Appl. Phys. Lett. 103, 162108 (2013)

Quantum dots are potentially an attractive source of single photons for applications in quantum information processing, because, unlike diamond–nitrogen vacancy centres and trapped ions, they can be controlled electrically and are amenable to on-chip integration. Although electrically driven resonant-injection quantum dots have been reported before, single-photon emission has not been demonstrated previously. Now, Michael Conterio and co-workers from Toshiba Research Europe and the University of Cambridge in the UK have observed just that. Their single-photon sources are p-i-n devices grown by molecular beam epitaxy. A layer of self-assembled quantum dots is grown inside a 30 nm intrinsic region of GaAs. Tuning the applied bias to induce resonant tunnelling in the dots allows the team to selectively measure the emission from a single dot in the ensemble, without using spectral filtering. A coherence time of 110 ± 2 ps was measured, corresponding to a linewidth of 20 ± 0.4 μeV, which is nearly an order of magnitude smaller than that previously achieved in resonant electrical injection devices.