Jeong-Dae Suh

Chemical states of Co and Fe in a specularly reflective oxide layer in spin valves

In an examination of near-edge x-ray absorption fine structure spectra and magnetoresistance responses of a spin valve with a partially oxidized Co90Fe10 layer, we found that oxygen preferentially reacted with the solute Fe rather than with the solvent Co, and the very oxidized Fe likely enhanced specular reflections leading to an increase in the magnetoresistance value. Most Fe oxides transformed into α-Fe2O3, which further improved the magnetoresistance response after the spin valves were annealed. Our results show that obtaining appropriate oxide phases and controlling their quantity are the key to optimizing the magnetoresistance performance and magnetic properties of spin valves with specularly reflective oxide layers.

Undoped homojunction chalcogen thin-film transistors on glass

A technique to develop an undoped homojunction chalcogen thin-film transistor (UHJ-c-TFT) on glass is described. The UHJ-c-TFT is based on ternary chalcogenide alloy amorphous (α) Ge2Sb2Te5 (GST) and the positively cooled crystalline (χ) GST. The α-GST and the positively cooled χ-GST are used as a channel layer and ohmic contact layer, respectively. In the UHJ-c-TFT, the authors realize electric rectification by the energy difference from the Fermi level of the α-GST and the Fermi level of the positively cooled χ-GST. The UHJ-c-TFT shows the clear gate characteristics of a typical p-channel enhancement mode.

Cubic Y–Ba–Cu–O thin films by high speed pulsed laser deposition

Abstract The crystal structure and properties of YBa2Cu3Ox (YBCO) thin films on LaSrGaO4 (100) substrate have been investigated as a function of deposition rates in the range of 0.1–12.2 nm/s using different repetition rate of pulsed laser. At a given substrate temperature of 700°C, when the film was deposited at low deposition rate of 0.1 nm/s, c-axis oriented orthorhombic YBCO thin film growth was observed. However, at high deposition rate of 12.2 nm/s, cubic YBCO thin film growth was observed. This demonstrates that the shortening of interval time between the vapor pulses is important for the cubic YBCO thin film growth. The cubic YBCO thin film growth under high deposition rates was explained by the cation kinetics.

Growth of CuInSe 2 Thin Film Using Non-Vacuum Solution Deposition Technique

Polycrystalline thin films of CuInSe 2 were prepared successfully using the chemical spray pyrolysis technique as a function of Cu/In atomic ratios and variation of selenium ratios. For the compositional and structural analysis, X-ray diffraction, UV-visible spectroscopy, the Hall effect measurement and scanning electron microscopy were carried out. The effects of the Cu/In ratio and selenium concentration were observed in the XRD, SEM, UV-visible spectrum and the Hall effect measurement analysis for fabricated thin films. The result of XRD and UV-visible analysis showed an increase or decrease of crystallinity and shift of transmittance tendency depending on the copper and selenium content. The grain size of thin films was increased with the increase of copper content. In the thin films, the variation of Cu/In ratios between 0.8 to 1 showed an increase on hole density, but a decrease of Hall mobility and resistivity. We suggest the formation of Cu x Se phase particles or layers depends on the spray solution. Based on these results, we will fabricate and characterize CISe/CIGSe thin film solar cells in further work.

Cubic Structure and Cation Disordering of YBCO Thin Film

We have systematically investigated the in-situ growth of YBa2Cu3O7-x (YBCO) thin films on SrTiO3 (100) substrate as a function of deposition rates in the range of 0.1–12.2 nm/s using different repetition rates of pulsed laser. As the deposition rates increases, YBCO thin film with cubic crystalline structure was observed at a substrate temperature of 650 °C and cation disordering in YBCO thin film was observed at a substrate temperature of 800 °C. The cubic YBCO thin film growth and the cation disordering in YBCO thin film at high deposition rates were explained by the cation kinetics model.

CUBIC STRUCTURE AND CATION DISORDERING IN YBCO THIN FILM DEPOSITED BY HIGH SPEED PULSED LASER DEPOSITION

We have investigated the crystalline structure of high rate deposited YBa2Cu3Ox thin films prepared by high speed pulsed laser deposition. A cation disordered cubic structure with lattice parameter of 0.39 nm was found in YBCO thin film deposited at 12.2 nm/s deposition rate and 650°C substrate temperature conditions. The short range ordered cubic YBa2Cu3Ox thin film growth at high deposition rate was explained by the short migration length of Y and Ba cation atoms owing to the high incident flux rate.