Hidenori Nakanishi

Growth of Buffer Layers on Si Substrate for High-Tc Superconducting Thin Films

We have investigated the crystalline properties and surface morphology of the buffer layers of Y2O3, ZrO2 and Y2O3/ZrO2 on a Si(100) substrate for a superconducting thin film. The results of RHEED and X-ray diffraction indicate the hetero-epitaxial growth of buffer layers on Si(100) substrates. Epitaxial planes of the buffer layers on the Si(100) surface are (110), (100) and (100)/(100) for Y2O3, ZrO2 and Y2O3/ZrO2, respectively. YBa2Cu3O7-x thin films have been grown on Si with each buffer layer. The highest critical temperature obtained was 88 K on the Si with the Y2O3/ZrO2 buffer layer.

Epitaxial Growth of MgO Layer on Y1Ba2Cu3O7-y Thin Film

A MgO/Y1Ba2Cu3O7-y (YBCO) structure on a MgO(100) substrate was prepared by a reactive vacuum evaporation method. The MgO layer with (100) orientation was obtained on each of the (001) and (100) YBCO thin films at the substrate temperature of 400°C. The crystallinity of the MgO layer as a function of the MgO thickness was investigated. The randomness of the crystallinity became smaller with a decrease in the thickness. The (100) epitaxial MgO layer without other orientations was obtained at a thickness of 5 nm. Structures of both YBCO/MgO/YBCO(001) and YBCO/MgO/YBCO(100) were studied. From the result of the cross-sectional TEM observation, it was confirmed that for both the (001) and (100) base YBCO layers, top YBCO layers with the same orientation were epitaxially grown via the intermediate MgO layer with a thickness of 5 nm.

Spin-dependent luminescence enhanced by interface stress between III-V alloy layers on excitation of circularly polarized light

The relation between the luminescence polarization for circularly polarized light and the band structure of zincblende semiconductor under two-dimensional stress is theoretically discussed. Two type of samples with an unstrained InP layer and a strained InP layer due to the lattice mismatch are prepared. The luminescence from the InP layer excited by circularly polarized light is analyzed using a Babinet-Soleil compensator, (or phase-modulator) and polarizer. The large luminescence polarization of circularly polarized light is observed in the strained sample. At temperatures below 60 K, the luminescence polarization exceeds 25% which is the maximum value predicted in the unstrained crystal. The experimental results show that the luminescence polarization is increased by the internal strain due to the lattice mismatch.