  The long dreamed quantum internet would consist of a network of quantum nodes
(solid-state or atomic systems) linked by flying qubits, naturally based on
photons, travelling over long distances at the speed of light, with negligible
decoherence. A key component is a light source, able to provide single or
entangled photon pairs. Among the different platforms, semiconductor quantum
dots are very attractive, as they can be integrated with other photonic and
electronic components in miniaturized chips. In the early 1990s two approaches
were developed to synthetize self-assembled epitaxial semiconductor quantum
dots (QDs), or artificial atoms, namely the Stranski-Krastanov (SK) and the
droplet epitaxy (DE) method. Because of its robustness and simplicity, the SK
method became the workhorse to achieve several breakthroughs in both
fundamental and technological areas. The need for specific emission wavelengths
or structural and optical properties has nevertheless motivated further
research on the DE method and its more recent development, the
local-droplet-etching (LDE), as complementary routes to obtain high quality
semiconductor nanostructures. The recent reports on the generation of highly
entangled photon pairs, combined with good photon indistinguishability, suggest
that DE and LDE QDs may complement (and sometime even outperform) conventional
SK InGaAs QDs as quantum emitters. We present here a critical survey of the
state of the art of DE and LDE, highlighting the advantages and weaknesses, the
obtained achievements and the still open challenges, in view of applications in
quantum communication and technology.
