A unipolar quantum dot diode structure for advanced quantum light sources

Triggered, indistinguishable, single photons play a central role in various quantum photonic implementations. Here, we realize a novel n${}^{+}-$i$-$n${}^{++}$ diode structure embedding semiconductor quantum dots: the gated device enables spectral tuning of the transitions and deterministic control of the observed charged states. Blinking-free single-photon emission and high two-photon indistinguishability is observed. The linewidth’s temporal evolution is investigated for timescales spanning more than $6$ orders of magnitude, combining photon-correlation Fourier spectroscopy, high-resolution photoluminescence spectroscopy, and two-photon interference (visibility of $V_{\text{TPI, 2ns}}=(85.5\pm 2.2)\mathrm{\%}$ and $V_{\text{TPI, 9ns}}=(78.3\pm 3.0)\mathrm{\%}$). No spectral diffusion or decoherence on timescales above $\sim 9\text{ns}$ is observed for most of the dots, and the emitted photons’ linewidth $\left((420\pm 30)\text{MHz}\right)$ deviates from the Fourier-transform limit only by a factor of $1.68$. Thus, for remote TPI experiments, visibilities above $74\mathrm{\%}$ are anticipated. The presence of n-doping only signifies higher available carrier mobility, making the presented device highly attractive for future development of high-speed tunable, high-performance quantum light sources.