Controllable synthesis and electronic structure characterization of multiple phases of iron telluride thin films

We present an investigation on the controlled growth of epitaxial iron telluride films of multiple phases by molecular beam epitaxy. By optimizing the substrate temperature, we fabricate different phases of \ensuremath{\alpha}-FeTe, \ensuremath{\beta}-FeTe, and $\mathrm{Fe}{\mathrm{Te}}_{2}$, respectively, whose crystalline morphologies are determined by means of in situ scanning tunneling microscopy/spectroscopy and ex situ scanning transmission electron microscopy. While both \ensuremath{\alpha}- and \ensuremath{\beta}-FeTe films are metallic, we uncover a \ensuremath{\sim}185- and 65-mV semiconducting band gap for the (100) and (011) facets of $\mathrm{Fe}{\mathrm{Te}}_{2}$ film, respectively, with the former one being compatible with the first principles calculations. Moreover, for $\mathrm{Fe}{\mathrm{Te}}_{2}$, we observe reduced gaps with enhanced conductance in the vicinity of edge boundaries, which are dependent on the geometries of step orientation and possibly in correlation to the magnetic anisotropy with structural distortion. Our study provides insight into the controllable synthesis of Fe-Te compounds with variation of stoichiometries and surface terminations, which may generalize to other epitaxial Fe chalcogenide films.