Structural Analysis of MgO/Fe Bi-Layer Films Epitaxially Grown on GaAs Single-Crystal Substrates with Different Orientations

MgO/Fe bi-layer films were prepared on GaAs single-crystal substrates of (100), (110), and (111) orientations by ultra-high vacuum radio-frequency magnetron sputtering. The effects of substrate orientation and substrate temperature on the film growth process and the crystallographic properties were investigated by reflection high energy electron diffraction and X-ray diffraction. Fe single-crystal layers of (100), (110), and (111) orientations epitaxially grow on GaAs substrates of (100), (110), and (111) orientations, respectively. MgO(100) single-crystal layers are obtained on the Fe(100) layers, whereas MgO layers epitaxially grow on the Fe(110) layers with two (111) variants whose orientations are rotated around the film normal by 180^° each other. On the contrary, MgO polycrystalline layers are formed on the Fe(111) layers. The out-of-plane lattice spacing of MgO(100) layer is expanded, while the in-plane spacing is shrunk with respect to the lattice constant of bulk MgO crystal due to an accommodation of lattice mismatch with the Fe(100) layer. The strain in the MgO(100) layer decreases by employing a higher substrate temperature for thin film deposition.