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  • 251. Forsberg, U.
    et al.
    Danielsson, O.
    Henry, A.
    Linnarsson, Margareta K.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Janzen, E.
    Nitrogen doping of epitaxial silicon carbide2002In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 236, no 03-jan, p. 101-112Article in journal (Refereed)
    Abstract [en]

    Intentional doping with nitrogen of 4H- and 6H-SiC has been performed using a hot-wall CVD reactor. The nitrogen doping dependence on the temperature, pressure, C/Si ratio, growth rate and nitrogen flow has been investigated. The nitrogen incorporation for C-face material showed to be C/Si ratio independent, whereas the doping decreased with increasing C/Si ratio for the Si-face material in accordance with the site-competition model. The nitrogen incorporation was constant in a temperature window of 75degreesC on Si-face material indicating a mass transport limited incorporation. Increasing the growth rate resulted in a decrease of nitrogen incorporation on Si-face but an increase on C-face material. Finally, a comparison between previously published results on cold-wall CVD-grown material and the present hot-wall-grown material is presented.

  • 252. Forsell, Martti
    et al.
    Soininen, Juha-Pekka
    Tiensyriä, Kari
    Jantsch, Axel
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kronlöf, Klaus
    Hadjiski, Bojidar
    Networks on Chip: Approaches and Challenges2004In: Research and Development Activities in Telecommunication Systems, VTT Electronics , 2004, p. 55-61Chapter in book (Refereed)
  • 253.
    Forsgren, Daniel
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Robust scalable video multicast and performance issues in wireless LANs2004Licentiate thesis, comprehensive summary (Other scientific)
  • 254.
    Fredlund, Lars-Åke
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    A Framework for Reasoning about ERLANG Code2001Doctoral thesis, monograph (Other scientific)
  • 255.
    Friberg, Ari T.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Partial polarization in arbitrary three-dimensional electromagnetic fields2004In: Free And Guided Optical Beams / [ed] Martellucci, S; Santarsiero, M, SINGAPORE: WORLD SCIENTIFIC PUBL CO PTE LTD , 2004, p. 15-25Conference paper (Refereed)
    Abstract [en]

    Although the theory of partial polarization of uniform electromagnetic beams is well-developed, it cannot be applied to random three-dimensional (3D) waves such as optical near fields. A general formulation of partial coherence and polarization in arbitrary 3D electromagnetic fields must be based on the 3 x 3 cross-spectral density tensors. After the fundamentals of electromagnetic coherence theory, we recall some recent researches on the spatial-coherence and spectral changes brought on by surface modes and evanescent waves. Partial polarization of arbitrary electromagnetic fields containing three orthogonal components is then addressed in terms of the 3 x 3 coherence matrix, and the variation of the 3D degree of polarization in near fields generated by semi-infinite thermal sources is analyzed. Finally, the similarities and differences of the conventional 2D and the new 3D formulations of partial polarization are briefly discussed.

  • 256.
    Friberg, Ari T.
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Visser, T. D.
    Wang, W.
    Wolf, E.
    Focal shifts of converging diffracted waves of any state of spatial coherence2001In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 196, no 06-jan, p. 1-7Article in journal (Refereed)
    Abstract [en]

    We analyze the focusing of wave fields of any state of coherence by systems with low Fresnel numbers. We study the optical intensity on the axis in the focal region. The dependence of the focal shift and of the maximum on-axis intensity on the state of coherence is examined for some model fields.

  • 257.
    Friberg, Ari T.
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Visser, T. D.
    Wolf, E.
    A reciprocity inequality for Gaussian Schell-model beams and some of its consequences2000In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 25, no 6, p. 366-368Article in journal (Refereed)
    Abstract [en]

    A reciprocity inequality is derived, involving the effective size of a planar, secondary, Gaussian Schell-model source and the effective angular spread of the beam that the source generates. The analysis is shown to imply that a fully spatially coherent source of that class (which generates the lowest-order Hermite-Gaussian laser mode) has certain minimal properties.

  • 258.
    Fu, Jing
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Hagsand, Olof
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    A Programming Model for a Forwarding Element2004In: 2nd Swedish National Computer Networking Workshop, SNCNW 2004, Karlstad, Sweden, 2004, p. 59-65Conference paper (Refereed)
    Abstract [en]

    The architectural complexity and diversity of current

    network devices make them complex to manage and

    difficult to program. In this work, we specify a

    programming model for network devices that function as

    forwarding elements. We first identify the key packet

    processing functions and analyze current network

    devices. Next, we derive a model that consists of

    processing blocks

    to represent simple packet processing

    functions running on a forwarding element. We further

    use a

    processing block topology

    to represent how the

    individual packet processing functions are interconnected

    on the datapath. We also demonstrate how to program a

    forwarding element and show an example IPv4

    forwarding service implementation. Finally, we evaluate

    programmability and the performance of the FE model.

  • 259.
    Färm, Petra
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Advanced algorithms for logic synthesis2004Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    In this thesis, new algorithms for logic synthesis areexplored. Our work is motivated by two observations: (1)Traditional logic synthesis applies literal count as theprimary quality metric during the technology independentoptimization phase. Thissimplistic metric often leads to badcircuit structures as it cannot foresee the impact of earlychoices on the final area, delay, power consumption, etc. (2)Although powerful, global Boolean optimization is not robustand corresponding algorithms cannot be used in practice withoutartificially restricting the application window. Othertechniques, such as algebraic methods scale well but provideweaker optimization power.

    In our most recent work, both problems are addressed byapplying a simulated annealing approach that is based on asimple circuit graph representation and a complete set of localtransformations, including algebraic and Boolean optimizationsteps. The objective of the annealing process can be tuned tocomplex cost functions, combining area, timing, routability,and power. Our experimental results on benchmark functionsdemonstrate the significant potential of the simulatedannealing approach.

    Earlier work includes a fast rule-based system fortechnology independent optimization. A Boolean network isoptimized by applying local structural transformations thatpreserve its functionality. NPN classes of Boolean functionsare used to identify replacement rules for localtransformations. It provides fast and roboust optimization, butuses a simplistic objective.

    Decomposition is one of the important steps of logicsynthesis. It can be applied during the technology independentoptimization phase as well as during the technology mapping. Wehave extended a conjunctive decomposition of Boolean functions[1]to multiple-valued input binary-valued output functions.Our extension provides a more efficient way for decomposingmutiple-output Boolean functions, since [1]only considerssingle-output functions.

    Furthermore, we address the problems of technology mappingand logic optimization for Chemically Assembled ElectronicNanotechnoloy (CAEN).CAEN is a promising alternative toCMOS-based technology, allowing construction of extremeleydense low-power computational elements with inexpensivechemical self-assembly.

