Third-Order Nonlinear Optical Properties of ALD Grown TiO2 Films by Thermally Managed Z-scan Method

Abstract

Thermally managed Z-scan performed on ALD grown TiO2 films demonstrated n2 values of 1.7x10-11 and 1.94 x10-10 cm 2 /W for films grown at 100°C and 250°C, respectivelygreater than 1000X that of other growth methods. OCIS codes: (190.0190) Nonlinear optics; (320.0320) Ultrafast optics Development of next-generation high-speed photonics devices, such as ultrafast integrated modulators, require novel materials will large optical nonlinearities [1]-[2]. Established nonlinear materials cut from bulk crystals or liquids are not suitable for integration with CMOS technology. In addition to all-optical on-a-chip device applications, materials that exhibit high nonlinear absorption and a fast response time are useful in optical limiting applications [3] for the protection of optical sensors and the human eye from high intensity light such as lasers [4]. Typical materials proposed in the past for optical limiting have been semiconductors, fullerenes, carbon nanotubes, nanostructured materials such as nanoparticles, graphene, nonlinear absorbers doped in xerogels and sol gel films, glasses, filters, organic/inorganic clusters, as well as 2D atomic crystals and organic dye molecules. For most of these materials, there is a tradeoff between their optical limiting ability and damage thresholds, and response time. The vast majority of these materials are not suitable for covering large-scale areas with consistent reproducibly required for sensitive applications such as infrared counter measures sensors. Therefore, there is a need for CMOScompatible materials with sizable nonlinear optical properties. Thin-films and nanolaminates, grown using atomic layer deposition (ALD), have the potential to meet this need.

Third-Order Nonlinear Optical Properties of ALD Grown TiO2 Thin Films

“…This work expands on our previous study [5] to evaluate the cause of the large n2 values for ALD grown TiO2 films. In addition to the fabrication of new ALD TiO2 films covering growth temperature ranges of 100-300C, comprehensive characterization of the films was performed using XPS, XRD and UV-Vis absorption.…”

“…These materials have demonstrated [4] large third-order optical nonlinearities with fast response times (~picosecond time scale). In particular, we have shown [5] that atomic layer deposition (ALD) grown TiO2, a highly studied material for its applications in high-K dielectrics [6] and photoelectrochemical [7] processes, has a very large nonlinear index of refraction, n2. At that time, the reason for the >1000X (1.94x10 -9 cm 2 /W for films grown at 250C) increase of the nonlinearity compared to other films grown methods (1x10 -15 [8] -5.9x10 -13 [9] cm 2 /W) was not yet understood but it was accompanied by an increase in absorption and the films appeared dark in color.…”