JeongYong Lee

Formation mechanism of V defects in the InGaN/GaN multiple quantum wells grown on GaN layers with low threading dislocation density

V-defect formation of the InxGa1−xN/GaN multiple quantum wells (MQWs) grown on GaN layers with different threading dislocation (TD) densities was investigated. From cross-sectional transmission electron microscopy, we found that all V defects are not always connected with TDs at their bottom. By increasing the indium composition in the InxGa1−xN well layer or decreasing the TD density of the thick GaN layer, many V defects are generated from the stacking mismatch boundaries induced by stacking faults which are formed within the MQW due to the strain relaxation. Also, TD density in the thick GaN layer affects not only the origin of V-defect formation but also the critical indium composition of the InxGa1−xN well on the formation of V defects.

Photoluminescence and heteroepitaxy of ZnO on sapphire substrate (0001) grown by rf magnetron sputtering

ZnO thin films were epitaxially grown on α-Al2O3 (0001) single-crystal substrates by rf magnetron sputtering. The films were grown at substrate temperatures of 550–600u200a°C for 1 h at a rf power of 60–120 W and Ar/O2 ratios of 1–4. The crystalline structure of the ZnO films was analyzed by four-circle x-ray diffraction (XRD) and Rutherford backscattering (RBS)/channeling. For the ZnO films deposited at 550u200a°C, the full width at half maximum (FWHM) of the XRD θ-rocking curve of the ZnO (0002) plane was found to be increased from 0.16° to 0.3° as the rf power was increased from 80 to 120 W. The in-plane epitaxial relationship of the ZnO film on α-Al2O3 (0001) substrates was found to be ZnO [1010]∥α-Al2O3[1120], indicating a 30° rotation of the ZnO unit cell with respect to the α-Al2O3 (0001) substrate. For the specimen grown at 600u200a°C, the FWHM of the XRD θ-rocking curve was 0.13°. In RBS/channeling studies, the films, which were deposited at 600u200a°C and 120 W, showed good crystallinity, with a channeling yi...

Nanoscale Silver-Based Al-Doped ZnO Multilayer Transparent-Conductive Oxide Films

Requirements of transparent-conductive oxide (TCO) films for solar cells and other optoelectronic applications are mainly focused on the electrical resistivity as low as 10- 5 Ω cm, optical transmittance above ∼85% in the visible region, a long-term stability in damp heat-treatment for 1000 h, a mechanical stability on flexible polymer substrates, and the large-area deposition technique for commercialization. In this study, the typical properties of the 45 nm thick Al-doped ZnO (AZO)/Ag/45 nm thick AZO multilayer films embedded by silver layers with various thicknesses were addressed to satisfy the requirements of TCO films for flexible electronic device applications. The AZO/9 nm thick Ag/AZO multilayer films as deposited on poly(ether sulfone) (PES) polymer substrates at 30°C by radio-frequency magnetron sputtering, which the deposition on large-area substrates is possible, exhibited the electrical resistivity of approximately 5 X 10- 5 Ω cm, optical transmittance of 88% at 550 nm wavelength, no appreciable change in electrical resistance and optical transmittance after damp heat-treatment for 1000 h, and a strong mechanical stability between multilayer films and PES substrates after a severe bending test. The results presented in the multilayer films can provide a platform for TCO films deposited on polymer substrates to enable the flexible electronic device applications.

Structure and gas-sensing characteristics of undoped tin oxide thin films fabricated by ion-assisted deposition

Abstract Undoped SnOx thin films were deposited by a reactive ion assisted deposition technique at various ion beam potential (VI) onto amorphous SiO2/Si substrates at room temperature. Crystalline structures of the films were investigated in terms of grain size, composition ratio, porosity and peak area percent of adsorbed oxygen. Sensitivities for propane (C3H8), methane (CH4) and hydrogen (H2) gas in SnOx gas sensor devices were characterized at the substrate temperatures of 100–500°C. The gas sensitivities depend on the grain size rather than the porosity. It is also proportioned to the amounts of adsorbed oxygen at room temperature by XPS analysis.

Growth mechanisms of thin-film columnar structures in zinc oxide on p-type silicon substrates

X-ray diffraction analysis reveals that the crystallinity of (0001)-oriented columnar grains in ZnO thin films grown on p-Si (100) substrates is enhanced with increasing growth temperature, and transmission electron microscopy confirms that the columnar structures become more stable at higher growth temperature. The morphological evolution of the columnar structure in ZnO thin films is described on the basis of experimental measurements.

