PREPARATION OF HIGH-QUALITY ELECTRONIC THIN FILMS BY LASER DROPLET EPITAXY

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Pulsed laser ablation (PLA) is known to have quite unique features in deposition process, I.e., the depositing particles consist of atomic species, clusters, and molten droplets with micron size. The aim of this study is to investigate the fabrication process of thin-film depositions by PLA using the molten droplets. In PLA process, it has been believed that droplets must be eliminated. Liquid phase epitaxy (LPE) is equilibrium process, while vapor phase epitaxy (VPE) is non-equilibrium process. In order to grow a high quality film with a low defect density, crystal growth by PLA using large number of molten droplets will be an attractive technique that allows LPE-like crystal growth using VPE-like vacuum system.First, germanium (Ge) was employed for this study. The second harmonic of YAG laser (532 nm) was employed for producing Ge droplets efficiently. Ge film prepared at room temperature was found to have a large number of solidified droplets on the substrate. As the substrate temperature was elevated up to 600 ℃ , Ge film was formed as island structure on (100)Si substrates. The x-ray pole figure measurement revealed that Ge film showed growth of Ge crystal aligned in plane as well as out of plane in a manner of cube-on-cube.Yttrium Iron Garnet (YIG) was the second target for this study. YIG is known to be a excellent material for microwave applications. YIG films were grown by PLA on (111)GGG substrates using the YAG laser. Highly oriented YIG crystal were grown on the (111)GGG substrate heated at 860 ℃ by PLA using a large number of molten droplets, suggesting an LPE-like growth. This YIG films shows a small ferromagnetic resonance linewidth of 7.5 Oe. This value is quite small for films prepared by vapor-phase epitaxy techniques.