Single layer lead iodide: computational exploration of structural, electronic and optical properties, strain induced band modulation and the role of spin--orbital-coupling

Graphitic like layered materials exhibit intriguing electronic structures and the search for new types of two-dimensional (2D) monolayer materials is of great interest for developing novel nano-devices. By using density functional theory method, we investigate the structure, stability, electronic and optical properties of monolayer lead iodide (PbI$_{\mathrm{2}})$. The stability of PbI$_{\mathrm{2}}$ monolayer is first confirmed by phonon dispersion calculation. Compared to the calculation using generalized gradient approximation, screened hybrid functional and spin--orbit coupling effects can predicts an accurate band gap (2.63 eV). The biaxial strain can tune its band gap size in a wide range from 1 eV to 3 eV, which can be understood by the strain induced uniformly change of electric field between Pb and I atomic layer. The calculated imaginary part of the dielectric function of 2D graphene/PbI$_{\mathrm{2}}$ van der Waals type hetero-structure shows significant red shift of absorption edge compared to that of a pure monolayer PbI$_{\mathrm{2}}$. Our findings highlight a new interesting 2D material with potential applications in nanoelectronics and optoelectronics.