Suppressing the efficiency droop in AlGaN-based UVB LEDs

Usman, Muhammad; Malik, Shahzeb; Khan, M. Ajmal; Hasegawa, Hideki

doi:10.1088/1361-6528/abe4f9

Cited by 34 publications

(14 citation statements)

References 48 publications

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“…Consequently, the performance of the UVB LEDs has been deteriorated at RT 4 , 8 , 12 , 23 , 24 , as presented in Table 1 . A reasonable level of 3D hole generation has been successfully realised in the AlGaN/GaN UVC LED by polarisation effect, which is supported by the distribution of Al composition profile from p-AlGaN HSL to the p-GaN contact-layer 33 , 34 , 47 . However, both the p-GaN contact layer and Ni/Au p-electrode can absorb a significant portion of the emitted UV light 8 , 23 .…”

Section: Resultsmentioning

confidence: 74%

“…It is computed from Eq. ( 1 ) to be about 5 × 10 13 × (x 2 − x 1 ) / d cm −3 , where x 1 and x 2 are the Al compositions at the ends of the graded layer of thickness d (in centimetres) 33 , 46 , 47 . Alongside the [0001]-direction (Ga-polar), the Al composition in the p-Al x Ga 1-x N HSL gradually changes from high Al content of 60% down to low Al content of 40% as observed in Fig.…”

Section: Resultsmentioning

confidence: 99%

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Achieving 9.6% efficiency in 304 nm p-AlGaN UVB LED via increasing the holes injection and light reflectance

Khan

Maeda

Yun

et al. 2022

Sci Rep

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Crystal growth of eco-friendly, ultrawide bandgap aluminium gallium nitride (AlGaN) semiconductor-based ultraviolet-B (UVB) light-emitting diodes (LEDs) hold the potential to replace toxic mercury-based 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 multi-quantum-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-quantum-wells 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 resin-like 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-AlGaN-based UVB LEDs and other optoelectronic devices in III–V semiconductors.

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Section: Resultsmentioning

confidence: 74%

Section: Resultsmentioning

confidence: 99%

Achieving 9.6% efficiency in 304 nm p-AlGaN UVB LED via increasing the holes injection and light reflectance

Khan

Maeda

Yun

et al. 2022

Sci Rep

Self Cite

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“…Although, there has been a significant improvement in fabricating of UV-LEDs with improved quantum efficiencies, both internal and external and with low density of threading dislocations but the effort is still going on to meet the market standards. Muhammad Usman et al numerically investigated AlGaN-based UVB LEDs for the suppression of efficiency droop and got enhanced hole injection in MQWs [ 15 ]. Their numerical simulation suggested that, compared to the conventional structure, the proposed structure had a high peak efficiency and very small efficiency droop.…”

Section: Fabrication Of Duv-ledsmentioning

confidence: 99%

Reliability Analysis of AlGaN-Based Deep UV-LEDs

2022

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The current pandemic crisis caused by SARS-CoV-2 has also pushed researchers to work on LEDs, especially in the range of 220–240 nm, for the purpose of disinfecting the environment, but the efficiency of such deep UV-LEDs is highly demanding for mass adoption. Over the last two decades, several research groups have worked out that the optical power of GaN-based LEDs significantly decreases during operation, and with the passage of time, many mechanisms responsible for the degradation of such devices start playing their roles. Only a few attempts, to explore the reliability of these LEDs, have been presented so far which provide very little information on the output power degradation of these LEDs with the passage of time. Therefore, the aim of this review is to summarize the degradation factors of AlGaN-based near UV-LEDs emitting in the range of 200–350 nm by means of combined optical and electrical characterization so that work groups may have an idea of the issues raised to date and to achieve a wavelength range needed for disinfecting the environment from SARS-CoV-2. The performance of devices submitted to different stress conditions has been reviewed for the reliability of AlGaN-based UV-LEDs based on the work of different research groups so far, according to our knowledge. In particular, we review: (1) fabrication strategies to improve the efficiency of UV-LEDs; (2) the intensity of variation under constant current stress for different durations; (3) creation of the defects that cause the degradation of LED performance; (4) effect of degradation on C-V characteristics of such LEDs; (5) I-V behavior variation under stress; (6) different structural schemes to enhance the reliability of LEDs; (7) reliability of LEDs ranging from 220–240 nm; and (8) degradation measurement strategies. Finally, concluding remarks for future research to enhance the reliability of near UV-LEDs is presented. This draft presents a comprehensive review for industry and academic research on the physical properties of an AlGaN near UV-LEDs that are affected by aging to help LED manufacturers and end users to construct and utilize such LEDs effectively and provide the community a better life standard.

