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  • 1. Abadei, S.
    et al.
    Gevorgian, S.
    Cho, C. R.
    Grishin, Alexander M.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Low-frequency and microwave performances of laser-ablated epitaxial Na0.5K0.5NbO3 films on high-resistivity SiO2/Si substrates2002In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 91, no 4, 2267-2276 p.Article in journal (Refereed)
    Abstract [en]

    The dielectric properties of laser-ablated 0.5-mum-thick c-axis epitaxial Na0.5K0.5NbO3 (NKN) films on high-resistivity (>7.7 kOmega cm) silicon SiO2/Si substrates are studied experimentally in the temperature interval of 30-320 K and at frequencies of 1.0 MHz-40 GHz. The films are grown by laser ablation from a stoichiometric target. For the measurements, planar 0.5-mum-thick gold electrodes (interdigital and straight slot) are photolithography defined on the top surface of NKN films. The slot width between the electrodes is 2.0 or 4.0 mum. At low frequencies (f<1.0 GHz), the structure performance is that of a typical metal-dielectric-semiconductor type, where two of this type of capacitor are connected back to back. At these frequencies, the large change in the capacitance (more than 10 times at 1.0 MHz), due to the applied dc field, is mainly due to the changes in depletion layer thickness at the surface of silicon. The associated losses are also large, tan delta>1. At microwave frequencies (f>10 GHz), the voltage dependence of the capacitance is given by the NKN film. More than a 13% capacitance change at 40 V dc bias and a Q factor of more than 15 are observed at 40 GHz, which make the structure useful for applications in electrically tunable millimeter-wave devices.

  • 2. Aberg, D
    et al.
    Linnarsson, M K
    KTH, School of Information and Communication Technology (ICT).
    Svensson, B G
    Hallberg, T
    Lindstrom, J L
    Ultrashallow thermal donor formation in silicon by annealing in ambient oxygen1999In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 85, 8054-8059 p.Article in journal (Refereed)
    Abstract [en]

    Czochralski-grown silicon wafers doped with phosphorus (similar to 10(14) cm(-3)) have been annealed in nitrogen, wet nitrogen, oxygen, argon, and vacuum ambients at 470 degrees C for times up to 500 h. Sample characterization was made using predominantly electrical techniques such as admittance spectroscopy and thermally stimulated capacitance measurements but also secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy were employed. In all samples, an increasing concentration of free carrier electrons is observed with increasing annealing time, reaching a maximum of similar to 10(16) cm(-3) at 100 h. For durations in excess of 100 h gradual decrease of the free electron concentration takes place except for the samples treated in wet nitrogen and oxygen atmospheres, which display donors stable even after 200 h. These stable centers are found to have shallower donor level positions in the energy band gap (similar to 25 meV below the conduction band edge E-c) than those of the centers formed in vacuum, argon, and nitrogen atmospheres (similar to 35 meV below E-c). The latter centers are associated with the well-established shallow thermal donors (STDs) while the origin of the former ones, which are labeled ultrashallow thermal donors (USTDs) is less known. However, on the basis of a wealth of experimental results we show that the USTDs are most likely perturbated STDs modified through interaction with fast-in diffusing oxygen species, possibly oxygen dimers. Further, comparison between the electrical data and the SIMS measurements reveals unambiguously that neither the STD nor the USTD centers involve nitrogen, in contrast to recent suggestions in the literature. (C) 1999 American Institute of Physics. [S0021-8979(99)06512-3].

  • 3. Aberg, J
    et al.
    Persson, S
    Hellberg, Per-Erik
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Zhang, Shi-Li
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Smith, U
    Ericson, F
    Engstrom, M
    Kaplan, W
    Electrical properties of the TiSi2-Si transition region in contacts: The influence of an interposed layer of Nb2001In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 90, no 5, 2380-2388 p.Article in journal (Refereed)
    Abstract [en]

    The influence of an interposed ultrathin Nb layer between Ti and Si on the silicide formation and the electrical contact between the silicide formed and the Si substrate is investigated. The presence of the Nb interlayer results in the formation of ternary alloy (Nb,Ti)Si-2 in the C40 crystallographic structure adjacent to the Si substrate. Depending on the nature of the Si substrates and/or the amount of the initial Nb, the interfacial C40 (Nb,Ti)Si-2 leads, in turn, to either epitaxial growth of a highly faulted metastable C40 TiSi2 or formation of the desired C54 TiSi2 at a lower temperature than needed for it to form in reference samples with Ti deposited directly on Si. On p-type substrates doped to various concentrations, the Nb also leads to a considerably lower specific contact resistivity than that obtained in the reference samples: a twofold to fourfold reduction in the contact resistivity is found using cross-bridge Kelvin structures in combination with two-dimensional numerical simulation. As C40 (Nb,Ti)Si-2 forms at the interface when an interfacial Nb is present, the interface characterized is likely to represent the one between (Nb,Ti)Si-2 and Si. For the reference samples, the interface studied is between TiSi2 and Si.

