Long-wavelength lasing from multiply stacked InAs/InGaAs quantum dots on GaAs substrates

An InAs quantum dot (QD) array covered by a thin InGaAs layer was used as the active region of diode lasers grown by molecular beam epitaxy on GaAs substrates. The wavelength of the ground-state transition in such heterostructures is in the 1.3 μm range. In the laser based on the single layer of QDs, lasing proceeds via the excited states due to insufficient gain of the ground level. Stacking of three QD planes prevents gain saturation and results in a low threshold $\text{(85\hspace{0.05em}}{\mathrm{A/cm}}^{\mathrm{2}}$ in broad-area 1.9-mm-long stripe) long-wavelength (1.25 μm) lasing at room temperature via the QD ground state with relatively high differential efficiency $\text{(>50\%).}$