene-C film as the substrate and also acting as a gate insulator in FETs.
Figure 1b shows the mobility as a function of carrier concentration of WS2 fabricated on a SiO2/Si substrate. MLG electrodes clearly gave higher carrier mobility than that contacted with Ti/Au electrodes. The mobility of WS2 with MLG electrodes reached 50 cm2 V-1 s-1, which is roughly ten-fold higher than one with Ti/Au electrodes and is the highest among other CVD-grown WS2 reported so far. The carrier mobility improvement is likely originated from the Fermi level tuning of MLG electrodes by the gate voltage. This reduces the Schottky barrier height between WS2 and MLG electrodes, leading to quasi-ohmic behavior.
In order to evaluate the stability of our flexible device that was fabricated on parylene-C, bending stress tests were performed with small curvatures (r = 2.3 mm) for more than 100× repetitions. The device transfer characteristics before (black) and after (red) subjected to bending tests are given in Figure 1c. The maximum current did not experience a degradation after subjected to the multiple bending, suggesting a robust electrical stability. This supports superior mechanical properties of WS2, MLG, and parylene-C altogether.
Finally, by illuminating with a 532-nm light source, the optical responses of the device were systematically studied. Figure 1c (green) shows the photoresponsivity values as a function of applied gate voltages. Without any applied gate voltage, the responsivity of the device reached a value of 2400 A W-1. The responsivity values increased with the increasing of applied gate voltages, representing the gate tunable behavior of the flexible device.
By utilizing MLG as the electrodes for 2D structures, we demonstrated a new approach not only to improves the performance of the device, but also broaden its applications to flexible photodetectors.
Figure 1b shows the mobility as a function of carrier concentration of WS2 fabricated on a SiO2/Si substrate. MLG electrodes clearly gave higher carrier mobility than that contacted with Ti/Au electrodes. The mobility of WS2 with MLG electrodes reached 50 cm2 V-1 s-1, which is roughly ten-fold higher than one with Ti/Au electrodes and is the highest among other CVD-grown WS2 reported so far. The carrier mobility improvement is likely originated from the Fermi level tuning of MLG electrodes by the gate voltage. This reduces the Schottky barrier height between WS2 and MLG electrodes, leading to quasi-ohmic behavior.
In order to evaluate the stability of our flexible device that was fabricated on parylene-C, bending stress tests were performed with small curvatures (r = 2.3 mm) for more than 100× repetitions. The device transfer characteristics before (black) and after (red) subjected to bending tests are given in Figure 1c. The maximum current did not experience a degradation after subjected to the multiple bending, suggesting a robust electrical stability. This supports superior mechanical properties of WS2, MLG, and parylene-C altogether.
Finally, by illuminating with a 532-nm light source, the optical responses of the device were systematically studied. Figure 1c (green) shows the photoresponsivity values as a function of applied gate voltages. Without any applied gate voltage, the responsivity of the device reached a value of 2400 A W-1. The responsivity values increased with the increasing of applied gate voltages, representing the gate tunable behavior of the flexible device.
By utilizing MLG as the electrodes for 2D structures, we demonstrated a new approach not only to improves the performance of the device, but also broaden its applications to flexible photodetectors.