  • 260. Gaarder, A.
    et al.
    Marcinkevicius, Saulius
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Barrios, C. A.
    Lourdudoss, Sebastian
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Time-resolved micro-photoluminescence studies of deep level distribution in selectively regrown GaInP: Fe and GaAs : Fe2002In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 17, no 2, p. 129-134Article in journal (Refereed)
    Abstract [en]

    We apply time-resolved photoluminescence with 1-2 mum spatial resolution for the characterization of deep centre distributions in semi-insulating GaInP:Fe and GaAs:Fe epitaxial layers regrown by hydride vapour phase epitaxy around etched GaAs mesas and GaAs/AlGaAs quantum well laser structures. In InGaP, Fe ions act as the main carrier recombination centres, while in Fe-doped GaAs both the Fe ions and As antisite defects have to be considered. The distribution of Fe ions in InGaP was found to be rather uniform and close to the target value. For GaAs:Fe, the number of ionized Fe and EL2 centres showed a certain increase at the mesa interfaces. In both cases, the high trap concentration was maintained throughout the regrown layers indicating good semi-insulating material properties.

  • 261. Gaarder, A.
    et al.
    Marcinkevicius, Saulius
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Barrios, C. A.
    Lourdudoss, Sebastian
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Time-resolved micro-photoluminescence studies of dopant distribution in selectively regrown GalnP: Fe around VCSELs2002In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T101, p. 89-91Article in journal (Refereed)
    Abstract [en]

    We apply time-resolved photoluminescence with 1.5 mum spatial resolution for characterization ofcarrier trap distribution in semi-insulating Ga0.51In0.49P:Fe layers regrown around GaAs/AlGaAs circular vertical cavity surface emitting laser mesas using hydride vapour phase epitaxy. The carrier trapping times are in the range from 10 to 15 ps and quite uniformly distributed throughout the burying GaInP:Fe layer, suggesting that the layer is semi-insulating everywhere. Simulations show that, in addition to the Fe dopants, the layer contains other, unintended carrier traps. The photoluminescence spectra reveal that the regrown GaInP:Fe material has several distinct regions with different band gaps. This is attributed to differences in the In/Ga composition and/or CuPt ordering of the GaInP.

  • 262. Gaarder, A.
    et al.
    Marcinkevicius, Saulius
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Messmer, E. R.
    Lourdudoss, Sebastian
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Dopant distribution in selectively regrown InP: Fe studied by time-resolved photoluminescence2001In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 226, no 4, p. 451-457Article in journal (Refereed)
    Abstract [en]

    We apply time-resolved photoluminescence with 1 mum spatial resolution for the characterization of iron distribution in semi-insulating InP:Fe epitaxial layers regrown by hydride vapor-phase epitaxy around etched mesas. The InP:Fe regrowth was carried out on InP:S mesas etched both along the [110] and [110] crystallographic directions, as well as on InP/InGaAsP in-plane lasers. In all cases, the Fe concentration was found to be close to the target values and showed little variation along the regrown layers.

  • 263.
    Gaarder, Andreas
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Simulation and optical characterisation of carrier trapping in semi-insulating semiconductors2001Licentiate thesis, comprehensive summary (Other scientific)
  • 264. Galeckas, A.
    et al.
    Grivickas, P.
    Grivickas, V.
    Bikbajevas, V.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Temperature dependence of the absorption coefficient in 4H-and 6H-silicon carbide at 355 nm laser pumping wavelength2002In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 191, no 2, p. 613-620Article in journal (Refereed)
    Abstract [en]

    We report on the absorption coefficient at 355 nm laser wavelength for 4H- and 6H-SiC over a wide temperature range. The measurements were carried out using a depth- and time-resolved free-carrier-absorption technique. The values of the absorption coefficient for the fundamental E perpendicular to

  • 265. Galeckas, A.
    et al.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Breitholtz, B.
    Bleichner, H.
    Application of optical emission microscopy for reliability studies in 4H-SiC p(+)/n(-)/n(+) diodes2001In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 90, no 2, p. 980-984Article in journal (Refereed)
    Abstract [en]

    An optical emission microscopy technique with spatial and spectral resolution capabilities is applied for stability studies of 4H-SiC material properties. From the example of a 4H-SiC p(+)/n(-)/n(+) diode imaged at different stages of electrical overstress the mechanism of degrading performance is directly unveiled. We correlate this phenomenon with irreversible structural changes within the active region created by a nonuniform heating related stress. The stress-generated features are interpreted as multiple stacking faults spreading throughout the whole base region and nucleated in the vicinity of built-in defects and process-induced structural deficiencies.

  • 266. Galeckas, A.
    et al.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Frischholz, M.
    Grivickas, V.
    Optical characterization of excess carrier lifetime and surface recombination in 4H/6H-SiC2001In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 79, no 3, p. 365-367Article in journal (Refereed)
    Abstract [en]

    The high-injection lifetime and surface recombination parameters have been investigated in as-grown 4H and 6H-SiC epilayers subjected to various process treatments. A depth-resolved optical transient absorption technique was utilized to evaluate the influence of film thickness and surface treatment on carrier lifetime. We demonstrate that besides polishing and ion implantation, both natural and thermal oxidation may also result in lifetime reduction due to enhanced surface losses. Moreover, a long-term stability test has revealed a substantial degradation of lifetime characteristics, consistent with a spontaneous surface oxidation and slow relaxation of SiO2/SiC interface states. We show that for common film thickness < 100 mum, the effective lifetime is dominated by surface leakage, which is found, generally, to be higher in 4H compared to 6H-SiC.

  • 267. Galeckas, A.
    et al.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Lindstedt, M.
    Characterization of carrier lifetime and diffusivity in 4H-SiC using time-resolved imaging spectroscopy of electroluminescence2003In: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 102, no 03-jan, p. 304-307Article in journal (Refereed)
    Abstract [en]

    We report on time- and spectrally resolved studies of recombination radiation in 4H-SiC by combining imaging spectroscopy and gated optical emission microscopy techniques. An insight into the basic characteristics of 3D carrier dynamics was attained by combining data of electroluminescence imaged from the backside and from the cross-sectional plane of a forward biased PN structures. We demonstrate the potential and efficiency of this method in mapping minority carrier lifetime and diffusivity parameters and also in locating and analysis of the structural defects in the active area. Finally, a detrimental impact of the intrinsic growth-related and long-term operation-induced defects on the carrier transport properties was directly revealed and quantified.

  • 268. Galeckas, A.
    et al.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Pirouz, P.
    Recombination-enhanced extension of stacking faults in 4H-SiC p-i-n diodes under forward bias2002In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 81, no 5, p. 883-885Article in journal (Refereed)
    Abstract [en]

    The extension of stacking faults in a forward-biased 4H-SiC PiN diodes by the recombination-enhanced motion of leading partial dislocations has been investigated by the technique of optical emission microscopy. From the temperature dependence of the measured velocity of the partials, an activation energy of 0.27 eV is obtained. Based on this and analysis of the emission spectra, a radiative recombination level of 2.8 eV for the stacking fault, and two energy levels for the partial dislocation, a radiative one at 1.8 eV and a nonradiative at 2.2 eV, have been determined.

