Tailoring pulsed laser deposition of phosphorus doped WOx films from (PO2)4(WO3)4 target by space-resolved optical emission spectroscopy.

Abstract

Phosphorus doped WOx films were deposited on fused silica substrates from a target of monophosphate tungsten bronze (PO2)4(WO3)2 m with m = 2. Different conditions of O2 pressures and substrate temperature depositions were performed in parallel to plasma investigations during the depositions step. Changes were observed in the film stoichiometries affecting the film properties while the increase of the O2 pressure. Optical bandgap was shifted from 3.39 eV to 3.86 eV as a function of the deposition pressure from 7.5 Pa to 20 Pa. In situ optical emission spectroscopy was carried out in all the O2 atmosphere conditions. With an increase in the oxygen pressure to 5 Pa, a change in the spectral composition of the plasma with a deficit of the phosphorus lines was observed. A complex plasma containing atoms and multiple ionized ions attributed to each composing species was observed at high O2 pressures of deposition. The increase in O2 pressure led to strong thermalization of the plasma and strong scattering of the plasma particle which created a favourable environment for the WO3 formation.