  • 4. Adachi, N.
    et al.
    Denysenkov, V. P.
    Khartsev, Sergiy
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Grishin, Alexander M.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Okuda, T.
    Epitaxial Bi3Fe5O12(001) films grown by pulsed laser deposition and reactive ion beam sputtering techniques2000In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 88, no 5, 2734-2739 p.Article in journal (Refereed)
    Abstract [en]

    We report on processing and comparative characterization of epitaxial Bi3Fe5O12 (BIG) films grown onto Gd-3(ScGa)(5)O-12[GSGG,(001)] single crystal using pulsed laser deposition (PLD) and reactive ion beam sputtering (RIBS) techniques. A very high deposition rate of about 0.8 mu m/h has been achieved in the PLD process. Comprehensive x-ray diffraction analyses reveal epitaxial quality both of the films: they are single phase, exclusively (001) oriented, the full width at half maximum of the rocking curve of (004) Bragg reflection is 0.06 deg for PLD and 0.05 deg for RIBS film, strongly in-plane textured with cube-on-cube film-to-substrate epitaxial relationship. Saturation magnetization 4 pi M-s and Faraday rotation at 635 nm were found to be 1400 Gs and -7.8 deg/mu m in PLD-BIG, and 1200 Gs and -6.9 deg/mu m in RIBS-BIG. Ferromagnetic resonance (FMR) measurements performed at 9.25 GHz yielded the gyromagnetic ratio gamma=1.797x10(7) l/s Oe, 1.826x10(7) l/s Oe; the constants of uniaxial magnetic anisotropy were K-u(*)=-8.66x10(4) erg/cm(3), -8.60x10(4) erg/cm(3); the cubic magnetic anisotropy K-1=-2.7x10(3) erg/cm(3),-3.8x10(3) erg/cm(3); and the FMR linewidth Delta H=25 and 34 Oe for PLD and RIBS films correspondingly. High Faraday rotation, low microwave loss, and low coercive field less than or equal to 40 Oe of BIG/GSGG(001) films promise their use in integrated magneto-optic applications.

  • 5.
    Agnarsson, Björn
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Olafsson, S.
    Gislason, H. P.
    Karlsson, Ulf O.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Influence of initial surface reconstruction on nitridation of Al2O3 (0001) using low pressure ammonia2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 1, 013519- p.Article in journal (Refereed)
    Abstract [en]

    The purpose of this study is to investigate the effect of initial surface reconstruction on the nitridation process of Al2O3 (0001). This was done by exposing differently reconstructed sapphire substrates at different temperatures to low pressure ammonia (NH3). Structural and chemical analysis were carried out using low-electron energy diffraction and x-ray photoelectron spectroscopy. The experiments revealed that using low pressure ammonia (P-NH3 < 1 X 10(-5) Torr), no nitridation takes place on (1x1) unreconstructed surfaces. However, when the unreconstructed surface starts to change to a (root 31 x root 31) R +/- 9 degrees reconstructed surface, with increasing substrate temperature, the nitridation becomes successful. When using the initially reconstructed surface, the nitridation is successful even from the lowest temperature used. These results suggest that the initial surface reconstruction has a major effect on the nitridation process. This kinetic behavior has not been reported before, with most nitridation studies mainly focusing on the effect of surface temperature on the resulting surface morphology, rather than the actual kinetics of the process itself.

  • 6. Ahuja, R.
    et al.
    Arwin, H.
    da Silva, A. F.
    Persson, Clas
    Osorio-Guillen, J. M.
    de Almeida, J. S.
    Araujo, C. M.
    Veje, E.
    Veissid, N.
    An, C. Y.
    Pepe, I.
    Johansson, Börje
    Electronic and optical properties of lead iodide2002In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 92, no 12, 7219-7224 p.Article in journal (Refereed)
    Abstract [en]

    The electronic properties and the optical absorption of lead iodide (PbI2) have been investigated experimentally by means of optical absorption and spectroscopic ellipsometry, and theoretically by a full-potential linear muffin-tin-orbital method. PbI2 has been recognized as a very promising detector material with a large technological applicability. Its band-gap energy as a function of temperature has also been measured by optical absorption. The temperature dependence has been fitted by two different relations, and a discussion of these fittings is given.

