Efficiency Optimization of Ge-V Quantum Emitters in Single-Crystal Diamond upon Ion Implantation and HPHT Annealing

The authors report on the characterization at the single-defect level of germanium-vacancy (GeV) centers in diamond produced upon Ge− ion implantation and different subsequent annealing processes, with a specific focus on the effect of high-pressure-high-temperature (HPHT) processing on their quantum-optical properties. Different post-implantation annealing conditions are explored for the optimal activation of GeV centers, namely, 900 °C 2 h, 1000 °C 10 h, 1500 °C 1 h under high vacuum, and 2000 °C 15 min at 6 GPa pressure. A systematic analysis of the relevant emission properties, including the emission intensity in saturation regime and the excited state radiative lifetime, is performed on the basis of a set of ion-implanted samples, with the scope of identifying the most suitable conditions for the creation of GeV centers with optimal quantum-optical emission properties. The main performance parameter adopted here to describe the excitation efficiency of GeV centers as single-photon emitters is the ratio between the saturation optical excitation power and the emission intensity at saturation. The results show an up to eightfold emission efficiency increase in HPHT-treated samples with respect to conventional annealing in vacuum conditions, suggesting a suitable thermodynamic pathway toward the repeatable fabrication of ultra-bright GeV centers for single-photon generation purposes.