Synthesis of In_2S_3 and In_6S_7 microcolumns and nanowires by a vapor-solid method

Abstract

Indium sulfide (In_2S_3) is a promising candidate for the replacement of CdS buffer layers in solar cell devices, while hexaindium heptasulfide (In_6S_7) presents interesting properties for its use as absorber material. In this work the fabrication of In_2S_3 microcolumns as well as novel In_6S_7 nanowires with diameters of about 70-120nm is reported. The structures are grown following a thermal evaporation-deposition method at temperatures between 900 and 1000º C. Control of the phase and morphology of the structures is achieved through both the evaporation and deposition temperatures, which can be tuned separately. Energy dispersive spectroscopy shows no traces of residual oxygen, while X-ray photoelectron spectroscopy indicates the presence of small amounts of oxygen incorporated at the surface of the structures. The In_6S_7 nanowires are found to be degenerated n-type semiconductors, with the Fermi level above the conduction band minimum. The origin of this n-type degeneracy is discussed in terms of S vacancies.