  Solid-state quantum light sources are being intensively investigated for
applications in quantum technology. A key challenge is to extract light from
host materials with high refractive index, where efficiency is limited by
refraction and total internal reflection. Here we show that an index-matched
solid immersion lens can, if placed sufficiently close to the semiconductor,
extract light coupled through the evanescent field at the surface. Using both
numerical simulations and experiments, we investigate how changing the
thickness of the spacer between the semiconductor and lens impacts the
collection efficiency (CE). Using automatic selection and measurement of 100 s
of individually addressable colour centres in several aluminium nitride samples
we demonstrate spacer-thickness dependent photon CE enhancement, with a mean
enhancement factor of 4.2 and a highest measured photon detection rate of 743
kcps.
