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Title: Light extraction enhancement of 265 nm deep-ultraviolet light-emitting diodes with over 90 mW output power via an AlN hybrid nanostructure

Abstract

Deep-ultraviolet (DUV) aluminum gallium nitride-based light-emitting diodes (LEDs) on transparent aluminum nitride (AlN) substrates with high light extraction efficiency and high power are proposed and demonstrated. The AlN bottom side surface configuration, which is composed of a hybrid structure of photonic crystals and subwavelength nanostructures, has been designed using finite-difference time-domain calculations to enhance light extraction. We have experimentally demonstrated an output power improvement of up to 196% as a result of the use of the embedded high-light-extraction hybrid nanophotonic structure. The DUV-LEDs produced have demonstrated output power as high as 90 mW in DC operation at a peak emission wavelength of 265 nm.

Authors:
 [1];  [1];  [2]; ; ;  [3]
  1. Advanced ICT Research Institute, National Institute of Information and Communications Technology (NICT), Kobe, Hyogo 651-2492 (Japan)
  2. (Japan)
  3. Tsukuba Research Laboratories, Tokuyama Corporation, Tsukuba, Ibaraki 300-4247 (Japan)
Publication Date:
OSTI Identifier:
22398799
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 106; Journal Issue: 13; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 77 NANOSCIENCE AND NANOTECHNOLOGY; ALUMINIUM; ALUMINIUM NITRIDES; CRYSTALS; EFFICIENCY; GALLIUM NITRIDES; LIGHT EMITTING DIODES; NANOSTRUCTURES; OPERATION; PHOTON EMISSION; SUBSTRATES; SURFACES; ULTRAVIOLET RADIATION; VISIBLE RADIATION

