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Air-gap embedding GaN template for enhanced emission from light-emitting diodes
Y.S. Katharria,박영재,Jae Hyoung Ryu,Kang Bok Ko,유버들,V.V. Lysak,Chang-Hee Hong 한국물리학회 2013 Current Applied Physics Vol.13 No.9
Selective growth by metal-organic chemical vapor deposition (MOCVD), and electrochemical etching of aheavily Si-doped GaN (n+-GaN) interlayer were employed to obtain air-gaps embedded in a u-GaN layer. As confirmed by Raman spectroscopy, the introduction of an nþ-GaN, which was later etched to obtainair-gaps, also enhanced the strain-compliance of GaN epilayer on sapphire substrate. An enhancedelectroluminescence emission was observed from the light-emitting diodes (LEDs) fabricated on the airgapembedding template. Using theoretical LED simulation, it was discerned that the increase in opticalemission from the LED was caused predominantly by the redirection of photons at GaN/air-gap interface. Finite-difference time domain (FDTD) simulation method was employed to understand the mechanismof optical emission enhancement and its spatial variation over the LED surface.
Chandramohan, S.,Bok Ko, Kang,Han Yang, Jong,Deul Ryu, Beo,Katharria, Y. S.,Yong Kim, Taek,Jin Cho, Byung,Hong, Chang-Hee American Institute of Physics 2014 Journal of Applied Physics Vol.115 No.5
This study elucidates the correlation among conductivity of graphene and interface aspects in GaN light-emitting diodes (LEDs). Using a multilayer graphene of low sheet resistance, it is demonstrated that graphene alone can make ohmic contact with p-GaN without necessitating additional interlayer. Large-area blue LED with relatively low contact resistance in the order of 10(-2) ohm-cm(2) and improved forward voltage of 3.2 +/- 0.1 V was realized irrespective of the use of the interlayer. The results from parallel evaluation experiments performed by varying the layer numbers of graphene with ultrathin NiOx interlayer revealed that the poor lateral conductivity of monolayer or few layer graphene can be well compensated by the interlayer. A combination of three layer graphene and NiOx offered device with enhanced electro-optical performance. But the Schottky barrier associated with the inadequate adhesion of transferred graphene dominates all the benefits and becomes a major bottleneck preventing the formation of low resistance stable ohmic contact. (c) 2014 AIP Publishing LLC.
High performance of InGaN light-emitting diodes by air-gap/GaN distributed Bragg reflectors.
Ryu, Jae Hyoung,Kim, Hee Yun,Kim, Hyun Kyu,Katharria, Yashpal Singh,Han, Nam,Kang, Ji Hye,Park, Young Jae,Han, Min,Ryu, Beo Deul,Ko, Kang Bok,Suh, Eun-Kyoung,Hong, Chang-Hee Optical Society of America 2012 Optics express Vol.20 No.9
<P>The effect of air-gap/GaN DBR structure, fabricated by selective lateral wet-etching, on InGaN light-emitting diodes (LEDs) is investigated. The air-gap/GaN DBR structures in LED acts as a light reflector, and thereby improve the light output power due to the redirection of light into escape cones on both front and back sides of the LED. At an injection current of 20 mA, the enhancement in the radiometric power as high as 1.91 times as compared to a conventional LED having no DBR structure and a far-field angle as low as 128.2° are realized with air-gap/GaN DBR structures.</P>