Growth and stability of rocksalt Zn1-xMgxO epilayers and ZnO/MgO superlattice on MgO (100) substrate by molecular beam epitaxy.
Zn1-xMgxO films with x = 0.04-0.50 grown on MgO (100) substrates by molecular beam epitaxy retain the rocksalt (rs) crystal structure and grow epitaxially for x ≥ 0.17. In addition, the rs-ZnO epilayer is observed to be stable up to a thickness of 5 nm and also in a ZnO/MgO superlattice sample. However, a portion of the superlattice has transformed to wurtzite (wz)-structure islands in a self-accommodated manner during growth. The transformation is a combination of a Bain distortion, an in-plane rotation of 14.5°, and a Peierls distortion, resulting in an orientation relationship of (100)rs//(101̄0)wz and 〈011〉rs ∼//〈1̄21̄3〉wz. In such a manner, the volume expansion is only necessary along the growth direction and the in-plane strains can be minimized. A negative pressure generated during the transformation of ZnO stabilizes the MgO into a wurtzite structure.
Department of Materials and Optoelectronic Science/Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan.
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Lu
Department of Materials and Optoelectronic Science/Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan.
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Tu
Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, People's Republic of China.
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Yan
Paul-Drude-Institut für Festkörperelektronik, 10117 Berlin, Germany.
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Trampert
Department of Materials and Optoelectronic Science/Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan.
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Chang
Department of Materials and Optoelectronic Science/Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan.
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