Heteroepitaxial growth of SnSe films by pulsed laser deposition using Se-rich targets

Abstract

Epitaxial growth of SnSe was studied using pulsed laser deposition on three kinds of single-crystalline substrates, MgO (100), NaCl (100), and SrF2 (100), along with silica glass. For polycrystalline SnSe grown on glass, we found that a 20% Se-rich polycrystalline target is effective for obtaining stoichiometric SnSe films. The crystal structure of all the obtained films was the same as that of bulk SnSe, and the optimum temperatures for epitaxial growth were 400–500 °C, where the highest temperature was limited by re-evaporation. All the epitaxial films exhibited an a-axis orientation. For in-plane epitaxial structures, a quasi cube-on-cube heteroepitaxy was observed for MgO, whereas a 45°-rotated heteroepitaxy was observed for NaCl and SrF2, which can be explained by in-plane lattice matching. The anisotropic lattice mismatching and thermal expansion explain the compressive strain induced along the in-plane c-axis and the tensile strains along the in-plane b-axis and the out-of-plane a-axis. The epitaxial films on NaCl exhibited the best crystallinity, but the highest hole mobility of 60 cm2/(V s) was obtained on MgO. The indirect optical gap of the best films was determined to be 0.8 eV. Plausible interface models were proposed based on density functional calculations.