Large domain growth of GaN epitaxial films on lattice-matched buffer layer ScAlMgO4

A homologous series compound ScAlO3(MgO) (SCAM) has a superior lattice matching as small as ∼1.4% in a-axis with GaN. This paper reports an efficient fabrication process of a single-crystalline SCAM buffer layer on a (1 1 1) yttria-stabilized zirconia (YSZ) substrate using pulsed laser deposition (PLD). A 10-nm thick ZnO epitaxial layer was used to induce solid-phase epitaxial growth of an amorphous (a-) SCAM layer formed at room temperature on (1 1 1) YSZ. It was found that the addition of excess Sc2O3 and ZnO to a SCAM target used for PLD was needed to obtain single-crystalline SCAM films with atomically flat terraces-and-steps surfaces. The resulting single-crystalline SCAM films were examined as buffer layers to grow GaN by molecular beam epitaxy with a plasma nitrogen source. The GaN films were grown epitaxially on the SCAM/YSZ substrates with the epitaxial relationship of [0 0 0 1] GaN||[0 0 0 1] SCAM||[1 1 1] YSZ and [1 0 0] GaN||[11-20] SCAM||[1-10] YSZ. The SCAM buffer layers enhanced lateral growth of the GaN films owing to the good lattice matching.