High-gain 11-layer InAs/GaAs quantum dot lasers with 25-nm GaAs spacers

Stacking multiple InAs quantum dot (QD) layers is essential to achieve sufficient modal gain in InAs/GaAs QD lasers, yet the resulting strain accumulation necessitates thick spacers, degrading carrier transport and optical confinement. Here, we reduce the spacer thickness from 37.5 to 25 nm by optimizing the spacer growth temperature, thereby preserving optical and structural quality, as confirmed by photoluminescence and cross-sectional transmission electron microscopy. 11-layer InAs/GaAs QD lasers with thin spacers exhibit a low threshold current density of 178 A/cm 2 at room temperature and sustain lasing up to 180°C, demonstrating that thinner spacers support robust thermal stability. Leveraging the increased volumetric dot density enabled by thinning spacers, ground-state lasing is observed in an ultra-short-cavity (200-μm) device, implying an estimated threshold modal gain above 60 cm −1 . These results establish a practical route to high-gain, high-speed QD lasers for data-communication applications.