Fabrication of ScAlMgO4 epitaxial thin films using ScGaO3(ZnO)m buffer layers and its application to lattice-matched buffer layer for ZnO epitaxial growth

Single-crystalline thin films of ScAlMgO4 (SCAM) were fabricated on YSZ (111) substrates by reactive solid-phase epitaxy (R-SPE) using ScGaO3(ZnO)m (SGZO) single-crystalline buffer layers, which suppress interface reactions between the SCAM layers and the YSZ substrates. First, post-annealing of the SCAM layers fabricated by the R-SPE process was examined. When annealing temperature was raised to > 1200 °C, the formation of a spinel MgAl2O4 phase was observed. This is due probably to out-diffusion of Sc ions from the SCAM layers to the YSZ substrates. By introducing an SGZO buffer layer, a single-phase SCAM layer with a step-and-terrace surface was obtained by annealing at 1450 °C without the spinel formation. The SCAM layer was grown heteroepitaxially with an epitaxial relationship of (000 l)SCAM  (111)YSZ and (110)SCAM  (11–0)YSZ. Atomically flat surfaces were eventually formed by chemical-mechanical polishing. The SCAM layer was applied to a lattice-matched buffer layer for the growth of ZnO film, leading to marked lateral growth of ZnO domains.