bluuebunny/crossref_metadata_2025 huggingface dataset:
TEM and XAS Characterization of Hard Magnetic Phase in Nd-Fe Alloys
Authors: Kumar G. , Eckert J. , Löser W. , Schilling P. , Ma E. , Mickel C. , Schultz L.
Published: April 2011

Nd80Fe20 alloys were prepared by copper mold casting and directional solidification (DS) to obtain a coarse microstructure, which can be identified unambigously. The mold-cast samples exhibit a fine globular eutectic structure and show high room temperature coercivity (∼ 5 kOe). Transmission electron microscopic (TEM) investigations reveal the presence of fcc (a = 5.32 Å) Nd-rich and nanocrystalline non-cubic Fe-rich phases. The directionally solidified (DS) samples exhibit large grains (composition close to NdFe2). The NdFe2 grains (formed in the DS samples) show clear magnetic domains with uniaxial anisotropy indicating that the NdFe2-type phase observed in the present samples is not a cubic phase. X-ray absorption spectroscopy (XAS) was used to analyze the local configuration around Fe atoms in the mold-cast samples. The XAS patterns do not match with the bcc and fcc standards, which supports the presence of NdFe2 phase with uniaxial symmetry in the DS samples.
Ab-initio Study of the Diffusion Coefficients in Fe-based Liquids
Authors: Fuentes-Cabrera Miguel , Nicholson Don , Widom Mike , Wang Yang , Mihalkovic Marek
Published: April 2011

With atomistic force fields derived from ab-initio energies and atomic forces, we cooled Fe80B20from the liquid to the glass state. The pair-distribution functions and the diffusion coefficients were used to characterize the structural changes that Fe80B20underwent during the simulation. In the FeFe and FeB pair-distribution functions, when the temperature is lowered the first neighbor-peak becomes narrower and the second-neighbor peak splits at around 1000K. In the BB pair-distribution we observed that the first peak undergoes a significant change at the glass transition temperature, and that the first BB peak remains present at low temperatures. That the first BB peak exists at low temperature seems to contradict the prevailing view of the structure of transition metal-metalloid glasses.
Influence of Al on Quasicrystal Formation in Zr-Ti-Nb-Cu-Ni-Al Metallic Glasses
Authors: Scudino Sergio , Eckert Jürgen , Kühn Uta , Breitzke Hergen , Lüders Klaus , Schultz Ludwig
Published: April 2011

The effect of Al on the crystallization behavior of (Zr0.616Ti0.087 Nb0.027Cu0.15Ni0.12)100−xAlx melt-spun glassy ribbons with x = 7.5, 5, 2.5 and 0 was investigated by differential scanning calorimetry, x-ray diffraction and transmission electron microscopy. The devitrification of the ribbons is characterized by the formation of a metastable quasicrystalline phase during the first stage of the crystallization process even for the alloy with x = 0. Therefore, Al is not essential for quasicrystal formation in the present alloys. However, it affects the properties of the amorphous as well as of the quasicrystalline phase. With decreasing Al content, the temperature range of stability of the quasicrystalline phase increases whereas the thermal stability of the amorphous phase decreases together with a slight decrease of the extension of the supercooled liquid region. Thus, it is concluded that although the addition of Al improves the stability of the glassy phase, it has no beneficial effect on the formation of quasicrystals.
Metastable States During Devitrification of a Zr70Pd20Cu10 Metallic Glass
Authors: Kramer M. J. , Sordelet D. J.
Published: April 2011

High energy synchrotron x-rays (124.63 keV) are used to investigate the initial stages of the devitrification for the Zr70Pd20Cu10 metallic glass prepared by melt-spinning (MS). Due to the excellent signal:noise, we are able to determine the initial nucleating phase by analyzing the differences in the total scattering function S (Q) as a function of time at a temperature ∼ 50 K below the crystallization temperature. The alloy undergoes a structural relaxation prior to nucleation and growth. Devitrification proceeds from nucleation of the icosahedral phase. The differential pair distribution function (dPDF) indicates that the as-quenched alloy may have icosahedral-like order which undergoes local rearrangement to true icosahedral order at an annealing temperature 50 K below the crystallization temperature. More importantly, time-resolved high-energy synchrotron is shown to have excellent sensitivity to the initial atomic rearrangements preceding nucleation in metallic glasses.
Quasicrystal Formation in a Zr-based Bulk Metallic Glass
Authors: Liu L. , Chan K. C. , Pang G. K. H.
Published: April 2011

Zr65Ni10Cu7.5Al7.5Ag10 bulk metallic glass with a diameter of 2 mm and a length of 50 mm was prepared by copper-mould casting. The metallic glass obtained follows two-step crystallization reactions with the initial formation of metastable quasicrystals from amorphous phase, followed by the formation of a stable intermetallic Zr2Cu from the post-formed quasicrystals. In this paper, the microprocess of the amorphous-to-quasicrystalline transformation of Zr65Ni10Cu7.5Al7.5Ag10 bulk metallic glass was studied in detail by TEM and high resolution TEM coupled with nanobeam EDX. It was found that the amorphous-to-quasicrystalline transformation in the present system does not follow the traditional nucleation/growth mechanism. Instead, it undergoes a series of inter-processes and follows the sequence of phase transformation of amorphous→FCC Zr2Ni →Tetragonal Zr2Ni → Quasicrystals. Nanobeam EDX revealed that atomic diffusion was involved in all inter-processes of the phase transformations, suggesting that the amorphous-to-quasicrystalline transformation in the present bulk metallic glass is a non-polymorphous reaction.
Enthalpy Relaxation Kinetics of the Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 Supercooled Liquid Close to the Glass Transition
Authors: Shah Minalben B. , Busch Ralf
Published: April 2011