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“…This radiation penetrates the skin and is absorbed by 7-dehydrocholesterol (7-DHC) to form cis-cis previtamin D 3 , which undergoes isomerization to produce more thermodynamically stable vitamin D 3 . Several reports have revealed that the hole injection efficiency can be improved in AlGaN-based DUV-LEDs through the functionalization of the p-AlGaN electron-blocking layer (EBL) [ 7 , 23 , 24 , 25 , 26 , 27 , 28 ]. AlGaN-based DUV-LEDs that operate nearly free of efficiency droop have also been prepared [ 23 , 24 , 25 ].…”

Section: Introductionmentioning

confidence: 99%

“…Several reports have revealed that the hole injection efficiency can be improved in AlGaN-based DUV-LEDs through the functionalization of the p-AlGaN electron-blocking layer (EBL) [ 7 , 23 , 24 , 25 , 26 , 27 , 28 ]. AlGaN-based DUV-LEDs that operate nearly free of efficiency droop have also been prepared [ 23 , 24 , 25 ]. Usman et al [ 23 ] found through numerical analysis that the efficiency droop at 500 A cm –2 decreased from 42 to 7% when using an optimized undoped-AlGaN final quantum barrier, a p-type multiple quantum barrier EBL, and an Al composition-graded p-AlGaN hole injection layer in their UVB-LED structure.…”

Section: Introductionmentioning

confidence: 99%

Very Low-Efficiency Droop in 293 nm AlGaN-Based Light-Emitting Diodes Featuring a Subtly Designed p-Type Layer

Lai¹,

Chang

Wang

et al. 2022

Molecules

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This paper reports an AlGaN-based ultraviolet-B light-emitting diode (UVB-LED) with a peak wavelength at 293 nm that was almost free of efficiency droop in the temperature range from 298 to 358 K. Its maximum external quantum efficiencies (EQEs), which were measured at a current density of 88.6 A cm–2, when operated at 298, 318, and 338 K were 2.93, 2.84, and 2.76%, respectively; notably, however, the current droop (J-droop) in each of these cases was less than 1%. When the temperature was 358 K, the maximum EQE of 2.61% occurred at a current density of 63.3 A cm–2, and the J-droop was 1.52%. We believe that the main mechanism responsible for overcoming the J-droop was the uniform distribution of the concentrations of injected electrons and holes within the multiple quantum wells. Through the subtle design of the p-type AlGaN layer, with the optimization of the composition and doping level, the hole injection efficiency was enhanced, and the Auger recombination mechanism was inhibited in an experimental setting.

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Suppressing the efficiency droop in AlGaN-based UVB LEDs

Cited by 34 publications

References 48 publications

Achieving 9.6% efficiency in 304 nm p-AlGaN UVB LED via increasing the holes injection and light reflectance

Achieving 9.6% efficiency in 304 nm p-AlGaN UVB LED via increasing the holes injection and light reflectance

Reliability Analysis of AlGaN-Based Deep UV-LEDs

Very Low-Efficiency Droop in 293 nm AlGaN-Based Light-Emitting Diodes Featuring a Subtly Designed p-Type Layer

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