Optical gain analysis of MOCVD-grown InAs/InP quantum dot lasers

The optical gain characteristics of InAs/InP quantum dot (QD) laser structures grown on an InP (001) substrate has been investigated at room temperature, using the segmented contact stripe length method. Results show that increasing the QD stacking number to five layers enhances the peak net modal gain to 37.5 cm−1 at 3.6 kA/cm2 and increases differential gain, while the three-layer structures provide a lower peak net modal gain of 31.8 cm−1 at 3.6 kA/cm2 but a broader gain spectra at lower current densities due to a lower total density of states requiring fewer filled states for inversion. Furthermore, the choice of capping materials significantly influences QD formation; using an In0.35Ga0.65As capping layer maintains QD-like characteristics, whereas an In0.45Al0.3Ga0.25As capping layer induces a transition to less localized, QD-like structures with a higher peak net modal gain of 41.7 cm−1 at 3.6 kA/cm2.These results suggest that careful optimization of both stacking number and capping layer composition is essential to balance gain requirements for metal-organic chemical vapor deposition grown InAs/InP QD lasers.