Two-dimensional carbon allotropes with tunable direct band gaps and high carrier mobility

Abstract

Using first-principles calculations, two sp2 + sp3-hybridized two-dimensional (2D) carbon allotropes with stable orthorhombic structures are predicted in this work. Both structures are composed of tetra-, penta-, and hexa-rings of carbon atoms, known as TPH-I carbon and TPH-II carbon. We demonstrate that they can be obtained from penta-graphene by the Stone-Wales (SW) transformation. TPH-I carbon has an inherent direct band gap of 2.704 eV, while TPH-II carbon has a quasi-direct band gap of 2.361 eV. After applying uniaxial strain, TPH-I and TPH-II carbon will have tunable direct band gaps in the range of 2.441–2.812 eV and 2.468–2.7562 eV, respectively. Their electrons and holes mobilities are found to be anisotropic. TPH-I carbon shows extraordinary room temperature in-plane electron mobility of ~7.9 × 104 cm2 V−1 s−1 and TPH-II carbon shows high hole mobility of ~1.5 × 104 cm2 V−1 s−1. Both novel carbon sheets exhibit strong absorption of visible light. And their intrinsic anisotropic optical properties allow optical determination of the crystalline orientation. In addition, TPH-I carbon is a potential photocatalyst for the water splitting reaction.