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Mumta Hena Mustary,유버들,한민,양종한,Volodymyr V. Lysak,홍창희 대한전자공학회 2015 Journal of semiconductor technology and science Vol.15 No.4
Light enhancement of GaN based light emitting diodes (LEDs) have been investigated by texturing the top p-GaN surface. Nano-textured LEDs have been fabricated using self-assembled Ni nano mask during dry etching process. Experimental results were further compared with simulation data. Three types of LEDs were fabricated: Conventional (planar LED), Surface nano-porous (porous LED) and Surface nano-cluster (cluster LED). Compared to planar LED there were about 100% and 54% enhancement of light output power for porous and cluster LED respectively at an injection current of 20 mA. Moreover, simulation result showed consistency with experimental result. The increased probability of light scattering at the nano-textured GaN-air interface is the major reason for increasing the light extraction efficiency.
Mustary, Mumta Hena,Ryu, Beo Deul,Han, Min,Yang, Jong Han,Lysak, Volodymyr V.,Hong, Chang-Hee The Institute of Electronics and Information Engin 2015 Journal of semiconductor technology and science Vol.15 No.4
Light enhancement of GaN based light emitting diodes (LEDs) have been investigated by texturing the top p-GaN surface. Nano-textured LEDs have been fabricated using self-assembled Ni nano mask during dry etching process. Experimental results were further compared with simulation data. Three types of LEDs were fabricated: Conventional (planar LED), Surface nano-porous (porous LED) and Surface nano-cluster (cluster LED). Compared to planar LED there were about 100% and 54% enhancement of light output power for porous and cluster LED respectively at an injection current of 20 mA. Moreover, simulation result showed consistency with experimental result. The increased probability of light scattering at the nano-textured GaN-air interface is the major reason for increasing the light extraction efficiency.
Sudhagar, P.,Devadoss, Anitha,Song, Taeseup,Lakshmipathiraj, P.,Han, Hyungkyu,Lysak, Volodymyr V.,Terashima, C.,Nakata, Kazuya,Fujishima, A.,Paik, Ungyu,Kang, Yong Soo The Royal Society of Chemistry 2014 Physical chemistry chemical physics Vol.16 No.33
<P>We demonstrate one-step gold nanoparticle (AuNP) coating and the surface nitridation of TiO<SUB>2</SUB> nanowires (TiO<SUB>2</SUB>-NWs) to amplify visible-light photon reflection. The surface nitridation of TiO<SUB>2</SUB>-NW arrays maximizes the anchoring of AuNPs, and the subsequent reduction of the band gap energy from 3.26 eV to 2.69 eV affords visible-light activity. The finite-difference time-domain (FDTD) simulation method clearly exhibits the enhancement in the strengths of localized electric fields between AuNPs and the nanowires, which significantly improves the photocatalytic (PC) performance. Both nitridation and AuNP decoration of TiO<SUB>2</SUB>-NWs result in beneficial effects of high (e<SUP>−</SUP>/h<SUP>+</SUP>) pair separation through healing of the oxygen vacancies. The combined effect of harvesting visible-light photons and reducing recombination in Au/N-doped TiO<SUB>2</SUB>-NWs promotes the photocatalytic activity towards degradation of methyl orange to an unprecedented level, ∼4 fold (1.1 × 10<SUP>−2</SUP> min) more than does TiO<SUB>2</SUB>-NWs (2.9 × 10<SUP>−3</SUP> min<SUP>−1</SUP>). The proposed AuNP decoration of nitridated TiO<SUB>2</SUB>-NW surfaces can be applied to a wide range of n-type metal oxides for photoanodes in photocatalytic applications.</P> <P>Graphic Abstract</P><P>Maximizing the Au nanoparticle decoration on TiO<SUB>2</SUB> nanowire through nitrogen doping for simultaneous enhancement in visible light scattering and electron–hole charge separation. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4cp02009j'> </P>
