Microwave properties of YBa2Cu3O7−δ hightransitiontemperature superconducting thin films measured by the power transmission methodThe microwave properties of epitaxial YBa&u~O,-, thin films with critical temperatures T, up to 91.5 K and critical current densities J, up to 6 X lo6 A/cm2 at 77 K have been investigated between 5 and 20 GHz using coplanar transmission line resonators. Information about the surface resistance R, and the magnetic penetration depth AzL has been obtained from temperature-and power-dependent measurements of the quality factors and resonance frequencies of the resonators. The lowest surface resistance was 105 ,ufi at 77 K and 38 pa at 9 K measured at 6.2 GHz, respectively. The dependence of R, on the surface magnetic field Bti showed that with decreasing film quality the films exhibit a granular behavior. At high critical current densities J,> 4~ lo6 A/cm', the intrinsic properties of the material show up. The magnetic penetration depth was in the range between 160 and 270 nm. Both R, and AL. turned out to be sensitive to the film quality represented by the transition width AT, and the critical current density J, at 77 K. 1866

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In this work we have studied the interface reactions during e‐beam evaporation of yttria‐stabilized zirconia (YSZ), yttria (Y2O3) and Y on Si(100) substrates by means of x‐ray photoelectron spectroscopy (XPS). A deposition process was developed for the heteroepitaxial growth of YSZ and Y2O3. A high amount of metallic Zr in the YSZ vapour results in an in situ reduction of the native silicon oxide layer, allowing the growth of high‐quality YSZ films even on uncleaned Si substrates. A similar in situ reduction process was achieved for the Y2O3 film growth on uncleaned substrates by a predeposition of metallic Y. The deposition of YBa2Cu3O7−δ (YBCO) films on YSZ/Y2O3/Si multilayers by dc magnetron sputtering resulted in critical current densities of the YBCO layer in excess of 2 × 106 A cm−2.

In this paper an overview is given on the epitaxial growth of SiC in a vertical CVD reactor. Results concerning impurity incorporation and ways to achieve background doping levels as low as 1014 cm—3 are discussed. Precise control of the C/Si ratio in the gas phase, which is easily achieved in the described reactor, and the use of reduced pressure, lead to good control of dopant incorporation over more than three orders of magnitude, and smooth surface morphology at growth rates higher than 5 μm/h. Doping variations <±12% across 35 mm wafers can routinely be obtained. The quality of the epilayers is proven by electrical brakdown fields as high as 2×106 V/cm at NA — ND = 5×10—15 cm—3 achieved in both pn and Schottky diodes and an electron mobility higher than 700 cm2/Vs at 300 K (4H‐SiC) estimated from the on‐resistance of these test devices. Another important experimental boundary condition, the influence of the gas composition at the end of the epitaxial growth process on the surface properties of the epitaxial layer, is described. It will be shown that surfaces nearly resistant against oxidation can be generated in a hydrogen free atmosphere. As a second main topic of this paper, results of an elaborate numerical process simulation will be described including both fluid mechanical and chemical behavior. The influence of the main process parameters like total flow, chamber pressure, and rotation speed on the stability of the flow was investigated. The results achieved are compared with experimental observations showing excellent agreement. The experimental observation of an irradiant layer in the gas phase in front of the wafer under typical process conditions is explained with the help of the numerical model. The usefulness of this specific feature for the optimization of process conditions is discussed.

The preparation parameters of epitaxially grown buffer layers on silicon (100) wafers were investigated. We found that an in situ removal of the native amorphous SiO2 layer from the Si surface is possible, avoiding the etching of the wafer prior to the deposition. YSZ and Y2O3 were chosen as buffer layers for subsequent YBa2Cu3O7−x thin-film deposition. The orientation of the thin films during the deposition process was analyzed by RHEED. Different orientations on the substrates are obtained depending on the evaporation parameters. TEM studies of the interfaces, x-ray diffraction analysis, and measurements of the superconducting properties were made after the deposition of the films.