Amorphous effect on the advancing of wide-range absorption and structural-phase transition in γ-In2Se3 polycrystalline layers

The exploitation of potential functions in material is crucial in materials research. In this study, we demonstrate a III-VI chalcogenide, polycrystalline gamma-In2Se3, which simultaneously possesses the capabilities of thickness-dependent optical gaps and wide-energy-range absorption existed in the polycrystalline layers of gamma-In2Se3. Transmission electron microscopy and Raman measurement show a lot of gamma-phase nanocrystals contained in the disordered and polycrystalline state of the chalcogenide with medium-range order (MRO). The MRO effects on the gamma-In2Se3 layers show thickness-dependent absorption-edge shift and thickness-dependent resistivities. The amorphous effect of MRO also renders a structural-phase transition of gamma -> alpha occurred inside the gamma-In2Se3 layer with a heat treatment of about 700 degrees C. Photo-voltage-current (Photo V-I) measurements of different-thickness gamma-In2Se3 layers propose a wide-energy-range photoelectric conversion unit ranging from visible to ultraviolet (UV) may be achieved by stacking gamma-In2Se3 layers in a staircase form containing dissimilar optical gaps.