Physics

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The temperature dependent Schottky diode characteristics of epitaxial junctions between Nb:SrTi O3 (Nb concentrations: 0.5%) and Fe3 O4 are studied. Epitaxial thin films of Fe3 O4 were grown on Nb:SrTi O3 substrates by pulsed laser deposition technique. The films and heterointerfaces were characterized by x-ray diffraction, Z -contrast transmission electron microscopy, magnetic susceptibility, four-probe in-plane resistivity, and the temperature dependent junction current-voltage (I-V) characteristics. The nonlinear nature of the characteristics is analyzed within the framework of thermionic emission theory. Junction parameters such as the Schottky barrier height (φB) and ideality factor (η) are extracted. The temperature evolution of these parameters shows interesting and systematic trends, with remarkable changes near the Verwey transition (TV =120 K). The magnetic field dependence of I-V characteristic data is also recorded and a spin polarization of ∼80% is estimated for the magnetite electrode. © 2006 American Institute of Physics.

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Journal of Applied Physics

Interfacial characteristics of a Fe 3O 4Nb/(0.5%): SrTiO 3 oxide junction

In this paper, structural and electrical studies of A-site lanthanum-substituted Sr1-xLaxBi 2Nb2O9; x=0.0-0.5 ceramics are reported. The introduction of lanthanum produces pore-free microstructure upto x=0.3. A diffuse ferroelectric to paraelectric phase transition is observed in the doped samples and positive temperature coefficient of resistance (PTCR) is observed in x=0.0, 0.4 and 0.5 samples whereas x=0.1-0.3 samples show negative temperature coefficient of resistance (NTCR). Curie temperature decreases continuously with increase in lanthanum content. © 2005 Elsevier B.V. All rights reserved.

Physica B: Condensed Matter

Structural and electrical studies in La-substituted SrBi2Nb 2O9 ferroelectric ceramics

In this paper, structural and dielectric studies of Sr1-xA xBi2Nb2O9 (A = La, Pb and x = 0.2) ceramics are reported. Tetragonal strain decreases on introduction of lanthanum while it increases for the lead doped sample. Addition of lead increases Curie temperature and sample with lanthanum content shows remarkable decrease in Curie temperature with broadened dielectric peak. The sample with x = 0.0 shows a rapid fall in dielectric constant value above 100 KHz. The lanthanum and lead doped samples show reduced dielectric loss values with frequency. © 2005 Elsevier B.V. All rights reserved.

Materials Letters

Dielectric studies of la and Pb doped SrBi2Nb2O 9 ferroelectric ceramic

Using a 100 MeV Au beam, the surface roughening kinetics of relaxed Si1-xGex alloy films for x = 0.5 and 0.7 are studied by means of ex-situ atomic force microscopy (AFM). Swift heavy ion (SHI) irradiation induced surface roughening behavior is demonstrated using the trend in variation of β as a function of fluence when the data are analyzed in terms of the Edwards-Wilkinson (EW) model. By employing the EW model, the observed surface roughening is explained on the basis of the competition between SHI induced sputtering and smoothening through redeposition of the sputtered atoms. The composition dependent variation of surface morphology with increasing fluence is discussed in the light of the strain distribution along the sample surface. © 2006 Elsevier Ltd. All rights reserved.

Solid State Communications

Surface roughening in Si1-xGex alloy films by 100 MeV Au: Composition dependency

We demonstrate a gradual surface modification process of relaxed Si0.5Ge0.5 alloy films by 100 MeV Au beam with fluence varying between 5 × 1010 and 1 × 1012 ions/cm2 at 80 K by means of atomic force microscopy (AFM). Presence of Ge quantum dots (QDs) was found in the virgin sample. The disappearance of the QDs were noticed when the samples were irradiated with a fluence of 5 × 1010 ions/cm2. Craters were found developing at a fluence of 1 × 1011 ions/cm2. Apart from the evolution of the craters, blisters were also detected at a fluence of 1 × 1012 ions/cm2. Variation of the average root mean square value of the surface roughness as a function of fluence was examined. © 2006 Elsevier B.V. All rights reserved.

Surface Science

Impact of 100 MeV Au on the surface of relaxed Si0.5Ge0.5 alloy films studied by atomic force microscopy

