OCCUPIED AND UNOCCUPIED ELECTRONIC BAND-STRUCTURE OF WSE2

An extensive investigation of the electronic band structure of the lay ered semiconductor 2H-WSe2 is presented. Angular-resolved photoemissio n (ARPES) and angular-resolved inverse photoemission spectroscopy (ARI PES) data are compared to a full-potential fully relativistic density- functional calculation, yielding a very gratifying correspondence betw een the experimental and the theoretical data. The topmost valence ban d is found to behave differently than previous calculations have predi cted, with the valence-band maximum (VBM) being situated at the sixfol d degenerate K point of the Brillouin zone. Furthermore, the so-far-ne glected spin-orbit interaction is shown to be essential for a correct description of the band structure in the vicinity of the VBM. The comb ination of ARPES and ARIPES spectra is used to determine the indirect and direct band gaps at various locations in the Brillouin zone and is compared to optical absorption data. We demonstrate that for a correc t interpretation of the photoemission data it is crucial to account fo r band-bending effects, which are presumably caused by photon-induced surface defect states. Implications of our results for the optical and electrical transport properties will be discussed.