Atomic and electronic structure of epitaxial PbS on InP(110) and InP(001)

Abstract

Thin films of PbS have been deposited on InP(110) and InP(001) surfaces. Epitaxial growth of the films was obtained already at room temperature (RT). Low-energy electron diffraction (LEED) patterns according to the PbS(001) surface were obtained on both substrate orientations. This result indicates a rather good lattice match on InP(001), while an incommensurate lattice matching was observed along [001] on InP(110). Core level photoemission studies have demonstrated that an abrupt interface forms at the (110) substrate orientation, while an interface reaction occurs on the In-terminated InP(001)-2×4 superstructure after PbS deposition. The electronic structure of PbS films was studied experimentally by using angle-resolved ultraviolet photoemission spectroscopy (ARUPS) and theoretically by applying supercell calculations on the density functional theory level in the local density approximation (DFT-LDA). The supercell calculations indicate surface rumpling and inward relaxation as well as the existence of up to three surface-related states on PbS(001). The experimental data for PbS bulk and thicker PbS films coincide well and agree reasonably with the simulations. The dispersion of the electronic states in ultrathin PbS films (2 nm) is significantly suppressed in comparison to bulk, indicating the incomplete development of the bulk-derived electronic states.