Atomic Nature of the Growth Mechanism of Atomic Layer Deposited High-κ Y2O3 on GaAs(001)-4 × 6 Based on in Situ Synchrotron Radiation Photoelectron Spectroscopy

Epitaxy from a Periodic Y-O Monolayer: Growth of Single-Crystal Hexagonal YAlO3 Perovskite

The role of an atomic-layer thick periodic Y–O array in inducing the epitaxial growth of single-crystal hexagonal YAlO₃ perovskite (H-YAP) films was studied using high-angle annular dark-field and annular bright-field scanning transmission electron microscopy in conjunction with a spherical aberration-corrected probe and in situ reflection high-energy electron diffraction. We observed the Y–O array at the interface of amorphous atomic layer deposition (ALD) sub-nano-laminated (snl) Al₂O₃/Y₂O₃ multilayers and GaAs(111)A, with the first film deposition being three cycles of ALD-Y₂O₃. This thin array was a seed layer for growing the H-YAP from the ALD snl multilayers with 900 °C rapid thermal annealing (RTA). The annealed film only contained H-YAP with an excellent crystallinity and an atomically sharp interface with the substrate. The initial Y–O array became the bottom layer of H-YAP, bonding with Ga, the top layer of GaAs. Using a similar ALD snl multilayer, but with the first film deposition of three ALD-Al₂O₃ cycles, there was no observation of a periodic atomic array at the interface. RTA of the sample to 900 °C resulted in a non-uniform film, mixing amorphous regions and island-like H-YAP domains. The results indicate that the epitaxial H-YAP was induced from the atomic-layer thick periodic Y–O array, rather than from GaAs(111)A.