Isothermal relaxation studies of the Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 bulk metallic glass forming alloy were performed using Differential Scanning Calorimetry in the glass transition and the supercooled liquid region. A new experimental method was developed to study the isothermal enthalpy relaxation kinetics. The results reveal that the enthalpy relaxes in an Arrhenius fashion. The activation energy obtained from the Arrhenius fit is comparable to the activation energy required for the diffusion of the medium size atoms. This suggests that the solid-state diffusion governs the enthalpy relaxation process. The stretching exponents for the relaxation are close to unity, which indicates that the alloy is a rather strong glass former.
Synchrotron Strain Measurements for in situ Formed Metallic Glass Matrix Composites
Authors: Ott R. T. , Sansoz F. , Molinari J. F. , Almer J. , Fan C. , Hufnagel T. C.
Published: April 2011

We have examined the micromechanical behavior of in situ formed metallic glass composites by performing in situ high-energy synchrotron X-ray scattering during uniaxial compression. The load partitioning between the amorphous matrix and the reinforcing particles was examined by measuring the lattice strains in the crystalline particles during compressive loading. The crystalline particles yield in compression during loading followed by tensile yielding during unloading. The large elastic mismatch between the two phases leads to large residual strains after each loading cycle. The load partitioning was also examined with finite element modeling (FEM). The predicted von Mises effective stress in the crystalline particles from the FEM calculations compares well with the experimentally determined von Mises effective stress so long as the deformation is elastic in both particles and matrix. After the particles yield, the model predicts strain hardening of the particles that is not observed experimentally.
Heating and Structural Disordering Effects of the Nonlinear Viscous Flow in a Zr55Al10Ni5Cu30 Bulk Metallic Glass
Authors: Kato Hidemi , Inoue Akihisa , Chen H. S.
Published: April 2011

Heat evolution of stress-induced structural disorder,ΔHs(ε), of a Zr55Al10Ni5Cu30bulk metallic glass (BMG) during constant ram-velocity deformation at the glass transition region (Tg= 680 K) was deduced from in-situ measurements of temperature change of the deforming sample. At the transition from the linear to nonlinear viscoelasticity, the behavior of viscosity change with strain, η(ε), is qualitatively consistent with the enthalpy evolution of the structural disordering,ΔHs(ε), but not with the temperature change, ΔT(ε). It is concluded that the initial softening deformation is due to the stress-induced structural disordering. The change in the nonlinearity, -log ñ ≡ −logη/ηN, is found to be proportional to theΔHsand the slope ofΔHs(–logñ) can be estimated to ∼ 400 J/mol, whereηNis the Newtonian viscosity. On the other hand, the temperature raise,ΔT(ε), is pronouncedly delayed as compared with theη(ε) andΔHs(ε) at the transition, but is determined by the product of stress and plastic strain-rate,σ·εp, and is nearly proportional to it at the steady-state. The slope ofΔT(σ·εp) can be estimated to 5.2×10-2K mol/W.
Strained Si-on-Insulator Fabricated from Elastically-Relaxed Si/SiGe Structures
Authors: Mooney P.M. , Cohen G.M. , Chen H. , Chu J.O. , Klymko N.
Published: April 2011

Blanket pseudomorphic Si0.8Ge0.2/Si layer structures grown by Rapid thermal Chemical Vapor Deposition (RTCVD) on SOI substrates were etched to form 5μm × 5μm slabs, supported by a single pedestal at the center. Symmetric tri-layer slabs, 20nm Si/236nm Si0.8Ge0.2/20nm Si supported by a SiO2 pedestal are flat and x-ray diffraction measurements of the strain and the thickness of the layers confirmed that the strain is shared between the Si and SiGe layers according to the ratio of the thickness of the SiGe and Si layers. These tri-layer structures were then firmly attached to the substrate using a filling material. A thermal oxide layer was grown on the upper and lower surface of the free-standing structures and then polycrystalline Si was deposited to fill the space between the free-standing structure and the Si substrate, thus attaching the bottom strained Si layer to the substrate. The polycrystalline Si was subsequently removed by reactive ion etching except from under the /SiGe/Si slab. The top SiO2 and Si layers as well as the SiGe layer were then removed selectively by wet etching. Raman spectroscopy measurements show that the strain in the attached strained Si-on-insulator layer is ε = 0.0067.
Reduced Pressure - Chemical Vapor Deposition of high Ge content (20% - 55%) SiGe virtual substrates
Authors: Bogumilowicz Y. , Hartmann J.M. , Laugier F. , Rolland G. , Billon T. , Renard V. , Olshanetsky E.B. , Estibals O. , Kvon Z.D. , Portal J.C.
Published: April 2011

We have studied the strain state, film and surface morphology of SiGe virtual substrates (Ge concentrations in-between 20% and 55%) grown by reduced pressure – chemical vapor deposition. The macroscopic degree of strain relaxation of those virtual substrates is equal to 97.2 ± 1.5%. The misfit dislocations generated to relax the lattice mismatch between Si and SiGe are mostly confined inside the graded layer. Indeed, the threading dislocations density obtained for Ge concentrations of 20% and 26% is indeed typically of the order of 7.5 ± 2.5 105 cm−2. Low surface root mean square roughness have been obtained, with values in-between 2 and 5 nm. In order to check the electronic quality of our layers, we have grown a MODFET-like heterostructure, with a buried tensile-strained Si channel 8 nm thick embedded inside SiGe 26%. We have obtained a well-behaved 2-dimensional electron gas in the Si channel, with electron sheet densities and mobilities at 1.45K of 5.4×1011 cm−2 and 212 000 cm2 V−1 s−1, respectively.
SiGe-on-Insulator and Ge-on-Insulator Substrates Fabricated by Ge-Condensation Technique for High-Mobility Channel CMOS Devices
Authors: Tezuka Tsutomu , Mizuno Tomohisa , Sugiyama Naoharu , Nakaharai Shu , Moriyama Yoshihiko , Usuda Koji , Numata Toshinori , Hirashita Norio , Maeda Tatsuro , Takagi Shin-ichi , Miyamura Yoshiji , Toyoda Eiji
Published: April 2011

