Linear and Nonlinear Optical Properties of SiO$_2$/TiO$_2$ Heterostructures Grown by Plasma Enhanced Atomic Layer Deposition

TL;DR

This study demonstrates the fabrication of SiO₂/TiO₂ heterostructures via plasma enhanced atomic layer deposition, revealing significant second harmonic generation and tunable nonlinear optical properties suitable for integrated photonics.

Contribution

It introduces a CMOS-compatible PEALD method to create amorphous SiO₂/TiO₂ heterostructures with enhanced nonlinear optical responses, especially strong SH signals from nanolaminates.

Findings

Effective second-order susceptibility χ^(2) = 1.30 pm/V at 1032 nm

Strong SH signals observed from nanolaminates, orders of magnitude larger than single layers

Form-birefringence enables phase matching in nonlinear optical applications

Abstract

Second harmonic (SH) radiation can only be generated in non-centrosymmetric bulk crystals under the electric-dipole approximation. Nonlinear thin films made from bulk crystals are technologically challenging because of complex and high temperature fabrication processes. In this work, heterostructures made of amorphous materials SiO$_2$ and TiO$_2$ were prepared by a CMOS-compatible technique named plasma enhanced atomic layer deposition (PEALD) with deposition temperature at 100 {\deg}C. By using the uniaxial dispersion model, we characterized the form-birefringence properties, which can enable the phase matching condition in waveguides or other nonlinear optical applications. By applying a fringe-based technique, we determined the largest diagonal component of the effective second-order bulk susceptibility $\chi_{zzz}^{(2)}$ = 1.30$\pm$0.13 pm/V at a wavelength of 1032 nm. Noteworthy, we observed strong SH signals from two-component nanolaminates, which are several orders of magnitude larger than from single layers. The SH signals from our samples only require the broken inversion symmetry at the interface. Here optical properties of nanocomposites can be precisely tuned by the promising PEALD technology.