Significant progress has been made in the advancement of light-emitting devices in both the blue and the red parts of the emission spectrum. However, the quantum efficiency of green light-emitting diodes is still significantly lower as compared to blue- and red-emitting devices. This efficiency lag is commonly known as the “green gap” in the solid-state lighting industry. The efficiency issues in the green emission spectrum restrain further advancement in solid-state lighting. A combination of efficient blue, green, and red light-emitting devices is a promising solution toward efficient white light-emitting diodes. Despite the efficiency gap in the green emission, the lighting industry continues to produce relatively efficient white light-emitting diodes using down-conversion phosphors. However, the fruits of the solid-state white lighting could be fully achieved through color-mixing approaches rather through phosphor-based conversion. Therefore, to produce efficient green light-emitting diodes, their inherent issues such as the density of different types of defects and internal electric field should be reduced. In this study, we review various challenges and prospects of green light-emitting diodes. Broadly, the first part of this review explains the complex factors that degrade the performance of InGaN/GaN multiquantum well green light-emitting diodes, whereas the second part focuses on different strategies to enhance the internal quantum efficiency of green light-emitting diodes.

The optoelectronic properties of semiconducting aluminum gallium nitride (AlGaN)-based ultraviolet-B (UVB) light-emitting diodes (LEDs) are crucial for real-world medical applications such as cancer therapy and immunotherapy. However, the performance of AlGaN-based UVB LED devices is still poor due to the low hole injection efficiency. Therefore, we have numerically investigated the performance of AlGaN-based UVB LEDs for the suppression of efficiency droop as well as for the enhancement of hole injection in the multiquantum wells (MQWs). The influence of the undoped (ud)-AlGaN final quantum barrier (FQB), as well as the Mg-doped multiquantum barrier electron blocking layer (p-MQB EBL), on the efficiency droop has been focused on specifically. To evaluate the performance of the proposed device, we have compared its internal quantum efficiency (IQE), carrier concentration, energy band diagram, and radiative recombination rate with the conventional device structure. Furthermore, the influence of Al composition in the Al-graded p-AlGaN hole source layer (HSL) on the operating voltages of the proposed UVB LEDs was considered. The simulation results suggest that our proposed structure has a high peak efficiency and much lower efficiency droop as compared to the reference structure (conventional). Ultimately, the radiative recombination rate in the MQWs of the proposed UVB LED-N structure has increased up to ∼73%, which is attributed to the enhanced level of electron and hole concentrations by ∼64% and 13%, respectively, in the active region. Finally, a high efficiency droop of up to ∼42% in RLED has been successfully suppressed, to ∼7%, by using the optimized ud-AlGaN FQB and the p-MQB EBL, as well as introducing Al-graded p-AlGaN HSL in the proposed UVB LED-N structure.

With the advancement in technology of efficient and high-quality lighting, white light-emitting diodes (WLEDs) are gradually gaining ground with their ever-increasing high efficiency, energy density excitation, high device stability, and high output power. In this review, various technological approaches that are used to produce white light are presented. The progress made in improving the efficiency of white LEDs, using different phosphors along with a blue LED chip, is discussed. Phosphor-based approach is better and efficient in comparison to other approaches to generate white light. Using different phosphors, the improvement in luminous efficacy of white LEDs is reviewed. This review may serve as a roadmap for easily-fabricated, low-cost, and a longer lifespan white light-emitting diodes for indoor and outdoor applications.

AGaN-based 222 nm-band Far-ultraviolet-C (Far-UVC) light-emitting-diodes (LEDs) offer a promising technology for the disinfection of surface, air, water, food and airborne disease transmission in occupied spaces, including COVID-19 (SARS-CoV-2) and other viral diseases, when it is meticulously designed, engineered, and applied.