Tae-Bong Hur

Photoluminescence of polycrystalline ZnO under different annealing conditions

We investigated polycrystalline zinc oxide (ZnO) with different annealing conditions in air by x-ray photoelectron spectroscopy and photoluminescence. We found that the concentration of antisite oxide (OZn) increases when ZnO ceramics were in an O-rich condition. As the concentration of antisite oxide (OZn) increased, the photoluminescence intensity of the green band emission increased. The crossover temperature of the free and bound excitons was roughly estimated as 100 K.

Impurity band characteristics near the band edge of Al-doped ZnO

The characteristics of impurity bands near the band edge of Al-doped and undoped ZnO ceramics were investigated by photoluminescence, photoluminescence excitation, and x-ray diffraction. We found that Al(0.6%)-doped ZnO had two impurity bands whose binding energies were roughly 13 and 99meV below the effective band edge. Also, we found that Al(1.1%)-doped ZnO had an impurity band of ∼80meV binding energy below the effective band edge. As the doping concentration of ZnO increases, Al-impurity bands degenerated from two localized levels to the single localized level. The green band emission of Al(0.6%)-doped ZnO is stronger than those of the pure and Al(1.1%)-doped ZnO because of the high charge transfer rate to the effective band.

Study of the structural evolution in ZnO thin film by in situ synchrotron x-ray scattering

The evolution of surface roughness and strain relaxation as a function of film thickness of ZnO films grown on sapphire(0001) were studied by in situ synchrotron x-ray scattering and atomic force microscopy measurements. The well-aligned two-dimensional (2D) planar layer dominated in layer-by-layer growth at the highly strained initial growth stage. As the film thickness increased, the discrete nucleations on the 2D planar layer continuously grew until the ZnO film reached the strain relaxed steady-state regime. When the 3D islands were quickly developed by the strain relaxation, the dynamic scaling exponent β was roughly 1.579. The strain relaxed steady-state regime was described as β∼0.234.

Strain effects in ZnO thin films and nanoparticles

We grew Stranski-Krastanow-type ZnO thin film and Volmer-Weber-type self-assembled ZnO nanocrystals using magnetron sputtering methods. The evolution of surface roughness and strain effects in thin ZnO films on Al2O3(0001) substrate and ZnO nanocrystals on Pt(111) surface studied by synchrotron x-ray scattering. The well-aligned two-dimensional (2D) planar layer dominated in layer-by-layer growth at the highly strained initial growth stage in the thin films. As the film thickness increased, the discrete nucleations on the 2D planar layer continuously grew until the ZnO film reached the strain relaxed steady-state regime. The accumulated strain energy in the thin film grown at low temperature slowly relaxed while the strain energy in the high temperature system rapidly relaxed. When the three-dimensional islands on the 2D surface of thin ZnO film grown at the low and high temperatures were quickly developed by strain relaxation, the critical exponent β were roughly 0.693 and 1.579, respectively. The thickn...

Quantum confinement in Volmer-Weber-type self-assembled ZnO nanocrystals

We have studied the quantum confinement effect on Volmer–Weber-type self-assembled ZnO nanocrystals. Volmer–Weber-type self-assembled ZnO nanocrystals were grown on the Pt(111) substrate by using a rf-magnetron sputtering method and were confirmed by the Auger electron spectroscopy. The free exciton transition energies of 57-, 38-, and 24‐nm-size nanocrystals were found to be roughly 3.298, 3.311, and 3.337eV, respectively, by photoluminescence measuremnets at room temperature. The blueshift of the photoluminescence peak energy of ZnO nanocrystals of 24nm in diameter roughly varied by 40meV compared to bulk ZnO.

Synchrotron x-ray scattering study on the evolution of surface morphology of the InN/Al2O3(0001) system

Dynamic scaling behavior was studied for InN films grown on sapphire(0001) substrates using high-resolution synchrotron x-ray reflectivity and atomic force microscopy measurements. In the early stage of growth, highly strained planar InN films were grown. As the film thickness approaches an effective critical thickness, the growth gradually crosses over to the island growth. Concurrently, the relaxation of the lattice strain begins and the growth front becomes rougher. The roughness increases mostly during the intermediate crossover regime where the strain is relieved. In this regime, the dynamic scaling exponent, β, is estimated as 1.754±0.071. The evolution of the surface roughness in the final-stage growth can be described by the dynamic scaling exponent of 0.236±0.022.

Morphological and structural characterization of epitaxial α-Fe2O3 (0001) deposited on Al2O3 (0001) by dc sputter deposition

We investigated α-Fe2O3 (0001) film growth on α-Al2O3 (0001) using a laboratory-built dc faced magnetron sputtering system with x-ray diffraction, x-ray reflectivity, and atomic force microscopy (AFM). The films were deposited from iron targets at a growth rate of ∼6.3nm∕min in an ambient argon and oxygen mixture. The structural properties and quality of the α-Fe2O3 thin films were characterized using high-resolution synchrotron x-ray scattering. Films thinner than 16nm were to be found highly strained due to the large lattice mismatch between film and substrate of 5.8%. This strain was found to decrease as the film thickness increased, and most of the strain was released through surface modulation once the film thickness reached 20nm. The epitaxial relationships were found to be α-Fe2O3 [0001]‖α-Al2O3 [0001] in the out-of-plane direction. That the film and substrate display the in-plane alignment anticipated for the epitaxy of isomorphous materials was established by verifying that the [112¯0] directions of film and substrate were coincident. X-ray reflectivity and AFM were used to show that layer-by-layer growth of α-Fe2O3 (0001) occurs up to a thickness of 11nm despite the large lattice mismatch.We investigated α-Fe2O3 (0001) film growth on α-Al2O3 (0001) using a laboratory-built dc faced magnetron sputtering system with x-ray diffraction, x-ray reflectivity, and atomic force microscopy (AFM). The films were deposited from iron targets at a growth rate of ∼6.3nm∕min in an ambient argon and oxygen mixture. The structural properties and quality of the α-Fe2O3 thin films were characterized using high-resolution synchrotron x-ray scattering. Films thinner than 16nm were to be found highly strained due to the large lattice mismatch between film and substrate of 5.8%. This strain was found to decrease as the film thickness increased, and most of the strain was released through surface modulation once the film thickness reached 20nm. The epitaxial relationships were found to be α-Fe2O3 [0001]‖α-Al2O3 [0001] in the out-of-plane direction. That the film and substrate display the in-plane alignment anticipated for the epitaxy of isomorphous materials was established by verifying that the [112¯0] directions...

Study of the strain in InN thin films using synchrotron X-ray scattering

Semiconductor InN films epitaxially grown by the radio frequency magnetron sputtering deposition method were studied in terms of the strain evolution as a function of the film thickness and growth temperature. The structure and surface morphology of the InN films were analyzed using synchrotron X-ray scattering and atomic force microscopy (AFM) experiments, respectively. The lattice strain of the InN films grown at 300°C was larger than that of the films grown at 490°C. As the film thickness increases, the lattice strain is reduced and completely relaxes when the thickness is larger than 350 A. The average roughness on the surface of the InN film increased with the growth temperature.

Characterization of Buried Ultrathin Layer and Multilayer System by X-Ray Scattering

We examine the interfacial layer and the height correlation function of the defective semiconductor thin SnO2 film on the sapphire and Mo/Si multilayer by X-ray reflectivity measurements. We focus on how to estimate the quality of the interfaces in the thin films quickly. In particular, it is easily found that for the SnO2 thin film, an ultrathin layer exists between the SnO2 film and the sapphire substrate, and for the Mo/Si multilayer, a silicide layer exists between each Mo/Si layer.