High-Q suspended optical resonators in 3C silicon carbide obtained by thermal annealing.

Keith Powell,Amirhassan Shams-Ansari,Mitchell Austin,Smit Desai,Neil Sinclair,Jiangdong Deng,Xiaoke Yi,Marko Lončar

doi:10.1364/oe.381601

Abstract

We fabricate suspended single-mode optical waveguides and ring resonators in 3C silicon carbide (SiC) that operate at telecommunication wavelength, and leverage post-fabrication thermal annealing to minimize optical propagation losses. Annealed optical resonators yield quality factors of over 41,000, which corresponds to a propagation loss of 7 dB/cm, and is a significant improvement over the 24 dB/cm in the case of the non-annealed chip. This improvement is attributed to the enhancement of SiC crystallinity and a significant reduction of waveguide surface roughness, from 2.4 nm to below 1.7 nm. The latter is attributed to surface layer oxide growth during the annealing step. We confirm that the thermo-optic coefficient, an important parameter governing high-power and temperature-dependent performance of SiC, does not vary with annealing and is comparable to that of bulk SiC. Our annealing-based approach, which is especially suitable for suspended structures, offers a straightforward way to realize high-performance 3C-SiC integrated circuits.

Highlights

An important goal in the development of integrated photonics is the possibility to achieve integration of efficient functionality between multiple components on a monolithic platform [1]
We investigate the mechanisms for annealing-induced loss reduction by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM) analysis
This results in an overall improvement to crystallinity of the 3C-silicon carbide (SiC) film which is supported by XRD and XPS analysis

Summary

Introduction

An important goal in the development of integrated photonics is the possibility to achieve integration of efficient functionality between multiple components on a monolithic platform [1]. In 3C-SiCOI a flip, bond, etch and polish method was developed to bond 3C-SiC onto an insulating wafer of thermal SiO2 on Si [26] With this technique the stacking faults and anti-phase boundaries at the SiC-Si interface were removed in the chemical mechanical polishing (CMP) step resulting in a propagation loss of 3 dB/cm [27]. Up to now, suspended 3C-SiC ring resonators feature optical quality (Q) factors in the range of 11000-24,000 [34,44], where the latest results show waveguides featuring propagation losses of 21 dB/cm using 1550 nm light [34] This is an impressive performance for a hard-to-etch polycrystalline material so far, these propagation losses inhibit suspended 3C-SiC devices for integrated photonic applications. We perform accurate measurement of the thermo-optic coefficient of 5.7×10−5/K in the fabricated 3C-SiC waveguides before and after annealing and confirm that our annealing technique does not alter this property

Fabrication method

Design and simulation

Device characterization

Optical characterization

Findings

Conclusion