12 February 2007 Nonperiodic binary optical structures for enhancing light extraction of emitters
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Abstract
This paper presents a new method of designing binary optical structures to improve light extraction efficiency for emitters. Using this method a novel binary optical structure is generated. Such structures with an approximate width of 300 nm, are non-period and small enough in size so that they do not generate diffraction orders other than the zero order. They are also insensitive to polarization. They serve as an antireflection layer, sending light outward that would otherwise be absorbed within the device. The experimental devices were GaN based LEDs emitting at 460nm. The non-periodic binary structures and some periodic structures such as triangle-lattice Photonic Crystals (PC), 12-fold Quasi-periodic Photonic Crystals (QPC) are fabricated on the same sapphire side of a LED's flip chip with a Focus Ion Beam (FIB) for comparison. The surface profile of the structures was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Near field scanning optical microscopy (NSOM) was used to measure the output spectral properties of the devices. Electrical Luminescence (EL) measurements show that the greatest enhancement of emission light intensity was achieved in non-periodic binary structures. This increase was 60~135% at room temperature. It demonstrates that this Non-Periodic Binary Optical Structures will be useful for fabricating high efficient GaN-based LED.
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Liming Hong, Xiaodong Hu, Tao Yu, Tao Dai, Zhensheng Zhang, Jun Xu, Guoyi Zhang, "Nonperiodic binary optical structures for enhancing light extraction of emitters", Proc. SPIE 6486, Light-Emitting Diodes: Research, Manufacturing, and Applications XI, 648605 (12 February 2007); doi: 10.1117/12.701783; https://doi.org/10.1117/12.701783
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