A new fabrication method of SiGe-on-Insulator (SGOI) and Ge-on-Insulator (GOI) structures are presented as well as the application to high-mobility channel CMOS devices. This method, the Ge-condensation technique, consists of epitaxial growth of a SiGe layer with a low Ge fraction on an SOI substrate and successive oxidation at high temperatures, which can be incorporated in conventional CMOS processes. During the oxidation, Ge atoms are pushed out from the oxide layer and condensed in the remaining SiGe layer. The interface between the Si and SiGe layers is disappeared due to the interdiffusion of Si and Ge atoms. Eventually, an SGOI layer with a higher Ge fraction is formed on the buried oxide layer. The Ge fraction in the SGOI layer can be controlled by the oxidation time because total amount of Ge atoms in the SGOI layer is conserved throughout the oxidation process. We found that the lattice relaxation in the SGOI layer also can be controlled through the initial SiGe thickness. P- and n-type strained SOI MOSFETs, which were fabricated on relaxed SGOI substrates formed by this technique, exhibited mobility enhancement of 50% and 80%, respectively. CMOS ring oscillators comprised of the MOSFETs exhibited reduction in propagation delay of 70%-30% compared to a conventional SOI-CMOS device. Ultrathin-body strained SGOI pMOSFETs with high Ge fraction and surface channels were also fabricated by this technique. These devices exhibited hole-mobility enhancement factors up to 2.3. Furthermore, Ge-on-Insulator (GOI) structures with thicknesses less than 10 nm were realized for ultrathin body GOI-CMOS applications by using the Ge-condensation technique. In conclusion, the Ge-condensation technique is a promising technique for fabricating various types of high-mobility channel-on-insulator devices.
Germanium-On-Insulator (GeOI) structure realized by the Smart Cut™ technology
Authors: Letertre F. , Deguet C. , Richtarch C. , Faure B. , Hartmann JM , Chieu F. , Beaumont A. , Dechamp J. , Morales C. , Allibert F. , Perreau P. , Pocas S. , Personnic S. , Lagahe-Blanchard C. , Ghyselen B. , Vaillant YM Le , Jalaguier  , Kernevez N. , Mazure C.
Published: April 2011

First results on formation of thin film GeOI structures by the Smart Cut™ technology are presented in this paper. Thin single crystal layers of Ge have been successfully transferred, via oxide bonding layer, onto standard Si substrates with diameters ranging from 100 to 200 mm. Compared to SOI manufacturing, the development of GeOI requires adaptation to the available germanium material, since the starting material can be either bulk Ge or an epitaxial layer. Some results will be presented for GeOI formation according to the different technological options. Germanium splitting kinetics will be discussed and compared to already published results. To show good quality of the GeOI structures, detailed characterization has been done by TEM cross sections for defect densities, interfaces abruptness and layers homogeneities evaluation. AFM was used for surface roughness measurements. These results help define procedures that are required to achieve large diameter high quality GeOI structures.
High-Performance SiGe MODFET Technology
Authors: Koester S. J. , Chu J. O. , Saenger K. L. , Ouyang Q. C. , Ott J.A. , Canaperi D. F. , Tornello J. A. , Jahnes C.V. , Steen S. E.
Published: April 2011

An overview of SiGe modulation-doped field-effect transistor (MODFET) technology is provided. The layer structures and mobility enhancements for both p- and n-channel modulation-doped quantum wells are described and compared to mobilities in Si/SiO2 inversion layers. Next, previous results on high-performance n- and p-MODFETs fabricated at IBM and elsewhere are reviewed, followed by recent results on laterally-scaled Si/SiGe n-MODFETs with gate lengths as small as 70 nm. We conclude with a discussion of the materials issues for the future vertical and lateral scaling of SiGe MODFETs.
Atomic Force Microscopy Study of Conformal Sputtering in Strained Silicon Samples
Authors: Chao Kuo-Jen , Goodman Gary
Published: April 2011

Precise determination of the Ge outdiffusion into the Si cap in strained Si/SiGe structures and the depth distribution of dopants have been critical to the industry and a challenge to the SIMS community. Will the rough cross-hatch surface topography degrade the SIMS depth resolution, or alter the accuracy of the depth profile?

