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The problem of crossover from BCS to Bose-Einstein condensation has recently attracted considerable interest owing to the discovery of high-$T_{\rm c}$ cuprates. Their short coherence length, $\xi$, places these materials in the interesting region between BCS and Bose-Einstein condensation. In the paper of F. Pistolesi and G.C. Strinati (Phys. Rev. B {\bf 49}, 6356 (1994)), the Nozi\`eres and Schmitt-Rink approach (NSR) is taken, which is valid for the weak coupling regime. They derive a relation between $T_{\rm c}$ and $T_{\rm F}$, which they insist is valid for any coupling strength. We present arguments that their assumptions are incorrect by using our fully self-consistent T-matrix formalism in two dimensions, and show that the NSR approach produces unphysical results in this case.
The perovskite SrHfO3 can be a potential candidate among the high-permittivity materials for gate oxide replacement in future metal-oxide semiconductor field-effect transistor technology. Thin films of SrHfO3 were grown by molecular beam epitaxy and compared with SrTiO3 films. Their optical properties were investigated using spectroscopic ellipsometry and analyzed with respect to their structural properties characterized by x-ray diffractometry, atomic force microscopy, and transmission electron microscopy. A band gap of E-g=6.1 +/- 0.1 eV is measured optically, which renders this material better suited for gate dielectric applications than SrTiO3 with E-g similar to 3.4 eV. At similar equivalent oxide thickness, SrHfO3 also exhibits lower gate leakage current than SrTiO3 does. (c) 2007 American Institute of Physics.
We use the reflection high-energy electron diffraction oscillation phase shift to monitor the stability of the Sr barrier, prepared by exposure of Si(100) to Sr at high temperatures, in situ during molecular beam epitaxy growth of (Ba,Sr)O on Si(100). Our results confirm that the deposition of additional metallic Sr at low temperature is essential for preventing the incorporation of the Sr termination layer in the (Ba,Sr)O layer during its growth, and for obtaining monolayer thin (Ba,Sr)O layers with good crystallinity and minimal density of interfacial Si-O bonds on Si(100). (c) 2005 American Institute of Physics.
Key aspects of the growth process of epitaxial SrTiO3 with crystalline interface on silicon are outlined. An important step in this process is the solid phase epitaxy in ultrahigh vacuum of amorphous SrTiO3 on top of a few monolayer thick, low-temperature grown, epitaxial (Ba,Sr)O/Si(100) template. Insufficient oxygen supply during the SrTiO3 deposition step causes the formation of amorphous alkaline-earth silicates and TiSix at the Si/epitaxial oxide interface during ultrahigh vacuum annealing. Performing SrTiO3 deposition in excess O-2, this interfacial reaction is suppressed, and a metal-insulator-semiconductor capacitance equivalent to 0.5 nm of SiO2 is obtained for a 10 unit cell SrTiO3/1 unit cell (Ba,Sr)O/p-Si(100) stack. (C) 2006 American Institute of Physics.
Thin films of La2SrCu2O6+y with varying Sr/La ratios have been grown by: molecular beam epitaxy on (001) SrTiO3; their structural as well as their transport properties are reported. Under appropriate conditions, thin films with a metal-like resistivity down to 8 K are obtained; i.e., these films are closer to the onset of superconductivity than previous results indicate for bulk samples. This observation might be explained by a: thin-film-specific alteration in site occupation of the La and Sr atoms in the lattice. In addition, the defect structures of a typical sample have been studied by transmission electron microscopy and the thin-film/substrate interface structure is determined. Out-of-phase boundaries with displacement vectors R = [00 1/5] occur throughout the entire film thickness. Such interfaces, which possibly originate at su...
The carrier mobility mu in low-doped silicon-on-insulator wafers is found to be strongly modified by the deposition of a thin ZrO2 or SrZrO3 top layer grown by molecular-beam epitaxy. Pseudo-metal-oxide-semiconductor field-effect-transistor measurements performed on several samples clearly show a correlation between mu and the density of interface traps (D-it) at the Si/buried-oxide interface. The reduction of D-it by a forming gas anneal leads to a corresponding increase in mobility. Moreover, the high-k/Si interface can contribute to the total drain current via the creation of an inversion channel induced by trapped charges in the high-k layer. Using Hall-effect measurements, we took advantage of this additional current to evaluate the carrier mobility at the high-k/Si interface, without the need of a top gate electrode. (C) 2003 Ame...
The authors demonstrate that the compound SrHfO3 grown epitaxially on Si(100) by molecular-beam epitaxy is a potential gate dielectric to fabricate n- and p-metal-oxide semiconductor field-effect transistors with equivalent oxide thickness (EOT) below 1 nm. The electrical properties on capacitors and transistors show low gate leakage and good capacitance and I-V output characteristics. The lower electron and hole mobilities, which are strongly limited by charge trapping, nevertheless fit well with the general trend of channel mobility reduction with decreasing EOT. (c) 2006 American Institute of Physics.
Thin epitaxial films of the high-K perovskite SrHfO3 were grown by molecular beam epitaxy on Si(100) and investigated by ellipsometry and X-ray photoelectron spectroscopy to determine its band gap and valence band offset. Conducting AFM shows a good correlation between topography and current mapping, pointing to direct tunneling conduction. Long channels MOSFETs with low equivalent oxide thickness (EOT) were fabricated and their channel mobility measured. Mobility enhancement can be achieved by post processing annealing in various gases but at the cost of interfacial regrowth. An alternative approach is to increase mobility without changing EOT is by electrically stressing the gate dielectric at similar to 150 degrees C.
The perovskite SrHfO3 can be a potential candidate among the high-permittivity materials for gate oxide replacement in future metal-oxide semiconductor field-effect transistor technology. Thin films of SrHfO3 were grown by molecular beam epitaxy and compared with SrTiO3 films. Their optical properties were investigated using spectroscopic ellipsometry and analyzed with respect to their structural properties characterized by x-ray diffractometry, atomic force microscopy, and transmission electron microscopy. A band gap of E-g=6.1 +/- 0.1 eV is measured optically, which renders this material better suited for gate dielectric applications than SrTiO3 with E-g similar to 3.4 eV. At similar equivalent oxide thickness, SrHfO3 also exhibits lower gate leakage current than SrTiO3 does. (c) 2007 American Institute of Physics.
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