  Electronic devices that are designed to use the properties of single atoms
such as donors or defects have become a reality with recent demonstrations of
donor spectroscopy, single photon emission sources, and magnetic imaging using
defect centers in diamond. Improving single ion detector sensitivity is linked
to improving control over the straggle of the ion as well as providing more
flexibility in lay-out integration with the active region of the single donor
device construction zone by allowing ion sensing at potentially greater
distances. Using a remotely located passively gated single ion Geiger mode
avalanche diode (SIGMA) detector we have demonstrated 100% detection efficiency
at a distance of >75 um from the center of the collecting junction. This
detection efficiency is achieved with sensitivity to ~600 or fewer
electron-hole pairs produced by the implanted ion. Ion detectors with this
sensitivity and integrated with a thin dielectric, for example 5 nm gate oxide,
using low energy Sb implantation would have an end of range straggle of <2.5
nm. Significant reduction in false count probability is achieved by modifying
the ion beam set-up to allow for cryogenic operation of the SIGMA detector.
Using a detection window of 230 ns at 1 Hz, the probability of a false count
was measured as 1E-1 and 1E-4 for operation temperatures of 300K and 77K,
respectively. Low temperature operation and reduced false, dark, counts are
critical to achieving high confidence in single ion arrival. For the device
performance in this work, the confidence is calculated as a probability of >98%
for counting one and only one ion for a false count probability of 1E-4 at an
average ion number per gated window of 0.015.
