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Nizamoglu, S.,Sari, E.,Jong-Hyeob Baek,In-Hwan Lee,Volkan Demir, H. IEEE 2009 IEEE journal of selected topics in quantum electro Vol.15 No.4
<P>LEDs made of In<SUB>x</SUB>Ga<SUB>1-x</SUB>N and (Al<SUB>x</SUB>Ga<SUB>1-x</SUB>)<SUB>1-y</SUB>In<SUB>y</SUB>P suffer from significantly reduced quantum efficiency and luminous efficiency in the green/yellow spectral ranges. To address these problems, we present the design, growth, fabrication, hybridization, and characterization of proof-of-concept green/yellow hybrid LEDs that utilize radiative and nonradiative [Forster resonance energy transfer (FRET)] energy transfers in their colloidal semiconductor nanocrystals (NCs) integrated on near-UV LEDs. In our first NC-LED, we realize a color-converted LED that incorporate green-emitting CdSe/ZnS core/shell NCs (lambda<SUB>PL</SUB> = 548 nm) on near-UV InGaN/GaN LEDs (lambda<SUB>EL</SUB> = 379 nm). In our second NC-LED, we implement a color-converted FRET-enhanced LED. For that, we hybridize a custom-design assembly of cyan- and green-emitting CdSe/ZnS core/shell NCs (lambda<SUB>PL</SUB> = 490 and 548 nm) on near-UV LEDs. Using a proper mixture of differently sized NCs, we obtain a quantum efficiency enhancement of 9% by recycling trapped excitons via FRET. With FRET-NC-LEDs, we show that it is possible to obtain a luminous efficacy of 425 lm/W opt and a luminous efficiency of 94 lm/W, using near-UV LEDs with a 40% external quantum efficiency. Finally, we investigate FRET-converted light-emitting structures that use nonradiative energy transfer directly from epitaxial quantum wells to colloidal NCs. These proof-of-concept demonstrations show that FRET-based NC-LEDs hold promise for efficient solid-state lighting in green/yellow.</P>
Efficiency enhancement of white light-emitting diodes via nano-textured silicone encapsulant.
Kim, Sang-Mook,Baek, Jong Hyeob,Hwang, Nam,Kim, Yong-Suk,Wi, Sung-Kwon,Um, Soong Ho,Jung, Gun Young American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.10
<P>We textured the surface of a silicone encapsulant to increase the extraction efficiency of white light-emitting diodes (LEDs) by using a plasma treatment. Here, the surface morphology could be controlled by changing the plasma condition and texturing morphology of the silicone encapsulant were proportion to the increased ratio of white LEDs. The luminous efficacy of the surface textured LEDs were increased 9.70% relative to the reference LED. Furthermore, the Fourier transform infrared spectroscopy spectrum showed that the chemical bonds of the silicone encapsulant were not changed by the argon-nitrogen plasma treatment, thereby reducing degradation of the optical characteristics and improving the reliability of LEDs.</P>
Sang-Mook Kim,Hwa Sub Oh,Jong Hyeob Baek,Kwang-Ho Lee,Gun Young Jung,Jae-Ho Song,Ho-Jong Kim,Byung-Jun Ahn,Dong Yanqun,Jung-Hoon Song IEEE 2010 IEEE electron device letters Vol.31 No.8
<P>The strain and piezoelectric fields in InGaN blue light-emitting diodes on a GaN layer, which is grown on a planar sapphire substrate or patterned sapphire substrates (PSSs), such as a microsized PSS and a nanosized PSS (NPSS), are investigated by micro-Raman spectroscopy and electroreflectance (ER) spectroscopy. The obtained piezoelectric field in InGaN multiple quantum wells (QWs) grown on the planar substrate is 0.83 MV/cm, and it is 0.70 MV/cm for the case of the NPSS. These results are attributed to the fact that the GaN layers on the PSSs have a smaller residual strain compared to that on the planar sapphire, and thus, strain reduction in the GaN layer can reduce the piezoelectric field in the InGaN QWs grown on top of it.</P>
저압 MOCVD 방법으로 성장된 InAlAs 에피층에서 상분리와 규칙 현상의 관찰
조형균,이번,백종협,한원석,이정용,권명석,Cho, Hyung-Koun,Lee, Bun,Baek, Jong-hyeob,Han, Won-Seok,Lee, Jeong-Yong,Kwon, Myoung-Seok 한국진공학회 1999 Applied Science and Convergence Technology Vol.8 No.3(2)
We have studied the phase separation and ordering phenomeon of InAlAs epilayers grown on InP substrate by LP-MOCVD with DCXRD, PL, and TEM. From the intensity and FWHM of DCXRD and PL, we observed that the structural and optical quality of InAlAs epilayers were improved as growth temperature increased. The band-gap reduction due to phase separation and ordering is 291, 246, and 28 meV in the InAlAs epilayers grown at $565^{\circ}C$, $615^{\circ}C$, and $700^{\circ}C$, respectively, and shows the same from the InAlAs epilayer town at 5$65^{\circ}C$ in which the HRTEM micrograph showed the lattice fringe between InAs-rich and AlAs-rich regions was tilted by $2^{\circ}$ due to composition difference. However the maximum degree of ordering by intensity of extra spots was obtained at medium growth temperature. The annealing experiment by RTA of sample grown at $565^{\circ}$ shows a maximum band-gap shift of 78eV at $880^{\circ}$ for 3 min, and TEM shows that the origin of the blue shift of band-gap is the complete disappearance of ordering. Through annealing we can conclude that short time annealing affects only ordering and that most of the total band-gap reduction (~3/4) occurs by phase separation.
자외선 수직형 LED 제작을 위한 Indium Tin Oxide 기반 반사전극
정기창,이인우,정탁,백종협,하준석,Jung, Ki-Chang,Lee, Inwoo,Jeong, Tak,Baek, Jong Hyeob,Ha, Jun-Seok 한국재료학회 2013 한국재료학회지 Vol.23 No.3
In this paper, we studied a p-type reflector based on indium tin oxide (ITO) for vertical-type ultraviolet light-emitting diodes (UV LEDs). We investigated the reflectance properties with different deposition methods. An ITO layer with a thickness of 50 nm was deposited by two different methods, sputtering and e-beam evaporation. From the measurement of the optical reflection, we obtained 70% reflectance at a wavelength of 382 nm by means of sputtering, while only 30% reflectance resulted when using the e-beam evaporation method. Also, the light output power of a $1mm{\times}1mm$ vertical chip created with the sputtering method recorded a twofold increase over a chip created with e-beam evaporation method. From the measurement of the root mean square (RMS), we obtained a RMS value 1.3 nm for the ITO layer using the sputtering method, while this value was 5.6 nm for the ITO layer when using the e-beam evaporation method. These decreases in the reflectance and light output power when using the e-beam evaporation method are thought to stem from the rough surface morphology of the ITO layer, which leads to diffused reflection and the absorption of light. However, the turn-on voltage and operation voltage of the two samples showed identical results of 2.42 V and 3.5 V, respectively. Given these results, we conclude that the two ITO layers created by different deposition methods showed no differences in the electric properties of the ohmic contact and series resistance.