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

Minghwei Hong,Chao-Kai Cheng,Chien-Ting Wu,Jueinai Kwo,Ren-Fong Cai,Yen-Hsun Lin,Chia-Hung Hsu,Lawrence Boyu Young

doi:10.3390/nano10081515

Abstract

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.

Highlights

Excellent hetero-epitaxial growth, which is a material science wonder, has had strong impacts on technologies and scientific advances
Examples are the growth of GaN/sapphire [1] and rare-earth metals/Nb/sapphire [2]. The former led to the development of the blue light-emitting diode and lasers, whilst the latter led to the discovery of long-range anti-ferromagnetic coupling through non-magnetic media [3,4], which subsequently led to the observation of a giant magnetoresistance (GMR) [5] for high-density magnetic recording
atomic layer deposition (ALD) crystalline LaAlO3 films were grown on Si(001) with a buffer layer of four unit cells of Molecular beam epitaxy (MBE)-SrTiO3 after 600 ◦C annealing under vacuum for 2 h [29]

Summary

Introduction

Excellent hetero-epitaxial growth, which is a material science wonder, has had strong impacts on technologies and scientific advances. Examples are the growth of GaN/sapphire [1] and rare-earth metals/Nb/sapphire [2]. ALD, has produced single-crystal rare-earth oxides on GaAs(001) [23,24], (111)A [23,25,26], and GaN [27]. MBE YBa2Cu3O7 single-crystalline films grew epitaxially on an SrTiO3 substrate by simultaneously evaporating separate sources of Y, Ba, Cu, and excited oxygen [28]. The epitaxial growth mechanism of single-crystal perovskite by ALD approach could be different from that of poly-crystalline perovskites prepared by powder sintering [31], hydrothermal synthesis [32], and sol–gel [33] methods. Single-crystal materials prepared by ALD are great platforms for studying initial monolayer-induced epitaxy

Methods

Results

Conclusion