Effect of InGaAs capping layer on the properties of InAs/InGaAs quantum dots and lasers

We report the effects of ${\mathrm{In}}_{\text{0.33}}{\mathrm{Ga}}_{\text{0.67}}\mathrm{As}$ capping layers on the structural and optical properties of InAs self-organized quantum dots grown by gas-source molecular-beam epitaxy. With different deposition methods for the InGaAs capping layer, the quantum-dot density can be adjusted from ${\text{2.3×10}}^{10}$ to ${\text{1.7×10}}^{11}\hspace{0.17em}{\mathrm{cm}}^{\text{−2}}.$ As-cleaved 3.98-mm-long diode laser using triple stacks of InAs quantum dots with the capping layer grown by GaAs/InAs sequential binary growth demonstrates an emission wavelength of 1305 nm and a threshold current density of $\text{360\hspace{0.17em}}{\mathrm{A/cm}}^2.$ A ground-state saturation gain of $\text{16.6\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ is achieved due to the high dot density.