Exploring semiconductor-to-semimetal transitions in Bi₂Se₃/TMD heterostructures

Vertically stacked Van der Waals heterostructures show great promise in the design of novel materials for nanoelectronic, photovoltaic and photonics applications. Recent experiments reveal that growing one quintuple layer of Bi₂Se₃ on TMD monolayers (2H-MoS₂, -WS₂, -MoSe₂) produces rotationally-aligned heterostructures, despite substantial lattice mismatch, with properties that are distinct from those of the parent films. [1] Intriguingly, our experiments show that the resulting heterostructures can also exhibit finite twisting angles between the stacked layers in a number of cases. In this connection, we have computed electronic structures and their evolution with twist angle of Bi₂Se₃/TMD and number of Bi₂Se₃ quintuple layers, within the first-principles density functional theory (DFT) framework. Our analysis reveals rich variations in electronic spectra and a transition from a semiconducting to a semimetallic state as a function of the twist angle, as well as with the number of Bi₂Se₃ layers. We explore the relationship of this phase transition with effects of interplay between interlayer coupling and strain in the films.

[1] Science Advances 14 Jul 2017: Vol. 3, no. 7, DOI: 10.1126/sciadv.1601741