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Soaram Kim,김민수,남기웅,임재영 대한금속·재료학회 2012 ELECTRONIC MATERIALS LETTERS Vol.8 No.4
ZnO seed layers were deposited on a quartz substrate using the sol-gel method, and Al-doped ZnO (AZO)nanorod array thin films were grown on the ZnO seed layers by the hydrothermal method with different Al concentrations ranging from 0 to 2.0 at. %. The structural and blue emission properties of the ZnO and AZO nanorod array thin films were investigated using scanning electron microscopy (SEM), x-ray diffraction,Ultraviolet-visible spectroscopy, and photoluminescence (PL). Al doping greatly affects the morphology of AZO nanorod array thin films. For an Al concentration of 2.0 at. %, it can be clearly seen from the SEM image that the hexagonal shape has changed into a prism-like shape. In the PL spectra, it is clear that the intensity ratio of the near-band-edge emission to the deep-level emission (DLE) increases as the Al concentration increases up to 2.0 at. %. The DLE peak (about 2.80 eV) in the blue emission region is found for the AZO nanorod array thin films. The transmittance spectra show that as compared to the ZnO nanorod array thin films, the AZO nanorod array thin films exhibited significantly improved transmittance in the visible region and a blue shift of the absorption edge.
Temperature-dependent Photoluminescence of Boron-doped ZnO Nanorods
Kim, Soaram,Park, Hyunggil,Nam, Giwoong,Yoon, Hyunsik,Kim, Jong Su,Kim, Jin Soo,Son, Jeong-Sik,Lee, Sang-Heon,Leem, Jae-Young Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.11
Boron-doped ZnO (BZO) nanorods were grown on quartz substrates using hydrothermal synthesis, and the temperature-dependence of their photoluminescence (PL) was measured in order to investigate the origins of their PL properties. In the UV range, near-band-edge emission (NBE) was observed from 3.1 to 3.4 eV; this was attributed to various transitions including recombination of free excitons and their longitudinal optical (LO) phonon replicas, and donor-acceptor pair (DAP) recombination, depending on the local lattice configuration and the presence of defects. At a temperature of 12 K, the NBE produces seven peaks at 3.386, 3.368, 3.337, 3.296, 3.258, 3.184, and 3.106 eV. These peaks are, respectively, assigned to free excitons (FX), neutral-donor bound excitons ($D^{\circ}X$), and the first LO phonon replicas of $D^{\circ}X$, DAP, DAP-1LO, DAP-2LO, and DAP-3LO. The peak position of the FX and DAP were also fitted to Varshni's empirical formula for the variation in the band gap energy with temperature. The activation energy of FX was about ~70 meV, while that of DAP was about ~38 meV. We also discuss the low temperature PL near 2.251 eV, related to structural defects.
Optical parameters of Al-doped ZnO nanorod array thin films grown via the hydrothermal method.
Kim, Soaram,Kim, Min Su,Nam, Giwoong,Park, Hyunggil,Yoon, Hyunsik,Leem, Jae-Young American Scientific Publishers 2013 Journal of nanoscience and nanotechnology Vol.13 No.9
<P>ZnO seed layers were deposited onto a quartz substrate using the sol--gel method, and Al-doped ZnO (AZO) nanorod array thin films with different Al concentrations that ranged from 0 to 2.0 at. % were grown on the ZnO seed layers via the hydrothermal method. Optical parameters, including the optical band gap, the absorption coefficient, the Urbach energy, the refractive index, the dispersion parameter, and the optical conductivity, were studied to investigate the effects of Al doping on the optical properties of AZO nanorod array thin films. The optical band gaps of the ZnO and AZO nanorod array thin films were 3.206 at 0 at.%, 3.214 at 0.5 at.%, 3.226 at 1.5 at.%, and 3.268 at 2.0 at.%. The Urbach energy gradually decreased from 126 meV (0 at.%) to 70 meV (2.0 at.%) as the Al concentration was increased. The dispersion energy, the single-oscillator energy, the average oscillator wavelength, the average oscillator strength, the refractive index, and the optical conductivity of the AZO nanorod array thin films were all affected by Al doping.</P>
Optical parameters of boron-doped ZnO nanorods grown by low-temperature hydrothermal reaction.
