Abstract
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.
Highlights
Introduction toexternalDevices management issues.The bandgap of GaN and AlN are 3.4 and 6.2 eV, respectively
The low light extraction efficiency (LEE) arises from large amounts of transverse magnetic (TM)-polarized light [45], the highly absorptive p-GaN ohmic contact layer [46], the total internal reflection (TIR), and Fresnel loss caused by the large refractive index contrast between AlGaN and air [47]
Many mechanisms have been identified, all of them involve et al inferred that efficiency droop in AlGaN quantum-we carriers bypassing the active region through a number of dislocation paths; tures are caused by an internal carrier loss process, analogous to what these carriers do not participate in the process of band-edge radiation recombination
Summary
Since the invention of the first nitride light-emitting diode (LED) by Pankove et al. With the rising international awareness of environmental protection, the International Minamata Convention in 2013 pushed the development of the high efficiency DUV LED, which is an interesting replacement for low-pressure mercury lamps. Another feature of DUV-LEDs is that the light-emitting band can be modified through the adjustment of the epitaxial structure. The wavelength of UV radiation is between the wavelengths of light and X-rays, covering 100 to 400 nm (12.4–3.1 eV) This wavelength range can be further subdivided into four bands, namely, long-wave ultraviolet UVA (315–400 nm), medium-wave ultraviolet UVB (280–315 nm), short-wave ultraviolet UVC (200–280 nm), and vacuum ultraviolet (100–200 nm). The future potential of UVC LEDs and the key parameters that affect the performance of UV emitters will be discussed
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