UV Light Emitting Diodes; Their Applications and Benefits (original) (raw)
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The emergence and prospects of deep-ultraviolet light-emitting diode technologies
Nature Photonics, 2019
undamental breakthroughs in GaN material technology in the late 1980s were followed less than five years later by the first practical demonstration of candela-class blue light-emitting diodes (LEDs) 1,2,3. Shortly after, GaN-based white LEDs were being manufactured on an industrial scale and today white LEDs have evolved into the most efficient man-made light source 4 , transforming all areas of illumination. Nevertheless, until now, only a narrow sliver of the emission spectrum of group III nitride materials has been utilized. By alloying GaN with AlN materials, the emission of AlGaN-based LEDs can be tuned to cover almost the entire ultraviolet (UV) spectral range (210-400 nm). Depending on their emission wavelength, UV LED devices can support a wide range of applications, including water purification, UV curing, environmental sensing, plant growth lighting and phototherapy 5. Although the performance of UV LEDs is not yet on par with their visible wavelength counterparts, there is no doubt that this new technology offers tremendous potential. Applications of UV emitters Depending on the specific wavelength, the effects of UV light on materials and organisms will vary greatly. Therefore, UV radiation is separated into three spectral bands: UVA (400 nm-320 nm), UVB (320 nm-280 nm) and UVC (280 nm-100 nm). In the following we will discuss key applications as well as photobiological and photochemical effects in these wavelength bands. NAture PHotoNIcs Key performance parameters. Here we compare UVC LEDs and blue LEDs. For many applications, the key performance parameters of UV LEDs are the optical output power P out , the EQE and the wall-plug efficiency (WPE). As shown in Box 1, the WPE can be calculated from the ratio of the optical output power P out and the electric input power and is determined by four key parameters that describe the efficiency of the different processes within the LED: the injection efficiency η inj , the radiative efficiency η rad , the electrical efficiency η elect and the light extraction efficiency (LEE), η extr. The injection efficiency η inj characterizes the charge transport and confinement of electrons and holes in the AlGaN quantum wells, while η rad corresponds to the ratio of UV photon generation by radiative recombination versus competing non-radiative processes. Often, the product of η inj and η rad is referred to as the internal quantum efficiency (IQE), η IQE. The electrical efficiency η elect represents voltage losses due to electrical resistances of the metal contacts and the semiconductor layers, and, finally, the LEE, η extr , describes the probability that a UV photon escapes the semiconductor chip. Accordingly, the EQE can be described as the product of η inj , η rad and η extr , whereas the WPE takes η elect into account as well.
Ultraviolet light emitting diodes
Lithuanian Journal of Physics, 2011
The paper presents a review of the recent development of III-nitride based deep UV light emitting diodes (lEDs). Main applications of the deep UV lEDs are introduced. Review of material issues is focused on the lattice mismatch between the substrate and the active layer and at heterojunctions in multiple quantum well structures forming the active layer, the localization of nonequilibrium carriers, the material properties limiting the internal quantum efficiency, and the effect of efficiency droop at high density of nonequilibrium carriers. AlGaN is currently the semiconductor of choice for development of deep UV lEDs, so this material is the most discussed one in this review, though some information on AlInGaN is also provided.
UV LED Technology : The Times They are A-Changin ’
2018
Introduction UV photonics, photoreaction and photoreactor systems are the key elements of many industries. Recent advances in a new UV source, the ultraviolet light emitting diode (UV LED), create the opportunity for the development of novel UV-based technologies and devices. In fact, UV LEDs could potentially transform the UV-based industry by not only advancing the design and application of current UV modules, but also enabling the creation of entirely new products and markets.
AlGaN-based ultraviolet light-emitting diodes grown on AlN epilayers
Applied Physics Letters, 2004
AlGaN-based deep-ultraviolet light-emitting diode (LED) structures, which radiate light at 305 and 290nm, have been grown on sapphire substrates using an AlN epilayer template. The fabricated devices have a circular geometry to enhance current spreading and light extraction. Circular UV LEDs of different sizes have been characterized. It was found that smaller disk LEDs had higher saturation optical power densities but lower optical powers than the larger devices. This trade-off between power and power density is a result of a compromise between electrical and thermal resistance, as well as the current crowding effect (which is due to the low electrical conductivity of high aluminum composition n- and p-AlGaN layers). Disk UV LEDs should thus have a moderate size to best utilize both total optical power and power density. For 0.85mm×0.85mm interdigitated LEDs, a saturation optical power of 2.9mW (1.8mW) at 305nm (290nm) was also obtained under dc operation.
Growth and design of deep-UV (240–290nm) light emitting diodes using AlGaN alloys
Journal of Crystal Growth, 2004
Solid-state light sources emitting at wavelengths less than 300 nm would enable technological advances in many areas such as fluorescence-based biological agent detection, non-line-of-sight communications, water purification, and industrial processing including ink drying and epoxy curing. In this paper, we present our recent progress in the development of LEDs with emission between 237 and 297 nm.We will discuss growth and design issues of deep-UV LEDs, including transport in Si-doped AlGaN layers. The LEDs are designed for bottom emission so that improved heat sinking and light extraction can be achieved by flip chipping. To date, we have demonstrated 2.25 mW of output power at 295 nm from 1 mm  1 mm LEDs operated at 500 mA. Shorter wavelength LEDs emitting at 276 nm have achieved an output power of 1.3 mW at 400 mA. The heterostructure designs that we have employed have suppressed deep level emission to intensities that are up to 330  lower than the primary quantum well emission.
