Engineering germanium-vacancy center arrays in diamond nanopillars for quantum applications

Among the color centers in diamond, germanium-vacancy (GeV) centers, are gaining attention for their potential in quantum technologies. These defects exhibit strong zero-phonon line (ZPL) emissions at 603 nm, even at room temperature, short excited-state lifetimes, and high optical coherence due to their inversion-symmetric (D3d) structure. In this study, we fabricated GeV centers in electronic-grade diamond using a Focused Ion Beam (FIB) with a liquid metal alloy ion source. FIB implantation offers precise, mask-free fabrication of GeV centers, ensuring accurate spatial positioning with minimal ion straggling. Implantation was performed at 35 keV and 70 keV with Ge ion doses from 10 to 1000 ions per beam spot. Post-implantation, the samples underwent thermal annealing in ultra-high vacuum at 1000°C for two hours. To enhance emission efficiency, nanopillar structures (20 nm in diameter) were precisely fabricated at the sites of the single-photon emitter arrays using electron-beam lithography and plasma etching. This process led to a significant improvement of a factor 8 in photon collection, emphasizing the effectiveness of this nanoscale engineering approach for quantum photonics applications. Photoluminescence (PL) measurements together with antibunching measurements, revealed that up to 33% of the fabricated nanopillars contained single emitters, with the exact percentage depending on ion implantation parameters.