AlGaN-based deep ultraviolet light-emitting diodes grown on nano-patterned sapphire substrates with significant improvement in internal quantum efficiency

Dong, Peng; Yan, Jianchang; Zhang, Yun; Wang, Junxi; Zeng, Jianping; Geng, Chong; Cong, Peipei; Sun, Lili; Wei, Tongbo; Zhao, Lixia; Yan, Qingfeng; He, Chenguang; Qin, Zhixin; Li, Jinmin

doi:10.1016/j.jcrysgro.2014.02.039

Cited by 70 publications

(37 citation statements)

References 20 publications

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“…The frequency of the E 2 high phonon mode was located at 658.6 cm −1 for AlN with 0-period SLs and at 658 cm −1 for AlN with 3∼30 period SL structures. For stress-free AlN 17 , 18 , the frequency was located at 657.4 cm −1 . Notably, the AlN epilayers with 0∼30 period SL structures exhibited a higher frequency compared to the stress-free frequency, which is indicative of compressive stress.…”

Section: Resultsmentioning

confidence: 99%

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85% internal quantum efficiency of 280-nm AlGaN multiple quantum wells by defect engineering

Wang

Tasi

Lin

et al. 2017

Sci Rep

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In this study, high internal-quantum-efficiency (IQE) AlGaN multiple quantum wells (MQWs) were successfully demonstrated on low-defect-density AlN templates with nano-patterned sapphire substrates. These templates consisted of AlN structures with 0∼30 periods superlattices (SLs) by alternating high (100) and low (25) V/III ratios under a low growth temperature (1130 °C). Compared to conventional high crystal-quality AlN epilayers achieved at temperatures ≥1300 °C, lower thermal budget can reduce the production cost and wafer warpage. Via optimization of the SL period, the AlN crystallinity was systematically improved. Strong dependence of SL period number on the X-ray full-width-at-half-maximum (FWHM) of the AlN epilayer was observed. The AlN template with 20-period SLs exhibited the lowest FWHM values for (0002) and (10ī2), namely 331 and 652 arcsec, respectively, as well as an ultra-low etching pit density of 1 × 105 cm−2. The relative IQE of 280 nm AlGaN MQWs exhibited a dramatically increase from 22.8% to 85% when the inserted SL increased from 0 to 20 periods. It has hardly ever been reported for the AlGaN MQW sample. The results indicate that the engineered AlN templates have high potential applications in deep ultraviolet light emitters.

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Section: Resultsmentioning

confidence: 99%

“…Notably, the AlN epilayers with 0∼30 period SL structures exhibited a higher frequency compared to the stress-free frequency, which is indicative of compressive stress. Moreover, the in-plane compressive stress (σ) of AlN can be evaluated by the following equation 17 , 18 : …”

Section: Resultsmentioning

confidence: 99%

85% internal quantum efficiency of 280-nm AlGaN multiple quantum wells by defect engineering

Wang

Tasi

Lin

et al. 2017

Sci Rep

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“…Closely packed PS monolayer was transferred to the sapphire substrate with an LT‐AlN buffer. Details on the AlGaN thin film preparation were described elsewhere . The diameter of PS sphere was then reduced by O 2 trimming, without changing the location of the spheres.…”

Section: Methodsmentioning

confidence: 99%

Lateral‐Polarity Structure of AlGaN Quantum Wells: A Promising Approach to Enhancing the Ultraviolet Luminescence

Guo

Sun

Torre

et al. 2018

Adv Funct Materials

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Aluminum-gallium-nitride alloys (Al x Ga 1-x N, 0 ≤ x ≤ 1) can emit light covering the ultraviolet spectrum from 210 to 360 nm. However, these emitters have not fulfilled their full promise to replace the toxic and fragile mercury UV lamps due to their low efficiencies. This study demonstrates a promising approach to enhancing the luminescence efficiency of AlGaN multiple quantum wells (MQWs) via the introduction of a lateral-polarity structure (LPS) comprising both III and N-polar domains. The enhanced luminescence in LPS is attributed to the surface roughening, and compositional inhomogeneities in the N-polar domain. The space-resolved internal quantum efficiency (IQE) mapping shows a higher relative IQE in N-polar domains and near inversion domain boundaries, providing strong evidence of enhanced radiative recombination efficiency in the LPS. These experimental observations are in good agreement with the theoretical calculations, where both lateral and vertical band diagrams are investigated. This work suggests that the introduction of the LPS in AlGaN-based MQWs can provide unprecedented tunability in achieving higher luminescence performance in the development of solid state light sources.

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“…When the perturbation introduced by the excitation source is very small (low injection regime), the IQE values describe the material properties in terms of radiative and non-radiative processes. However, it is difficult to compare these data with the literature since most reported values are measured under pulsed excitation [49][50][51][52][53][54][55][56][57][58], using power densities in the range of 5-1000 kW/cm 2 [49][50][51][52]54,55], to emulate the carrier injection at LED operating conditions. In this pumping regime, the photogenerated carrier densities are higher than the doping level of the original structure (high injection) and nonradiative recombination paths are partially saturated.…”

Section: Nanowires Vs Planar Layersmentioning

confidence: 99%

Assessment of AlGaN/AlN superlattices on GaN nanowires as active region of electron-pumped ultraviolet sources

Dimkou¹,

Harikumar²,

Donatini³

et al. 2020

Nanotechnology

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In this paper, we describe the design and characterization of 400-nm-long (88 periods) AlxGa1-xN/AlN (0 ≤ x ≤ 0.1) quantum dot superlattices deposited on self-assembled GaN nanowires for application in electron-pumped ultraviolet sources. The optical performance of GaN/AlN superlattices on nanowires is compared with the emission of planar GaN/AlN superlattices with the same periodicity and thickness grown on bulk GaN substrates along the N-polar and metal-polar crystallographic axes. The nanowire samples are less sensitive to nonradiative recombination than planar layers, attaining internal quantum efficiencies (IQE) in excess of 60% at room temperature even under low injection conditions. The IQE remains stable for higher excitation power densities, up to 50 kW/cm 2 . We demonstrate that the nanowire superlattice is long enough to collect the electron-hole pairs generated by an electron beam with an acceleration voltage VA = 5 kV.At such VA, the light emitted from the nanowire ensemble does not show any sign of quenching under constant electron beam excitation (tested for an excitation power density around 8 kW/cm 2 over the scale of minutes). Varying the dot/barrier thickness ratio and the Al content in the dots, the nanowire peak emission can be tuned in the range from 340 to 258 nm.

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AlGaN-based deep ultraviolet light-emitting diodes grown on nano-patterned sapphire substrates with significant improvement in internal quantum efficiency

Cited by 70 publications

References 20 publications

85% internal quantum efficiency of 280-nm AlGaN multiple quantum wells by defect engineering

85% internal quantum efficiency of 280-nm AlGaN multiple quantum wells by defect engineering

Lateral‐Polarity Structure of AlGaN Quantum Wells: A Promising Approach to Enhancing the Ultraviolet Luminescence

Assessment of AlGaN/AlN superlattices on GaN nanowires as active region of electron-pumped ultraviolet sources

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