Enhancement in the gain of quantum dot laser by increasing overlap integral between electron and hole wave-functions

We report the influences of quantum dot (QD) shape on the lasing characteristics such as threshold current, slope efficiency, and wavelength stability. The average heights of the shape-engineered InAs/InAlGaAs QDs (SEQDs) and the conventionally-grown Stranski-Krastanov InAs QDs (CQD) were 10 ± 0.5 and 2.5 ± 0.5 nm, respectively. For the cavity length of 0.5 mm, the threshold current of the laser diodes (LDs) with the InAs/InAlGaAs SEQDs as an active layer (SEQD-LD) was decreased by 3.6 times smaller than that of the LDs with the InAs CQDs (CQD-LD). Also the slope efficiency for the SEQD-LD was increased to 0.15 from 0.087 W/A of the CQD-LD. While the lasing wavelength of the CQD-LD was red-shifted by 0.032 μm with increasing cavity length from 0.5 to 0.75 mm, the lasing emission of the SEQD-LD was red-shifted only by 0.012 μm with increasing cavity length from 0.5 to 1.5 mm. From these results, the gain of the QDLDs was enhanced by increasing the height of the QDs due to the enhancement in the confinement of the carrier wave-functions.