C-band InAs/InP quantum dots: alternative growth versus indium-flush for self-assembled growth

1550 nm InAs/InP quantum dot (QD) lasers are critical for C-band optical communication. To realise narrow photo-luminescence linewidth emission in this wavelength range, the indium flush (IF) technique for self-assembled QDs and the alternative growth (AG) technique have been developed, enabling wavelength tuning and control of dot uniformity. This work investigates the stacking effect on nanostructures grown by these two methods by comparing five-stacked AG and IF nanostructures with identical spacer thickness. Structural and optical characterisations were performed using scanning transmission electron microscopy, atomic force microscopy, and photoluminescence measurements. The IF approach produces truncated, height-controlled QDs with reduced strain accumulation across stacked layers. In contrast, AG samples display quantum well-like morphology with sharp interfaces and no observable dislocations, but fail to consistently produce distinct QD nanostructures. These results suggest that IF provides a more reliable optimisation strategy for achieving C-band QDs within the framework of self-assembled growth, whereas AG requires further optimisation for use in InP-based systems.