Quantum dot lasers represent a significant advancement in semiconductor laser technology, offering superior performance metrics compared to conventional quantum well lasers. Their unique electronic density of states, derived from three-dimensional quantum confinement, enables lower threshold currents, enhanced temperature stability, and precise wavelength tunability. Three primary architectures dominate quantum dot laser designs: edge-emitting lasers, vertical-cavity surface-emitting lasers (VCSELs), and nanolasers. Material systems such as InAs/GaAs and metal-halide perovskites have emerged as leading candidates due to their exceptional optical and electronic properties.

Edge-emitting quantum dot lasers are the most mature among the three designs. They utilize a waveguide structure where light propagates parallel to the semiconductor substrate. The active region consists of multiple layers of self-assembled quantum dots, typically formed via the Stranski-Krastanov growth mode during molecular beam epitaxy. InAs quantum dots embedded in a GaAs matrix exhibit a broad gain spectrum due to inhomogeneous dot size distribution, which can be engineered to achieve lasing across the near-infrared range, particularly between 1.0 and 1.3 micrometers. The threshold current density for such devices can reach as low as 10 A/cm² at room temperature, a substantial improvement over quantum well lasers. Temperature stability is another critical advantage, with characteristic temperatures (T₀) exceeding 150 K in optimized structures, reducing the need for active cooling in high-temperature environments.

Vertical-cavity surface-emitting lasers (VCSELs) incorporating quantum dots benefit from their compact form factor and low power consumption. The distributed Bragg reflectors (DBRs) sandwiching the active region enable single-mode operation with narrow linewidths. InAs/GaAs quantum dot VCSELs exhibit threshold currents below 1 mA, making them ideal for high-density photonic integration. Wavelength tuning in these devices can be achieved through temperature or current modulation, with shifts of up to 0.1 nm/mA reported. The temperature insensitivity of quantum dots also translates to VCSELs, with minimal variation in output power across a broad operating range. Recent developments have extended emission wavelengths to 1.55 micrometers, aligning with telecommunications standards.

Nanolasers push the boundaries of miniaturization, leveraging quantum dots to achieve lasing at sub-wavelength scales. Plasmonic nanocavities and photonic crystal resonators enhance light-matter interaction, compensating for the reduced active volume. Room-temperature operation has been demonstrated in InAs/GaAs quantum dot nanolasers with cavity volumes below 0.1 cubic micrometers. These devices exhibit ultra-low threshold powers, often in the microwatt range, due to the high spontaneous emission coupling factor (β) approaching unity. Perovskite quantum dots, particularly cesium lead halide variants (CsPbX₃, X = Cl, Br, I), have recently entered this domain, offering solution-processability and tunable emission across the visible spectrum. Their high photoluminescence quantum yields (>90%) and large absorption coefficients make them promising for nanolaser applications.

Threshold reduction remains a central focus in quantum dot laser research. Techniques such as p-type modulation doping and tunnel injection have proven effective in suppressing non-radiative recombination and Auger processes. Modulation doping introduces excess holes into the quantum dot layers, improving carrier injection efficiency and reducing transparency current densities. Tunnel injection structures separate carrier transport and recombination regions, minimizing hot carrier effects. These approaches have yielded threshold current densities below 5 A/cm² in some edge-emitting designs.

Temperature stability in quantum dot lasers stems from the discrete energy levels and reduced carrier leakage. Unlike quantum wells, where thermal excitation leads to significant carrier redistribution, quantum dots localize carriers more effectively. This localization suppresses the temperature dependence of threshold current, enabling operation up to 100°C without significant degradation. InGaAs quantum dots with AlGaAs barriers demonstrate particularly robust thermal performance due to the large conduction band offset.

Wavelength tuning is achievable through several methods. Strain engineering during epitaxial growth allows precise control over quantum dot size and composition, shifting emission wavelengths. Post-growth techniques such as thermal annealing can further modify the emission profile. For perovskite quantum dots, halide composition directly dictates the bandgap, enabling continuous tuning from 400 to 800 nm. Mixed-halide compositions (e.g., CsPbBr₃₋ₓIₓ) provide additional flexibility, though phase segregation under illumination remains a challenge.

InAs/GaAs quantum dot lasers dominate near-infrared applications, with commercial deployment in optical communications and sensing. Their compatibility with existing III-V fabrication processes facilitates integration with photonic circuits. Perovskite quantum dot lasers, while less mature, offer distinct advantages in visible light applications, including displays and biomedical imaging. Their solution-processability enables low-cost manufacturing, though long-term stability under continuous operation requires further improvement.

Future developments will likely focus on improving material quality and device architectures. Reducing inhomogeneous broadening in quantum dot ensembles could narrow emission linewidths, benefiting wavelength-division multiplexing systems. Hybrid integration of III-V and perovskite quantum dots may unlock new functionalities, combining near-infrared and visible emission in a single platform. Advances in nanofabrication will further push the limits of nanolaser performance, potentially enabling on-chip optical interconnects with unprecedented energy efficiency.

The continued evolution of quantum dot lasers hinges on interdisciplinary collaboration between material scientists, device physicists, and engineers. By addressing remaining challenges in reproducibility, stability, and scalability, these lasers could redefine optoelectronic systems across telecommunications, computing, and sensing industries.