  • 269.
    Galeckas, Augustinas
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kuznetsov, A.Y.
    Chassagne, T.
    Ferro, G.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Grivickas, V.
    Optical investigation of the built-in strain in 3C-SiC epilayers2004In: SILICON CARBIDE AND RELATED MATERIALS 2003, PRTS 1 AND 2 / [ed] Madar, R; Camassel, J, 2004, Vol. 457-460, p. 657-660Conference paper (Refereed)
    Abstract [en]

    The impact of the residual strain ranging from -2.5 GPa to + 0.436 GPa on the electronic properties of 3C-SiC/Si(100) heteroepitaxial layers is investigated by imaging PL spectroscopy. An anomalous above band-gap emission is observed in the blue/green region of spectrum and is tentatively attributed to the manifestation of defect-rich SiC/Si interfaces. A direct correlation of the accumulated strain with the energy gap and the temperature dependence of the band-gap are determined from the analysis of the peak shifts in the fundamental luminescence spectra. The differential pressure coefficient of the band-gap is found to be dE(G)/dp = -5 meV/GPa at room temperature. The observed energy gap narrowing in the temperature interval from 70 to 320 K can be described by the Varshni equation E-G = 2.417 - alphaT(2) (beta + T)(-1) with the parameters alpha = 3.4x10(-4) eV/K and beta = 700 K.

  • 270. Gao, Y. C.
    et al.
    Wikner, J. J.
    Tenhunen, Hannu
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Design and analysis of an oversampling D/A converter in DMT-ADSL systems2002In: Analog Integrated Circuits and Signal Processing, ISSN 0925-1030, E-ISSN 1573-1979, Vol. 32, no 3, p. 201-210Article in journal (Refereed)
    Abstract [en]

    Oversampling sigma-delta digital-to-analog converters are crucial building blocks for telecommunication applications. To reduce power consumption, lower oversampling ratios are preferred thus high-order digital sigma-delta modulators are needed to meet the dynamic performance requirements. This paper presents an oversampling DAC with 1.104 MHz signal bandwidth for DMT-ADSL application and focuses on the design issues of the high-order one-bit multiple feedback modulators (such as the stability problem, good inband SNDR performance, limit cycles, etc.). A new approach to obtain and optimize the stable feedback coefficients has been presented. From our analysis results it is found that the extra feedback coefficients and scaling coefficients in the modulator have non-negligible impact on the behavior of the limit cycles, and design guide for selecting the scaling coefficients is provided. Finally a 5th-order modulator with an oversampling ratio of 32 and 14-bit input has been implemented in a 0.6 mum 3.3 V CMOS process and integrated into the whole DAC chip.

  • 271. Gao, Y. H.
    et al.
    Jia, L. H.
    Isoaho, J.
    Tenhunen, Hannu
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    A comparison design of comb decimators for sigma-delta analog-to-digital converters2000In: Analog Integrated Circuits and Signal Processing, ISSN 0925-1030, E-ISSN 1573-1979, Vol. 22, no 1, p. 51-60Article in journal (Refereed)
    Abstract [en]

    This paper presents a comparison design of comb decimators based on the non-recursive algorithm and the recursive algorithm. Compared with the recursive algorithm, the main advantage of the non-recursive algorithm is its abilities of reducing power consumption and increasing circuit speed especially when the decimation ratio and filter order are high. Based on the non-recursive algorithm, a decimator with programmable filter orders (3rd, 4th and 5th), decimation ratios (8, 16, 32 and 64) and input bits (1 and 2 bits) has been implemented in a 0.6 mu m 3.3 V CMOS process. Its measured core power consumption is 44 mW at the oversampling rate of 25 MHz and its highest input data rate is 110 MHz.

  • 272. Ghiringhelli, G.
    et al.
    Brookes, N. B.
    Tjeng, L. H.
    Mizokawa, T.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Steeneken, P. G.
    Menovsky, A. A.
    Probing the singlet character of the two-hole states in cuprate superconductors2002In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 312, p. 34-35Article in journal (Refereed)
    Abstract [en]

    Using spin-resolved resonant photoemission we have probed the singlet vs. triplet character of the two-hole state in the layered cuprates Bi2Sr2CaCu2O8+delta La2-xSrxCuO4 and Sr2CuO2Cl2. The combination of the photon circular polarization with the photoelectron spin detection gives access to the character of the photoemission final states, which correspond to the two-hole configurations localized at a (CuO4) site. In particular, the lowest energy state is found to have a very high singlet character in all the measured compounds. This can be considered as a strong indication of the existence and stability of the so-called Zhang-Rice singlets in the layered cuprates.

  • 273. Ghiringhelli, G.
    et al.
    Tjeng, L. H.
    Tanaka, A.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Mizokawa, T.
    de Boer, J. L.
    Brookes, N. B.
    3d spin-orbit photoemission spectrum of nonferromagnetic materials: The test cases of CoO and Cu2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 7Article in journal (Refereed)
    Abstract [en]

    The x-ray photoemission spectrum of the valence states of 3d transition-metal systems is spin polarized when using circularly polarized photons. The integral of the spin-orbit spectrum is proportional to the expectation value of the angular part of the 3d spin-orbit operator in the initial state. We show that this quantity can be used to get an estimate of the atomic orbital moment. While the measurement is sensitive to the magnetization axis, it does not require a net macroscopic magnetization nor the presence of a long-range magnetic order, and is therefore suitable for any transition-metal systems being antiferromagnetic or paramagnetic or magnetically disordered. In the case of full 3d shell the integral of the spin-orbit spectrum is zero, but the spectral shape can give a direct estimate of the 3d spin-orbit energy splitting DeltaE(SO). We have used Cu and CoO to experimentally test this technique. As expected Cu provides a vanishing result for , whereas for Co2+ in CoO we find =1.36h at 0 K. On the other hand we find DeltaE(SO)similar or equal to280 meV for Cu.

  • 274. Ghiu, I.
    et al.
    Bourennane, M.
    Karlsson, Anders
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Entanglement-assisted local transformations between inequivalent classes of three-particle entangled states2001In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 287, no 02-jan, p. 12-18Article in journal (Refereed)
    Abstract [en]

    We show that bipartite and tripartite entangled states cannot be used as catalysis states to enable local transformations inbetween inequivalent classes of three-particle entangled states which are non-interchangeable under local transformations. We find the optimal protocol for conversion of a certain family of the W-states and an EPR-pair into the GHZ-state.

