Structural and strain relaxation study of epitaxially grown nano-thick Nd2O3/Si(111) heterostructure

This paper presents experimental work on studying the detailed structure and strain relaxation of nanometer thick Nd₂O₃ films epitaxially grown on Si(111) substrates using molecular beam epitaxy (MBE). Investigations by various diffraction methods demonstrate that the Nd₂O₃ layers exhibit a well-ordered cubic bixbyite structure with a single orientation, perfect crystallinity and a sharp interface. The epitaxial relationship between the Nd₂O₃ layer and the Si substrate is [111]_Nd2O3//[111]_Si and [1-10]Nd₂O₃//[-110]_Si. Three-fold in-plane symmetry is observed by both in-situ reflection high-energy electron diffraction after growth and ex situ X-ray diffraction Phi-cone scans. By two orthogonal X-ray diffraction scans with high resolutions, the out-of-plane and in-plane lattice mismatches between an 8 nm Nd₂O₃ layer and Si substrate were precisely estimated to be 3.25% and 0.66% (if we consider two Si unit cells), respectively. We conclude that the 8 nm Nd₂O₃ layer is partially relaxed with a compressive strain of -1.32% in the in-plane direction and a tensile strain of 1.22% in the out-of-plane directions.