Crystal structure and strain state of molecular beam epitaxial grown Gd_2O_3 on Si(111) substrates: a diffraction study

摘要

In this work, Gd_2O_3 thin films grown by molecular beam epitaxy on Si(111) substrates were investigated by various diffraction methods. The Gd_2O_3 layers exhibit a highly perfect cubic bixbyite structure with a single domain orientation, low lattice mismatch with Si and good crystallinity. Threefold in-plane symmetry and bright streaky patterns were observed during the oxide growth by in situ high-energy electron diffraction. X-ray diffraction results demonstrate that Gd_2O_3 on Si(111) is fully epitaxial with a single domain orientation with a [111]_(Gd_2O_3)//[111]_(si) and [1 -10]_(Gd_2O_3)//[-110]_(si) epitaxial relationship. The lattice parameter of Gd_2O_3 is slightly smaller than the one of the Si substrate. In the in-plane direction, the Gd_2O_3 layer is only -0.1% mismatched with the Si substrate (relative to 2a_(si)). This indicates a pseudomorphic growth of Gd_2O_3 on Si(111), where the Gd_2O_3 layer experiences tensile strain in the in-plane direction and compressive strain in the out-of-plane direction.