High-Quality Epitaxial Film Growth of Transparent Oxide Semiconductors

Abstract

We review the single-crystalline film growth techniques for transparent oxide semiconductors including ITO, NiO:Li, InGaO₃(ZnO)_m and LaCuOS on single-crystalline YSZ substrates. Single-crystalline ITO films were grown by a PLD method at 900°C, whereas those of NiO:Li, InGaO₃(ZnO)_m and LaCuOS were not obtained by a simple PLD process. Their chemical compositions are difficult to control because high vapor pressure elements evaporate much faster than lower vapor pressure elements. Thus, we used a solid-phase epitaxy, where polycrystalline epitaxial films deposited at room temperature were converted to single-crystalline by thermal annealing. It successfully led to the formation of single-crystalline NiO:Li films. In reactive solid-phase epitaxy (R-SPE) for InGaO₃(ZnO)_m and LaCuOS, it is necessary, in addition to the thermal anneal, to form an epitaxial template layer before the film deposition. As the layers subsequently deposited on a template layer are amorphous or polycrystalline, chemical composition of the epitaxial films can be controlled.