# Optical bandgap engineering in nonlinear silicon nitride waveguides

## TL;DR

This paper demonstrates how to control and optimize the optical bandgap and nonlinear Kerr coefficient of silicon nitride waveguides through precise LPCVD process parameters, enhancing their suitability for nonlinear optical applications.

## Contribution

It introduces a reproducible method to tune the optical bandgap of silicon nitride during deposition, enabling tailored nonlinear Kerr properties for photonic devices.

## Key findings

- Gas flow ratio during LPCVD controls the optical bandgap.
- Optimized deposition conditions improve Kerr nonlinearity.
- Guidelines for fabricating silicon nitride waveguides for nonlinear optics.

## Abstract

Silicon nitride is awell-established material for photonic devices and integrated circuits. It displays a broad transparency window spanning from the visible to the mid-IR and waveguides can be manufactured with low losses. An absence of nonlinear multi-photon absorption in the erbium lightwave communications band has enabled various nonlinear optic applications in the past decade. Silicon nitride is a dielectric material whose optical and mechanical properties strongly depend on the deposition conditions. In particular, the optical bandgap can be modified with the gas flow ratio during low-pressure chemical vapor deposition (LPCVD). Here we show that this parameter can be controlled in a highly reproducible manner, providing an approach to synthesize the nonlinear Kerr coefficient of the material. This holistic empirical study provides relevant guidelines to optimize the properties of LPCVD silicon nitride waveguides for nonlinear optics applications that rely on the Kerr effect.