Fig. 1. Epitaxial structure and material characterization of the quantum dot laser. (a) Epitaxial structure; (b) scanning transmission electron microscopy (STEM) image; (c) photoluminescence (PL) spectrum of the quantum dots, where the inset is atomic force microscopy (AFM) image of the quantum dots measured within an area of 1 μm×1 μm

Fig. 2. Cross-sectional schematic of the laser and equivalent circuit. (a) Schematic of the conventional cathode structure; (b) equivalent circuit of the conventional cathode structure; (c) schematic of the symmetrical cathode structure; (d) equivalent circuit of the symmetrical cathode structure

Fig. 3. Structural schematic of the chip. (a)(b) Plan-view image of the chip with various scale bars; (c) plan-view SEM image of the chip; (d) cross-sectional SEM image of the chip; (e) three-dimensional structural schematic of the chip

Fig. 4. Characteristics of the quantum dot laser. (a) Light-current-voltage characteristics; (b) spectral characteristics

Fig. 5. Performance comparison of the lasers with different structures. (a) Current-voltage characteristics; (b) differential resistance; (c) lasing wavelength at different currents; (d) temperature characteristics

Fig. 6. Performance comparison of the lasers with different structures. (a) Wall-plug-efficiency (WPE); (b) slope efficiency and maximum single-side output power