Kim, Soaram,Park, Hyunggil,Nam, Giwoong,Yoon, Hyunsik,Kim, Younggyu,Kim, Byunggu,Ji, Iksoo,Kim, Jong Su,Kim, Jin Soo,Kim, Do Yeob,Kim, Sung-O,Leem, Jae-Young American Scientific Publishers 2014 Journal of nanoscience and nanotechnology Vol.14 No.11
<P>Sol-gel spin-coating was used to deposit ZnO seed layers onto quartz substrates, and ZnO nanorods doped with various concentrations of B (i.e., BZO nanorods) ranging from 0 to 2.0 at% were hydrothermally grown on the ZnO seed layers. The effects of B doping on the absorption coefficient, optical band gap, Urbach energy, refractive index, extinction coefficient, single-oscillator energy, dispersion energy, average oscillator strength, average oscillator wavelength, dielectric constant, and optical conductivity of the hydrothermally grown BZO nanorods were investigated. The optical band gaps were 3.255, 3.243, 3.254, 3.258, and 3.228 eV for the nanorods grwon at 0, 0.5, 1.0, 1.5 and 2.0 at% B, respectively. B doping increased the Urbach energy from 40.7 to 65.1 meV for the nanorods grown at 0 and 2.0 at% B, respectively, and significantly affected the dispersion energy, the single-oscillator energy, the average oscillator wavelength, the average oscillator strength, the refractive index, and the optical conductivity of the hydrothermally grown BZO nanorods.</P>
Photoluminescence properties of defect emissions in Al-doped ZnO nanorod array thin films.
Kim, Soaram,Nam, Giwoong,Park, Hyunggil,Yoon, Hyunsik,Kim, Min Su,Kim, Do Yeob,Kim, Sung-O,Leem, Jae-Young American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.9
<P>The power- and temperature-dependent photoluminescence properties of Al-doped ZnO nanorod array thin films grown by the hydrothermal method were investigated. The intensities of both the near-band-edge emission (NBE) and deep-level emission (DLE) as well as the overall spectral line shape were strongly affected by the excitation power. At low excitation power, the blue emission was found to show the highest intensity among the different emission lights. A low-temperature photoluminescence analysis revealed the bound-exciton-related luminescence peak at 3.362 eV. The dependence of peak energy with the excitation power indicates that these DLE processes are generated by DAP transitions. The overall intensity of DLE was found to decrease as the temperature increases. With regard to the blue emission (around 2.52 eV), it showed a well-pronounced shoulder at 200 K. The activation energy for this blue emission was 51.93 meV, which corresponds to the thermal dissociation energy required for the donor-acceptor pair transitions.</P>
Kim, Soaram,Nam, Giwoong,Park, Hyunggil,Yoon, Hyunsik,Lee, Sang-Heon,Kim, Jong Su,Kim, Jin Soo,Kim, Do Yeob,Kim, Sung-O,Leem, Jae-Young Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.4
The structural and optical properties of the ZnO, Al-doped ZnO, Ga-doped ZnO, and In-doped ZnO nanorods were investigated using field-emission scanning electron microscopy, X-ray diffraction, photoluminescence (PL) and ultraviolet-visible spectroscopy. All the nanorods grew with good alignment on the ZnO seed layers and the ZnO nanorod dimensions could be controlled by the addition of the various dopants. For instance, the diameter of the nanorods decreased with increasing atomic number of the dopants. The ratio between the near-band-edge emission (NBE) and the deep-level emission (DLE) intensities ($I_{NBE}/I_{DLE}$) obtained by PL gradually decreased because the DLE intensity from the nanorods gradually increased with increase in the atomic number of the dopants. We found that the dopants affected the structural and optical properties of the ZnO nanorods including their dimensions, lattice constants, residual stresses, bond lengths, PL properties, transmittance values, optical band gaps, and Urbach energies.