Engineering of Large Third-Order Nonlinearities in Atomic Layer Deposition Grown Nitrogen-Enriched TiO₂

Abstract

The third-order nonlinear optical properties of Nitrogen-enriched TiO₂ films deposited by Atomic Layer Deposition (ALD) at a temperature between 100 – 300°C on quartz substrates were studied using thermally managed Z-scan technique. TiO₂ oxide films prepared by Physical Vapor Deposition (PVD) at room temperature were used as control samples. The as-grown ALD films deposited at 150 – 300°C exhibited values for the nonlinear index of refraction, n₂, between 0.6x10ˉ¹¹ and 1x10ˉ⁹ cm²/W, which is 4–6 order larger than previously reported. Annealing the films, for 3 hours at 450°C in air, reduced the nonlinearities below the detection limit of the experimental setup. Similarly, as-grown 100°C ALD and PVD films did not produce a discernible Zscan trace. Composition analysis performed by x-ray photoelectrons spectroscopy (XPS) reveals the presence of Ti-O-N metallic bonds in the films that showed high nonlinear optical response. The presence of the metallic bonding gives the films deposited on Si (100) a golden color. These results demonstrate the possibility of a new class of thin-film nonlinear materials that their properties can be tailored by controlling the film composition.