Silicon photonic crystal cavities at near band-edge wavelengths

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.