Spectroscopic ellipsometry and optical transmission study of LiPON thin films prepared by RF sputtering

Lithium phosphorus oxynitride (LiPON) film with high ionic conductivity, low electronic conductivity and high transparency in UV–VIS range offers the possible applications as electrolyte for optical devices, e.g. electrochromic device. In this work, the optical properties of LiPON are investigated by means of variable-angle spectroscopic ellipsometry (VASE) and optical transmission spectra. LiPON thin films with composition of Li3.13PO1.69N1.39 and ionic conductivity of 4.9 × 10−6 S cm−1 at room temperature were prepared by RF magnetron sputtering. Optical constants have been derived on multiple samples with film thickness from 400 to 2000 nm in the energy range of 0.58–5.5 eV. The optical bandgap (Eg) of LiPON film is shown to be 3.07 eV by a Tauc plot. It is found that when E < Eg the Urbach exponential decay of absorption is observed. The Urbach tail width at room temperature is estimated to be 0.361 eV for the LiPON film.