Crystal structure and strain state of molecular beam epitaxial grown Gd2O3 on Si(111) substrates: a diffraction study

In this work, Gd2O3 thin films grown by molecular beam epitaxy on Si(1 1 1) substrates were investigated by various diffraction methods. The Gd2O3 layers exhibit a highly perfect cubic bixbyite structure with a single domain orientation, low lattice mismatch with Si and good crystallinity. Three fold 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 Gd2O3 on Si(1 1 1) is fully epitaxial with a single domain orientation with a [111](Gd2O3)//[111](Si) and [1-10](Gd2O3)//[-110](Si) epitaxial relationship. The lattice parameter of Gd2O3 is slightly smaller than the one of the Si substrate. In the in-plane direction, the Gd2O3 layer is only -0.1% mismatched with the Si substrate (relative to 2a(Si)). This indicates a pseudomorphic growth of Gd2O3 on Si(1 1 1), where the Gd2O3 layer experiences tensile strain in the in-plane direction and compressive strain in the out-of-plane direction.