  • 275.
    Ghodsi, Ali
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Onana Alima, Luc
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    El-Ansary, Sameh
    Swedish Institute of Computer Science.
    Brand, Per
    Swedish Institute of Computer Science.
    Haridi, Seif
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Self-Correcting Broadcast in Distributed Hash Tables2003In: Proceedings of the Fifteenth IASTED International Conference on Parallel and Distributed Computing and Systems / [ed] Gonzalez, T., 2003, p. 93-98Conference paper (Refereed)
    Abstract [en]

    We present two broadcast algorithms that can be used on top of distributed hash tables (DHTs) to perform group communication and arbitrary queries. Unlike other P2P group communication mechanisms, which either embed extra information in the DHTs or use random overlay networks, our algorithms take advantage of the structured DHT overlay networks without maintaining additional information. The proposed algorithms do not send any redundant messages. Furthermore the two algorithms ensure 100% coverage of the nodes in the system even when routing information is outdated as a result of dynamism in the network. The first algorithm performs some correction of outdated routing table entries with a low cost of correction traffic. The second algorithm exploits the nature of the broadcasts to extensively update erroneous routing information at the cost of higher correction traffic. The algorithms are validated and evaluated in our stochastic distributed-algorithms simulator.

  • 276. Ghorbani, S. R.
    et al.
    Andersson, Magnus
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Rapp, Ö.
    Thermoelectric power of charge-neutral Nd1-2xCaxMxBa2Cu3O7-delta (M = Th and Pr): Evidence for different types of localization2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 10Article in journal (Refereed)
    Abstract [en]

    The superconducting T-c of Nd1-2xCaxMxBa2Cu3O7-delta (M=Th or Pr) is strongly depressed with increasing doping concentration in spite of the fact that these dopings are nominally charge neutral for small x. We have inquired into the reasons for this behavior by studies of the thermoelectric power S in sintered samples with x up to 0.1 and for temperatures from T-c up to room temperature. S(x,T) was analyzed in terms of two different semiempirical models, which assume the existence of a narrow electron band. In both models and for both dopings the bands broaden with increasing x and the tendency for localization increases. For Ca-Th doping this can be explained by weak electronic disorder. For Ca-Pr doping, the increase of electronic disorder is weaker, and the results indicate that charge localization in addition is important.

  • 277. Ghorbani, S. R.
    et al.
    Rapp, Östen.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    An anomalous dip in thermoelectric power of Nd1-xPrxBa2Cu3O7-delta2003In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 388, p. 351-352Article in journal (Refereed)
    Abstract [en]

    The thermoelectric power, S, has been studied for sintered samples of Nd1-xPrxBa2Cu3O7-delta with 0 less than or equal to x less than or equal to 0.30 in the temperature range from the superconducting T-c to room temperature. S increases with decreasing temperature,and has a broad maximum at T-max in the region around 120 K before decreasing strongly when T-e is approached. Several properties indicate a decrease of charge concentration with increasing doping, x, from S(x, 290 K), T-max, and the resistivity rho(x, 290 K). An anomaly has been observed in S(T) for x greater than or equal to 0.20 in the form of a dip at 78 K of order 15% of S. The origin of this feature is not known.

  • 278.
    Ghorbani, Shaban Reza
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Andersson, Magnus
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Rapp, Östen
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Neutron diffraction studies of Nd1-xPrxBa2Cu3O7-delta: Evidence for hole localization2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, no 1, p. 145031-Article in journal (Refereed)
    Abstract [en]

    Sintered samples of Nd1-xPrxBa2Cu3O7-delta with x=0, 0.05, 0.10, 0.15, 0.20, and 0.30 have been studied by neutron diffraction, x-ray diffraction, and resistivity measurements. Sample stoichiometry was carefully checked. Atomic distances within the unit cell and the oxygen content were shown to be almost independent of Pr doping. Bond valence sums (BVSs) were calculated from the neutron diffraction data assuming either a constant valence or a mixed valence for Cu and Pr ions. The planar Cu2 valence is independent of Pr doping and the chain Cu1 valence is roughly constant, while the hole concentration in the planes and chains decrease with increasing Pr doping for both BVS calculation methods. All together, this indicates that hole localization on the Nd(Pr) site is a main reason for the decrease of the hole concentration in the planes. A consistent relation between the hole concentration in the planes calculated from the constant valence method and the depression of the critical temperature is also obtained, both for Pr-doped Nd-123 and for Y(Pr)-123 studied previously.

  • 279.
    Ghorbani, Shaban Reza
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Andersson, Magnus
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Rapp, Östen
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Normal state Hall effect in Nd1-xCaxBa2Cu3O7-delta: competition between added charge and disorder2003In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 390, no 2, p. 160-166Article in journal (Refereed)
    Abstract [en]

    The transport properties of sintered samples of Nd1-xCaxBa2CU3O7-delta with 0 less than or equal to x less than or equal to 0.20 have been studied in the normal state by Hall resistivity measurements. The Hall coefficient, R-H(x, T) was well described in terms of two different models. In a phenomenological narrow band model, the conduction band width became narrower with increasing Ca concentration while the density of states band width decreased slightly. A competition between two effects (i) added charge, and (ii) disorder introduced into the CuO2 planes by doping, could be the main reason for the observed small decrease of the band widths. In the Anderson model, the temperature dependent part of the Hall angle was independent of hole concentration and disorder while the temperature independent part increased linearly with increasing Ca content. The results in both models support that Ca introduces disorder in the CuO2 planes.

  • 280.
    Ghorbani, Shaban Reza
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Lundqvist, Pieter
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Andersson, Magnus
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Valldor, M.
    Rapp, Östen
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Thermoelectric power and resistivity of Nd1-xPrxBa2Cu3O7-delta2001In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 353, no 1-2, p. 77-84Article in journal (Refereed)
    Abstract [en]

    The structural and transport properties of Nd1-xPrxBa2Cu3O7-delta (x = 0.0, 0.05, 0.10, and 0.15), have been studied by X-ray powder diffraction, electrical resistivity measurements, and thermoelectric power measurements. The decrease of the superconducting critical temperature with doping is described by a parabolic term and a linear term. The c-axis lattice parameter and the cell volume decrease with doping up to x = 0.10. Analyses of the thermoelectric power, critical temperature, c-axis lattice parameter, and the cell volume suggest that the Pr ions have a valence close to +4 at low doping concentration. The room temperature resistivity indicates that hole concentration decreases with increasing Pr doping. The room temperature thermoelectric power is positive for all samples and increases with increasing Pr doping due to a decrease in the carrier concentration. We analyzed the thermoelectric power as a function of temperature with a two-band model with an additional linear T term. An excellent agreement between model and data was obtained. The band width of the narrow band increases and its peak position moves away from the Fermi energy with increasing doping concentration.

  • 281.
    Giambiagi, Pablo
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Secrecy for mobile implementations of security protocols2001Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    Mobile code technology offers interesting possibilities tothe practitioner, but also raises strong concerns aboutsecurity. One aspect of security is secrecy, the preservationof confidential information. This thesis investigates themodelling, specification and verification of secrecy in mobileapplications which access and transmit confidential informationthrough a possibly compromised medium (e.g. the Internet).These applications can be expected to communicate secretinformation using a security protocol, a mechanism to guaranteethat the transmitted data does not reach unauthorizedentities.

