Growth and characterization of a novel In2Se3 structure

Thin films of ${\mathrm{In}}_{\mathrm{2}}{\mathrm{Se}}_{\mathrm{3}}$ deposited by thermal co-evaporation crystallize upon vacuum annealing almost single phase into an, up to now, unknown structure. Only when the films are capped with a thin oxide layer before annealing, the reportedly stable $\mathrm{\gamma -}{\mathrm{In}}_{\mathrm{2}}{\mathrm{Se}}_{\mathrm{3}}$ structure, single phase and aligned along the c axis forms. Rutherford backscattering confirms an In to Se ratio of 2 to 3 for both structures. Nevertheless, the new structure has distinct x-ray diffraction peaks and Raman spectra. The new structure has a much lower resistivity than the $\mathrm{\gamma -}{\mathrm{In}}_{\mathrm{2}}{\mathrm{Se}}_{\mathrm{3}}$ structure, consistent with its smaller electrical and optical energy gap. Both structures show large photoconductivity.