Structural formation yield of GeV centers from implanted Ge in diamond

In order to study the structural formation yield of germanium-vacancy (GeV) centers from implanted Ge in diamond, we have investigated its lattice location by using the β− emission channeling technique from the radioactive isotope 75Ge (t 1/2=83 min) produced at the ISOLDE/CERN facility. 75Ge was introduced via recoil implantation following 30 keV ion implantation of the precursor isotope 75Ga (126 s) with fluences around 2×1012 - 5×1013 cm−2. While for room temperature implantation fractions around 20% were observed in split-vacancy configuration and 45% substitutional Ge, following implantation or annealing up to 900°C, the split-vacancy fraction dropped to 6-9% and the substitutional fraction reached 85-96%. GeV complexes thus show a lower structural formation yield than other impurities, with substitutional Ge being the dominant configuration. Moreover, annealing or high-temperature implantation seem to favour the formation of substitutional Ge over GeV. Our results strongly suggest that GeV complexes are thermally unstable, and transformed to substitutional Ge by capture of mobile carbon interstitials, which is likely to contribute to the difficulties in achieving high formation yields of these optically active centers.