Moderate strain induced indirect bandgap and conduction electrons in MoS2 single layers

• Published in: NPJ 2D materials and applications 2019-10, Vol.3 (1), Article 39
• Main Authors: Pető, János, Dobrik, Gergely, Kukucska, Gergő, Vancsó, Péter, Koós, Antal A., Koltai, János, Nemes-Incze, Péter, Hwang, Chanyong, Tapasztó, Levente
• Format: Article
• Language: English
• Subjects: 639/301/1005/1007; 639/925/357; Carrier density; Charge density; Chemistry and Materials Science; Conduction bands; Conduction electrons; Current carriers; Energy gap; Materials Science; Molybdenum disulfide; Nanotechnology; Optoelectronics; Photoluminescence; Surfaces and Interfaces; Tensile strain; Thin Films
• ISSN: 2397-7132; 2397-7132
• DOI: 10.1038/s41699-019-0123-5

MoS 2 single layers are valued for their sizeable direct bandgap at the heart of the envisaged electronic and optoelectronic applications. Here we experimentally demonstrate that moderate strain values (~2%) can already trigger an indirect bandgap transition and induce a finite charge carrier density in 2D MoS 2 layers. A conclusive proof of the direct-to-indirect bandgap transition is provided by directly comparing the electronic and optical bandgaps of strained MoS 2 single layers obtained from tunneling spectroscopy and photoluminescence measurements of MoS 2 nanobubbles. Upon 2% biaxial tensile strain, the electronic gap becomes significantly smaller (1.45 ± 0.15 eV) than the optical direct gap (1.73 ± 0.1 eV), clearly evidencing a strain-induced direct to indirect bandgap transition. Moreover, the Fermi level can shift inside the conduction band already in moderately strained (~2%) MoS 2 single layers conferring them a metallic character.