Lasing in quantum-dot ensembles with sharp adjustable electronic shells

Quantum-dot laser diodes with up to five well-defined electronic shells are fabricated using self-assembled quantum dots (QDs) grown by molecular-beam epitaxy. Shape-engineered stacks of self-aligned QDs with improved uniformity are used to increase the gain in the active region. Lasing is observed in the upper QD shells for small-gain media, and progresses towards the QD ground states for longer cavity lengths. We obtained at 77 K thresholds of $J_{\mathrm{th}}\text{=15\hspace{0.05em}}{\mathrm{A/cm}}^{\mathrm{2}}$ for a 2 mm cavity lasing in the first excited state (p shell), and $J_{\mathrm{th}}\text{=125\hspace{0.05em}}{\mathrm{A/cm}}^{\mathrm{2}}$ for a 1 mm cavity lasing in $\text{n=3}$ (d shell). At 300 K for a 1 mm cavity, $J_{\mathrm{th}}$ is $\text{490\hspace{0.05em}}{\mathrm{A/cm}}^2$ with lasing in $\text{n=4}$ (f shell).