High-quality AlN epitaxy on nano-patterned sapphire substrates prepared by nano-imprint lithography

Zhang, Lisheng; Xu, Fujun; Wang, Jiaming; He, Chenguang; Guo, Weiwei; Wang, Mingxing; Sheng, Bowen; Lü, Lin; Qin, Zhixin; Wang, Xinqiang; Shen, Bo

doi:10.1038/srep35934

Cited by 113 publications

(92 citation statements)

References 19 publications

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“…Meanwhile, the dislocation defects of the AlN template strongly affect the internal quantum efficiency (IQE) of multiple quantum wells (MQWs) 3 . Therefore, several researchers have proposed methods to improve the crystallinity of AlN, including the enhancement of surface migration for Al adatoms 4 , use of AlN grown at high temperatures (≥1300 °C) 5 , AlN superlattices (SLs) with the alternation of low and high temperatures as a buffer structure 6 , the use of an AlGaN/AlN SL buffer structure 7 , and an AlN epilayer grown on a nano-patterned sapphire substrate (NPSS) 8 . Besides these methods, Shatalov et al .…”

Section: Introductionmentioning

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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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: Introductionmentioning

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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“…Where θ and φ represent the polar and azimuthal angles, respectively. [50,51]. In each of the array types the diameter D (frustums: diameter at half height) of the inclusion was set to D = P/2 and the height H of the inclusion was set to H = P/4.…”

Section: Methodsmentioning

confidence: 99%

Nanopatterned sapphire substrates in deep-UV LEDs: is there an optical benefit?

Manley¹,

Walde²,

Hagedorn³

et al. 2020

Opt. Express

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Light emitting diodes (LEDs) in the deep ultra-violet (DUV) offer new perspectives for multiple applications ranging from 3D printing to sterilization. However, insufficient light extraction severely limits their efficiency. Nanostructured sapphire substrates in aluminum nitride based LED devices have recently shown to improve crystal growth properties, while their impact on light extraction has not been fully verified. We present a model for understanding the impact of nanostructures on the light extraction capability of DUV-LEDs. The model assumes an isotropic light source in the semiconductor layer stack and combines rigorously computed scattering matrices with a multilayer solver. We find that the optical benefit of using a nanopatterned as opposed to a planar sapphire substrate to be negligible, if parasitic absorption in the p-side of the LED is dominant. If losses in the p-side are reduced to 20%, then for a wavelength of 265 nm an increase of light extraction efficiency from 7.8% to 25.0% is possible due to nanostructuring. We introduce a concept using a diffuse ('Lambertian') reflector as p-contact, further increasing the light extraction efficiency to 34.2%. The results underline that transparent p-sides and reflective p-contacts in DUV-LEDs are indispensable for enhanced light extraction regardless of the interface texture between semiconductor and sapphire substrate. The optical design guidelines presented in this study will accelerate the development of high-efficiency DUV-LEDs, but the model is also readily applicable to other multilayer opto-electronic nanostructured devices such as photovoltaics or photodetectors.

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“…It is well known that the weak surface migration of Al adatoms on the growth front limited the improvement of crystal quality. Therefore, many growth techniques have been developed for high quality AlN growth [11][12][13][14][15]. It has been demonstrated that high temperature annealing could significantly improve the AlN crystal quality [11].…”

Section: Introductionmentioning

confidence: 99%

“…Sun et al revealed the mechanism of different initial conditions on the quality of AlN and got high quality AlN on sapphire substrate by a "two-step" method [13]. In addition, nano-patterned sapphire and AlN/sapphire templates were used for high-quality AlN growth [14,15]. As the crystal quality increased, the efficiency can be increased effectively [16].…”

Section: Introductionmentioning

confidence: 99%

Influence of Quantum-Well Number and an AlN Electron Blocking Layer on the Electroluminescence Properties of AlGaN Deep Ultraviolet Light-Emitting Diodes

et al. 2018

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The influence of quantum-well (QW) number on electroluminescence properties was investigated and compared with that of AlN electron blocking layer (EBL) for deep ultraviolet light-emitting diodes (DUV-LEDs). By increasing the QW number, the band emission around 265 nm increased and the parasitic peak around 304 nm was suppressed. From the theoretical calculation, the electron current overflowing to the p-type layer was decreased as the QW number increased under the same injection. Correspondingly, the light output power also increased. The increment of output power from 5 QWs to 10 QWs was less than that from 10 QWs to 40 QWs, which was very different from what has been reported for blue and near-UV LEDs. The parasitic peak was still observed even when the QW number increased to 40. However, it can be suppressed efficiently by 1 nm AlN EBL for LEDs with 5 QWs. The simulation showed that the insertion of a thin EBL increased the barrier height for electron overflow and the electron current in p-type layers decreased significantly. The results contributed to the understanding of behavior of electron overflow in DUV-LEDs.

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High-quality AlN epitaxy on nano-patterned sapphire substrates prepared by nano-imprint lithography

Cited by 113 publications

References 19 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

Nanopatterned sapphire substrates in deep-UV LEDs: is there an optical benefit?

Influence of Quantum-Well Number and an AlN Electron Blocking Layer on the Electroluminescence Properties of AlGaN Deep Ultraviolet Light-Emitting Diodes

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