Effect of Au nanosandwiching on the structural, optical and dielectric properties of the as grown and annealed InSe thin films

In the current work, the structural, optical and dielectric properties of the InSe/Au/InSe nanosandwiched structures are investigated by means of X-ray diffraction and UV-visible light spectrophotometry techniques. The insertion of a 20 and 100 nm thick Au metal slabs between two InSe layers did not alter the amorphous nature of the as grown InSe films but decreased the energy band gap and the free carrier density. It also increased; the absorption ratio and the values of dielectric constant by ~ 3 times. The insertion of 100 nm Au layers as a nanosandwich enhanced the drift mobility (31.3 cm2/V s) and plasmon frequency (1.53 GHz) of the InSe films. On the other hand, upon annealing, a metal induced crystallization process is observed for the InSe/Au (100 nm)/InSe sandwiches. Particularly, while the samples sandwiched with a layer of 20 nm thickness hardly revealed hexagonal γ−In2Se3 when annealed at 300 °C, those sandwiched with 100 nm Au slab, displayed well crystalline phase of hexagonal γ−In2Se3 at annealing temperature of 200 °C. The further annealing at 300 °C, forced the appearing of the orthorhombic In4Se3 phase. Optically, the annealing of the InSe/Au(100 nm)/InSe at 200 °C improved the absorption ratio by ~ 9 times and decreased the energy band gap. The nanosandwiching technique of InSe seems to be promising for the engineering of the optical properties of the InSe photovoltaic material.