In this paper we report recent advances in pulsed-laser-deposited AlN thin films for high-temperature capping of SiC, passivation of SiC-based devices, and fabrication of a piezoelectric MEMS/NEMS resonator on Pt-metallized SiCySi. The AlN films grown using the reactive laser ablation technique were found to be highly stoichiometric, dense with an optical band gap of 6.2 eV, and with a surface smoothness of less than 1 nm. A low-temperature buffer-layer approach was used to reduce the lattice and thermal mismatch strains. The dependence of the quality of AlN thin films and its characteristics as a function of processing parameters are discussed. Due to high crystallinity, near-perfect stoichiometry, and high packing density, pulsed-laser-deposited AlN thin films show a tendency to withstand high temperatures up to 1600°C, and which enables it to be used as an anneal capping layer for SiC wafers for removing ion-implantation damage and dopant activation. The laser-deposited AlN thin films show conformal coverage on SiC-based devices and exhibit an electrical break-down strength of 1.66 MV/cm up to 350°C when used as an insulator in Ni/AlN/SiC metal-insulator-semi-conductor (MIS) devices. Pulsed laser deposition (PLD) AlN films grown on Pt/SiCVSi (100) substrates for radio-frequency microelectrical and mechanical systems and nanoelectrical and mechanical systems (MEMS and NEMS) demonstrated resonators having high Q values ranging from 8,000 to 17,000 in the frequency range of 2.5-0.45 MHz. AlN thin films were characterized by x-ray diffraction, Rutherford backscattering spectrometry (in normal and oxygen resonance mode), atomic force microscopy, ultraviolet (UV)-visible spectroscopy, and scanning electron microscopy. Applications exploiting characteristics of high bandgap, high bond strength, excellent piezoelectric characteristics, extremely high chemical inertness, high electrical resistivity, high breakdown strength, and high thermal stability of the pulsed-laser-deposited thin films have been discussed in the context of emerging developments of SiC power devices, for high-temperature electronics, and for radio frequency (RF) MEMS.

Journal of Electronic Materials

Advances in pulsed-laser-deposited AlN Thin Films for high-temperature capping, device passivation, and piezoelectric-based RF MEMS/NEMS resonator applications

Ion implantation is a promising route for doping quartz with luminescent impurity atoms and nanoparticles at moderate fluences. The present work focuses on the comparison of epitaxy and cathodoluminescence (CL) after Ba, Ge, Na and Rb ion implantation as well as Rb/Ge double implantation in α-quartz, under the conditions of either dynamic or chemical epitaxy. In addition to the known intrinsic sub-bands in the CL spectra, due to the silica matrix or electron irradiation, we were able to line up several new blue or violet bands with the implanted ion species and follow their thermal behaviour. In the case of Na and Rb ions, complete chemical epitaxy has been achieved, but only rather weak CL output. For Ba ions, almost complete dynamic epitaxy and fairly high CL efficiency have been realized, but no epitaxy for Ge implantation. The case of dual Rb/Ge ion implantation appears as the most promising route to gain a high CL light output and full epitaxy. © 2006 Elsevier B.V. All rights reserved.

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms

Cathodoluminescence and epitaxy after group-IV and alkali-ion implantation in α-quartz

In the course of a systematic investigation of dynamic, chemical, and laser-induced solid phase epitaxy of α-quartz after ion implantation, we have studied epitaxy and cathodoluminescence emission after 250 keV Cs-ion implantation and subsequent pulsed excimer laser treatment in air. Rutherford backscattering channelling analysis showed partial epitaxy for all the laser-irradiated samples; however, no full epitaxy was achieved. The optical properties of these samples were analyzed using cathodoluminescence spectroscopy, giving evidence of five emission bands at 2.42, 2.79, 3.25, 3.65, and 4.30 eV photon energy. Their intensity relation to the laser power and retained Cs-ion fraction are discussed and the present results will be compared with those obtained after chemical and dynamic epitaxy of quartz after alkali-ion, Ge, and Ba implantation. © 2005 Elsevier B.V. All rights reserved.

Applied Surface Science

Cathodoluminescence and epitaxy after laser annealing of Cs + -irradiated α-quartz

We report on the search for ferromagnetism in undoped and cobalt-doped high- k dielectric Hf O2 films. Over a broad range of growth conditions, we do not observe ferromagnetism in undoped Hf O2 films. On the other hand, we do observe room temperature ferromagnetism in dilutely Co-doped Hf O2 films, but the origin of the same appears extrinsic (a Co rich surface layer) at least for the regime of growth conditions explored. © 2006 American Institute of Physics.

Applied Physics Letters

Search for ferromagnetism in undoped and cobalt-doped Hf O 2-δ

We report on the fabrication and electrical characterization of epitaxial metal-semiconductor junctions between Y1 Ba2 Cu3 O7-δ (YBCO) (optimally doped and Zn doped) and (001) Nb:SrTi O3 with different Nb concentrations (0.05%, 0.1%, and 0.5%). The current-voltage characteristics of such epitaxial junctions are nonlinear and rectifying, and these are dramatically enhanced with decreasing Nb concentration and Zn doping. Indeed, for the case of 0.05% Nb:STO, reverse breakdown voltage as high as -18 V (-28 V) is realized for optimally doped (Zn doped) YBCO. These data are analyzed within the framework of thermionic emissiondiffusion models for Schottky and metal-insulator- semiconductor-type junctions. © 2006 American Institute of Physics.