Here we report on a novel AFM approach to show that the SIMS measurement process results in conformal sputtering. Therefore, maintaining excellent depth resolution and the depth distribution accuracy capabilities of SIMS for these material systems.
Characterization of Structural Quality of Bonded Silicon-On-Insulator Wafers by Spectroscopic Ellipsometry and Raman Spectroscopy
Authors: Nguyen N. V. , Maslar J. E. , Kim Jin-Yong , Han Jin-Ping , Park Jin-Won , Chandler-Horowitz D. , Vogel E. M.
Published: April 2011

The crystalline quality of bonded Silicon-On-Insulator (SOI) wafers were examined by spectroscopic ellipsometry and Raman spectroscopy. Both techniques detect slight structural defects in the SOI layer. If a pure crystalline silicon dielectric function is assumed for the SOI layer, the spectroscopic ellipsometry data fitting yields an unacceptably large discrepancy between the experimental and modeled data. The best fits for all the samples result in a dielectric function of the SOI layer that consists of a physical mixture of crystalline silicon and about 4 % to 7 % of amorphous silicon. Using such a mixture indicates that there are still some defects in the SOI layer when compared with the high-quality bulk crystalline silicon. This observation is further supported by Raman spectroscopy measurements. The Raman spectra of all SOI samples exhibit a feature at about 495 cm−1 that is not observed in the crystalline silicon spectrum. Features similar to the 495 cm−1 feature have been reported in the literature and attributed to dislocations or faults in the silicon lattice.
Relaxation of Strained SiGe on Insulator by Direct Wafer Bonding
Authors: Maa Jer-shen , Lee Jong-Jan , Tweet Douglas , Hsu Sheng Teng
Published: April 2011

Strained SiGe was bonded to silicon dioxide by direct wafer bonding and Smart-cut technique. Strained SiGe with a graded 20%-30% Ge concentration was deposited by RTCVD on (100) Si to a thickness between 300nm to 350nm. H2+ for wafer splitting was implanted at an energy varied from 40 keV to 150 keV and a dose between 2.5E16 and 4.5E16 ions/cm2. SiGe relaxation was found to depend on wafer split temperature, and on post-split annealing temperature. SiGe relaxation of greater than 80% was observed after wafer splitting and annealing. Was it from gliding of a SiGe film weakly bonded to an oxide surface? In order to determine the relaxation mechanism, samples with different film structure were prepared. The films were then annealed at various temperatures. Some film showed a high degree of relaxation, and some showed minimal relaxation, depending mostly on hydrogen implant depth. The results indicated that the generation of dislocation is the possible cause of SiGe relaxation.
Effect of Point Defect Injection on B diffusion in C containing Si and SiGe
Authors: Karunaratne Mudith S. A. , Bonar Janet M. , Zhang Jing , Willoughby Arthur F. W.
Published: April 2011

In this paper, we compare B diffusion in epitaxial Si, Si with 0.1%C, SiGe with 11% Ge and SiGe:C with 11%Ge and 0.1%C at 1000°C under interstitial, vacancy and non-injection annealing conditions. Diffusion coefficients of B in each material were extracted by computer simulation, using secondary ion mass spectroscopy (SIMS) profiles obtained from samples before and after annealing.

Interstitial injection enhances B diffusion considerably in all materials compared to inert annealing. In samples which experienced vacancy injection, B diffusion was suppressed. The results are consistent with the view that B diffusion in these materials occurs primarily via interstitialcy type defects.
Bulk-like ferroelectric and piezoeletric properties of transferred-BaTiO3 single crystal thin films
Authors: Park Young-Bae , Ruglovsky Jennifer L. , Dicken Matthew J. , Atwater Harry A. , Watson Thomas J.
Published: April 2011

Layer transfer of thin BaTiO3 films onto silicon-based substrates has been investigated. H+ and He+ ion implantation created a buried sacrificial layer in the BaTiO3 single crystals. Thermodynamics and kinetics of cavity nucleation and growth at the bonding interface have been investigated and single crystal thin film layers were transferred onto amorphous Si3N4 and Pt substrates. We have found that defects generated by ion implantation in ferroelectric materials can be significantly recovered with the subsequent annealing for layer splitting. Also, after high dose ion implantation, the films remain single crystal and stoichiometry. Finally, characterization proves the layer-transferred thin films are ferroelectrically active, with domains and piezoresponse similar to bulk crystals.
Comparison of Sol-Gel Derived and Pulsed Laser Deposited Epitaxial La0.67Ca0.33MnO3 Films for IR Bolometer
Authors: Fors Rickard , Pohl Annika , Khartsev Sergey , Grishin Alexander , Westin Gunnar
Published: April 2011

Epitaxial La0.67Ca0.33MnO3 films have been prepared on LaAlO3 crystals by pulsed laser deposition (PLD) and by a novel all-alkoxide sol-gel technique. Different out-of-plane lattice parameters are found for the as-prepared films, and scanning electron microscopy shows a more porous structure for sol-gel films as compared to PLD films. These differences are largely removed by post-annealing at 1000 °C. Transport measurements show maximum temperature coefficient of resistivity of 8.2 % K−1 at 258 K (PLD) and 6.1 % K−1 at 241 K (sol-gel) and colossal magnetoresistance at 7 kOe of 35 % at 263 K (PLD) and 32 % at 246 K (sol-gel).
Carrier transport of extended and localized states in InGaO3(ZnO)5
Authors: Nomura Kenji , Ohta Hiromichi , Ueda Kazushige , Kamiya Toshio , Hirano Masahiro , Hosono Hideo
Published: April 2011

Carrier transport properties and electronic structure of an n-type transparent oxide semiconductor, InGaO3(ZnO)5, were investigated using single-crystalline thin films. Room-temperature Hall mobility strongly depends on carrier concentration, and rapidly increased from ∼ 2 cm2(Vs)-1 to > 10 cm2(Vs)-1 around the carrier concentration (Nth ∼3 × 1018 cm−3. This change is associatedwith insulator-metal transition. These results are explained by a model similar to Anderson localization, in which shallow semi-localized states are formed originating from random distribution of Ga3+ and Zn2+ ions in the intrinsic crystal structure of InGaO3(ZnO)5. The present conclusion suggests that electron densities larger than Nth are necessary to attain high performances in drift carrier devices fabricated using InGaO3(ZnO)5. It was demonstrated that transparent filed-effect transistors exhibited good performances such as a “normally-offcharacteristics”, an on/off current ratios as large as 105 and a field-effect mobility ∼80 cm2(Vs)-1when high-k material, amorphous HfOx, was used as a gate insulator.
Structural and Electrical Properties of Ba0.5Sr0.5TiO3 Thin Films for Tunable Microwave Applications
Authors: Manavalan Sriraj G. , Kumar Ashok , Weller T. , Sikder A.K.
Published: April 2011

