Fabrication of Diamond Membranes and Photonic Nanostructures for Integration of Color Centers

Single-crystal diamond (SCD) in form of thin membranes with incorporated color centers, such as nitrogen-vacancy (NV) centers or silicon-vacancy (SiV) centers, has gained an ever-increasing interest over the years as a highly promising platform for photonic integrated devices or for envisioned applications in quantum information technologies (QITs). To achieve the desired long optical and spin coherence times for QIT applications, such membranes need to be free from lattice defects, paramagnetic impurities, and charge traps. This requires an initial removal of the damaged surface layers from the cut and polished starting material. Additionally, further processing of diamond by e.g., dry etching for fabrication of photonic structures, can lead to higher roughening of the surface due to a micro-masking effect from particles, originating from the polishing procedure. In our work we address the importance of the SCD surface preparation to overcome the above mentioned challenges, which affect the structuring process and critically influence the final quality of the membrane or structured photonic devices as well as their performance.<br/>The fabrication process of SCD membranes with various diameters and thicknesses, exhibiting a low surface roughness down to 0.2 nm, applying inductively coupled plasma reactive ion etching (ICP-RIE) with Ar/Cl₂ and O₂ plasma will be demonstrated. By a variation of the major etching parameters, an enhanced planarization of the surface can be obtained, especially due to a low etch rate of a few nm/min and the Ar/Cl₂ chemistry. These planarized SCD membranes can be successfully bonded via van der Waals forces or via PMMA on plane cavity mirrors and optically characterized in a fiber-based Fabry–Pérot microcavity system regarding their mode structure and finesse. They can be also used as starting material for fabrication of 1D or 2D photonic crystal structures applying electron beam lithography (EBL).<br/>The work is financially supported by the German Federal Ministry of Education and Research (BMBF) under the Project “Quantenrepeater.Link” (QR.X).