Linear and non-linear optical properties of Ag-doped Ge2Sb2Te5 thin films estimated by single transmission spectra

Abstract

In this paper we have studied the effect of Ag addition on linear and non-linear optical properties of thermally evaporated (Ge2Sb2Te5)100−xAgx (x = 0, 1, 3 and 10) thin films (thickness ∼700 nm) from single transmission spectra. Energy dispersive spectroscopy, x-ray diffraction and Raman spectroscopy were used to verify the composition, amorphous nature and structure of the fabricated thin films respectively. Swanpoel’s method was used to calculate the thickness (d), refractive index (n) and extinction coefficient (k). The refractive index and extinction coefficient were used to obtain all linear and non linear optical parameters. The compositional dependence of the refractive index, extinction coefficient, volume energy loss function, surface energy loss function, dielectric constant, dielectric loss function, optical conductivity and third order non-linear optical susceptibility were determined. All these optical parameters have minimum values for 3% Ag-doped Ge2Sb2Te5 (GST). The decrease in measured optical parameters up to 3% Ag doping is due to a decrease in the density of localized states in the mobility gap. The increase in the optical parameters at 10% Ag doping was ascribed to the distortion of the host lattice, because incorporation of Ag has been done at the expense of Ge, Sb and Te. The optical parameters of the GST films were found to be strongly dependent upon Ag content. The results revealed that 3% Ag-doped GST is a promising candidate for phase change optical storage applications.