The epitaxial growth of transparent p-AlGaN-based ultraviolet-A (UVA), lightemitting diodes (LEDs) may solve the problems of UVA light absorption through the GaN buffers and p-GaN contact layers at (326–341 nm)-band emission, respectively. Herein, first, an idea of conventional n-AlGaN buffer layer (BL) and n-AlGaN electron source layer (ESL) for the suppression of threading dislocation density (TDD) and enhancement of internal quantum efficiency (IQE) of UVA emitters, using lowpressure metalorganic vapor-phase epitaxy (LP-MOVPE) is attempted. As a result, the total-TDDs is reduced from 3 109 cm2 to 1 109 cm2 in the n-AlGaN ESL of a 326 nm-band UVA multiquantum-wells (MQWs), and IQE is also improved from 30% to 52% at room temperature (RT). Second, an idea of Si-doped n-AlGaN Superlattices (SLs)-based BL, using LP-MOVPE is challenged. Subsequently, a record IQE of 56% at RT and high crystal quality in 341 nm-band UVA MQWs are observed. Finally, using a well thickness 2 nm in SLs-based UVA MQWs, the light power and external quantum efficiency (EQE), respectively, are remarkably enhanced from 3.5 mW and 0.5% to 7.5 mW and 1.4% on wafer in 341 nm-Band UVA LED. The perspective for the improvements of UVA emitter’s performances is also discussed.
Advances in group III-nitride-based deep UV light-emitting diode technology
Semiconductor Science and Technology, 2011
The field of AlGaInN ultraviolet UV light-emitting diodes (LEDs) is reviewed, with a summary of the state-of-the-art in device performance and enumeration of applications. Performance-limiting factors for high-efficiency UV LEDs are identified and recent advances in the development of deep UV emitters are presented.
Crystal growth of eco-friendly, ultrawide bandgap aluminium gallium nitride (AlGaN) semiconductorbased ultraviolet-B (UVB) light-emitting diodes (LEDs) hold the potential to replace toxic mercurybased ultraviolet lamps. One of the major drawbacks in the utilisation of AlGaN-based UVB LEDs is their low efficiency of about 6.5%. The study investigates the influence of Al-graded p-type multiquantum-barrier electron-blocking-layer (Al-grad p-MQB EBL) and Al-graded p-AlGaN hole source layer (HSL) on the generation and injection of 3D holes in the active region. Using the new UVB LED design, a significant improvement in the experimental efficiency and light output power of about 8.2% and 36 mW is noticed. This is accomplished by the transparent nature of Al-graded Mg-doped p-AlGaN HSL for 3D holes generation and p-MQB EBL structure for holes transport toward multi-quantumwells via intra-band tunnelling. Based on both the numerical and experimental studies, the influence of sub-nanometre scale Ni film deposited underneath the 200 nm-thick Al-film p-electrode on the optical reflectance in UVB LED is investigated. A remarkable improvement in the efficiency of up to 9.6% and light output power of 40 mW, even in the absence of standard package, flip-chip, and resinlike lenses, is achieved on bare-wafer under continuous-wave operation at room temperature. The enhanced performance is attributed to the use of Al-graded p-MQB EBL coupled with softly polarised p-AlGaN HSL and the highly reflective 0.4 nm-thick Ni and 200 nm-thick Al p-electrode in the UVB LED. This research study provides a new avenue to improve the performance of high-power p-AlGaNbased UVB LEDs and other optoelectronic devices in III-V semiconductors. Aluminium gallium nitride (AlGaN) based semiconductors are one of the most promising candidates for the fabrication of smart, eco-friendly ultraviolet-B (UVB) and deep ultraviolet (DUV) emitters that would meet the requirements of the Minamata Convention of 2020 1 and the 17 sustainable development goals (17 SDGs) of the UN 2. Both Minamata Convention and 17 SDGs, with an aim to mitigate climate change, strive to eliminate the use of mercury vapour ultraviolet (UV) lamps in order to reduce the associated issue of CO 2 emission 1,2. Earlier studies show the use of UVB light of 310 nm narrow-band in cancer immunotherapy 3,4 , in vulgaris treatment 4,5 and for plant growth with enriched phytochemicals 4,6. Similarly, UVB light of 294 nm-band is used in the prevention of plant diseases 7,8 and in the production of vitamin D 3 in the human body 8,9. Safe and smart DUV and ultraviolet-C (UVC) light sources are extremely important as a disinfectant for air, water, food and surfaces that can help to mitigate the risk of infection due to close contact with the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), and other similar viruses 10-15. Currently, toxic mercury-based UV light sources are frequently used for many industrial, agricultural and medical applications 4,8. To replace the toxic mercury UV light sources with eco-friendly alternatives, we need to explore safe and green materials for crystal growth and device fabrication of UV light sources. Among such favourable and affordable materials, crystal growth of AlGaN compounds on AlN templates is currently being investigated for next-generation UVB light-emitting diodes (LEDs) and laser diodes (LD) 4,8,12. Environmentfriendly AlGaN-based UVB LEDs with monochromatic light emission are inevitable for both medical and agricultural applications 1-9. The selection of green AlGaN material has many other promising features, such as