The primary objective of this research is to optimize the different deposition conditions to obtain high tunability and low dielectric loss of Barium Strontium Titanate (BST) thin films at microwave frequencies. Ba0.5Sr0.5TiO3thin films were deposited on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition technique (PLD). Deposition conditions like temperature, oxygen pressure, substrate to target distance and laser energy are varied to obtain the objective. Deposition of the BST thin films on the Pt/TiO2/SiO2/Si substrates was carried out at temperatures of 450°°C, 550°°C, 650°°C and oxygen pressures of 250mTorr and 450mTorr with laser fluence of 250 mJ/cm2 and 450mJ/cm2 at 10 pulses per second. The microstructural and phase analysis of the deposited BST films at different temperatures and different oxygen pressures were performed using X-ray diffraction (XRD) method. The diffraction patterns are attributed to cubic (perovskite) crystal system. Atomic force microscopy (AFM) was used to perform the surface analysis of the films deposited at different substrate to target distances, varied laser energies and oxygen pressures. The BST capacitor was fabricated using the Coplanar Waveguide Structure and the capacitance and dielectric constant were measured using the Vector Network Analyzer (VNA). Tunability of 3.1:1 and loss tangent of 0.0121 was achieved at 0.4 – 0.8 GHz.
Hydrogen-Nitrogen Tailors Semiconductor Optoelectronics: The Case of Dilute Nitride III-V Alloys
Authors: Janotti A.
Published: April 2011

Hydrogen is an omnipresent impurity in semiconductors, often associated with other impurities and native defects, strongly affecting their electronic properties by passivating deep and shallow levels, or activating isoelectronic centers, and can be intentionally or unintentionally incorporated. On the other hand, nitrogen has profound effects on the electronic structure of conventional III-V compounds: just a few percent of N can drastically lower the band gap of GaAs making it suitable for long-wavelength optical devices; isovalent doping of GaP by N leads to a quasidirect band gap with enhanced optical functionality. The large difference in electronegativity between N and other group V elements is expected to couple with the high chemical activity of H, raising crucial questions about the behavior of H in dilute nitride alloys that theories of hydrogen in conventional semiconductors or in commom-anion nitrides are unable to answer. Here we show that N can qualitatively alter the electronic behavior of hydrogen: In GaAsN, an H atom bonds to N and can act as a donor in its own right, whereas in GaAs and GaN, H is amphoteric; Nitrogen also stabilizes the complex, that is otherwise unstable against the formation of interstitial H2 molecules, reversing the effect of N on the band gap of GaAs, allowing us to interpret several recent experiments.
Donor Behaviour of Implanted Hydrogen Ions in Silicon Wafers
Authors: Barakel Damien , Martinuzzi Santo
Published: April 2011

P type Czochralski (Cz) and float-zone (FZ) grown silicon wafers were investigated with doping levels of 5×1014 and 2×1015 cm−3, respectively. Hydrogen ions are implanted at a dose of 2×1016 cm−2, at energies in the range 20 to 250 keV and are accumulated at depth Rp in the range 0.2 to 2.4 μm. After implantation the wafers are annealed between 350 and 600°C for 30 min, under argon flow. It is found that a graduated n-p junction is formed, and after metallization a photovoltaic device is obtained, which works like a solar cell. SIMS analysis shows that, around Rp, hydrogen concentration achieves 1021 cm−3. I-V and C-V curves confirm the formation of a N-type layer in which the donor concentration is about 5×1017 cm−3. When the samples are annealed at temperatures higher than 550°C the counter-doping vanishes. The observed behaviour of hydrogen is irrespective of oxygen concentrations in the wafers as it occurs in Cz (oxygen rich) like in FZ (oxygen poor) wafers. If the wafers are ion implanted with helium at the same dose and energy no junction appears. It is concluded that the agglomeration of hydrogen in silicon after ion implantation at a dose exceeding 1016 cm−2 gives rise to the formation of shallow donors.
Charge Controlled Silicon Carbide Switching Devices
Authors: Friedrichs Peter
Published: April 2011

Charge controlled power switching devices fabricated in 4H-Silicon Carbide are discussed in this paper. After comparing possible structures, results on prototype devices are presented. The presentation will give an overview about the developments of SiC power switches at SiCED, in addition some potential applications serving as an accelerator for the SiC power switch development will be sketched. The performance of vertical JFETs will be analyzed in detail. These can be operated as a single device as well as in combination with a low voltage silicon power MOSFET. The result of the hybrid assembly is a normally off device which behaves for the user more and more like a classical MOSFET with respect to the input as well as the output characteristic. Several improvements where performed which make the device more attractive for the customer. It will be shown which factors drive these optimization and how they can be implemented. Although the primary target for this device is the >1000V blocking voltage range, it will be discussed how the huge 600V power switch market can be made accessible for SiC power devices too. Intensively the high temperature performance of SiC JFETs and Si/SiC cascodes is discussed. Additionally, other developments like silicon power MOSFETs or high voltage switches will be mentioned.
Large area single and stacked p-i-n photodiodes as a color image sensors
Authors: Louro P. , Fernandes M. , Fantoni A. , Maçarico A. , de Carvalho C.Nunes , Lavareda G. , Vieira M.
Published: April 2011

