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We report on the effects of the quantum well (QW) thickness on the spectral response and other characteristics of In0.5Ga0.5As/GaAs/Al0.2Ga0.8As quantum dots-in-a-well infrared photodetectors grown by low-pressure metal-organic chemical vapor deposition. The main device properties are observed to have a strong dependence on the QW parameters. [ABSTRACT FROM AUTHOR]

We present experimental demonstration of all-optical switching using long-period gratings (LPGs) in highly nonlinear As2Se3 chalcogenide fiber. We use a 135 mm grating which is generated using acoustic waves. We characterize the nonlinear pulse propagation through the LPG using picosecond pulses tuned to different wavelengths with respect to the grating resonance. We compare the results with numerical simulations and observe switching at pulse peak powers around 50 W, two orders of magnitude smaller than previously demonstrated in silica. [ABSTRACT FROM AUTHOR]

Thin films of (0.5%, 1%) Nb:SrTiO3 dilutely doped with (2 at. %) magnetic transition elements (Cr, Co, Fe, Mn) are examined for ferromagnetism. X-ray diffraction, Rutherford backscattering ion channeling, scanning transmission electron microscopy Z-contrast imaging, and electron energy loss spectroscopy techniques establish high crystalline quality of the films with no impurity phase(s) and highly uniform dopant distribution. Although the film conductivity improves dramatically by Nb doping, no ferromagnetism is found in any of our samples over the temperature range of 365 down to 5 K. This is contrasted to the case of ferromagnetism reported in cobalt doped (La,Sr)TiO3. [ABSTRACT FROM AUTHOR]

We report on the search for ferromagnetism in undoped and cobalt-doped high-k dielectric HfO2 films. Over a broad range of growth conditions, we do not observe ferromagnetism in undoped HfO2 films. On the other hand, we do observe room temperature ferromagnetism in dilutely Co-doped HfO2 films, but the origin of the same appears extrinsic (a Co rich surface layer) at least for the regime of growth conditions explored. [ABSTRACT FROM AUTHOR]

It is shown that dilute niobium doping has a significant effect on the ferromagnetism and microstructure of dilutely cobalt-doped anatase TiO2 films. Epitaxial films of anatase TiO2 with 3% Co, without and with 1% niobium doping were grown by pulsed-laser deposition at 875°C at different oxygen pressures. For growth at 10-5 Torr niobium doping suppresses the ferromagnetism, while it enhances the same in films grown at 10-4 Torr. High-resolution Z-contrast scanning transmission electron microscopy and electron energy loss spectroscopy show uniform surface segregation of cobalt-rich Ti1-x-yCoxNbyO2-δ phase, but without cobalt metal clusters. [ABSTRACT FROM AUTHOR]

Scanning transmission electron microscopy and electron energy loss spectroscopy have been applied to investigate the possible structural origins of ferroelectric polarization degradation at PbTiO3/Pt interfaces. The microscopic analysis revealed that an amorphous Ti-rich interfacial layer as well as nanometer size precipitates was formed at PbTiO3/Pt interfaces. The interfacial layer appears to form through decomposition of the PbTiO3 film due to a ferroelectric-electrode reaction during Pt deposition. The formation of the interfacial layer and precipitates could contribute to the polarization degradation typically observed for Pt-electroded PbTiO3-based ferroelectric capacitors. [ABSTRACT FROM AUTHOR]

The effects of thermal annealing on C-doped InGaAs/AlGaAs quantum well laser structures capped with titanium dioxide (TiO2) layers were investigated. The atomic interdiffusion was greatly suppressed by the presence of a TiO2 capping layer during annealing, inhibiting even the thermal intermixing observed in the uncapped sample. An increase in the amount of lattice contraction associated with the presence of substitutional carbon CAs after annealing without a capping layer was observed, but not after annealing with a TiO2 capping layer. Capacitance–voltage measurements confirmed the electrical activation of carbon after annealing without a dielectric layer and show a negligible change after annealing using a TiO2 capping layer. The possible mechanisms involving both the atomic intermixing on the group III sublattice and carbon activation on the group V sublattice and the implications for optoelectronic device integration using impurity-free intermixing are discussed. [ABSTRACT FROM AUTHOR]

Thermal-stress controlled interdiffusion in InGaAsN/GaAs quantum dots (QDs) has been studied by deposition of titanium oxide (TiO2) layers combined with rapid thermal annealing. Without TiO2 cap layers, blueshifting of the band gap from 1.033 to 1.180 eV at 77 K has been observed after annealing at 850 °C for 30 s due to the thermal interdiffusion. The thermal interdiffusion has been effectively suppressed by depositing TiO2 layers on the samples without degrading the photoluminescence properties. By a combination of annealing temperature and TiO2 thickness, controlled blueshifting of the band gap has been achieved. We suggest that the mechanism of suppression of thermal interdiffusion is the thermal stress imposed on the QD structure generated by TiO2 layers during annealing. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on the search for ferromagnetism in undoped and cobalt-doped high-k dielectric HfO2 films. Over a broad range of growth conditions, we do not observe ferromagnetism in undoped HfO2 films. On the other hand, we do observe room temperature ferromagnetism in dilutely Co-doped HfO2 films, but the origin of the same appears extrinsic (a Co rich surface layer) at least for the regime of growth conditions explored. [ABSTRACT FROM AUTHOR]