Acta Physico-Chimica Sinica ›› 2019, Vol. 35 ›› Issue (4): 385-393.

• ARTICLE •

### 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*()

• Received:2018-04-09 Accepted:2018-05-25 Published:2018-09-13
• Contact: Wanzhen LIANG E-mail:liangwz@xmu.edu.cn
• Supported by:
the National Natural Science Foundation of China(21573177)

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.

MSC2000:

• O649