Single and stacked p-i-n sensing elements for image recognition and color extraction applications are presented. The aim of this work is to optimize the performance of the a-SiC:H thin films layers in order to enhance its performance when making part of the structure of large area image and color sensors. The efforts are focused mainly on doped n- and p-type layers at high and low doping levels with and without carbon. The structural and optoelectronic properties of the single layers were determined through infrared and visible spectroscopy, temperature-dependent conductivity, and were complemented by CPM measurements. Junction properties, carrier transport, photogeneration and collection efficiency are investigated from dark and illuminated current-voltage characteristics and spectral response measurements, with and without additional background illumination and under different light bias conditions. The spectral response dependence on the applied voltage and on optical bias was also studied. Results show that the spectral sensitivity is strongly dependent on the applied voltage, namely the maximum spectral sensitivity shifts with the voltage, and at certain wavelengths the spectral response goes down to zero, which allows a different selectivity, and enables color recognition.
6H and 4H-SiC Bulk Growth by PVT and Advanced PVT (APVT)
Authors: Gupta A. , Yoganathan M. , Semenas E. , Zwieback I. , Emorhokpor E. , Martin C. , Kerr T. , Souzis A. , Anderson T. , Chen J. , Tanner C. , Barrett D. , Hopkins R. , Johnson C.
Published: April 2011

II-VI, Inc. is a commercial supplier of high-quality SiC substrates (including 2-inch and 3-inch diameter) for RF and power applications to the US market. Semi-insulating 6H-SiC single crystals, doped with vanadium and undoped (vanadium-free), as well as ntype 4H crystals have been grown using the PVT and Advanced PVT (APVT) growth techniques. The APVT process incorporates insitu synthesis and growth of of SiC crystal from Si and C precursors.

Grown 6H-SiC and 4H-SiC crystals have been extensively characterized with respect to their purity, crystal quality and electrical properties. COREMA resistivity maps demonstrate that V-compensated boules exhibited axially and radially uniform resistivity around 1011 ω.cm at room temperature. Undoped (V-free) wafers contained residual boron and nitrogen at levels below 1016 atoms/cm3, and demonstrated semi-insulating properties (resistivity between 106 and 1011 ω.cm) as a result of compensation by native point defects with deep levels in the bandgap. The undoped semi-insulating crystals grown by APVT contained boron and nitrogen at 1.9ω1015 cm−3 and 3.8.1015 cm−3, respectively.

High-quality 2-inch SiC wafers exhibited micropipe densities on the order of 10 cm−2 and dislocation density on the order of 104 cm−2.
Microstructural Aspects and Mechanism of Degradation of 4H-SiC PiN Diodes under Forward Biasing
Authors: Pirouz Pirouz , Zhang Ming , Galeckas Augustinas , Linnros Jan
Published: April 2011

Devices fabricated from the wide bandgap semiconductor SiC have many advantages over those made from conventional semiconductors. Thus, performance characteristics of some 4H-SiC devices can be two orders of magnitude better than equivalent devices made from silicon. On the other hand, new and unexpected problems have emerged with the operation of some SiC devices that need to be understood and solved before further progress can be made in this area. One of the most intriguing problems has been the degradation of bipolar PiN diodes that have major advantages over unipolar Schottky barrier diodes at high blocking voltages. The electrical degradation of the PiN diodes refers to a drop in voltage under extended forward current operation. The degradation appears to be associated with the appearance of stacking faults (SFs) in the entire base region of the diode. In this paper, we discuss some puzzling aspects of stacking fault formation in such diodes. Electroluminescence as well as TEM has been used to investigate the degradation problem and, based on experimental results, the formation of stacking faults within the device, possible sources of partial dislocations responsible for the stacking faults, and the enhanced motion of dislocations under forward biasing are considered.
Characterization of SiC epilayers using high-resolution X-ray diffraction and synchrotron topography imaging
Authors: Huang Xianrong , Dudley Michael , Okojie Robert S.
Published: April 2011

High-resolution X-ray diffraction is one of the most powerful and widely used techniques for accurate characterization of the lattice parameters, mismatch, alloy composition, dopant concentrations, and thickness of epitaxial materials. In this presentation, we use a series of advanced X-ray diffraction techniques, including double-axis diffraction, triple-axis diffraction, reciprocal space mapping (RSM), and synchrotron white beam X-ray topography, to characterize highly nitrogen-doped homoepitaxial 4H-SiC epilayers. Measurements reported in this work have determined that in single crystal 4H-SiC, increasing the nitrogen doping level above 4 × 1017cm#x2212;3results in corresponding increase in lattice contraction. The increase in epilayer/mismatch mismatch with doping, and the corresponding strain energy, is attributed to the substitutional nitrogen incorporated preferentially in the host carbon sites of the 4H-SiC epilayer. Also, significant lattice tilts, generally along the [1120] offcut direction (8°), exist, which are believed to be induced by the Nagai epitaxial tilt.
Extreme Service Packaging for Silicon Carbide Electronic Devices
Authors: Guinel Maxime J. F. , Rodriguez-Marek Diego , Norton M. Grant , Davis Robert B. , Bahr David F.
Published: April 2011

Electronic devices based on single crystal SiC represent a good choice for a variety of new high temperature, high power electronics applications. The challenge is to develop a package that is resistant to thermal degradation in harsh environments. Conditions are extreme and this all but rules out only a handful of materials and materials systems. Polycrystalline SiC is the material that we have chosen to study as a suitable package and materials suitability/compatibility has been considered on several levels.
Investigation of Mechanical Integrity and its effect on Polishing for Novel Polyurethane Polishing Pad
Authors: Zantye Parshuram , Mudhivarthi S. , Sikder A. K. , Kumar Ashok , Ostapenko S. , Harmon Julie
Published: April 2011

