Enhanced Light Extraction Efficiency of AlGaN-Based Deep Ultraviolet Light-Emitting Diodes by Incorporating High-Reflective n-Type Electrode Made of Cr/Al

Gao, Yang; Chen, Qian; Zhang, Shuang; Long, Hanling; Dai, Jiangnan; Sun, Haiding; Chen, Chang

doi:10.1109/ted.2019.2914487

Cited by 25 publications

(16 citation statements)

References 28 publications

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“…EQE values of some of the highest reported nitride UV LEDs are shown in Figure 6a for different emission wavelengths covering the UV band. Research initiatives regarding the further enhancement of the figure-of-merits of UV LEDs are being made on multiple fronts, such as the growth of better quality materials by reducing threading dislocations in AlGaN [93], better n-and p-doping of AlGaN to achieve higher conductivity [106][107][108], design of better contacts and heterostructures for efficient carrier recombination in the active region [92,106,[109][110][111], and the application of photon management techniques for enhancing light extraction efficiency [103,104,[112][113][114][115][116]. It may be noted that for efficient carrier injection and to prevent carrier overflow from the active region, different heterostructures of DUV LEDs have been explored for band engineering [92].…”

Section: Nitride-based Uv Ledsmentioning

confidence: 99%

III-Nitride Light-Emitting Devices

et al. 2021

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III-nitride light-emitting devices have been subjects of intense research for the last several decades owing to the versatility of their applications for fundamental research, as well as their widespread commercial utilization. Nitride light-emitters in the form of light-emitting diodes (LEDs) and lasers have made remarkable progress in recent years, especially in the form of blue LEDs and lasers. However, to further extend the scope of these devices, both below and above the blue emission region of the electromagnetic spectrum, and also to expand their range of practical applications, a number of issues and challenges related to the growth of materials, device design, and fabrication need to be overcome. This review provides a detailed overview of nitride-based LEDs and lasers, starting from their early days of development to the present state-of-the-art light-emitting devices. Besides delineating the scientific and engineering milestones achieved in the path towards the development of the highly matured blue LEDs and lasers, this review provides a sketch of the prevailing challenges associated with the development of long-wavelength, as well as ultraviolet nitride LEDs and lasers. In addition to these, recent progress and future challenges related to the development of next-generation nitride emitters, which include exciton-polariton lasers, spin-LEDs and lasers, and nanostructured emitters based on nanowires and quantum dots, have also been elucidated in this review. The review concludes by touching on the more recent topic of hexagonal boron nitride-based light-emitting devices, which have already shown significant promise as deep ultraviolet and single-photon emitters.

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Section: Nitride-based Uv Ledsmentioning

confidence: 99%

III-Nitride Light-Emitting Devices

et al. 2021

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“…Due to the high concentration of doping impurities and compensating defects, 16 ohmic contact was hard to achieve between metal and n‐AlGaN. To optimize the electrical characteristics, two types of metal combinations were designed in the fabrication split: a widely researched Cr/Al/Ti/Au metal stacks 17 as electrodes for Type A and Ti(20 nm)/Al(150 nm)/Ni(50 nm)/Au(80 nm) electrodes deposited for Type B. As the electron affinity of AlGaN χ AlGaN is 3.8 eV, 18 chromium (work function Φ Cr = 4.5 eV) and titanium (work function Φ Ti = 4.3 eV) 19 were firstly adopted as the metal in contact with n‐AlGaN.…”

Section: Methodsmentioning

confidence: 99%

AlGaN multiple quantum well deep‐ultraviolet micro‐light‐emitting diodes for high color conversion efficiency quantum dots display

et al. 2022

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Displays based on inorganic micro-light-emitting diodes (micro-LEDs) are highly anticipated for next-generation technologies. AlGaN-based deepultraviolet (deep-UV) micro-LED as the excitation source for quantum dots display with high efficiency was reported in this paper. To achieve optimized electro-optical performance, deep-UV micro-LEDs with different electrodes were fabricated and analyzed in sizes from 200 Â 200 to 10 Â 10 μm 2 . At the same forward bias, the devices with Ti/Al-based electrodes achieved 10 times injection current and three times electroluminescence intensity than those with Cr/Al-based electrodes. The blueshift phenomenon of deep-UV light was observed from 292 nm at 2 A/cm 2 to 287 nm at 200 A/cm 2 with the increasing current density. By the excitation of deep-UV micro-LED, quantum dot film achieved high light conversion efficiency and optimized color rendering, as the converted color emission peak was separate from the pumping source. The high energy of deep-UV photons and the narrow emission bandwidth of QDs resulted in prominent color purity. The forward voltage and electroluminescence intensity uniformity of a 250 Â 250 micro-LED array with each pixel size of 30 Â 30 μm 2 were further discussed. The optical microscope images of green QD film pumped by a deep-UV micro-LED demonstrated its competitive application in the color-converted display.

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“…The main factors that limit the LEE include the optical polarization of Al-rich AlGaN multiple quantum wells (MQWs), the total internal reflection at the interface between two layers with different refractive indexs, and the strong absorption of DUV light by p-GaN layer, which is essential for hole supply and the formation of Ohmic contact [7], [8], [9], [10], [11]. Many research groups have made efforts to overcome these difficulties and put forward various approaches: introducing a large-area AlN nanophotonic light extraction structure or moth-eye microstructure to enlarge the light escape cone thus weakening the limitation of the total reflection [12], [13], increasing the in-plane compressive strain of the quantum wells to obtain a higher polarization degree or taking micro-LED or arrays to help in-plane TM photons to escape [14], [15], [16], [17], [18], and adopting inclined sidewalls covered by a MgF2/Al omni-directional mirror, distributed Bragg reflectors, Cr/Al n-type electrode or reflective photonic crystals to improve the reflection [19], [20], [21], [22]. In addition, many methods have been adopted to reduce the absorption of p-GaN and Ni/Au electrodes for improving the LEE, such as tunnel-injected LED, laterally over-etched p-GaN layer, micro-ring array DUV-LED and so on [23], [24], [25].…”

Section: Introductionmentioning

confidence: 99%

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

Lang

et al. 2023

IEEE Photonics J.

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Improving light extraction efficiency (LEE) of AlGaN-based deep-ultraviolet (DUV) light emitting diodes (LEDs) has been attempted by thinning the p-AlGaN/p-GaN layer and adopting Ni/Au/Al composite electrodes. It is found that the thin p-AlGaN/p-GaN layer can reduce the light absorption and the Ni/Au/Al electrodes achieve high reflectivity and Ohmic contact to ensure the enhancement of the light extraction and maintain fine electrical properties. By this approach, the maximum external quantum efficiency of the DUV-LEDs with optimized Ni/Au/Al reflective electrodes is increased by 40%, compared to that with conventional Ni/Au electrodes over the whole current range.

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Enhanced Light Extraction Efficiency of AlGaN-Based Deep Ultraviolet Light-Emitting Diodes by Incorporating High-Reflective n-Type Electrode Made of Cr/Al

Cited by 25 publications

References 28 publications

III-Nitride Light-Emitting Devices

III-Nitride Light-Emitting Devices

AlGaN multiple quantum well deep‐ultraviolet micro‐light‐emitting diodes for high color conversion efficiency quantum dots display

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

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