Epitaxy of Single-Crystal Hexagonal Perovskite YAlO3 on Y2O3/GaAs(111)A
C. K. Cheng1*, L. B. Young1, K. Y. Lin1, Y. H. Lin1, H. W. Wan1, R. F. Cai2, S. C. Lo2, C. H. Hsu3, J. Kwo4, M. Hong1
1Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei, Taiwan
2Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan
3National Synchrotron Radiation Research Center, Hsinchu, Taiwan
4Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
* Presenter:C. K. Cheng
Materials with a Perovskite-related structure exhibit various scientifically interesting and industrially important properties, such as high dielectric constants, photovoltaics, broadband optical emission, and superconductivity. Integrating single-crystal perovskite thin films onto semiconductors to form advanced electronic and optoelectronics devices using mass-production growth methods such as atomic layer deposition (ALD) may enable new technologies.
In this work, single crystal hexagonal perovskite YAlO3 (H-YAP) films were epitaxially grown on GaAs(111)A substrates by utilizing sub-nano-laminated (snl) ALD-Y2O3/Al2O3 multilayers with a post-deposition rapid thermal annealing (RTA) at 900°C in He ambience. However, using the same snl structure on a SiO2/Si(001) substrate, H-YAP was not formed by 900°C RTA, indicating that the substrate plays a critical role in the development of epitaxial H-YAP. The initial layer of ALD-Y2O3 on GaAs(111)A was single crystal and the following Al2O3/Y2O3 multi-layer was amorphous, as observed using scanning transmission electron microscopy (STEM). Despite a large lattice mismatch between H-YAP and GaAs, H-YAP formed after 900°C annealing and the interface between H-YAP and GaAs was very sharp, again as revealed by STEM. The narrow rocking curve (0.019°) of H-YAP(0004) and the surface normal scan with clear thickness fringes of H-YAP were obtained using synchrotron radiation X-ray diffraction (SR-XRD). The excellent crystallinity of H-YAP on GaAs(111)A is consistent with the STEM observation. From the atomic model of Y2O3 and H-YAP, the lateral arrangement of yttrium atoms of the two structures are very similar. The initial periodic single layer Y2O3 right next to the top Ga on the GaAs(111)A surface, as observed using STEM, provides an excellent platform to induce and stabilize the formation of the metastable H-YAP.

Keywords: metastable phase, perovskite YAlO3, hexagonal, atomic layer deposition