Molecular beam epitaxy synthesis of In2Se3 films

The effects of substrate choice, substrate temperature, Se/In flux ratio, and cooling rate after deposition on the phase composition, surface morphology, and stoichiometry of indium selenide films synthesized via molecular beam epitaxy are presented. In2Se3 films were synthesized on sapphire, Si(111) and highly oriented, pyrolytic graphite (HOPG) substrates. The phase composition, stoichiometry, and surface morphology of the films were characterized via Raman spectroscopy, x-ray photoelectron spectroscopy, and atomic force microscopy, respectively. Higher substrate temperature combined with higher Se/In ratio promoted formation of β-In2Se3 over γ and/or κ-In2Se3 on all substrates. Higher Se/In ratio also independently promoted β-In2Se3 over γ and/or κ-In2Se3 on all substrates at 673 K. The lateral dimensions of In2Se3 flakes increased as the substrate temperature increased on all substrates, and the largest lateral dimensions were observed for β-In2Se3 flakes on HOPG at 973 K. No evidence of α-In2Se3 was observed in the Raman spectra of any of the films at any of the synthesis conditions in this study. β-In2Se3 films on HOPG were cooled at 1200, 120, and 12 K/h and no evidence of a β to α-In2Se3 phase transition was observed. Some evidence of β to α-In2Se3 phase transition was observed in temperature-dependent XRD of In2Se3 powders, suggesting that another parameter besides cooling rate is locking the In2Se3 films into the β-phase.