  Self-organized semiconductor quantum dots represent almost ideal two-level
systems, which have strong potential to applications in photonic quantum
technologies. For instance, they can act as emitters in close-to-ideal quantum
light sources. Coupled quantum dot systems with significantly increased
functionality are potentially of even stronger interest since they can be used
to host ultra-stable singlet-triplet spin qubits for efficient spin-photon
interfaces and for a deterministic photonic 2D cluster-state generation. We
realize an advanced quantum dot molecule (QDM) device and demonstrate excellent
optical properties. The device includes electrically controllable QDMs based on
stacked quantum dots in a pin-diode structure. The QDMs are deterministically
integrated into a photonic structure with a circular Bragg grating using
in-situ electron beam lithography. We measure a photon extraction efficiency of
up to (24$\pm$4)% in good agreement with numerical simulations. The coupling
character of the QDMs is clearly demonstrated by bias voltage dependent
spectroscopy that also controls the orbital couplings of the QDMs and their
charge state in quantitative agreement with theory. The QDM devices show
excellent single-photon emission properties with a multi-photon suppression of
$g^{(2)}(0) = (3.9 \pm 0.5) \cdot 10^{-3}$. These metrics make the developed
QDM devices attractive building blocks for use in future photonic quantum
networks using advanced nanophotonic hardware.
