  Compact and reliable sources of non-classical light could find many
applications in emerging technologies such as quantum cryptography, quantum
imaging and also in fundamental tests of quantum physics. Single self-assembled
quantum dots have been widely studied for this reason, but the vast majority of
reported work has been limited to optically excited sources. Here we discuss
the progress made so far, and prospects for, electrically driven
single-photon-emitting diodes (SPEDs).