There is a widespread interest in development and characterization of CMP consumables due to an existing and potential market, as the CMP process becomes widely accepted in the field of microelectronics fabrication. A non-destructive Ultra Sound Testing (UST) technique developed at the University of South Florida has been successfully used in the past to map the variation of specific gravity over the entire volume of the pad. To gage the impact of the variation in specific gravity with in the body of the polishing pad, the results of UST of pads need to be correlated with actual polishing performance of the pad. In this research, UST was performed on IC 1000 Suba IV/ A4 polishing pad, and novel polyurethane pads, Pad A (with sub pad) and Pad B (without sub pad). The novel pads have been specifically developed for Interlayer Dielectric (ILD) polishing. 6 inch coupons from polishing pad regions of interest (high and low ultra sound transmission) determined after the ultrasound map were punched out and further evaluated. The mechanical properties of the pad material from the coupons were evaluated using Dynamic Mechanical Analysis (DMA) and tribological properties were evaluated by performing CMP on 6 inch coupons in the CETR CMP tester.
Micro Feature Pad Development and Its Performance in Chemical Mechanical Planarization
Authors: Lee Sunghoon , Dornfeld David A.
Published: April 2011

There are many elements affecting CMP performance such as the slurry, pad, process parameters and pad conditioning. Among these, the pad is considered to be one of the most important parts because of its deterioration during polishing. However, specific pad design techniques have not yet been fully investigated. In this paper, conventional polyurethane pad characteristics are investigated. A pad design based on this analysis is suggested. Prototype pads are fabricated using micro molding and are used in an experiment for examining the pad deterioration mechanism.
Characterization of CMP Pad Surface Texture and Pad-Wafer Contact
Authors: Muldowney Gregory P. , James David B.
Published: April 2011

Surface texture of CMP polishing pads varies considerably with the intrinsic microstructure of the pad, the addition of perforations or grooves, and the means of surface conditioning. The state of pad-wafer contact is determined by both large and small-scale texture in the top pad asperity layer and by the interaction of the top pad and sub-pad.

A flow-based texture characterization test was applied to several types of CMP polishing pads to describe the asperity layer as a porous media having a void fraction and characteristic length. Fluid pressure loss profiles were measured in a radial flow geometry across pad samples pressed against a flat instrumented plate. Symmetry of the profiles revealed the extent of contact between the pad and the plate, and curvature of the profiles showed the relative contributions of viscous and inertial flow among the asperities. Sub-pads, grooving, and conditioning all increased padwafer contact and the effective resistance of the surface texture, improving flow uniformity. Soft pads showed higher inertial flow influence than fixed abrasives with regularly spaced asperities. The results demonstrate that pad surface texture has a strong influence on heat and mass transfer at the wafer surface in CMP. Implications are discussed for both pad design and CMP modeling.
Metrology of Psiloquest's Application Specific Pads (ASP) for CMP Applications
Authors: Zantye Parshuram B. , Mudhivarthi S. , Sikder Arun K. , Kumar Ashok , Obeng Yaw
Published: April 2011

There is a need to develop a metrology metrics for evaluation of pad CMP performance before putting them in to service. This has been attempted on Psiloquest's application specific pads (ASP) in which the pad surface is tuned to match the mechanical properties of the target substrate. The ASP is made up of thermoplastic foams co extruded with condensed polyolefin. The chemical and mechanical properties of the pad-wafer interface are tuned by coating the pad with ceramic thin films by surface coating method such as chemical vapor deposition (CVD). The surface of the pad is characterized using metrology techniques such as ultra sound reflectivity, XPS and nanoindentation. The cross section of the pads was characterized using SEM. The mechanical properties of bulk pad materials were studied using Dynamic Mechanical Analysis (DMA). A test was performed on the pads to measure the static coefficient of friction (COF) and wear rate. The pads were polished using CETR CP-4 bench top CMP tester to evaluate the dynamic COF, Acoustic Emission (AE) signal and removal rate during a simulated Tungsten CMP process. The thickness of the ceramic coating on the surface of the ASP played an important role in determining these tribological properties. The results of the various static and dynamic tests performed on the pad were cross tabulated to evaluate their correlation.
WID Rnit Variation Improvements for HSS STI CMP Process using Modified Scribe Lane Pattern Design
Authors: Kwon Hyuk , Choi Yong-Soo , Lee Sang-Hwa , Choi Geun-Min , Song Yong-Wook , Yoon Gyu-Han
Published: April 2011

In the scribe lane, which is located at the frame neighboring two chips, most of the test patterns for monitoring electrical characteristics of memory device as well as various key patterns for photo process are formed. The pattern density of these regions is lower than that of the main chip area, and cause nitride erosion by dishing phenomena during HSS STI CMP process. Nitride erosion occurred in the scribe lane region, could the affect erosion properties of cell region in main chip area, results in within die remain nitride variation and marginal fail in device operation. In this work, in order to prevent these problems, pattern design in the scribe lane was modified so as not to occurs within die remain nitride variation. The effects of improvement in within die remain nitride variation were investigated by FIB-TEM analysis and its correlation with electrical properties were explained.
Rare-earth doped Si nanostructures for Microphotonics
Authors: Pacifici D. , Franzò G. , Iacona F. , Irrera A. , Boninelli S. , Miritello M. , Priolo F.
Published: April 2011

