  We present an in-situ counted ion implantation experiment reducing the error
on the ion number to 5 % enabling the fabrication of high-yield single photon
emitter devices in wide bandgap semiconductors for quantum applications.
Typical focused ion beam implantation relies on knowing the beam current and
setting a pulse length of the ion pulse to define the number of ions implanted
at each location, referred to as timed implantation in this paper. This process
is dominated by Poisson statistics resulting in large errors for low number of
implanted ions. Instead, we use in-situ detection to measure the number of ions
arriving at the substrate resulting in a two-fold reduction in the error on the
number of implanted ions used to generate a single optically active silicon
vacancy (SiV) defect in diamond compared to timed implantation. Additionally,
through post-implantation analysis, we can further reduce the error resulting
in a seven-fold improvement compared to timed implantation, allowing us to
better estimate the conversion yield of implanted Si to SiV. We detect SiV
emitters by photoluminescence spectroscopy, determine the number of emitters
per location and calculate the yield to be 2.98 + 0.21 / - 0.24 %. Candidates
for single photon emitters are investigated further by Hanbury-Brown-Twiss
interferometry confirming that 82 % of the locations exhibit single photon
emission statistics. This counted ion implantation technique paves the way
towards deterministic creation of SiV when ion counting is used in combination
with methods that improve the activation yield of SiV.
