Impact of Stoichiometric Silicon Nitride Growth Conditions on Dispersion Engineering of Broadband Microresonator Frequency Combs

TL;DR

This paper demonstrates how adjusting LPCVD growth conditions of silicon nitride films influences their material dispersion, enabling better control of microresonator dispersion for broadband microcombs.

Contribution

It reveals the impact of precursor ratio modifications on material dispersion and shows how geometric dispersion tuning can compensate for these changes.

Findings

Growth conditions significantly affect material dispersion.

Geometric dispersion tuning can offset material dispersion variations.

Enhanced control over microcomb dispersion achieved.

Abstract

Microresonator frequency combs, or microcombs, have gained wide appeal for their rich nonlinear physics and wide range of applications. Stoichiometric silicon nitride films grown via low-pressure chemical vapor deposition (LPCVD), in particular, are widely used in chip-integrated Kerr microcombs. Critical to such devices is the ability to control the microresonator dispersion, which has contributions from both material refractive index dispersion and geometric confinement. Here, we show that modifications to the LPCVD growth conditions, specifically the ratio of the gaseous precursors, has a significant impact on material dispersion and hence the overall microresonator dispersion. In contrast to the many efforts focused on comparison between Si-rich films and stoichiometric (Si$_3$N$_4$) films, here we entirely focus on films that are within the nominally stoichiometric growth regime. We further show that microresonator geometric dispersion can be tuned to compensate for changes in the material dispersion.