    The central idea is therefore to relate the secrecyproperties of the application to those of the protocol itimplements, through the definition of a "confidential protocolimplementation" relation. The argument takes an indirect form,showing that a confidential implementation transmits secretdata only in the ways indicated by the protocol. We define theimplementation relation using labelled transition semantics,bisimulations and relabelling functions. To justify itstechnical definition, we relate this property to a notion ofnoninterference for nondeterministic systems derived fromCohen’s definition of Selective Independency. We alsoprovide simple and local conditions that greatly simplify itsverification, and report on our experiments on an architectureshowing how the proposed formulations could be used in practiceto enforce secrecy of mobile code.

  • 282.
    Glitho, Roch H.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    A Mobile Agent Based Service Architecture for Internet Telephony2002Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Internet Telephony defined as real time voice or multimediacommunications over packet switched networks dates back to theearly days of the Internet. ARPA's Network SecureCommunications project had implemented, as early as December1973, an infrastructure for local and transnet real time voicecommunication. Two main sets of standards have emerged: H. 323from the ITU-T and the session initiation protocol (SIP) fromthe Internet Engineering Task Force (IETF). Both includespecifications for value added services. Value added services,or more simply services, are critical to service providers'survival and success. Unfortunately, the service architecturesthat come with the ITU-T and the IETF sets of standards arerather weak. Although they are constantly evolving,alternatives and complements need to be researched. This thesiswhich is made up of a formal dissertation and 6 appendices,proposes a novel mobile agent based service architecture forInternet Telephony. The architecture addresses the issues noneof the existing architectures solves in a satisfactory manner.Furthermore it adds mobile agents to the panoply of servicecreation tools. The appendices are reprints of articlespublished in refereed magazines/journals or under considerationfor publication. The formal dissertation is a summary of thepublications. A consistent and comprehensive set ofrequirements are derived. They are TINA-C flavored, but adaptedto Internet Telephony. They are used to critically reviewrelated work and also used to motivate the use of mobile agentsas the pillars of a novel architecture. The components of thisnovel architecture are identified. The key component is themobile service agent. It acts as a folder and carriesservice(s) to which the end-user has subscribed. Mobile serviceagents need to be upgraded when new versions of service logicare available and when end-users make changes to service data.This thesis proposes a novel upgrading framework. The currentInternet infrastructure comprises a wide range of hosts. Mobileagent platforms are now available for most of thesehosts/clients including memory/processing power constrainedPDAs. Our mobile service agents need to adapt to hostvariability when roaming. A novel adaptivity framework is alsoproposed. These two frameworks are general and can be appliedto any other mobile agent which meets a basic set ofassumptions. A key advantage of a mobile agent based servicearchitecture is that it enables the developement of mobileagent based services. The thesis proposes a novel mobile agentbased multi-party session scheduler. The feasibility and theadvantages of the architecture proposed by this thesis havebeen demonstrated by a prototype on which measurements havebeen made. Future work includes the addition of a securityframework to the architecture, and refinenements to theupgrading and adaptivity frameworks. More mobile agent basedservices, especially mobile multi agent based services willalso be developed.

  • 283. Gorniak, R. J. T.
    et al.
    Kramer, E. L.
    New York University.
    Maguire Jr., Gerald Q.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Noz, Marilyn E.
    New York University.
    Schettino, C. J.
    Zeleznik, Michael P.
    Evaluation of a semiautomatic 3D fusion technique applied to molecular imaging and MRI brain/frame volume data sets2003In: Journal of medical systems, ISSN 0148-5598, E-ISSN 1573-689X, Vol. 27, no 2, p. 141-156Article in journal (Refereed)
    Abstract [en]

    A generally applicable {3D} fusion method was evaluated using molecular imaging and {MRI} volumetric data sets from 15 brain tumor patients with stereotactic frames attached to their skull. Point pairs, placed on the frame only, were chosen, polynomial warping coefficients were generated to map voxels from one coordinate space to the other. The {MRI} frame was considered the reference structure and the standard for "correct" registration. An {ANOVA} test (p {\textgreater} 0.05) confirmed the point pair choice to be consistent. The 95\% confidence interval for the t-test showed the measured distance difference between the registered volumes was within one {MRI} voxel. A further experiment was conducted to independently evaluate the brain registration based on testing for consistency of randomly selected interior/exterior points. A t-test result (p {\textless} 0.05) showed that the consistency (i.e., both interior or both exterior) before and after volume registration were significantly different. This fusion method may be a viable alternative when other methods fail.

  • 284. Gothenberg, A.
    et al.
    Tenhunen, Hannu
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Improved cascaded sigma-delta noise shaper architecture with reduced sensitivity to circuit nonlinearities2002In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 38, no 14, p. 683-685Article in journal (Refereed)
    Abstract [en]

    An improved cascaded sigma-delta noise shaper with reduced sensitivity to switch and opamp nonlinearities is presented. The architecture can be used for wideband applications, i.e. RF-front ends, at low oversampling ratio, as well as for high-resolution audio applications.

  • 285. Gothenberg, A.
    et al.
    Tenhunen, Hannu
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Nonlinear quantization in low oversampling ratio sigma-delta noise shapers for RF applications2002In: Analog Integrated Circuits and Signal Processing, ISSN 0925-1030, E-ISSN 1573-1979, Vol. 30, no 3, p. 193-206Article in journal (Refereed)
    Abstract [en]

    Baseband signal processing for current base stations or 3rd generation mobile systems will impose high bandwidth and high VLSI integration demand. Many of the desired integration aspects can be satisfied with sigma-delta converter front-ends. However, under the technology constraints there are simultaneous requirements for high sample rate and low oversampling ratio in order to achieve the desired baseband width. In this paper, we present system architecture results for the 4th-order cascaded noise shaper architectures to be used in baseband front-ends. We show that the cascaded structures with proper scaling will satisfy simultaneous demand on linearity (spurious free dynamic range) and high SQNR with low oversampling ratio based on usage of multibit quantizers outside the actual signal noise shaping path. We also present results for nonlinear quantization effects in low oversampling ratio cascaded noise shaper architectures. We analyse the effect of the non-linearity in both the A/D and D/A-block in quantization error quantizer path for the 4th-order cascaded topology and the design constraints associated to the performance of the used A/D and D/A structures. The performance requirement for the multi-bit quantizer for high SQNR is shown for the case of low oversampling ratios. The results show that non-uniform quantization around zero input are far more crucial to the SQNR than nonlinear quantization deviating from the ideal transfer function. As the key difference to standard multibit quantizers, no special error correction or error distribution schemes are required; the linearity requirements are satisfied with 0.2 LSB accuracy of the few bit quantizer. Finally, the performance of non-linear quantization using multitone test signals are also shown.

