Research Progress of AlGaN-Based Deep Ultraviolet Light-Emitting Diodes

254 nm Ultraviolet C Light Emitting Diode (LED) Radiation Enhances Wound Healing in a Rat Model of Full-Thickness Skin Defects

SIGNIFICANCE

254 nm short wave ultraviolet (UVC) emitted by low-pressure mercury lamp is effective in the treatment of skin wounds. With the emergence of deep ultraviolet light-emitting diodes (LED), it is expected to significantly expand the clinical indications of UVC. However, whether 254 nm UVC generated by LED light source can promote skin wound healing has not been reported.

AIM

To clarify the effect of 254 nm UVC-LED light source on promoting skin wound healing and explore the mechanism of UVC-LED promoting wound healing.

APPROACH

The full-thickness wound model of rat back skin was constructed, and the skin wounds of rats were treated with low-pressure mercury lamp and 254 nm UVC-LED equipment respectively. The curative effect of UVC-LED was determined by wound healing rate and histopathological changes. The expression of transforming growth factor-alpha (TGF-α), epidermal growth factor receptor (EGFR), cluster of differentiation 31 (CD31), cluster of differentiation 68 (CD68), vascular endothelial growth factor (VEGF) and the mRNA content of TGF-α, EGFR, tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and VEGF were detected to clarify the mechanism of UVC-LED promoting wound healing.

RESULTS

Histopathology showed that both low-pressure mercury lamp and UVC-LED irradiation could promote skin wound healing, reduce the degree of inflammatory response, and promote angiogenesis. UVC-LED could better promote collagen fiber proliferation. UVC-LED promotes the expression of key cytokines in wound re-epithelialization by increasing the levels of TGF-α and EGFR, dynamically regulates wound healing by bidirectionally regulating the expression of inflammatory factors TNF-α and IL-6, promotes wound angiogenesis by increasing the levels of CD31 and VEGF, and reduces and regulates inflammation by increasing the number of macrophages by increasing CD68.

CONCLUSIONS

254 nm UVC-LED can significantly promote skin wound healing in rats and play a role by regulating tissue regeneration cytokines, inflammatory factors and angiogenesis mechanisms.

Performance Study of Ultraviolet AlGaN/GaN Light-Emitting Diodes Based on Superlattice Tunneling Junction

In this study, we aim to enhance the internal quantum efficiency (IQE) of AlGaN-based ultraviolet (UV) light-emitting diodes (LEDs) by using the short-period AlGaN/GaN superlattice as a tunnel junction (TJ) to construct polarized structures. We analyze in detail the effect of this polarized TJ on the carrier injection efficiency and investigate the increase in hole and electron density caused by the formation of 2D hole gas (2DHG) and 2D electron gas (2DEG) in the superlattice structure. In addition, a dielectric layer is introduced to evaluate the effect of stress changes on the tunneling probability and current spread in TJ. At a current of 140 mA, this method demonstrates effective current expansion. Our results not only improve the performance of UV LEDs but also provide an important theoretical and experimental basis for future research on UV LEDs based on superlattice TJ. In addition, our study also highlights the key role of group III nitride materials in achieving efficient UV luminescence, and the polarization characteristics and band structure of these materials are critical for optimizing carrier injection and recombination processes.

A critical review of ultra-violet light emitting diodes as a one water disinfection technology

UV light emitting diode (LED) disinfection technologies have advanced over the last decade and expanded the design space for applications in point of use, industrial, and now full-scale water treatment. This literature review examines the progression of UV LED technologies from 2007 to 2023 using key features such as total optical power, price, and wall-plug efficiency. The review found that optical power is increasing while the price per Watt is decreasing; however, the wall plug energy (WPE) is slowly improving over the last decade. These factors govern the feasibility of many UV LEDs applications and establish the current state of the art for these technologies. An analysis of inactivation rate constants for low-pressure, medium-pressure, and UV LED sources was undertaken and provides a comprehensive view of how current UV LED technologies compare to traditional technologies. This comparison found that UV LEDs perform comparably vs conventional UV technologies when disinfecting bacteria and viruses. Furthermore, comparison of reported reduction equivalent fluences for UV LED flow-through reactors at the bench-, pilot-, and full-scale were explored in this review, and it was found that LED treatment is becoming more effective at handling increased flowrates and has been proven to work at full-scale. UV LEDs do however require additional research into the impacts of water matrices at different wavelengths and the impact that each available LED wavelength has on disinfection. Overall, this work provides a broad assessment of UV disinfection technologies and serves as a state-of-the-art reference document for those who are interested in understanding this rapidly developing technology.

