Optical characterization of a-As2S3 thin films prepared by magnetron sputtering

It is well known that thermally evaporated a-As2S3 thin films are prone to oxidation when exposed to ambient environment. These As2O3 crystals can have a devastating effect on propagating light by introducing a major source of scattering loss in submicron optically integrated circuits. Magnetron sputtering a-As2S3 not only produces films that have optical properties closer to their equilibrium state like their bulk glass counter parts, the as-deposited films also show no detectable signs of As2O3 crystals in them when they are exposed to the ambient environment. These attributes are unique to a magnetron sputtered a-As2S3 film and are probably caused by the “photoannealing” effect from the visible light emitted by the argon plasma during the sputtering process. The optical properties of a magnetron sputtered a-As2S3 film and its propagation loss on a Ti diffused LiNbO3 waveguide are reported here. The thin film results agree closely with published data on As2S3 bulk glass, and the optical properties of the as-deposited film are found to be closer to its bulk glass values than films made by thermal evaporation and pulsed laser deposition. The TM propagation loss at λ=1.5 μm of the as-deposited a-As2S3 waveguide on Ti:LiNbO3 was 0.20±0.05 dB/cm.