  • 286. Grahn, J. V.
    et al.
    Fosshaug, H.
    Jargelius, M.
    Jonsson, P.
    Linder, M.
    Malm, B. Gunnar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Mohadjeri, B.
    Pejnefors, J.
    Radamson, Henry H.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Sanden, M.
    Wang, Yong-Bin
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Landgren, Gunnar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    A low-complexity 62-GHz f(T) SiGe heterojunction bipolar transistor process using differential epitaxy and in situ phosphorus-doped poly-Si emitter at very low thermal budget2000In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 44, no 3, p. 549-554Article in journal (Refereed)
    Abstract [en]

    A low-complexity SiGe heterojunction bipolar transistor process based on differential epitaxy and in situ phosphorus doped polysilicon emitter technology is described. Silane-based chemical vapor deposition at reduced pressure was used for low-temperature SiGe epitaxy. Following SiGe epitaxy, the process temperature budget was kept very low with 900 degrees C for 10 s as the highest temperature step. A very high current gain of almost 2000 and cut off frequency of 62 GHz were achieved for a uniform 12% Ge profile. The breakdown voltage BVCEO and forward Early voltage were equal to 2.9 and 6.5 V, respectively.

  • 287. Grins, J.
    et al.
    Esmaeilzadeh, S.
    Andersson, Magnus
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Morawski, A.
    Synthesis and magnetic susceptibility of the rutile phase MnTaO42000In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 10, no 9, p. 2197-2200Article in journal (Refereed)
    Abstract [en]

    The Mn3+-containing oxide MnTaO4 was synthesized at 1050 degrees C and 2 kbar partial oxygen gas pressure. It has a rutile-type structure, space group P4(2)/mnm, with a = 4.7189(3), c = 2.9843(3) Angstrom, and a statistical distribution of Mn/Ta. The structure was refined by the Rietveld method using both X-ray and neutron powder diffraction. The refinements, and energy-dispersive X-ray microanalysis, indicate that the phase may contain a small amount of Mn4+ and have the actual composition Mn1.08(2)Ta0.92(2)O4. The magnetic susceptibility shows a maximum at 16 K and Curie-Weiss behavior at higher temperatures, with mu(eff) = 5.11(4) mu(B) per Mn atom. The susceptibility is consistent with spin-glass behavior: (i) the temperature at the susceptibility maximum is frequency-dependent and (ii) field cooled and zero-field cooled susceptibility curves differ below the maximum. Neutron powder diffraction data collected at 10 K does not show any sharp magnetic reflections, but a very broad reflection, with a full width at half maximum height of 7 degrees, at a position corresponding to the 100 reflection is seen.

  • 288.
    Grishin, Alexander
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Khartsev, Sergey
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Electro-optical properties of Na0.5K0.5NbO3 films on Si by free-space coupling technique2004In: New Materials For Microphotonics / [ed] Shin, JH; Brongersma, M; Buchal, C; Priolo, F, 2004, Vol. 817, p. 225-229Conference paper (Refereed)
    Abstract [en]

    We report electro-optic performance of highly polar axis oriented Na0.5K0.5NbO3 (NKN) films grown directly on Pt(100nm)/Ti(10nm)/SiO2/Si(001) substrates by rf-magnetron sputtering. Semitransparent gold electrodes (diameter circle divide = 2 mm) were deposited ontop the NKN films by a thermal evaporation through the contact mask. Processing parameters have been specially optimized to obtain "electrosoft" NKN films with a non-linear fatigue-free P-E characteristics: low remnant P-r = 3.6 muC/cm(2) and high induced polarization P = 26 muC/cm(2) @ 522 kV/cm, and the coercive field E-c = 39 kV/cm. Electro-optical characterization of NKN/Pt/Si films has been performed using waveguide refractometry: a free-space coupling of a light beam into the thin-film waveguide modes. Intensity of TM- and TE-polarized light of 670 nm laser diode reflected from the free surface of NKN film and Au-cladding NKN/PL/Si waveguide was recorded at zero and 30 V (100 kV/cm) bias electric field. Extraordinary and ordinary refractive indices as well as electro-optic coefficient have been determined by fitting these experimental data to the Fresnel formulas. Applying 160 V (530 kV/cm) across the parallel plate NKN capacitor (circle divide = 2 mm, thickness 3 mum), modulation of the reflected light as high as 40% was achieved.

  • 289.
    Grishin, Alexander
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kim, Joo-Hyung
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Khartsev, Sergey
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Processing and on-wafer measurements of ferroelectric interdigitated tunable microwave capacitors2004In: Integration Of Advanced Micro-And Nanoelectronic Devices-Critical Issues And Solutions / [ed] Morais, J; Kumar, D; Houssa, M; Singh, RK; Landheer, D; Ramesh, R; Wallace, RM; Guha, S; Koinuma, H, 2004, Vol. 811, p. 307-312Conference paper (Refereed)
    Abstract [en]

    Na0.5K0.5NbO3 (NKN) and Pb(Zr0.53Ti0.47)O-3 (PZT) films have been grown by rf-magnetron sputtering and pulsed laser deposition techniques, correspondingly, on sapphire (Al2O3-0112, r-cut), YAlO3 + 1% Nd (Nd:YAlPO3-001), and quartz (Y+36degrees-cut) single crystal substrates. Interdigital capacitor (IDC) of coplanar waveguide (CPW) structures were defined by a standard lift off technique in a Au(0.5mum)/Cr(10nm) electrode electron beam evaporated on ferroelectric film surface. IDCs consisted of five pairs of fingers separated by 2 and 4 mum gap. On-wafer microwave characterization was performed using a workbench equipped with a coplanar probe station (Cascade Microtech) with G-S-G (Ground-Signal-Ground) Picoprobe, a network analyzer (Agilent Technologies E8364A) operating in 45 MHz to 40 GHz range and programmable power supply for de DUT (Device Under Test) biasing. Assumed equivalent circuit for the IDC/CPW structure contains planar capacitor under test C, the coplanar line with a complex impedance sigma and a parasitic capacitance C, between the signal and ground lines. The de-embedding technique has been employed to determine all six complex parameters C, sigma and C-p from S-parameter measurements performed for three different device structures: device, open and thru. NKN film interdigital capacitors on sapphire show superior performance in this microwave range: the frequency dispersion was as low as 18%, voltage tunability = 1 - C(40V)/C(0) (40 V, 200 kV/cm) about 14%, loss tangent similar to0.11, K-factor = tunability/tandelta from 131% @ 10 GHz: to 56% @ 40 GHz. The reliability of the de-embedding procedure is clearly proved by analysis of the frequency dependences of the parasitic capacitance and loss tangent as well as impedance of the coplanar line. Within the accuracy of experimental data and de-embedding calculations these values appear to be voltage independent: C-p similar to 70 fF, tan delta(p) changes from 0.07 @ 10 GHz to 0.15 @ 40 GHz; real and imaginary part of interconnect impedance increases with frequency from 0.16 Omega @ 10 GHz to 0.36 Omega @ 40 GHz and from 1.6 Omega @ 10 GHz to 5.84 Omega @ 40 GHz respectively.

