気相法による酸化亜鉛半導体薄膜のステップフローホモエピタキシャル成長

概要

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As a safe, simple, and low energy-consumption growth method of oxide semiconductors, we have developed a mist-chemical vapor deposition (CVD) technique. This technique has been applied to homoepitaxial growth of zinc oxide (ZnO) semiconductor thin films on ZnO bulk substrates. Step-flow growth has been achieved at the growth temperatures of 950∼1000°C. The step height was 0.26nm, that is, one molecular-layer height, in the initial growth stage (20∼50nm in ZnO epilayer thickness) and it is enhanced as 0.52nm, that is, two molecular-layers height, for the thicker (>200nm) films, due to coalescence of two terrace layers. Terrace shapes have been well interpreted in terms of the balance between incorporation and evaporation of adatoms at the terrace edges. The homoepitaxial ZnO layers exhibited good crystallinity comparable to that of substrates, but the inclusion of impurities, probably from the source materials due to their insufficient purity as semiconductor sources, remained as one of the most important problems to be overcome for future evolution of this unique growth technique.