Ultrathin All-2D Lateral Diodes Using Top and Bottom Contacted Laterally Spaced Graphene Electrodes to WS2 Semiconductor Monolayers

The ultrathin nature of two-dimensional (2D) materials opens up opportunities for creating devices that are substantially thinner than using traditional bulk materials. In this article, monolayer 2D materials grown by the chemical vapor deposition method are used to fabricate ultrathin all-2D lateral diodes. We show that placing graphene electrodes below and above the WS2 monolayer, instead of the same side, results in a lateral device with two different Schottky barrier heights. Due to the natural dielectric environment, the bottom graphene layer is wedged between the WS2 and the SiO2 substrate, which has a different doping level than the top graphene layer that is in contact with WS2 and air. The lateral separation of these two graphene electrodes results in a lateral metal-semiconductor-metal junction with two asymmetric barriers but yet retains its ultrathin form of two-layer thickness. The rectification and diode behavior can be exploited in transistors, photodiodes, and light-emitting devices. We show that the device exhibits a rectification ratio up to 90 under a laser power of 1.37 mu W at a bias voltage of +/- 3 V. We demonstrate that both the back-gate voltage and laser illumination can tune the rectification behavior of the device. Furthermore, the device can generate strong red electroluminescence in the WS2 area across the two graphene electrodes under an average flowing current of 2.16 x 10-5 A. This work contributes to the current understanding of the 2D metal-semiconductor heterojunction and offers an idea to obtain all-2D Schottky diodes by retaining the ultrathin device concept.