Citation Formats

Inoue, Shin-ichiro, E-mail: s-inoue@nict.go.jp, Naoki, Tamari, Tsukuba Research Laboratories, Tokuyama Corporation, Tsukuba, Ibaraki 300-4247, Kinoshita, Toru, Obata, Toshiyuki, and Yanagi, Hiroyuki. Light extraction enhancement of 265 nm deep-ultraviolet light-emitting diodes with over 90 mW output power via an AlN hybrid nanostructure. United States: N. p., 2015. Web. doi:10.1063/1.4915255.
Inoue, Shin-ichiro, E-mail: s-inoue@nict.go.jp, Naoki, Tamari, Tsukuba Research Laboratories, Tokuyama Corporation, Tsukuba, Ibaraki 300-4247, Kinoshita, Toru, Obata, Toshiyuki, & Yanagi, Hiroyuki. Light extraction enhancement of 265 nm deep-ultraviolet light-emitting diodes with over 90 mW output power via an AlN hybrid nanostructure. United States. doi:10.1063/1.4915255.
Inoue, Shin-ichiro, E-mail: s-inoue@nict.go.jp, Naoki, Tamari, Tsukuba Research Laboratories, Tokuyama Corporation, Tsukuba, Ibaraki 300-4247, Kinoshita, Toru, Obata, Toshiyuki, and Yanagi, Hiroyuki. Mon . "Light extraction enhancement of 265 nm deep-ultraviolet light-emitting diodes with over 90 mW output power via an AlN hybrid nanostructure". United States. doi:10.1063/1.4915255.
@article{osti_22398799,
title = {Light extraction enhancement of 265 nm deep-ultraviolet light-emitting diodes with over 90 mW output power via an AlN hybrid nanostructure},
author = {Inoue, Shin-ichiro, E-mail: s-inoue@nict.go.jp and Naoki, Tamari and Tsukuba Research Laboratories, Tokuyama Corporation, Tsukuba, Ibaraki 300-4247 and Kinoshita, Toru and Obata, Toshiyuki and Yanagi, Hiroyuki},
abstractNote = {Deep-ultraviolet (DUV) aluminum gallium nitride-based light-emitting diodes (LEDs) on transparent aluminum nitride (AlN) substrates with high light extraction efficiency and high power are proposed and demonstrated. The AlN bottom side surface configuration, which is composed of a hybrid structure of photonic crystals and subwavelength nanostructures, has been designed using finite-difference time-domain calculations to enhance light extraction. We have experimentally demonstrated an output power improvement of up to 196% as a result of the use of the embedded high-light-extraction hybrid nanophotonic structure. The DUV-LEDs produced have demonstrated output power as high as 90 mW in DC operation at a peak emission wavelength of 265 nm.},
doi = {10.1063/1.4915255},
journal = {Applied Physics Letters},
number = 13,
volume = 106,
place = {United States},
year = {Mon Mar 30 00:00:00 EDT 2015},
month = {Mon Mar 30 00:00:00 EDT 2015}
}
  • Enhanced light extraction efficiency was demonstrated on nanostructure patterned GaN and AlGaN/AlN Multiple-Quantum-Well (MQW) structures using mass production techniques including natural lithography and interference lithography with feature size as small as 100 nm. Periodic nanostructures showed higher light extraction efficiency and modified emission profile compared to non-periodic structures based on integral reflection and angular-resolved transmission measurement. Light extraction mechanism of macroscopic and microscopic nanopatterning is discussed, and the advantage of using periodic nanostructure patterning is provided. An enhanced photoluminescence emission intensity was observed on nanostructure patterned AlGaN/AlN MQW compared to as-grown structure, demonstrating a large-scale and mass-producible pathway to higher lightmore » extraction efficiency in deep-ultra-violet light-emitting diodes.« less
  • We report on the growth of low-defect thick films of AlN and AlGaN on trenched AlGaN/sapphire templates using migration enhanced lateral epitaxial overgrowth. Incoherent coalescence-related defects were alleviated by controlling the tilt angle of growth fronts and by allowing Al adatoms sufficient residence time to incorporate at the most energetically favorable lattice sites. Deep ultraviolet light emitting diode structures (310 nm) deposited over fully coalesced thick AlN films exhibited cw output power of 1.6 mW at 50 mA current with extrapolated lifetime in excess of 5000 hours. The results demonstrate substantial improvement in the device lifetime, primarily due to themore » reduced density of growth defects.« less
  • Mg-doped AlN/AlGaN superlattice (Mg-SL) and Mg-doped AlGaN epilayers have been investigated in the 284 nm deep ultraviolet (DUV) light emitting diodes (LEDs) as electron blocking layers. It was found that the use of Mg-SL improved the material quality of the p-GaN contact layer, as evidenced in the decreased density of surface pits and improved surface morphology and crystalline quality. The performance of the DUV LEDs fabricated using Mg-SL was significantly improved, as manifested by enhanced light intensity and output power, and reduced turn-on voltage. The improved performance is attributed to the enhanced blocking of electron overflow, and enhanced hole injection.
  • The performance of conventional AlGaN deep ultraviolet light emitting diodes has been limited by the extremely low light extraction efficiency (<10%), due to the unique transverse magnetic (TM) polarized light emission. Here, we show that, by exploiting the lateral side emission, the extraction efficiency of TM polarized light can be significantly enhanced in AlGaN nanowire structures. Using the three-dimensional finite-difference time domain simulation, we demonstrate that the nanowire structures can be designed to inhibit the emission of guided modes and redirect trapped light into radiated modes. A light extraction efficiency of more than 70% can, in principle, be achieved bymore » carefully optimizing the nanowire size, nanowire spacing, and p-GaN thickness.« less
  • AlGaN-based deep-ultraviolet light-emitting diode (LED) structures, which radiate light at 305 and 290 nm, have been grown on sapphire substrates using an AlN epilayer template. The fabricated devices have a circular geometry to enhance current spreading and light extraction. Circular UV LEDs of different sizes have been characterized. It was found that smaller disk LEDs had higher saturation optical power densities but lower optical powers than the larger devices. This trade-off between power and power density is a result of a compromise between electrical and thermal resistance, as well as the current crowding effect (which is due to the lowmore » electrical conductivity of high aluminum composition n- and p-AlGaN layers). Disk UV LEDs should thus have a moderate size to best utilize both total optical power and power density. For 0.85 mmx0.85 mm interdigitated LEDs, a saturation optical power of 2.9 mW (1.8 mW) at 305 nm (290 nm) was also obtained under dc operation.« less