Effect of deposition method on the density of InAs/InGaAs quantum dot

InAs self-organized quantum dots covered with In_0.33Ga_0.67As layer have been grown on GaAs substrates by gas-source molecular beam epitaxy. With three different deposition methods for growing the InGaAs capping layer, the quantum-dot density can be controllably changed from 2.3×10¹⁰ to 1.7×10¹¹ cm^-2. Photoluminescence at 1,318nm of quantum dots with the dot density as high as 7.6×10¹⁰ cm^-2 can be achieved by sub-monolayer deposition (SMD) capping method. As-cleaved 3.98-mm-long laser diode using triple stacks of InAs/InGaAs quantum dots with SMD method demonstrates a lasing wavelength of 1,305nm and a threshold current density of 360A/cm². The ground-state saturation gain of 16.6cm^-1 is achieved due to the high dot density.