Silicon photonic crystal cavities at near band-edge wavelengths

TL;DR

This paper reports the design and fabrication of silicon photonic crystal cavities near the band-edge wavelength of 1.078 μm, achieving quality factors around 5,000, optimized for enhancing emission from phosphorus donors.

Contribution

It introduces a fabrication process using common materials to produce high-Q photonic crystal cavities at near band-edge wavelengths in silicon-on-insulator.

Findings

Achieved Q factor of ~5,000 at 1.078 μm

Q decreases to below 3,000 at shorter wavelengths due to silicon absorption

Optimized fabrication process with bilayer resist and CVD oxide mask

Abstract

We demonstrate photonic crystal L3 cavities with resonant wavelength around 1.078 \textmu m on undoped silicon-on-insulator, designed to enhance spontaneous emission from phosphorus donor-bound excitons.\enspace We have optimised a fabrication recipe using readily available process materials such as polymethyl methacrylate (PMMA) as a soft electron-beam mask and a Chemical Vapour Deposition (CVD) grown oxide layer as a hard mask. Our bilayer resist technique efficiently produces photonic crystal cavities with a quality factor ($Q$) of $\sim 5,000$ at a wavelength of $1.078$ \textmu m, measured using cavity reflection measurements at room temperature. We observe a decrease of $Q$ as the cavity resonance shifts to shorter wavelengths ($Q \lesssim3,000$ at wavelengths $< 1.070$ \textmu m), which is mostly due to the intrinsic absorption of silicon.