Single-Crystalline Film Growth of Transparent Oxide Semiconductors

Abstract

We review the single-crystalline film growth 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^oC, 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. 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 contrast, it is necessary to form an epitaxial template layer before the film deposition and thermal annealing (Reactive Solid-Phase Epitaxy (R-SPE)) for InGaO₃(ZnO)_m and LaCuOS. In the R-SPE method, the layers subsequently deposited on the template layer may be amorphous or polycrystalline, which allows control of chemical composition of resultant films.