Ab initio study of electronic and optical behavior of two- dimensional silicon carbide† Xiao Lin,‡ abcd Shisheng Lin,‡ acd Yang Xu, * acd Ayaz Ali Hakro, ad Tawfique Hasan, e Baile Zhang, f Bin Yu, g Jikui Luo, ad Erping Li ad and Hongsheng Chen abcd Two-dimensional graphene-like silicon carbide (2d-SiC) has emerged as an intriguing new class of layered nanostructure. Using density functional theory, key electronic and optical properties of 2d-SiC nanosheets, in particular, of mono- and bilayer 2d-SiC, are investigated. The properties of these nanosheets are found to be highly dependent on their physical thickness and geometric configuration. Multilayer 2d-SiC exhibits an indirect bandgap. We find that monolayer 2d-SiC, on the other hand, has a direct bandgap (2.5 eV) that can be tuned through in-plane strain. We also show that the optical conductivity of multilayer 2d-SiC is sensitive to the interlayer spacing. The results suggest that unlike graphene, silicene and even multilayer 2d-SiC, monolayer 2d-SiC could be a good candidate for optoelectronic devices such as light-emitting diodes. Introduction Silicon carbide (SiC), a binary compound of carbon and silicon, has attracted extensive research interest due to its unique properties. It has been widely used in high-tempera- ture, high-power, and high-frequency devices. 1,2 Among all semiconductors, SiC exhibits the widest range of energy bandgap, varying from 2.3 eV in a cubic polytype b-SiC up to 3.4 eV in a hexagonal polytype 2H a-SiC. 2 This intriguing property allows the fabrication of light-emitting diodes (LEDs) covering the entire visible and ultraviolet spectrum. 2 Bulk SiC exists in either a sphalerite or wurtzite structure with an indirect bandgap. 2 Theoretical calculations have also predicted that two-dimensional SiC (2d-SiC) with a honeycomb struc- ture, 3–7 similar to graphene 8–12 and silicene, 13–20 could be energetically stable. 5,6 For optoelectronic device applications, such as LEDs or solar cells, in addition to an appropriate bandgap, a large exciton binding energy is also desirable. This is to attain high internal quantum efficiency which cannot be easily reached using pristine graphene and silicene. 8,15 Monolayer 2d-SiC exhibits a large direct bandgap and an exciton binding energy of up to 2.0 eV. 21 It also shows improved photoluminescence (PL) than its sphalerite or wurtzite counterparts. 22 The Bose–Einstein condensate (BEC) effect may be observed in such a material system with a high exciton binding energy, in analogy to Cu 2 O. 23 Compared with silicene and other graphene-like compound semiconductors (GaN, BP, AlN, etc.), monolayer 2d-SiC has a larger in-plane stiffness. 17 Magnetic properties of ordered vacancies in 2d hexagonal structures (graphene, 2d-SiC, etc.) have recently been investigated by density functional theory (DFT) with Perdew-Wang 91 (PW91) gradient corrections, where in 2d-SiC, the local magnetic moment appears only in the presence of silicon vacancy. 24 Recent progress in the fabrication of ultra- thin layered 2d-SiC 22,25 down to a monolayer makes it an emerging semiconductor attractive to both fundamental research and practical applications. 26–29 Here, we compara- tively study the electronic and optical behaviors of layered 2d- SiC with graphene and silicene by DFT. We nd that the sp 2 - bonded layered 2d-SiC could gradually transform from having an indirect bandgap to a direct bandgap, as the thickness (or layer number) decreases from multilayer to monolayer. We also show that the direct bandgap in monolayer 2d-SiC can be tuned through in-plane strain. Calculation methods In this paper, the 2d materials are investigated through DFT in a generalized gradient approximation (GGA) by using SIESTA a Department of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310027, P. R. China. E-mail: yangxu-isee@zju.edu.cn b The Electromagnetics Academy at Zhejiang University, Zhejiang University, Hangzhou 310027, P. R. China c State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027, P. R. China d Cyrus Tang Center for Sensor Materials and Applications, Zhejiang University, Hangzhou 310027, P. R. China e Department of Engineering, University of Cambridge, Cambridge CB3 0FA, UK f Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore g College of Nanoscale Science and Engineering, State University of New York, Albany, New York 12203, USA † Electronic supplementary information (ESI) available. See DOI: 10.1039/c3tc00629h ‡ These authors contributed equally to this work. Cite this: J. Mater. Chem. C, 2013, 1, 2131 Received 14th November 2012 Accepted 23rd January 2013 DOI: 10.1039/c3tc00629h www.rsc.org/MaterialsC This journal is ª The Royal Society of Chemistry 2013 J. Mater. Chem. C, 2013, 1, 2131–2135 | 2131 Journal of Materials Chemistry C PAPER Published on 24 January 2013. Downloaded by Zhejiang University on 30/10/2016 09:47:14. View Article Online View Journal | View Issue