Optimization of top polymer gratings to improve GaN LEDs light transmission

Jin, Xiaomin; Zhang, Bei; Dai, Tao; Wei, Wei; Kang, Xiaoning; Zhang, Guoyi; Trieu, Simeon; Wang, Fei

doi:10.3788/col20080610.0788

Cited by 6 publications

References 4 publications

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Development of a cost effective surface-patterned transparent conductive coating as top-contact of light emitting diodes

Haldar

Bera

Jana

et al. 2014

Journal of Applied Physics

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Edge effect enhanced electron field emission in top assembled reduced graphene oxide assisted by amorphous CNT-coated carbon cloth substrate AIP Advances 3, 012115 (2013); 10.1063/1.4789409Theoretical and experimental approach on dielectric properties of ZnO nanoparticles and polyurethane/ZnO nanocomposites J.Sol-gel process has been used to form indium zinc oxide films using an optimized combination of zinc to indium concentration in the precursor solutions. Different structures, like one (1D) and two-dimensional (2D) gratings and diffractive optical elements (DOEs) in the form of Fresnel lens are fabricated on the film surface of proposed top metal contact of LED by imprint soft lithography technique. These structures can enhance the LED's light extraction efficiency (LEE) or can shape the output beam pattern, respectively. Several characterizations are done to analyze the material and structural properties of the films. The presence of 1D and 2D gratings as well as DOEs is confirmed from field emission scanning electron and atomic force microscopes analyses. Although, X-ray diffraction shows amorphous nature of the film, but transmission electron microscopy study shows that it is nano crystalline in nature having fine particles ($8 nm) of hexagonal ZnO. Shrinkage behaviour of gratings as a function of curing temperature is explained by Fourier transform infra-red spectra and thermo gravimetric-differential thermal analysis. The visible transmission and sheet resistance of the sample are found comparable to tin doped indium oxide (ITO). Therefore, the film can compete as low cost substitute of ITO as top metal contact of LEDs. V C 2014 AIP Publishing LLC. [http://dx.

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Development of a cost effective surface-patterned transparent conductive coating as top-contact of light emitting diodes

Haldar

Bera

Jana

et al. 2014

Journal of Applied Physics

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Study of Top and Bottom Photonic Gratings on GaN LED With Error Grating Models

Trieu

Jin

2010

IEEE J. Quantum Electron.

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The gallium nitride (GaN) light-emitting-diode (LED) top-bottom (or transmission-reflection) grating simulation results with error grating model are presented. The microstruc ture GaN bottom hole and top pillar gratings are calculated and compared with the non-grating (flat) case. Grating shapes simu lated are either conical or cylindrical. A direct comparison of 181 different combined transmission-reflection grating cases using the finite difference time domain method is presented. The simulation results show that simple or direct combinations of the optimized top grating with the optimized bottom grating only produce a 42% light extraction improvement compared to the non-grating case, which is much lower than that of an optimized single grating case. This is due to the mismatch of grating parameters with the direct addition of the second grating structure, which changes the optical field distribution in the LEDs. Therefore, it is very im portant to optimize both top and bottom gratings simultaneously for the double-grating design. We also show the optimization of a double grating structure can achieve better performance than a single grating. Finally, transmission-reflection error gratings are also presented. It is also the first time to present randomization in GaN LED grating design and its effects in fabrication. Our data shows that the favorable light extraction improvement is at approximately 10-15% randomization. The randomization can achieve 230% improvement over the original grating at a randomization intensity factor of 12.8%.

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Light extraction improvement of GaN-based light-emitting diodes using patterned undoped GaN bottom reflection gratings

et al. 2009

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The Gallium Nitride (GaN) Light-Emitting-Diode (LED) bottom refection grating simulation and results are presented. A microstructure GaN bottom grating, either conical holes or cylindrical holes, was calculated and compared with the non-grating (flat) case. A time monitor was also placed just above the top of the LED to measure both time and power output from the top of the LED. Many different scenarios were simulated by sweeping three parameters that affected the structure of the micro-structure grating: unit cell period (Α) from 1 to 6 microns, unit cell width (w) from 1 to 6 microns, and unit cell grating height (d) from 50 to 200nm. The simulation results show that the cylindrical grating case has a 98% light extraction improvement, and the conical grating case has a 109% light extraction improvement compared to the flat plate case.

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Optimization of top polymer gratings to improve GaN LEDs light transmission

Cited by 6 publications

References 4 publications

Development of a cost effective surface-patterned transparent conductive coating as top-contact of light emitting diodes

Development of a cost effective surface-patterned transparent conductive coating as top-contact of light emitting diodes

Study of Top and Bottom Photonic Gratings on GaN LED With Error Grating Models

Light extraction improvement of GaN-based light-emitting diodes using patterned undoped GaN bottom reflection gratings

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