Enhanced light extraction efficiency for the inclined-sidewall-shaped AlGaN-based DUV LED by using an omni-directional reflector with a thin hybrid dielectric layer

In this Letter, an omni-directional reflector (ODR) with a thin hybrid dielectric layer (hybrid-ODR) is proposed to enhance the light extraction efficiency (LEE) for inclined-sidewall-shaped AlGaN-based deep ultraviolet light-emitting diode (DUV LED) by inserting a thin diamond with high refraction index into a conventional Al/Al2O3-based ODR. The three-dimensional finite-difference time-domain (3D FDTD) simulation results show that the LEE of TM-polarized light for the DUV LED with hybrid-ODR is enhanced by 18.5% compared with Al/Al2O3-based ODR. It is because the diamond can transform the evanescent wave in Al2O3 into the propagating light wave in diamond, thereby preventing effective excitation of the surface plasmon polariton (SPP) on the surface of the metal Al. Moreover, the Brewster's angle effect causes the TM-polarized light in diamond to propagate effectively into AlGaN. Furthermore, decreasing the total thickness of the dielectric layer also improves the scattering effect of the inclined sidewall. However, the utilization of hybrid-ODR results in a slight reduction in the LEE for transverse electric (TE) polarized light because the light is confined to the diamond layer and eventually absorbed by the metal Al.

Optical and Electrical Properties of AlxGa1-xN/GaN Epilayers Modulated by Aluminum Content

AlGaN-based LEDs are promising for many applications in deep ultraviolet fields, especially for water-purification projects, air sterilization, fluorescence sensing, etc. However, in order to realize these potentials, it is critical to understand the factors that influence the optical and electrical properties of the device. In this work, AlxGa1-xN (x = 0.24, 0.34, 0.47) epilayers grown on c-plane patterned sapphire substrate with GaN template by the metal organic chemical vapor deposition (MOCVD). It is demonstrated that the increase of the aluminum content leads to the deterioration of the surface morphology and crystal quality of the AlGaN epitaxial layer. The dislocation densities of AlxGa1-xN epilayers were determined from symmetric and asymmetric planes of the ω-scan rocking curve and the minimum value is 1.01 × 109 cm-2. The (101¯5) plane reciprocal space mapping was employed to measure the in-plane strain of the AlxGa1-xN layers grown on GaN. The surface barrier heights of the AlxGa1-xN samples derived from XPS are 1.57, 1.65, and 1.75 eV, respectively. The results of the bandgap obtained by PL spectroscopy are in good accordance with those of XRD. The Hall mobility and sheet electron concentration of the samples are successfully determined by preparing simple indium sphere electrodes.

Impacts of p-GaN layer thickness on the photoelectric and thermal performance of AlGaN-based deep-UV LEDs

The effects of different p-GaN layer thickness on the photoelectric and thermal properties of AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) were investigated. The results revealed that appropriate thinning of the p-GaN layer enhances the photoelectric performance and thermal stability of DUV-LEDs, reducing current crowding effects that affect the external quantum efficiency and chip heat dissipation. The ABC + f(n) model was used to analyse the EQE, which helped in identifying the different physical mechanisms for DUV-LEDs with different p-GaN layer thickness. Moreover, the finite difference time domain simulation results revealed that the light-extraction efficiency of the DUV-LEDs exhibits a trend similar to that of damped vibration as the thickness of the p-GaN layer increases. The AlGaN-based DUV-LED with a p-GaN layer thickness of 20 nm exhibited the best photoelectric characteristics and thermal stability.