Beyond 53% internal quantum efficiency in a AlGaN quantum well at 326  nm UVA emission and single-peak operation of UVA LED: publisher’s note

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The epitaxial growth of transparent p‐AlGaN‐based ultraviolet‐A (UVA), light‐emitting 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 low‐pressure metalorganic vapor‐phase epitaxy (LP‐MOVPE) is attempted. As a result, the total‐TDDs is reduced from ≈ 3 × 109 cm−2 to ≈ 1 × 109 cm−2 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.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Highly Transparent p‐AlGaN‐Based (326–341 nm)‐Band Ultraviolet‐A Light‐Emitting Diodes on AlN Templates: Recent Advances and Perspectives

Khan

Maeda

et al. 2022

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Improved Performance of InGaN/AlGaN Multiple‐Quantum‐Well Near‐UV Light‐Emitting Diodes with Convex Barriers and Staggered Wells

Cai

Lin

et al. 2022

The physical mechanism of improving the photoelectric performance of InGaN/AlGaN‐based near UV light‐emitting diode (LED) with convex quantum barrier and staggered quantum well (QW) is studied by numerical simulation. The simulation results indicate that the voltage–current characteristics of the LED structure with convex quantum barrier and staggered QW are effectively improved compared with the traditional multiple quantum well (MQW) structure, and its electroluminescence (EL) intensity and light output power are significantly improved. The main physical mechanisms are: on the one hand, the convex quantum barrier with a lower average Al component can reduce the polarization electric field at the interface between the quantum barrier and QW as well as the effective potential barrier of holes, improve the spatial separation of electron and hole wave functions, promote the injection efficiency of carriers, and improve the uniformity of carrier distribution in the MQWs active region; On the other hand, staggered QWs can provide stronger carrier confinement effect and further increase the overlap of electron and hole wave functions, so as to improve the carrier radiative recombination efficiency; In a word, this work provides a valuable reference for obtaining high‐performance near‐ultraviolet LED.

Progress and Outlook of 10% Efficient AlGaN‐Based (290–310 nm) Band UVB LEDs

Khan,

Yamada,

Hirayama

2024

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Eco‐friendly aluminum gallium nitride (AlGaN) materials for the epitaxial growth of ultraviolet‐B (UVB) light emitting diodes (LEDs) on c‐Sapphire have attracted much attention due to their low fabrication cost and possibility of high external‐quantum efficiency (EQE) and light power. However, the long‐term low wall plugs efficiency (WPE) and light power remain a significant bottleneck impeding the commercialization of UVB LED modules. Our special growth techniques for 50% relaxed and 4µm‐thick AlGaN buffer layer (BL) are available to achieve a maximum internal‐quantum efficiency (IQE) surpassing 57% in 300 nm‐Band UVB LEDs. In this review paper, we describe the impact of special growth of thick AlGaN BL as well as n‐AlGaN electron injection layer (EIL) and their crystal quality on the (290‐310nm)‐Band LED’s performances, compared to the conventional n‐AlGaN/p‐GaN based UVB LEDs. The last 6 years have seen large improvements in the AlGaN‐based UVB LED, with efficiencies improved by over 10% at Riken. The main drivers have been improved electrical, optical design, better carriers confinement in the multi‐quantum wells (MQWs) of the UVB LEDs and the generation as well as transportation of hole toward the MQWs. Also, the influence of a thin “Valley” layer in p‐type multi‐quantum barrier electron‐blocking‐layer (p‐MQB EBL) on 2D hole generation and hole injection via intra‐band tunneling (HIT) was attempted. Briefly, these improvements at Riken in the development of high‐efficiency transparent UVB LEDs are including the modulation of Al compositions in the p‐AlGaN hole injection layer (HIL), fabrication methods in MOCVD, and p‐side contact materials including highly reflective p‐electrodes. Notably, we highlight the effects of undoped (ud)‐AlGaN final barrier (FB) of quantum‐well strategies against the electron blocking and promoting the hole tunneling and incorporation of the soft polarized Mg‐doped p‐type AlGaN HIL for better hole injection toward the MQWs to improve the performance of UVB LEDs. As a result, high hole concentration ∽ 2 × 1016 cm−3 in the Al‐graded p‐AlGaN HIL, where the hole‐trap level appeared to have been effectively suppressed by excimer laser annealing (ELA) treatment, and quite low resistivity of 24 Ω‐cm at room temperature (RT) was achieved. Optically, enhanced reflection from Ni/Mg or Ni/Al p‐electrode and improved light extraction within the transparent p‐AlGaN LED have had a large impact. In particular, the transparent AlGaN‐based 290‐310 nm UVB LED has improved significantly in recent years and is now almost approaching that of UVC LED (EQE ∽ 10%). Such new features have increased the efficiencies of transparent 310 nm and 290‐304 nm UVB LEDs, respectively, to a recently confirmed 4.7% and 9.6% with light powers of 29 mW and 40 mW on wafer, world record values of a mere 2 year ago. Finally, we give our perspectives to combine photonic, crystals and electrical constraints into practical architectures for AlGaN‐based UVB LEDs and also identify future research directions as well as potential applications of UVB LED modules technologies, such as those in immunotherapy (psoriasis, vitiligo), vulgaris treatment (310 nm), plant growth under UVB lightning (310 nm), the production of vitamin D3 in the human body (293‐304 nm), the production of phytochemicals in green leaves of vegetables (310 nm) and inactivation of SARS‐CoV‐2.This article is protected by copyright. All rights reserved.