Improving Light Extraction Efficiency of AlGaN-Based Deep Ultraviolet Light-Emitting Diodes by Combining Thinning p-AlGaN/p-GaN Layer With Ni/Au/Al High-Reflectivity Electrodes

Wang, Liubing; Xu, Fujun; Lang, Jing; Wang, Jiaming; Zhang, Lisheng; Guo, Xueqi; Chen, Ji; Kang, Xiaoning; Yang, Xuelin; Wang, Xinqiang; Qin, Zhixin; Ge, Weikun; Shen, Bo

doi:10.1109/jphot.2023.3250433

Cited by 10 publications

(3 citation statements)

References 31 publications

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“…[12,13] The lack of electrical conductivity in the top layer is especially relevant as highly conductive materials like indium tin oxide (ITO), aluminum-doped zinc oxide (AZO) or p-GaN, usually applied in blue InGaN/GaNbased LEDs cannot be used as current spreading layers in UV-C LEDs due to their strong UV-C absorption limiting light extraction in standard geometry. [14][15][16] This challenge is often being targeted by flip-chip mounting for emission through the UV-transparent sapphire substrate. [17,18] With a theoretical reflectivity of >90% in the UV-C regime, Al would be an ideal mirror material for the flip-chip geometry.…”

Section: Doi: 101002/adma202313037mentioning

confidence: 99%

Graphene‐Enhanced UV‐C LEDs

Meier,

Zhang,

Kaya

et al. 2024

Advanced Materials

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Light‐emitting diodes in the UV‐C spectral range (UV‐C LEDs) can potentially replace bulky and toxic mercury lamps in a wide range of applications including sterilization and water purification. Several obstacles still limit the efficiencies of UV‐C LEDs. Devices in flip‐chip geometry suffer from a huge difference in the work functions between the p‐AlGaN and high‐reflective Al mirrors, whereas the absence of UV‐C transparent current spreading layers limits the development of UV‐C LEDs in standard geometry. Here it is demonstrated that transfer‐free graphene implemented directly onto the p‐AlGaN top layer by a plasma enhanced chemical vapor deposition approach enables highly efficient 275 nm UV‐C LEDs in both, flip‐chip and standard geometry. In flip‐chip geometry, the graphene acts as a contact interlayer between the Al‐mirror and the p‐AlGaN enabling an external quantum efficiency (EQE) of 9.5% and a wall‐plug efficiency (WPE) of 5.5% at 8 V. Graphene combined with a ∼1 nm NiOx support layer allows a turn‐on voltage <5 V. In standard geometry graphene acts as a current spreading layer on a length scale up to 1 mm. These top‐emitting devices exhibit a EQE of 2.1% at 8.7 V and a WPE of 1.1%.This article is protected by copyright. All rights reserved

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Section: Doi: 101002/adma202313037mentioning

confidence: 99%

Graphene‐Enhanced UV‐C LEDs

Meier,

Zhang,

Kaya

et al. 2024

Advanced Materials

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“…In addition, conventional Ni/Au p-electrode exhibits high absorption of DUV light. Al, with a reflectivity of 92% at 250-280 nm, is widely used in sidewall reflectors and reflective electrodes for DUV FCLEDs [12,[14][15][16][17]. However, the Al sidewall reflector is often underutilized due to the limited sidewall area in DUV FCLEDs.…”

Section: Introductionmentioning

confidence: 99%

Enhanced efficiency of deep ultraviolet light-emitting diodes utilizing full-coverage Al reflector and highly reflective Ni/Rh p-electrode

Lv,

Liao,

Zhou

2024

Semicond. Sci. Technol.

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Increasing the reflection of p-side is an effective way to improve the optoelectronic performance of flip-chip light-emitting diodes (FCLEDs). Here, we propose a full-coverage Al reflector (FAR) and a highly reflective Ni/Rh p-electrode to enhance the performance of DUV FCLEDs. The physical mechanism for the impact of the FAR and Ni/Rh electrode on the light extraction efficiency (LEE) is discussed theoretically. Simulations demonstrate that the combination of the FAR and Ni/Rh electrode improves the LEEs of transverse electric- and transverse magnetic-polarized light by 13.62% and 27.08%, respectively. At an injection current of 100 mA, the fabricated DUV FCLEDs with FAR and Ni/Rh electrode exhibits an external quantum efficiency of 4.01% and a wall plugging efficiency of 3.01%, which are 17.19% and 16.67% higher than those of conventional DUV FCLEDs, respectively. These results support the promise of the FAR and Ni/Rh electrode for high-power DUV LED applications.

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“…However, the luminous efficiency of AlGaN-based DUV-LEDs is still at a low level, which seriously affects the application effectiveness of AlGaN-based DUV LED [6], [7], [8], [9]. The main reasons for the low luminous efficiency of AlGaN-based DUV-LEDs are as follows: 1) High-quality AlGaN-based are difficult to prepare [10]; 2) p-AlGaN with high doping efficiency is difficult to realize [11]; 3) the drift rate of electrons is faster compared to that of holes, which results in the occurrence of electron leakage in the active region and the uneven distribution of carriers [12]; 4) the quantum confinement stark effect (QCSE) leads to the separation of the electron and hole wavefunctions in multiple quantum wells (MQWs), which reduces the chance of radiative recombination of carriers in MQWs [13]; 5) the light extraction efficiency (LEE) of AlGaN-based DUV-LEDs is still at a very low value [14].…”

mentioning

confidence: 99%

A Review of Recent Research Advances on AlGaN-Based Deep Ultraviolet Light-Emitting Diodes

Huang,

Li,

Xiang

2024

IEEE Access

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Due to environmental friendliness, small size, long lifetime, and adjustable light-emitting wavelength, AlGaN-based deep ultraviolet light-emitting diodes (DUV-LEDs) have great development potential in the fields of biochemical detection, sterilization and disinfection, and non-line-of-sight communication. After decades of research, AlGaN-based DUV-LEDs have significantly improved in the direction of luminous efficiency. However, the luminous efficiency of the present AlGaN-based DUV-LEDs is still at a low level compared with that of the fully commercialised nitride blue LEDs, making it difficult to meet the market demand. This paper first introduces the present development status of AlGaN-based DUV-LEDs and the reasons for the low luminous efficiency. Then from the preparation of AlGaN-based, AlGaN doping and the design of AlGaN-based DUV-LEDs structure to elaborate the research progress in recent years in the direction of improving the luminous efficiency of AlGaN-based DUV-LEDs. Finally discusses the challenges that the AlGaN-based DUV-LEDs are presently faced with, and their future opportunities for development. INDEX TERMS AlGaN-based DUV-LEDs;luminous efficiency;AlGaN-based;AlGaN doping;AlGaNbased DUV-LEDs structure I. INTRODUCTION

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Improving Light Extraction Efficiency of AlGaN-Based Deep Ultraviolet Light-Emitting Diodes by Combining Thinning p-AlGaN/p-GaN Layer With Ni/Au/Al High-Reflectivity Electrodes

Cited by 10 publications

References 31 publications

Graphene‐Enhanced UV‐C LEDs

Graphene‐Enhanced UV‐C LEDs

Enhanced efficiency of deep ultraviolet light-emitting diodes utilizing full-coverage Al reflector and highly reflective Ni/Rh p-electrode

A Review of Recent Research Advances on AlGaN-Based Deep Ultraviolet Light-Emitting Diodes

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