Surface Encapsulation for Low-Loss Silicon Photonics

TL;DR

This paper investigates surface encapsulation layers, specifically SiNx and SiO2, to passivate silicon surfaces and reduce optical absorption losses in silicon photonics at 1500 nm, using microdisk resonators for testing.

Contribution

It introduces an optimized encapsulation process involving dry thermal oxidation and high-temperature annealing to effectively reduce surface-related optical losses in silicon photonics.

Findings

Long-term encapsulation achieved with dry thermal oxidation and N2 annealing.

Reduction in surface states and hydrogen improves optical loss.

Encapsulation enhances silicon photonics performance at 1500 nm.

Abstract

Encapsulation layers are explored for passivating the surfaces of silicon to reduce optical absorption in the 1500-nm wavelength band. Surface-sensitive test structures consisting of microdisk resonators are fabricated for this purpose. Based on previous work in silicon photovoltaics, coatings of SiNx and SiO2 are applied under varying deposition and annealing conditions. A short dry thermal oxidation followed by a long high-temperature N2 anneal is found to be most effective at long-term encapsulation and reduction of interface absorption. Minimization of the optical loss is attributed to simultaneous reduction in sub-bandgap silicon surface states and hydrogen in the capping material.