High-quality epitaxial layers are directly related to internal quantum efficiency. The methods used to design such epitaxial layers are reviewed in this article. The ultraviolet C (UVC) light-emitting diode (LED) epitaxial layer structure exhibits electron leakage; therefore, many research groups have proposed the design of blocking layers and carrier transportation to generate high electron–hole recombination rates. This also aids in increasing the internal quantum efficiency. The cap layer, p-GaN, exhibits high absorption in deep UV radiation; thus, a small thickness is usually chosen. Flip chip design is more popular for such devices in the UV band, and the main factors for consideration are light extraction and heat transportation. However, the choice of encapsulation materials is important, because unsuitable encapsulation materials will be degraded by ultraviolet light irradiation. A suitable package design can account for light extraction and heat transportation. Finally, an atomic layer deposition Al2O3 film has been proposed as a mesa passivation layer. It can provide a low reverse current leakage. Moreover, it can help increase the quantum efficiency, enhance the moisture resistance, and improve reliability. UVC LED applications can be used in sterilization, water purification, air purification, and medical and military fields.
An all-inorganic cesium lead halide perovskite is particularly attractive as an alternative to next-generation display with high quantum yields and color purity for lasers, light-emitting diode (LED) devices, and single-photon sources. Unfortunately, the vulnerable properties induced by moisture limit the hopeful application of CsPbBr 3 , especially for high-performance devices. In this work, a monoclinic CsPbBr 3 derived from hexagonal Cs 4 PbBr 6 with the assistance of water was presented. Moisture-induced decomposition and phase segregation were recorded at the atomic level in detail. Moreover, the obtained monoclinic CsPbBr 3 nanocrystals (NCs) are demonstrated to be decorated with hydroxyl (OH) ligands, which provide a valid approach for the resistance to further moisture attack. The highly stable CsPbBr 3 NCs could preserve the photoluminescence intensity above 97% even after the sample was deposited in water for 30 days. Furthermore, a white LED constructed with the as-prepared green-emitting CsPbBr 3 and a commercial N628 red phosphor demonstrate the monoclinic CsPbBr 3 as a compelling material platform well suited to applications as next-generation light emitters.
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