This paper reports on the structures and properties of Y1Ba2Cu3O9−x samples prepared in precisely controlled oxygen environments using a solid-state ionic technique. By titrating out oxygen at low temperatures, orthorhombic Y1Ba2Cu3O9−x samples were prepared with oxygen contents below 6.50. Resistivity and magnetometry studies indicated that these reduced, orthorhombic samples were marginally superconducting, with their superconductivity probably arising from local regions of higher oxygen content.

We have investigated boron diffusion in Si and strained Si1−xGex, in situ doped, epitaxial layers. During inert ambient annealing at 860 °C, boron diffusion is observed to be slower in Si0.83Ge0.17 than in Si for boron concentration levels between 5×1016 and 2.5×1019 cm−3. Computer simulations of the measured boron profiles for annealed samples indicate that the effective boron diffusivity Deff in Si0.83Ge0.17 is approximately an order of magnitude lower than that in Si. This disparity is found to increase with increasing boron concentration.

A novel solid source metalorganic chemical vapor deposition (MOCVD) process has been used to grow highly textured thin films of CeO2 and MgO, and highly oriented thin films of Sr1-xBaxNb2O6 (SBN). Both (100)-oriented and (111)-oriented CeO2 films were reproducibly grown on (1102BAR)-oriented Al2O3 (r-plane sapphire) substrates. Higher substrate temperatures and higher growth rates were found to favor the (111) orientation. The epitaxial (100) CeO2 films, 150 angstrom thick, had very smooth surfaces, with an RMS surface roughness of 7 angstrom, as measured by atomic force microscopy. MgO films with (100) orientation were readily grown on both r-plane sapphire and (100) SrTiO3 substrates at temperatures below 600-degrees-C. SBN films, 1.6 mum thick, were also grown on r-plane sapphire substrates at 700-800-degrees-C using a CeO2 buffer layer and all tetramethylheptanedionate (Sr, Ba, and Nb) metalorganic sources.

The linearly-graded low-temperature buffer (LGLTB) approach developed by Harmand et al. [1] for growing materials with lattice parameters different from the substrate was extended to thick layers and minority carrier devices, using InxGa1-xAs alloys with x = 0.53 to 0.80 on InP. Structurally, the device layers were 90% to 100% relaxed with less than mid 10(5) cm-2 threading dislocations. Mobilities for 3 mum thick layers as well as modulation-doped structures of In0.80Ga0.20As were as high as 16,300 cm2/V.s at room temperature. p-n Homojunction diodes were nearly ideal and could be modeled with a diffusion-controlled leakage current using minority carrier lifetimes of tau(n) = tau(p) = 5 X 10(-9) s.

Diodes have been fabricated in layers of Si1−x Ge x and silicon deposited selectively on patterned wafers, and the electrical characteristics of the diodes have been examined. For 50 nm thick Si1−x Ge x layers containing about 22% Ge, the forward characteristics of larger diodes are nearly ideal. However, the reverse leakage current is higher when the edges of the diode intersect the oxide defining the selectively deposited layers than when the diode edges are separated from this oxide. The diode characteristics are more ideal when the diode edges are aligned along the [100] directions than when aligned along the [110] directions. Higher-temperature hydrogen pre-treatments before epitaxial deposition can degrade the diode characteristics.

This paper reports on the processes used to achieve low resistance silver contacts to YBCO thin films that have either c-axis or a-axis orientation. Characterization by x-ray diffraction and TEM verified that these films are highly oriented with either the a or the c axis oriented perpendicular to the substrate surface. TEM examination of some of the Ag/YBCO interfaces reveals the presence of an amorphous layer. We will describe the effects of ion beam etching and RTA alloying on the contact resistivity for both orientations.

Epitaxial thin films of YBa2Cu3O7 (YBCO) have been deposited by off-axis sputtering onto substrates of r-plane sapphire coated with a CeO2 diffusion barrier which had been previously deposited by metalorganic chemical vapor deposition process. The YBCO films display excellent superconducting properties, with critical current densities and microwave surface resistances comparable to state of the art YBCO films deposited directly onto LaAlO3 or MgO substrates. The volume fraction of YBCO with large-angle in-plane misalignment relative to the underlying layers is comparable to, or smaller than that obtained for YBCO directly deposited onto MgO substrates.

The characteristics of diodes fabricated in thick Si/sub 1-x/Ge/sub x/ layers formed by selective epitaxial deposition have been examined by DC electrical measurements, transmission electron microscopy, and X-ray topography. Because depositing in restricted areas limits the propagation of misfit dislocations in thick layers, a lower misfit dislocation density is found in small-area deposited regions. Similarly, diodes fabricated in small deposited regions have more ideal forward characteristics than diodes fabricated in large regions.< >

YBa2Cu3O7 films 2000–7500 Å thick were deposited onto [100] LaAlO3 substrates using a novel single source metalorganic chemical vapor deposition technique. We have so far observed critical currents as high as 4×106 A/cm2 at 77 K, transition temperatures (Tc at R=0) as high as 91 K, and the 10 GHz microwave surface resistance Rs as low as 40 μΩ at 4.2 K and 400 μΩ at 77 K.