  • 290.
    Grishin, Alexander M.
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Khartsev, Sergiy
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kim, Joo-Hyung
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Lu, J.
    Epitaxial colossal magnetoresistive/ferroelectric heterostructures on Si2004In: Integrated Ferroelectrics, ISSN 1058-4587, E-ISSN 1607-8489, Vol. 67, p. 69-76Article in journal (Refereed)
    Abstract [en]

    We report on processing and properties of La-0.67(SrCa)(0.33)MnO3 (LSCMO) films grown by pulsed laser deposition technique on Si(001) substrates buffered with Bi4Ti3O12/CeO2/YSZ heteroepitaxial layers. X-ray diffraction shows cube-on-cube growth of epitaxial Bi4Ti3O12/CeO2/YSZ/Si heterostructure whereas the LSCMO layer grows in the diagonal-on-side manner onto the Bi4Ti3O12 (BTO) template. High resolution TEM images demonstrate sharp interfaces between the buffer layers and LSCMO film as well as rare misfit dislocations on the CeO2/YSZ interface. LSCMO film processing conditions have been optimized to get maximum temperature coefficient of resistivity TCR = 4.4% K-1 and colossal magnetoresistance (CMR) Deltarho/rho similar to 2.9% kOe(-1) @ 294 K. Almost ultimate CMR performance at room temperature has been achieved due to successive improvement of c-axis orientation of layers: full widths at half-maximum (FWHM) = 0.65, 0.58, 0.65, 1.13 and 0.18 degrees in LSCMO/BTO/CeO2/YSZ/Si stack, respectively. Characterization of electrical noise in CMR film yields Noise Equivalent Temperature Difference (NETD) as low as 1.2 muK/rootHz @ 30 Hz and 294 K.

  • 291.
    Grishin, Alexander M.
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Khartsev, Sergiy
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kim, Joo-Hyung
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Lu, J.
    Epitaxial La-0.67(Sr,Ca)(0.33)MnO3 films on Si for IR bolometer applications2004In: Integration Of Advanced Micro-And Nanoelectronic Devices-Critical Issues And Solutions / [ed] Morais, J; Kumar, D; Houssa, M; Singh, RK; Landheer, D; Ramesh, R; Wallace, RM; Guha, S; Koinuma, H, 2004, Vol. 811, p. 405-410Conference paper (Refereed)
    Abstract [en]

    We report on processing and properties of La-0.67(Sr,Ca)(0.33)MnO3 (LSCMO) films grown by pulsed laser deposition technique on Si(001) substrates buffered with Bi4Ti3O12/CeO2/YSZ heteroepitaxial layers. X-ray diffraction shows cube-on-cube growth of epitaxial Bi4Ti3O12/CeO2/YSZ/Si heterostructure whereas the LSCMO layer grows in the "diagonal-on-side" manner onto the Bi4Ti3O12 (BTO) template. High resolution TEM images demonstrate sharp interfaces between the buffer layers and LSCMO film as well as rare misfit dislocations on the CeO2/YSZ interface. LSCMO film processing conditions have been optimized to get maximum temperature coefficient of resistivity TCR = 4.4%K-1 and colossal magnetoresistance (CMR) Deltarho/rho similar to 2.9%kOe(-1) @ 294K. Almost ultimate CMR performance at room temperature has been achieved due to successive improvement of c-axis orientation of layers: full widths at half-maximum (FWHM) 0.65, 0.58, 0.65, 1.13 and 0.18 degrees in LSCMO/BTO/CeO2/YSZ/Si stack, respectively. Characterization of electrical noise in CMR film yields noise equivalent temperature difference (NETD) as low as 1.2 muK/rootHz @ 30Hz and 294K.

  • 292.
    Grishin, Michael A.
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Grishin, Alexander M.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Khartsev, Sergiy
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Karlsson, Ulf O.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    High performance films of binary system SrTiO3-PbZr0.52Ti0.48O3 on sapphire2001In: Integrated Ferroelectrics, ISSN 1058-4587, E-ISSN 1607-8489, Vol. 39, no 1-4, p. 351-358Article in journal (Refereed)
    Abstract [en]

    Continuous series of solid solutions x.SrTiO3-(1-x).PbZr0.52Ti0.48O3 (SPZT) have been grown by pulsed laser deposition technique onto La0.7Sr0.3CoO3/Al2O3(01 (1) under bar2) single crystal. Films properties have been characterized in Au/SPZT/La0.7Sr0.3CoO3(LSCO)/Al2O3 vertical capacitive cell. X-ray diffraction shows SPZT/LSCO bilayer grows in strict epitaxial relationship with sapphire substrate: (001) SPZT parallel to (001) LSCO parallel to (01 (1) under bar2) Al2O3; [010] SPZT parallel to [010] LSCO parallel to [421] Al2O3. LSCO layer was found to be tensile strained, while SPZT film experiences tetragonal distortions c/a -1 approximate to 0.86% which are much lower than 2.73% in pure PZT ceramics. Curie temperature in SPZT film has been tailored continuously in the explored temperature range 77 K to 400 K by controlling SrTiO3:PZT ratio. Processing parameters have been optimized to get the highest tunability factor K = epsilon'(0) - epsilon'(V)/epsilon'(0) x 1/tandelta . SrTiO3:PZT=83:17 film exhibits superior properties: at I kHz maximum dielectric perinittivity and minimum loss tandelta were found to be 870 and 0.005, respectively; while K-factor exceeds value of 60 in the temperature range 280 to 350 degreesC reaching the maximum value of 64 at 325 degreesC. SPZT films can withstand prolonged pre-breakdown electric field and has resistivity as high as 3.5 10(12) Omega cm at 186 kV/cm.

  • 293.
    Grishin, Michael A.
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Karlsson, Henrik S.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Månsson, Martin
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Karlsson, Ulf O.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Electron structure and electron dynamics at InSb(111)2×2 semiconductor surface2003In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 76, no 3, p. 299-302Article in journal (Refereed)
    Abstract [en]

    The conduction band electronic structure and the electron dynamics of the clean InSb(111)2 x 2 surface have been studied by laser based pump-and-probe photoemission. The results are compared to earlier studies of the InSb(110) surface. It is found that both the energy location and the time dependence of the photoexcited structures are very similar for the two surfaces. This indicates that the dominant part of the photoemission signal in the conduction band region is due to excitations of electrons in the bulk region and that the surface electronic states play a minor role. The fast decay of the excited state, tau similar to 12 ps, indicates that diffusion of hot electrons into the bulk is an important mechanism.