Sudhagar, P.,Song, Taeseup,Devadoss, Anitha,Lee, Jung Woo,Haro, Marta,Terashima, Chiaki,Lysak, Volodymyr V.,Bisquert, Juan,Fujishima, Akira,Gimenez, Sixto,Paik, Ungyu The Royal Society of Chemistry 2015 Physical chemistry chemical physics Vol.17 No.29
<P>The interaction strength of Au nanoparticles with pristine and nitrogen doped TiO<SUB>2</SUB> nanowire surfaces was analysed using density functional theory and their significance in enhancing the solar driven photoelectrocatalytic properties was elucidated. In this article, we prepared 4-dimethylaminopyridine capped Au nanoparticle decorated TiO<SUB>2</SUB> nanowire systems. The density functional theory calculations show {101} facets of TiO<SUB>2</SUB> as the preferred phase for dimethylaminopyridine–Au nanoparticles anchoring with a binding energy of −8.282 kcal mol<SUP>−1</SUP>. Besides, the interaction strength of Au nanoparticles was enhanced nearly four-fold (−35.559 kcal mol<SUP>−1</SUP>) at {101} facets <I>via</I> nitrogen doping, which indeed amplified the Au nanoparticle density on nitrided TiO<SUB>2</SUB>. The Au coated nitrogen doped TiO<SUB>2</SUB> (N–TiO<SUB>2</SUB>–Au) hybrid electrodes show higher absorbance owing to the light scattering effect of Au nanoparticles. In addition, N–TiO<SUB>2</SUB>–Au hybrid electrodes block the charge leakage from the electrode to the electrolyte and thus reduce the charge recombination at the electrode/electrolyte interface. Despite the beneficial band narrowing effect of nitrogen in TiO<SUB>2</SUB> on the electrochemical and visible light activity in N–TiO<SUB>2</SUB>–Au hybrid electrodes, it results in low photocurrent generation at higher Au NP loading (3.4 × 10<SUP>−7</SUP> M) due to light blocking the N–TiO<SUB>2</SUB> surface. Strikingly, even with a ten-fold lower Au NP loading (0.34 × 10<SUP>−7</SUP> M), the synergistic effects of nitrogen doping and Au NPs on the N–TiO<SUB>2</SUB>–Au hybrid system yield high photocurrent compared to TiO<SUB>2</SUB> and TiO<SUB>2</SUB>–Au electrodes. As a result, the N–TiO<SUB>2</SUB>–Au electrode produces nearly 270 μmol h<SUP>−1</SUP> cm<SUP>−2</SUP> hydrogen, which is nearly two-fold higher than the pristine TiO<SUB>2</SUB> counterpart. The implications of these findings for the design of efficient hybrid photoelectrocatalytic electrodes are discussed.</P> <P>Graphic Abstract</P><P>The interaction strength of Au nanoparticles with pristine and nitrogen doped TiO<SUB>2</SUB> nanowire surfaces was analysed using density functional theory and their significance in enhancing the solar driven photoelectrocatalytic properties was elucidated. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5cp01175b'> </P>
Kang, Ji Hye,Kim, Hyung Gu,Chandramohan, S,Kim, Hyun Kyu,Kim, Hee Yun,Ryu, Jae Hyoung,Park, Young Jae,Beak, Yun Seon,Lee, Jeong-Sik,Park, Joong Seo,Lysak, Volodymyr V,Hong, Chang-Hee Optical Society of America 2012 Optics letters Vol.37 No.1
<P>The effect of triangular air prism (TAP) arrays with different distance-to-width (d/w) ratios on the enhancement of light extraction efficiency (LEE) of InGaN light-emitting diodes (LEDs) is investigated. The TAP arrays embedded at the sapphire/GaN interface act as light reflectors and refractors, and thereby improve the light output power due to the redirection of light into escape cones on both the front and back sides of the LED. Enhancement in radiometric power as high as 117% and far-field angle as low as 129 are realized with a compact arrangement of TAP arrays compared with that of a conventional LED made without TAP arrays under an injection current of 20 mA.</P>