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Song, Hooyoung,Kim, Eun Kyu,Han, Il Ki,Lee, Sung-Ho,Hwang, Sung-Min American Scientific Publishers 2011 Journal of Nanoscience and Nanotechnology Vol.11 No.10
<P>We fabricated yellow (575 nm) emitting a-plane InGaN/GaN light emitting diode (LED). Microstructure and stress relaxation of the InGaN well layer were observed from the images of dark field transmission electron microscopy. The LED chip was operated at 3.7 V, 20 mA, and the polarization-free characteristic in nonpolar InGaN layer was confirmed from a small blue-shift of approximaely 1.7 nm with increase of current density. The high photoluminescence (PL) efficiency of 30.4% showed that this non-polar InGaN layer has a potential of application to green-red long wavelength light emitters. The PL polarization ratio at 290 K was 0.25 and the energy difference between two subbands was estimated to be 40.2 meV. The low values of polarization and energy difference were due to the stress relaxation of InGaN well layer.</P>
Studies of defect states of ZnO thin films under different annealing conditions
Song, Hooyoung,Kim, Jae-Hoon,Kim, Eun Kyu Elsevier 2009 Microelectronics journal Vol.40 No.2
<P><B>Abstract</B></P><P>ZnO thin films were grown by the pulsed laser deposition technique on <I>c</I>-plane sapphire substrates at a substrate temperature of 500°C with 1×10<SUP>−4</SUP>Torr ambient gas. After the deposition process, ZnO thin films were annealed at 1000°C for 5min under N<SUB>2</SUB> or O<SUB>2</SUB> ambient gas, respectively. In the X-ray patterns, the (002) peak of the annealed sample was shifted from that of the as-grown sample, which indicates a reduced lattice constant of about 1%. Even though the X-ray diffraction patterns in the samples annealed under O<SUB>2</SUB> and N<SUB>2</SUB> annealing gases were almost the same, photoluminescence spectra showed the generation of a shallow level with a few meV, and deep-level states were generated at <I>E</I><SUB>v</SUB>+0.594eV. In addition, a defect state appeared at <I>E</I><SUB>c</SUB>−0.607eV, which originated from hydrogen plasma irradiation on the ZnO sample.</P>
Efficiency enhancement in a-plane InGaN/GaN light emitters with carbon nanotubes.
Song, Hooyoung,Suh, Jooyoung,Kim, Eun Kyu,Shin, Kwonwoo,Han, Jong Hun,Hwang, Sung-Min,Song, Keun Man American Scientific Publishers 2012 Journal of Nanoscience and Nanotechnology Vol.12 No.4
<P>This study investigates the coupling modes of a-plane InGaN/GaN mutiquantum wells (MQWs) with single-walled carbon nanotubes (SWCNTs). The enhancement of light emissions at resonance photon energies can be explained by the surface plasmon coupling of the MQW-SWCNT hybrid structure. The photoluminescence (PL) enhancement ratios of the indigo (2.90 eV) emission from MQWs with SWCNTs reveal three coupling modes at 2.50 eV, 2.97 eV, and 3.42 eV. In addition, the trend of the PL intensity ratios and efficiencies corresponds to that of the PL enhancement ratios. The PL efficiencies for the green (2.46 eV) and indigo (2.90 eV) emissions of SWCNT-coated MQWs are 32% and 110% better than the corresponding values of uncoated MQWs, respectively. The results show that the MQW-SWCNT hybrid structure has the potential to be applied in high-efficiency light emitters in the visible and ultraviolet range.</P>