  • 294.
    Grishin, Michael A.
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Månsson, Martin
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Claesson, Thomas
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Karlsson, Henrik S.
    Optillion AB.
    Karlsson, Ulf O.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    A bandgap surface state at the GaSb(001) surface observed by femtosecond laser pump-and-probe photoemission spectroscopyManuscript (Other academic)
  • 295.
    Grishin, Michael A.
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Månsson, Martin
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Tjernberg, Oscar
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Karlsson, Henrik S.
    Optillion AB.
    Karlsson, Ulf O.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    A new two-dimensional angle-resolving multi-anode electron detector for femtosecond photoemission spectroscopyArticle in journal (Other academic)
  • 296. Grivickas, P.
    et al.
    Galeckas, A.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Syvajarvi, M.
    Yakimova, R.
    Grivickas, V.
    Tellefsen, J. A.
    Carrier lifetime investigation in 4H-SiC grown by CVD and sublimation epitaxy2001In: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 4, no 03-jan, p. 191-194Article in journal (Refereed)
    Abstract [en]

    Depth-resolved carrier lifetime measurements were performed in low-doped epitaxial layers of 4H silicon carbide samples. The technique used was a pump-and-probe technique where carriers are excited by an above-bandgap laser pulse and probed by free carrier absorption. Results from chemical vapour deposition samples show that lifetimes as high as 2 mus may be observed in the mid-region of 40 mum thick epilayers. For epilayers grown by the sublimation method decay transients were characterised by a fast (few nanoseconds) initial recombination, tentatively assigned to the 'true' lifetime, whereas a slow tail of several hundred microsecond decay time was assigned to trapping centres. From the saturation of this level at increased pumping we could derive the trapping concentration and their depth distribution peaking at the epilayer/substrate interface.

  • 297. Grivickas, P.
    et al.
    Grivickas, V.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Excitonic absorption above the Mott transition in Si2003In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 91, no 24Article in journal (Refereed)
    Abstract [en]

    We present experimental evidence for the existence of excitonic states above the excitonic Mott transition in both highly doped and highly excited silicon. Previous limitations to resolve the fundamental absorption edge of Si at dense carrier plasmas are overcome employing a novel spatially and time-resolved spectroscopy. We show that the obtained density dependent excess absorption at 75 K represents an excitonic enhancement effect, which is attributed to persisting many-body interactions.

  • 298. Grivickas, P.
    et al.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Grivickas, V.
    Carrier diffusion characterization in epitaxial 4H-SiC2001In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 16, no 2, p. 524-528Article in journal (Refereed)
    Abstract [en]

    Carrier diffusivity has been experimentally determined in low-doped n-type epitaxial 4H-SiC over a wide injection range using a Fourier transient grating technique. The data showed that, with injection, the diffusion coefficient increased from a minority-hole diffusivity D-h = 2.3 cm(2)/s to an ambipolar diffusivity D-a = 4.2 cm(2)/s at approximately 10(16) cm(-3) with a substantial decrease occurring at higher injections. The derived D-h value corresponded to a minority-hole drift mobility of mu (h) = 90 cm(2)/Vs, about 30% lower than available majority-hole mobilities. Also. the temperature dependence of the ambipolar diffusivity in the 296-523 K range has been determined. It followed a power law D-a similar to T-1.3 which notably differed from the expected one using the majority-hole mobility temperature dependence.

  • 299.
    Grivickas, Paulius
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Optical studies of carrier transport and fundamental absorption in 4H-SiC and Si2004Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The Fourier transient grating (FTG) technique and a novelspectroscopic technique, both based on free carrier absorption(FCA) probing, have been applied to study the carrierdiffusivity in 4H-SiC and the fundamental absorption edge in4H-SiC and Si, respectively.

    FTG is a unique technique capable of detecting diffusioncoefficient dependence over a broad injection interval rangingfrom minority carrier diffusion to the ambipolar case. In thiswork the technique is used for thin epitaxial 4H-SiC layers,increasing the time- and spatial-resolution of the experimentalsetup by factors of ~100 and ~10, respectively, in comparisonto the established Si measurements. It is found that thediffusion coefficient within the detected excitation range inn-type 4H-SiC appears to be lower than the analyticalprediction from Hall-mobility data. To explain this, it issuggested that the minority hole mobility is reduced withrespect to that of the majority one or that the hole mobilityvalue is in general lower than previously reported. Observeddifferences between the temperature dependency of the ambipolardiffusion and the Hall-prediction, on the other hand, areattributed to the unknown Hall factor for holes and theadditional carrier-carrier scattering mechanism in Hallmeasurements. Furthermore, at high excitations a substantialdecrease in the ambipolar diffusion is observed andadditionally confirmed by the holographic transient gratingtechnique. It is shown that at least half of the decrease canbe explained by incorporating into the theoretical fittingprocedure the calculated band-gap narrowing effect, taken fromthe literature. Finally, it is demonstrated that numerical datasimulation can remove miscalculations in the analytical Fourierdata analysis in the presence of Auger recombination.

    Measurements with variable excitation wavelength pump-probeare established in this work as a novel spectroscopic techniquefor detecting the fundamental band edge absorption in indirectband-gap semiconductors. It is shown that the techniqueprovides unique results at high carrier densities in doped orhighly excited material. In intrinsic epilayers of 4H-SiC,absorption data are obtained over a wide absorption range, atdifferent temperatures and at various polarizations withrespect to the c-axis. Experimental spectra are modeled usingthe indirect transition theory, subsequently extracting thedominat phonon energies, the approximate excitonic bindingenergy and the temperature induced band-gap narrowing (BGN)effect in the material. Measurements in highly dopedsubstrates, on the other hand, provide the first experimentalindication of the values of doping induced BGN in 4HSiC. Thefundamental absorption edge is also detected in highly dopedand excited Si at carrier concentrations exceeding theexcitonic Mott transition by several orders of magnitude. Incomparison to theoretical predictions representing the currentunderstanding of absorption behavior in dense carrier plasmas,a density dependent excess absorption is revealed at 75 K.Summarizing the mainfeatures of the subtracted absorption, itis concluded that an excitonic enhancement effect is present inSi.

  • 300. Grivickas, V.
    et al.
    Galeckas, A.
    Bikbajevas, V.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Tellefsen, J. A.
    Spatially and time-resolved infrared absorption for optical and electrical characterization of indirect band gap semiconductors2000In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 364, no 02-jan, p. 181-185Article in journal (Refereed)
    Abstract [en]

    The current status of the spatially and time-resolved free-carrier absorption (FCA) method is provided. The FCA technique allows monitoring carrier dynamics in a time scale from nanoseconds to miliseconds by employing either collinear or orthogonal geometry between pump and probe beams. A high spatial resolution is achieved allowing in-depth carrier profiles to be extracted. The method is particularly suited for investigation of injection-dependent optical and recombination phenomena: band gap optical absorption, Shockley-Read-Hall (SRH) lifetime, Auger recombination coefficient, and the injection-dependent surface (interface) recombination velocity. We summarize important aspects of the technique demonstrating numerous measurements that have been implemented in studies of bulk Si, epilaxial 4H-SiC and porous silicon.

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