  We report on the realization of scalable single-photon sources (SPSs) based
on single site-controlled quantum dots (SCQDs) and deterministically fabricated
microlenses. The fabrication process comprises the buried-stressor growth
technique complemented with low-temperature in-situ electron-beam lithography
for the integration of SCQDs into microlens structures with high yield and high
alignment accuracy. The microlens-approach leads to a broadband enhancement of
the photon-extraction efficiency of up to (21 $\pm$ 2) $\%$ and a high
suppression of multi-photon events with g$^{(2)}$($\tau$ = 0) $<$ 0.06 without
background subtraction. The demonstrated combination of site-controlled growth
of QDs and in-situ electron-beam lithography is relevant for arrays of
efficient SPSs which can be applied in photonic quantum circuits and advanced
quantum computation schemes.
