  Spectrally-tunable quantum-light sources are key elements for the realization
of long-distance quantum communication. A deterministically fabricated
single-photon source with a photon-extraction efficiency of {\eta}=(20 +- 2) %
and a tuning range of {\Delta}E=2.5 meV is presented here. The device consists
of a single pre-selected quantum dot monolithically integrated into a microlens
which is bonded onto a piezoelectric actuator via thermocompression
goldbonding. The thin gold layer simultaneously acts as a backside mirror for
the quantum dot emission, which is efficiently extracted from the device by an
optimized lens structure patterned via 3D in-situ electron-beam lithography.
The single-photon nature of the emission is proven by photon-autocorrelation
measurements with $g^{(2)}$ ({\tau}=0)=0.04 +- 0.02. The combination of
deterministic fabrication, spectral-tunability and high broadband
photon-extraction efficiency makes the microlens single-photon source an
interesting building block towards the realization of quantum repeaters
networks.