Epitaxial YBa2Cu3O7 films were grown on Al2O3 {1012} by a laser ablation technique. X‐ray diffraction shows that films are epitaxial with the c axis perpendicular to the substrate surface and ‘‘123’’ [110] aligned with sapphire [1011], although the full width at half maximum of the rocking curve is larger than those of epitaxial films on SrTiO3. Typical Tc’s are between 85 and 88 K with transition widths between 0.5 and 3 K. The normal‐state resistivity is 270 μΩ cm at 300 K and extrapolates to zero at zero temperature while the magnetization Jc is as high as 5×106 A/cm2 at 4.2 K. High‐frequency loss measurements show that 2000‐A‐thick epitaxial films on Al2O3 {1012} have a surface impedance about 1 mΩ at 13 GHz at 4.2 K.

Microwave surface resistance data were measured on pairs of YBa2Cu3O7 thin films on Al2O3 {11_02} substrates by a parallel plate resonator technique. The surface resistance Rs at 10 GHz was 65 μΩ at 10 K and 850 μΩ at 77 K. These epitaxial YBa2Cu3O7 films were grown on 500-Å-thick buffer layers of SrTiO3. X-ray diffraction data showed that the YBCO thin films with the SrTiO3 buffer layers have better in-plane epitaxy than those without such buffer layers. Critical current density of 2×106 A/cm2 at 74 K was measured by the ac mutual inductance response of the films. The improved microwave surface resistance and the higher critical current density are believed to be the results of better in-plane epitaxy.

Synthese et caracterisation des monocristaux dopes. Le dopage par des ions provoque de petits changements de la transition supraconductrice pour les niveaux de substitution inferieurs a 20-25%. Au-dela, le signal de Meissner s'elargit et diminue aux basses temperatures. Caracterisation de la structure par microsonde electronique et diffraction RX

YBa 2 Cu 3 O 7 films have been grown epitaxially on SrTiO 3 (100) and LaAlO 3 (100) substrates with nearly pure a -axis orientation and with transition temperature T c ( R = 0) of 85 K. A unique feature of these films is their smooth surface. These smooth surfaces enable the growth of short-period superlattices with well-defined modulations. The films are untwinned and the grains grow with their c -axis along one of two perpendicular directions on the substrate ([100] or [010]). The fabrication of sandwich-type Josephson junctions with good characteristics may now be possible because unlike c -axis—oriented films, the superconducting coherence length of these smooth films is appreciably large perpendicular to their surfaces.

A directional solidification method for growing large single crystals in the ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ system is reported. Ion doping, with replacement of La for Sr and Y for Ca, as well as oxygen doping in these crystals has been explored. Doped and undoped crystals have been characterized using microprobe analysis, x-ray diffraction, thermogravimetric analysis, and magnetic and Hall measurements. Ion doping results in little change of the superconducting transition for substitution levels below 20--25%, while beyond this level the Meissner signal broadens and the low-temperature Meissner signal decreases. Microprobe analysis and x-ray diffraction performed on these more highly substituted single crystals provide evidence for inhomogeneity and phase segregation into regions of distinct composition. Annealing unsubstituted crystals in increasing partial pressures of oxygen reversibly depresses the superconducting transition temperature from 90 (as made) to 77 K (oxygen pressure annealed), while the carrier concentrations, as determined from Hall effect measurements, increase from n=3.1(3)\ifmmode\times\else\texttimes\fi{}${10}^{21}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ (0.34 holes per Cu site) to 4.6(3)\ifmmode\times\else\texttimes\fi{}${10}^{21}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ (0.50 holes per Cu site).No degradation of the Meissner transition or other indications of inhomogeneity or phase segregation with doping are noted, suggesting that oxygen-doped ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ is a suitable system for pursuing doping studies. The decrease in ${\mathit{T}}_{\mathit{c}}$ with concentration for 0.34\ensuremath{\le}n\ensuremath{\le}0.50 indicates that a high-carrier-concentration regime exists in which ${\mathit{T}}_{\mathit{c}}$ decreases with n and suggests that this decrease does not arise from material inhomogeneity or other materials problems. An examination of the variation of ${\mathit{T}}_{\mathit{c}}$ with the density of states and lattice constants for all of the doped and undoped superconducting samples considered here indicates that changes in ${\mathit{T}}_{\mathit{c}}$ with doping are primarily affected by changes in the density of states (or carrier concentration) rather than by structural variation induced by the doping.

We report on the effect of rare-earth substitution on the Raman spectra of $R{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ perovskites where $R=\mathrm{Y},\mathrm{La},\mathrm{Pr},\mathrm{Nd},\mathrm{Sm},\mathrm{Eu},\mathrm{Gd},\mathrm{Dy},\mathrm{Ho},\mathrm{Tm},\mathrm{and} \mathrm{Lu}$. These spectra show both the presence of Raman modes that are intrinsic to the superconducting material and also those due to impurity phases. The intrinsic Raman modes near 340 ${\mathrm{cm}}^{\ensuremath{-}1}$ and 500 ${\mathrm{cm}}^{\ensuremath{-}1}$ which have been attributed, respectively, to Cu(2)-O(2,3) bending and Cu(1)-O(4) stretching vibrations, show substantial and systematic variations in vibrational frequency as a function of the ionic radius of the rare earth. These variations are in good agreement with neutron-scattering determinations of bond lengths, which supports the vibrational assignment of these modes. Pr${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ shows no anomalous behavior in its vibrational spectrum even though it was the only sample studied that was not superconducting. This suggests that the valency of Pr is similar to the other rare earths studied and cannot account for the absence of superconductivity in this material. Assignment of other Raman modes in the rare-earth spectra requires identification of impurity phases, which even in small concentrations, can significantly contribute to the Raman spectra. Impurity phases can be preferentially at the surface of samples and can be substantially modified by heat treatment in an argon atmosphere. These impurity phases have previously been confused with disorder-induced Raman modes.