Keun-Ho Auh

Properties of Freestanding GaN Substrates Grown by Hydride Vapor Phase Epitaxy

We report on freestanding GaN thick films with a thickness of 300 µm grown on 2-inch sapphire (0001) substrates by hydride vapor phase epitaxy. In order to improve the surface morphology of GaN with hillocks, we polished its surface with diamond abrasives and investigated the photoluminescence properties of the polished GaN. Transmission electron microscopy measurement was used to observe the subsurface damage layers. We used the dry etching method, chemically assisted ion-beam etching (CAIBE), for the removal of the damage layer and identified the recovery of photoluminescence properties. As a result, the morphology of the homoepitaxial GaN regrown layer was improved by ion-beam etching compared to that of the not-etched layer.

Electrical properties of ferroelectric SBT thin films prepared using photosensitive sol-gel solution

Self-patterning of thin films using photosensitive sol-gel solution has advantages such as simple manufacturing process compared to photoresist/dry etching process. In this study, ferroelectric Sr0.9Bi2.1Ta2O9 thin films have been prepared by spin coating method using photosensitive sol-gel solution. Strontium ethoxide, tetramethylheptanedionato bismuth and tantalum ethoxide were used as starting materials. As UV exposure time to the SBT thin film increases, the intensity of UV absorption peak of metal beta-diketonate decreases due to degradation of solubility resulted from Metal-Oxygen-Metal (M–O–M) bond formation. The solubility difference by UV irradiation on SBT thin film allows to obtain a fine patterning of thin film. The ferroelectric properties of the UV irradiated SBT thin films are superior to those of the non-UV irradiated film.

Self-patterning Technique of Photosensitive La 0.5 Sr 0.5 CoO₃ Electrode on Ferroelectric Sr 0.9 Bi 2.1 Ta₂O 9 Thin Films

La 0.5 Sr 0.5 CoO₃ (LSCO) electrodes were prepared on ferroelectric Sr 0.9 Bi 2.1 Ta₂O 9 (SBT) thin films by spin coating method using photosensitive sol-gel solution. Self-patterning technique of photosensitive sol-gel solution has advantages such as simple manufacturing process compared to photoresist/dry etching process. Lanthanum(Ⅲ) 2-methoxyethoxide, Strontium diethoxide, Cobalt(Ⅱ)2-methoxyethoxide were used as starting materials for LSCO electrode. UV irradiation on LSCO thin films lead to decreases solubility by M-O-M bond formation and the solubility difference allows us to obtain self-patterning. There was little composition change of the LSCO thin films between before leaching and after leaching in 2-methoxyethanol. The lowest resistivity of LSCO thin films deposited on SiO₂/Si substrate was 1.1×10 -2 Ωcm when the thin film was annealed at 740℃. The values of Pr/Ps and 2Pr of LSCO/SBT/Pt capacitor on the applied voltage of 5 V were 0.51, 8.89 μC/㎠, respectively.