GaN-based light-emitting diodes with photonic crystals structures fabricated by porous anodic alumina template

School of Physics and State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, Peking University, Beijing, China
Optics Express (Impact Factor: 3.49). 09/2011; 19 Suppl 5(19):A1104-8. DOI: 10.1364/OE.19.0A1104
Source: PubMed


In this paper, we propose and demonstrate a convenient and flexible approach for preparation large-area of photonic crystals (PhCs) structures on the GaN-based LED chip. The highly-ordered porous anodic alumina (AAO) with pitch of wavelength scale was adopted as a selective dry etching mask for PhCs-pattern transfer. The PhCs with different pore depths were simultaneously formed on the entire surfaces of GaN-based LED chip including ITO, GaN surrounding contacts and the sidewall of the mesa by one-step reactive ion etching (RIE). The light output power improvement of PhCs-based GaN LED was achieved as high as 94% compared to that of the conventional GaN-based LED.

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Available from: Xiangning Kang, Dec 03, 2014
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    • "The commercial value outstands in the widespread use of solar cells [11], [12], lenses [13] and transparent polymer [14], etc. Recently, the AAO method has been invited to LED field, and the use of AAO to pattern Si substrate [15], AlN buffer layer [16], un-doped GaN [17], n-GaN [18], [19], p-GaN [20]–[22] and ITO [21], [22] have demonstrated a success for enhancing the light extraction efficiency of corresponding LED devices. Yet, among all these applications adopting AAOs, the direct substrate patterning scheme by Al deposition and subsequent anodization need to remove the Al 2 O 3 layer at any single fabrication cycle, thus it fails to meet the repeatable requirement. "
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    ABSTRACT: Nanostructured GaN-based light-emitting diode (LED), with its high performance on light extraction efficiency, has attracted significant attention for the potential application in solid state lighting. However, patterning structures at nanoscale feature size with large area and low cost is of great importance and hardness. In this paper, a 2 inch anodic aluminum oxide (AAO) template was used as the initial mold to copy the photonic-crystal-like structures (PCLSs) on a blue-light LED by soft UV nanoimprint lithography. An additional solute, aluminum oxalate hydrate, is employed to overcome the burn-through issue in the high-voltage anodization which is critical for the fabrication of the large-pore (250–500 nm) AAO. The photoluminescence and electroluminescence enhancements of the patterned LED device with 150-nm-deep PCLSs are, respectively, 45% and 11.4% compared with the un-patterned LED device. A 3-D finite-difference time-domain simulation confirms that the light extraction efficiency is enhanced when PCLSs are formed. The proposed method is simple, cheap, repeatable in large area and compatible with the high volume production lines.
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    • "However, in conventional planar LEDs, the light extraction efficiency is limited by several factors including the high refractive index of p-GaN (approximately 2.52), leading to a low total internal reflection (TIR) angle [2]. To enhance the output light power, various approaches, such as surface texturing [3,4], photonic crystals [5-7], and metal oxide nanoparticles [8-11], have been studied. "
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    ABSTRACT: Significant enhancement in the light output from GaN-based green light-emitting diodes (LEDs) was achieved with a hemicylindrical grating structure on the top layer of the diodes. The grating structure was first optimized by the finite-difference time-domain (FDTD) method, which showed that the profile of the grating structure was critical for light extraction efficiency. It was found that the transmission efficiency of the 530 nm light emitted from the inside of the GaN LED increased for incidence angles between 23.58° and 60°. Such a structure was fabricated by electron-beam lithography and an etching method. The light output power from the LED was increased approximately 4.7 times compared with that from a conventional LED. The structure optimization is the key to the great increase in transmission efficiency. Furthermore, the light emitted from the edge of the LED units could be collected and extracted by the grating structures in adjacent LED units, thus enhancing the performance of the whole LED chip.
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