Nitride-Based Quantum Structures in Optoelectronics-A Survey of Colors.

Modern optoelectronic devices, such as light-emitting diodes (LEDs) and laser diodes, rely on nitride-based (GaN, AlN, and InN) quantum structures, which underpin current technologies. These systems enable emission across a broad spectral range from ultraviolet to infrared with properties tunable via composition, strain, and quantum confinement. This review summarizes progress in the performance of nitride emitters across the full spectral range, with particular emphasis on the evolution of external quantum efficiency (EQE). Nitride emitters are primarily based on InGaN quantum wells, while AlGaN quantum wells are used for ultraviolet operation. Device performance is governed by the intrinsic properties of these structures, which also determine key physical challenges across different wavelength regions. Blue InGaN LEDs achieve the highest efficiencies (~60-80% EQE), while green devices are limited to ~20-35% due to the "green gap," with further reduction (~5-20%) toward longer wavelengths. In the ultraviolet, AlGaN-based emitters exhibit lower performance due to material and structural challenges, although steady progress is being made. Special attention is given to mechanisms limiting EQE, including efficiency droop in the green-red region, and ongoing efforts to mitigate these effects. Finally, perspectives for future applications of [ are outlined.