Strain-induced diffusion in a strained Si1−xGex/Si heterostructure

Diffusivity of a strained heterostructure was theoretically investigated, and general diffusion equations with strain potential were deduced. There was an additional diffusivity by the strain potential gradient as well as by the concentration gradient. The strain-induced diffusivity was a function of concentration, and its temperature dependence was formulated. The activation energy of the strain-induced diffusivity was measured by high-resolution transmission electron microscopy. This result can be generally applied for the investigation of the diffusion in strained heterostructures.

INTERFACIAL LAYER FORMATION OF THE CDTE/INSB HETEROINTERFACES GROWN BY TEMPERATURE GRADIENT VAPOR TRANSPORT DEPOSITION

CdTe epitaxial films were grown by a simple method of temperature gradient vapor transport deposition on p‐InSb (111) orientation substrates in the growth temperature range between 200 and 300u2009°C. The stoichiometry of the CdTe/InSb heterostructure was observed by Auger electron spectroscopy, and Auger depth profiles demonstrated that the CdTe/InSb heterointerface was not abrupt. Transmission electron microscopy verified the formation of an interfacial layer in the CdTe/InSb interface and the formation of the stacking faults in the CdTe thin film. These results indicated that the films grown at approximately 270u2009°C contained a formation problem of an interfacial layer due to interdiffusion from the InSb prior to the growth of the CdTe, and that the interfacial layer might deteriorate the electrical property of the CdTe epitaxial layer.

TiC and TiN coatings formed on Si3N4TiC composite ceramics by chemical vapour deposition

Abstract Titanium carbide (TiC) and titanium nitride (TiN) films were deposited on Si3N4ue5f8TiC composite cutting tools by chemical vapour deposition using TiCl4ue5f8CH4ue5f8H2 and TiCl4ue5f8H2ue5f8N2 gas mixtures respectively. An Auger electron spectroscopy survey was performed in order to find out the non-metal to metal ratio of the coated layer at various deposition conditions. The non-metal to metal ratio of deposit increases with increasing mC:Ti (mole ratio of CH4 to TiCl4 in the input) for TiC coatings and mN:Ti (mole ratio of N2 to TiCl4 in the input) for TiN coatings. Nearly stoichiometric films could be obtained with mC:Ti = 1.15−1.61 for TiC and with mN:Ti = 25–28 for TiN. Also, maximum microhardness of the coatings can be obtained in these ranges. An interfacial region between the coated layer and the substrate was investigated by Auger depth profile analysis. The interfacial region of TiC coatings on Si3N4ue5f8TiC ceramics is wider than that of TiN coatings according to Auger depth profile analysis, which indicates good interfacial bonding for TiC. The microstructure and thermal shock resistance of the coated layer were also investigated. Experimental results show that TiC coatings have an equiaxed structure and TiN coatings have a columnar structure with a (220) preferred orientation. Also, TiC coatings on Si3N4ue5f8TiC ceramics have more resistance to thermal shock than do TiN coatings.

Formation mechanism of ZnSiO3 nanoparticles embedded in an amorphous interfacial layer between a ZnO thin film and an n-Si (001) substrate due to thermal treatment

The x-ray diffraction patterns, transmission electron microscopy images, and selected-area electron diffraction patterns for the ZnO∕Si heterostructures annealed at 900°C showed that orthorhombic ZnSiO3 nanoparticles were formed in the amorphous layer between the ZnO film and the Si substrate, resulting from the interdiffusion between the ZnO film and the Si substrate due to thermal treatment. Auger electron spectroscopy depth profiles for the ZnO∕Si heterostructures annealed at 900°C demonstrated the formation of amorphous Zn2xSi1−xO2, an interfacial layer. A formation mechanism for the orthorhombic ZnSiO3 nanoparticles embedded in the amorphous Zn2xSi1−xO2 layer is described on the basis of the experimental results.

Strong bonding of titanium to copper through the elimination of the brittle interfacial intermetallics

The microstructures, interfacial reactions, and bonding strength properties of the Ti–Cu dissimilar joints using a commercially available Ag–28Cu–2Ti filler were studied, particularly as they relate to the role of an Ag barrier layer at the Ti interface. A joint microstructure and interfacial reactions closely related to the formation of brittle interfacial Ti–Cu intermetallics were fully dominated by the presence of the Ag layer at the Ti interface. Reliable Ti(base)/TiAg/Ag/Ag–Cu eutectic/Cu(base) joints without any detrimental Ti–Cu intermetallics were achieved at low brazing temperatures below 810 °C by applying an Ag interlayer of suitable thickness. It was notable that their bonding strengths were strong enough to exceed the strength of a Cu bulk base metal. This research demonstrates the potential application of an Ag interlayer for the reliable Ti–Cu dissimilar joints.