Epitaxial properties of ZnO thin films on SrTiO3 substrates grown by laser molecular beam epitaxy

Abstract

Epitaxial ZnO thin films with different orientations have been grown by laser molecular beam epitaxy on (001)-, (011)-, and (111)-orientated SrTiO3 single-crystal substrates. The growth behavior was in situ monitored by reflection high-energy electron diffraction, and the epitaxial orientation relations were reconfirmed by ex situ x-ray diffraction measurements. In the case of ZnO on SrTiO3(001), four orthogonal domains coexisted in the ZnO epilayer, i.e., ZnO(110)‖SrTiO3(001) and ZnO[−111]‖SrTiO3⟨100⟩. For (011)- and (111)-orientated substrates, single-domain epitaxy with c axial orientation was observed, in which the in-plane relationship was ZnO[110]‖SrTiO3[110] irrespective of the substrate orientations. Additionally, the crystalline quality of ZnO on SrTiO3(111) was better than that of ZnO on SrTiO3(011) because of the same symmetry between the (111) substrates and (001) films. The obtained results can be attributed to the difference of the in-plane crystallographic symmetry. Furthermore, those alignments can be explained by the interface stress between the substrates and the films.