In the present paper, we will review our work on rare-earth doped Si nanoclusters. The samples have been obtained by implanting the rare-earth (e.g. Er) in a film containing preformed Si nanocrystals. After the implant, samples have been treated at 900°C for 1h. This annealing temperature is not enough to re-crystallize all of the amorphized Si clusters. However, even if the Si nanoclusters are in the amorphous phase, they can still efficiently transfer the energy to nearby rare-earth ions. We developed a model for the Si nanoclusters-Er system, based on an energy level scheme taking into account the coupling between each Si nanocluster and the neighboring Er ions. By fitting the data, we were able to determine a value of 3×10−15cm3s−1for the Si nanocluster-Er coupling coefficient. Moreover, a strong cooperative up-conversion mechanism between two excited Er ions and characterized by a coefficient of 7×10−17cm3s−1, is shown to be active in the system, demonstrating that more than one Er ion can be excited by the same nanocluster. We show that the overall light emission yield of the Er related luminescence can be enhanced by using higher concentrations of very small nanoaggregates. Eventually, electroluminescent devices based on rare-earth doped Si nanoclusters will be demonstrated.
The dot size effect of amorphous silicon quantum dot on 1.54-μmErluminescence
Authors: Park Nae-Man , Kim Tae-Youb , Sung Gun Yong , Kim Baek-Hyun , Park Seong-Ju , Cho Kwan Sik , Shin Jung H. , Lee Jung-Kun , Nastasi Michael
Published: April 2011

The role of the size of amorphous silicon quantum dots in the Er luminescence at 1.54 μm was investigated. As the dot size was increased, the more Er ions were located near one dot due to its large surface area and more Er ions interacted with other ones. This Er-Er interaction caused a weak photoluminescence intensity despite the increase in the effective excitation cross section. The critical dot size, needed to take advantage of the positive effect on Er luminescence, is considered to be about 2.0 nm, below which a small dot is very effective in the efficient luminescence of Er.
Omnidirectional reflectance and optical gap properties of Si/SiO2Thue-Morse quasicrystals
Authors: Negro L. Dal , Stolfi M. , Yi Y. , Michel J. , Duan X. , Kimerling L.C. , Leblanc J. , Haavisto J.
Published: April 2011

Aperiodic one dimensional Si/SiO2Thue-Morse (T-M) multilayer structures have been fabricated, for the first time, in order to investigate both the band-gap behavior, with respect to the system size (band-gap scaling), and the omnidirectional reflectance of the fundamental optical band-gap. Variable angle reflectance data have experimentally demonstrated a large reflectance band-gap in the optical spectrum of a T-M quasicrystal, in agreement with transfer matrix simulations. We have explained the physical origin of the T-M omnidirectional band-gap as a result of periodic spatial correlations in the self-similar T-M structure, as revealed by Fourier Transform and Wavelet analysis. The unprecedented degree of structural flexibility showed by T-M systems can provide an attractive alternative to photonic crystals for the fabrication of photonic devices.
Preparation of opal-based PBG crystals to develop multiple stop bands
Authors: Chen Yen-Tai , Liau Leo Chau-Kuang
Published: April 2011

Opal-based photonic band gap (PBG) crystals with multiple stop bands were prepared utilizing a sol-gel method. The fabricating procedure includes colloidal crystal syntheses, dispersion, sedimentation, coating, and thermal treatments. Each of the steps can affect the PBG properties, such as stop band locations and ranges. Different stop bands of the photonic crystals can be produced by controlling the particle sizes prepared by the colloidal crystal syntheses. A PBG crystal film with a certain stop band was formed using a particular size of the colloidal crystals coated on glass substrates. In this study, two layers of different particle sizes of PBG crystal were fabricated by different deposition conditions to demonstrate the feasibility of producing multiple stop bands. These conditions can affect the stack layers and structural regularity for forming the PBG layers. In addition, the stop band intensity of the PBG layer can be further improved by the step of thermal treatments. Results imply that multiple stop bands can be feasibly designed and produced as multiple PBG layers coating with a certain SiO2particle size for each layer.
Hybrid Integrated Microphotonics and It's Applications
Authors: Jung Suntae , Kim Taeil
Published: April 2011

Hybrid Integration of passive and opto-electronic devices is emerging as a key technology of optical component, because it can increase functionality and reliability of optical device module, lowers the packaging cost and enables automated manufacturing. Main applications of hybrid integrated microphotonic devices are FTTH system and metro access network.

There are various technical issues in hybrid integration modules. It requires connecting an active device to a passive waveguide. The embedded functional devices such as grating, coupler, switch and filter are essential elements to improve optical performance of integrated devices. The package solution for low cost and small size is also required.

We have developed SSC LD(Spot Size Converted Laser Diode) and RMF PD(Reflection Mirror Facet Photo Diode) for connecting to planar waveguide. Simple and cost-effective silica PLC platform with terraced-silica, PLC grating and coupler have been developed. Using these technologies, we have made bi-directional diplexer, triplexer and ECL(External Cavity Laser).
Optoelectronic Simulation of the Klein Paradox based on Negative Refraction Phenomenon
Authors: Güney Durdu Ö. , Meyer David A.
Published: April 2011

Having shown elsewhere [1] that the Klein paradox for the Klein-Gordon (KG) equation of spin-zero particle manifests exactly the same kind of wave propagation and negative refraction phenomena, which also exist in the scattering of TM (transverse-magnetic) –polarized electromagnetic (EM) wave incident on a left handed medium (LHM), we show in this paper that it is possible to simulate the Klein paradox, using this peculiar feature of LHMs. Real time control and processing of certain quantum systems, involving controlled pair production rate and distribution, among others, could be achieved by this optoelectronic simulator using appropriate transformations and approximations.