High-resolution electron microscopy of epitaxial YBCO/Y₂O₃/YSZ on Si(001)

Abstract

The microstructures of YBa2Cu307_5 (YBCO) thin films grown on Si with Y-stabilized ZrO2 (YSZ) and Y2O3 buffer layers were characterized by means of high-resolution electron microscopy. At the Si-YSZ interface, a 2.5 nm thick layer of regrown amorphous SiO* is present. The layer is interrupted by crystalline regions, typically 5 to 10 nm wide and 10 to 50 nm apart. Close to the crystalline regions, {111} defects are present in the Si substrate. The typical defect observed is an extrinsic stacking fault plus a perfect dislocation close to the stacking fault which terminates extra {111} planes in the upper part of the Si. These defects are probably formed by condensation of Si self-interstitials created during oxide regrowth. Precipitates are present in the Si close to the Si-YSZ interface and indicate that in-diffusion of Zr has occurred. The YSZ-Y2O3 interface is atomically sharp and essentially planar and contains no second phases. Perfect misfit dislocations with Burgers vector 1/2(110) are present at this interface along with unrelaxed elastic misfit stresses. The Y2O3-YBCO interface is atomically sharp and planar, but contains steps. (001) stacking faults are present in the YBCO above these steps; the faults are, however, healed a few unit cells away from the interface. By HREM analysis of ultrathin specimen areas, the atomic layer of the YBCO closest to the Y2O3 was found to be a barium-oxygen layer.

EELS study of oxygen superstructure in epitaxial Y2O3 layers

“…In the course of previous work [9,10], we found that several regions of the Y 2 O 3 layers produced by molecular beam epitaxy (MBE), contained a superstructure which we assigned to ordering of oxygen vacancies. A similar type of superstructure has been observed previously [11,12] for the Y 2 O 3 /Si system, but no explanation of its origin has been given.…”

Temperature dependence of the properties of heteroepitaxial Y2O3 films grown on Si by ion assisted evaporation

“…[1][2][3][4][5][6] The epitaxial films on these fluorite type oxides on Si are attractive materials for potential application in making highly integrated circuits as an alternative SiO 2 layer, and for use in superconductors with high critical current density as buffer layers between oxide superconductor and Si. Especially, Y 2 O 3 has a cubic Mn 2 O 3 structure with a well-matched lattice parameter of 10.60 Å to Si ͑as compared to 5.43 Å for Si͒ and has a good chemical stability with a high melting point of 2350°C.…”

X-ray absorption study of the growth ofY2O3on Si(001)

“…5,[7][8][9][10][11][12][13][14] We summarize here the most important results. It has been found 7,9,15 that, notwithstanding the similar cubic structure, at growth temperatures ranging between 450°C and 550°C Y 2 O 3 grows on Si with its ͑110͒ plane parallel to the ͑001͒ plane of the substrate. At lower growth temperatures ͑280°C͒ a fraction of the epilayer grows with the ͑111͒ planes parallel to the substrate surface, while at 610°C the formation of hexagonal YSi 2 has been detected.…”