Tuning optical and electronic properties of 2D ZnI2/CdS heterostructure by biaxial strains for optical nanodevices: A first-principles study

Abstract

The structural and optoelectronic properties of a novel ZnI2/CdS van der Waals (vdW) heterostructure are studied under the effect of biaxial strain based on the density functional theory. Our results show that the ZnI2/CdS vdW heterostructure is dynamically and thermally stable depending on the molecular dynamics simulation and phonon dispersion curve. The results also indicate that the ZnI2/CdS heterostructure exhibits type-II band alignment with an indirect energy gap of 0.886 and 1.336 eV according to the Perdew-Burke-Ernzerhof and Heyd-Scuseria-Ernzerhof methods, respectively. Besides, the biaxial strain has a significant impact on the electronic properties. The energy bandgap of the ZnI2/CdS heterostructure decreases gradually as the compressive strain increases, reaching a minimum value of 1.162 eV at −6%. Also, a transformation from indirect bandgap to direct bandgap appears at strains of 4% and 6%. Broadly, it has been found that the optical properties of the ZnI2/CdS vdW heterostructure improve under the influence of strain, and the absorption coefficient can reach 105 cm−1 with the emergence of a shift phenomenon that expands the absorption capacity. Therefore, the application of strain will drastically improve the optical and electronic properties of the ZnI2/CdS vdW heterostructure, providing a roadmap for enhancing optical efficiency in photocatalytic and photovoltaic devices.