Fig. 1. Structural diagrams. (a)Tunnel-coupled quantum well－dot composite structure^[29]; (b) quantum dots-in-a-well composite structure^[23]

Fig. 2. Atomic force microscope photographs of InAs quantum dots in tunnel-coupled well－dot composite structures with different GaAs barrier layer thicknesses^[28]. (a) 5 nm; (b) 0.5 nm

Fig. 3. σ^＋ and σ^－ polarized PL spectra at 20 K and corresponding CPDs for well－dot tunnel-coupled nanostructure with different GaAs barrier layer thicknesses^[37]. (a) 6 nm ; (b) 20 nm

Fig. 4. Effects of barrier layer thickness on optical properties of well－dot tunnel-coupled nanostructure. (a) Spin-injection time and CPD of PL spectrum versus barrier layer thickness^[37]; (b) normalized quantum dot PLE intensity under resonant excitation of quantum well versus GaAs barrier layer thickness^[38]

Fig. 5. Polarized-gain characteristics of well－dot tunnel-coupled optical amplifier^[39]. Polarized gain spectra for (a) well－dot tunnel-coupled optical amplifier and (b) tensile-strained quantum well optical amplifier; (c) percentage of TE polarized gain contributed by quantum dots

Fig. 6. Linewidth enhancement factor of tunnel-coupled well－dot laser^[40]

Fig. 7. Atomic force microscopy photographs of InAs quantum dots in different well layers^[44]. (a) In_0.06Ga_0.94As；(b) In_0.12Ga_0.88As ; (c) In_0.15Ga_0.85As

Fig. 8. Atomic force microscopy photographs of quantum dots or dashes in dots-in-a-well structure^[46]. (a) Grown on GaAs; (b) grown on InP

Fig. 9. PL spectra of dots-in-a-well structure under different temperatures^[43]. (a) InAs quantum dots; (b) surrounding InGaAs quantum well with energy band diagram of InAs quantum dots and surrounding InGaAs quantum well shown in inset

Fig. 10. Effect of indium content in InGaAs well on optical properties of InAs/InGaAs dots-in-a-well structure^[44]. (a) PL spectra of InAs/InGaAs dots-in-a-well structures under room temperature; (b) full width at half-maximum, (c) peak wavelength, and (d) relative PL intensity of InAs/InGaAs dots-in-a-well structure at ground state under room temperature

Fig. 11. Positive effects of dots-in-a-well structure on performances of optoelectronic devices. (a) Temperature dependence of threshold current density of 5-layer 1.3-μm InAs/GaAs quantum dot laser with uncoated facets under continuous wave operation and laser spectra at room temperature (RT) and 100 ℃ are shown in insets^[44]; (b) current gains (triangles) and quantum efficiencies (squares) of InAs/In_0.15Ga_0.85As dots-in-a-well (DWELL) sample and confinement enhanced dots-in-a-well (CE-DWELL) sample at different voltages at 77 K^[53]

Fig. 12. Influence of temperature on epitaxial growth of highly-strained InGaAs/GaAs quantum well^[57]. (a) Maximum indium content available in well at different growth temperatures; (b) PL intensities of highly-strained InGaAs/GaAs well grown in 530－570 ℃

Fig. 13. Structural characteristics of InGaAs self-assembled well－dot composite quantum structure^[31]. (a) Schematic of indium-rich cluster effect and InGaAs self-assembled well－dot composite quantum structure; (b) atomic force microscopy photograph of indium-rich clusters

Fig. 14. PL spectrum characteristics of InGaAs self-assembled well－dot composite quantum structure^[32]. (a) TE- and TM-polarized PL spectra under different injection energies; (b) Gaussian fitting of TE-polarized PL spectrum

Fig. 15. Dual-wavelength lasing characteristics of InGaAs self-assembled well－dot composite quantum structure^[32]. (a) Lattice matching, band structure, and wave function of InGaAs indium-rich cluster self-assembled well－dot composite quantum structure; (b) TE-polarized dual-wavelength lasing at 970 nm and 980 nm under different injection energies; (c) dual-wavelength lasing under different temperatures; (d) thermal red-drift of lasing dual-wavelengths

Fig. 16. Optical characteristics of InGaAs self-assembled well－dot composite quantum structure. Experimental (a) TE and (b) TM spontaneous emission spectra under different injection carrier densities^[34]; experimental (c) TE and (d) TM absorption spectra^[36]; (e) polarized gain spectra under different injection carrier densities from experiment^[31]; (f) theoretical gain spectrum of In_0.17Ga_0.83As/GaAs/GaAsP standard single quantum well with thickness of 10 nm under injection carrier density of 9.6×10¹⁷ cm^－3[31]

Fig. 17. Output power characteristics of various tunable semiconductor lasers. (a)(b) Output spectral powers of different tunable semiconductor lasers^[31]; (c) some tuning spectra within 33 nm tuning range^[62]; (d) output powers under different input currents^[64]; (e) TE-polarized spectral power output from InGaAs self-assembled well－dot composite structure^[31]; (f) TE-polarized differential spectral power^[31]

Fig. 18. Performance advantages of InGaAs self-assembled composite quantum structure in polarization-independent semiconductor optical amplifier devices and tunable dual-wavelength lasers^[35]. (a) Polarized light amplification output intensities of InGaAs indium-rich cluster self-assembled composite quantum structure under different injection carrier densities; (b) amplification intensity difference between TE- and TM-polarized light; (c) TE-polarized PL spectra; (d) tunable dual-wavelength laser output