State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Fujian Province, P. R. China
基金项目：
the National Natural Science Foundation of China(21573177)
摘 要：
二维材料过渡金属硫属化物(TMDs),因其优越的物理化学特性及其在光电子器件、光催化等领域的潜在应用价值,得到了人们的广泛关注。基于TMDs材料可以构建具有不同性能的范德华(vdW)异质结,但构建的异质结由于其固有的能带带隙大小限制了其在全光谱上的响应,因而对其能带带隙调控变得十分重要。本文基于第一性原理方法系统地研究了WX_2 (X=S, Se, Te)从单层到体相的结构和性质,以及由此组装的vdW异质结构WS_2/WSe_2、WS_2/WTe_2和WSe_2/WTe_2的结构和性质以及应力应变对异质结构的能带带隙的影响。结果表明:结合HSE06泛函和自旋轨道耦合(SOC)效应的计算方案可以精确描述WX_2体系;异质结构WS_2/WSe_2,WS_2/WTe_2和WSe_2/WTe_2呈现type-II能带分类;在施加单轴或双轴的应力应变后,能带带隙大小发生相应改变,当晶格形变大于4%后,异质结构由半导体特性变成具有金属性。这些研究为光电子器件的设计提供了重要的指导意义。
Theoretical Study on Intrinsic Structures and Properties of vdW Heterostructures of Transition Metal Dichalcogenides (WX2) and Effect of Strains
Miao TAN,Lei ZHANG,Wanzhen LIANG.Theoretical Study on Intrinsic Structures and Properties of vdW Heterostructures of Transition Metal Dichalcogenides (WX2) and Effect of Strains[J].Acta Physico-Chimica Sinica,2019,35(4):385-393.
State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Fujian Province, P. R. China
Abstract:
Two-dimensional transition metal dichalcogenides (TMDs) possess the potential to be widely applied in optoelectronic devices, sensors, photocatalysis, and many other fields because of their intrinsic physical, chemical, and mechanical properties. Generally, the van der Waals (vdW) heterostructures fabricated from these TMDs exhibit excellent electronic properties. However, the spectral responses of most vdW heterostructures are limited by the inherent band gaps; it is thus essential to tune the band gaps for specific applications. In this paper, we performed a first-principles theoretical study on the structures and properties of WX2 (X = S, Se, Te), as well as the vdW heterostructures WS2/WSe2, WS2/WTe2, and WSe2/WTe2. The impacts of the number of layers on the properties of WX2 and the strain on the band gaps of vdW heterostructures were demonstrated. We found that every monolayer WX2 (X = S, Se, Te) is a direct gap semiconductor, and as the number of layers increases, their band gaps decrease and they become indirect bandgap semiconductors. The spin-orbit coupling (SOC) effect on their band structures is significant and can decrease the band gap by approximately 300 meV compared with those that do no incorporate SOC effects. The properties of WX2 can be accurately described by the HSE06 + SOC approach. WS2/WSe2, WS2/WTe2, and WSe2/WTe2 heterostructures are direct gap semiconductors with band gaps of 1.10, 0.32, and 0.61 eV, respectively. These three heterostructures exhibit type-II band alignments, which facilitate photo-induced electron-hole separation. In addition, they have quite small electron and hole effective masses, indicating that the separated electrons and holes can move very quickly to reduce the recombination rate of electrons and holes. There is an explicit red-shift of the optical absorption spectra of the three heterostructures compared with those of the monolayer components, and the most obvious redshift occurs in WSe2/WTe2. Both uniaxial and biaxial strains can alter the band gaps of these vdW heterostructures. Once the strain exceeds 4%, a transition from semiconductor to metal characteristics occurs. This work provides a way to tune the electronic properties and band gaps of vdW heterostructures for incorporation in high-performance optoelectronic devices.
