Unraveling the interlayer coupling effect on layer-dependent electronic and optoelectronic properties in two-dimensional semiconductors

Abstract

Layer-dependent electronic and optoelectronic properties in two-dimensional (2D) semiconductors provide a large degree of freedom to exploit high-performance devices for next-generation electronic and optoelctronics. However, there is still a lack of a deep understanding of the interlayer coupling effect on electronic structures of 2D semiconductors, which significantly limits their device applications. Herein, by means of first-principles calculations, we reveal how the interlayer coupling determines the layer-dependent bandgap, carrier transport, and optical response in 2D semiconductors by using PtSe₂ and HfSe₂ as model systems. Our results indicate that strong interlayer coupling leads to a dramatic reduction of bandgap from 1.93 eV to negative values and a large redshift of absorption edge in PtSe₂ with increasing layer thickness while weak interlayer interactions make that the bandgap (1.0–1.27 eV) and absorption spectra of HfSe₂ insensitive to the change of the layer number. Moreover, the threshold volatge, photocurrent, and optical polarization of PtSe₂ devices significantly depend on the layer thickness but the change of thickness leads to few changes in electrical transport and optical response of HfSe₂ devices. The significant difference in the layer-dependent properties between PtSe₂ and HfSe₂ arises from a competition between the in-plane and out-of-plane orbital interactions. These findings suggest that interlayer interactions can be utilized as an efficient strategy to tailor the electronic and optoelectronic properties of 2D semiconductors for practical device applications.