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 uniform ity 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(th)=15 A/cm(2) for a 2 mm cavity lasing in the first excited state (p she ll), and J(th)=125 A/cm(2) for a 1 mm cavity lasing in n=3 (d shell). At 30 0 K for a 1 mm cavity, J(th) is 490 A/cm(2) with lasing in n=4 (f shell). ( C) 1999 American Institute of Physics. [S0003-6951(99)04433-2].