PbTe(core)/PbS(shell) Nanowire: Electronic Structure, Thermodynamic Stability, and Mechanical and Optical Properties

Abstract

Core/shell nanostructures offer exciting opportunities for a wide range of applications from solar cells and light-emitting diodes to field-effect transistors and logic circuits to spin-filtering and switching devices. Here, using first-principles density functional theory, we predict PbTe/PbS core/shell nanowires as semiconductors with direct bandgap along the ⟨111⟩ direction and indirect bandgap in the ⟨200⟩ direction. The inclusion of the spin–orbit coupling shifts the conduction band minimum (dominated by Pb atoms) toward the Fermi energy, thus reducing the energy gap of these nanowires while retaining their semiconducting features. The application of compressive strains (>11.30%) causes semiconductor to metallic phase transitions in these nanowires with transition pressure ranging from ∼3 to ∼6 GPa, which is within the range reported in lead chalcogenides nanowires and nanoparticles. The Young’s modulus is ∼20 GPa along the ⟨111⟩ direction and ∼48 GPa in the ⟨200⟩ direction. We also report that the optical absorption in these materials is broad and extends from the infrared to ultraviolet (∼0.39–13 eV) region. Furthermore, our calculations of cohesive energy reveal that wires along the ⟨200⟩ direction are more stable compared to the wires in the ⟨111⟩ direction; ab initio molecular dynamics simulations at room temperature show that the ⟨111⟩ nanowire is more prone to core-to-shell diffusion.