Epitaxial growth mechanism of perovskite (1 1 1) SrTiO3 on wurtzite (0 0 0 2) GaN with single unit-cell TiN buffer layers

Abstract

Epitaxial integration of SrTiO3 (STO) with GaN plays a key role in exploring monolithic and multifunctional GaN-based devices. Herein, high quality perovskite (1 1 1) STO thin films were epitaxially grown on wurtzite (0 0 0 2) GaN substrates with novel designed single unit-cell TiN buffer layers by pulsed laser deposition. Epitaxial relationship model is proposed to be (1 1 1) [1 1¯ 0] STO//(1 1 1)[1 1¯ 0] TiN//(0 0 0 2)[1 1 2¯ 0] GaN. Furthermore, interfacial structure and epitaxial relationship of STO/TiN/GaN heterostructure is directly confirmed on atomic scale by high-resolution transmission electron microscopy. With the insertion of TiN, lattice mismatch between (1 1 1) STO and (0 0 0 2) GaN is reduced tremendously from 13.3% to 7.9%. More significantly, relaxation process and N atom vacancies in surface atom layer of single unit-cell (1 1 1) TiN could further release lattice mismatch strain between STO and GaN, and thus enormously facilitates epitaxial growth of STO. Moreover, the formation mechanism of twin domain structures and tilted twin grain-boundaries in STO is also discussed to clarify the epitaxial growth process of perovskite (1 1 1) STO on wurtzite (0 0 0 2) GaN.