Mono- and Bilayer WS2 Light-Emitting Transistors

• Published in: Nano letters Vol. 14; no. 4; pp. 2019 - 2025
• Main Authors: Jo, Sanghyun, Ubrig, Nicolas, Berger, Helmuth, Kuzmenko, Alexey B, Morpurgo, Alberto F
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 09.04.2014
• Subjects: Applied sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electron states and collective excitations in thin films, multilayers, quantum wells, mesoscopic and nanoscale systems; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronics; Exact sciences and technology; Molecular electronics, nanoelectronics; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures; Physics; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Transistors; light-emitting transistor; ionic liquid gating; ambipolar transport; transition metal dichalcogenides; 2D Crystals; WS2; Monolayer; Electronic properties; Transport properties; Charge carrier density; Transition metal; Nanoelectronics; Field effect transistor; Energy gap; Light emission; Binding energy; Optical properties; Quantitative analysis; Bilayers
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl500171v

We have realized ambipolar ionic liquid gated field-effect transistors based on WS2 mono- and bilayers, and investigated their opto-electronic response. A thorough characterization of the transport properties demonstrates the high quality of these devices for both electron and hole accumulation, which enables the quantitative determination of the band gap (Δ1L = 2.14 eV for monolayers and Δ2L = 1.82 eV for bilayers). It also enables the operation of the transistors in the ambipolar injection regime with electrons and holes injected simultaneously at the two opposite contacts of the devices in which we observe light emission from the FET channel. A quantitative analysis of the spectral properties of the emitted light, together with a comparison with the band gap values obtained from transport, show the internal consistency of our results and allow a quantitative estimate of the excitonic binding energies to be made. Our results demonstrate the power of ionic liquid gating in combination with nanoelectronic systems, as well as the compatibility of this technique with optical measurements on semiconducting transition metal dichalcogenides. These findings further open the way to the investigation of the optical properties of these systems in a carrier density range much broader than that explored until now.