  • 7. Ahuja, R.
    et al.
    Eriksson, O.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Electronic and optical properties of BaTiO3 and SrTiO32001In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 90, no 4, 1854-1859 p.Article in journal (Refereed)
  • 8. Ahuja, R.
    et al.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Theoretical prediction of the Cmca phase in Ge under high pressure2001In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 89, no 5, 2547-2549 p.Article in journal (Refereed)
  • 9. Ahuja, Rajeev
    et al.
    da Silva, A. F.
    Persson, Clas
    Osorio-Guillen, J. M.
    Pepe, I.
    Jarrendahl, K.
    Lindquist, O. P. A.
    Edwards, N. V.
    Wahab, Q.
    Johansson, Börje
    Optical properties of 4H-SiC2002In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 91, no 4, 2099-2103 p.Article in journal (Refereed)
    Abstract [en]

    The optical band gap energy and the dielectric functions of n-type 4H-SiC have been investigated experimentally by transmission spectroscopy and spectroscopic ellipsometry and theoretically by an ab initio full-potential linear muffin-tin-orbital method. We present the real and imaginary parts of the dielectric functions, resolved into the transverse and longitudinal photon moment a, and we show that the anisotropy is small in 4H-SiC. The measurements and the calculations fall closely together in a wide range of energies.

  • 10.
    Ahuja, Rajeev
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Persson, Clas
    da Silva, A. F.
    de Almeida, J. S.
    Araujo, C. M.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Optical properties of SiGe alloys2003In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 93, no 7, 3832-3836 p.Article in journal (Refereed)
    Abstract [en]

    The optical properties of Si1-xGex have been investigated theoretically using a full-potential linear muffin-tin-orbital method. We present the density-of-states as well as the real and imaginary parts of the dielectric function. The calculated dielectric function was found to be in good agreement with the spectroscopic ellipsometry measurements by J. Bahng , J. Phys.: Condens. Matter 13, 777 (2001), and we obtained a static dielectric constant of epsilon(0)=12.19+2.45x in the Si rich regime (xless than or equal to0.5).

  • 11. Aiempanakit, Montri
    et al.
    Aijaz, Asim
    Lundin, Daniel
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Helmersson, Ulf
    Kubart, Tomas
    Understanding the discharge current behavior in reactive high power impulse magnetron sputtering of oxides2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 13, 133302- p.Article in journal (Refereed)
    Abstract [en]

    The discharge current behavior in reactive high power impulse magnetron sputtering (HiPIMS) of Ti-O and Al-O is investigated. It is found that for both metals, the discharge peak current significantly increases in the oxide mode in contrast to the behavior in reactive direct current magnetron sputtering where the discharge current increases for Al but decreases for Ti when oxygen is introduced. In order to investigate the increase in the discharge current in HiPIMS-mode, the ionic contribution of the discharge in the oxide and metal mode is measured using time-resolved mass spectrometry. The energy distributions and time evolution are investigated during the pulse-on time as well as in the post-discharge. In the oxide mode, the discharge is dominated by ionized oxygen, which has been preferentially sputtered from the target surface. The ionized oxygen determines the discharge behavior in reactive HiPIMS.

  • 12. Akabori, M.
    et al.
    Hidaka, S.
    Iwase, H.
    Yamada, S.
    Ekenberg, Ulf
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Realization of In0.75Ga0.25As two-dimensional electron gas bilayer system for spintronics devices based on Rashba spin-orbit interaction2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 112, no 11, 113711- p.Article in journal (Refereed)
    Abstract [en]

    Narrow gap InGaAs two-dimensional electron gas (2DEG) bilayer samples are fabricated and confirmed to have good electronic qualities as well as strong Rashba-type spin-orbit interactions (SOIs). The 2DEG systems are realized by molecular beam epitaxy in the form of wide quantum wells (QWs) with thicknesses tQW∼40-120nm modulation doped in both the upper and lower InAlAs barriers. From the Hall measurements, the overall mobility values of μe ∼15 m2/V s are found for the total sheet electron density of ns ∼8 × 1011/cm2, although the ns is distributed asymmetrically as about 1:3 in the upper and lower 2DEGs, respectively. Careful low temperature magneto-resistance analysis gives large SO coupling constants of α ∼20 × 10 -12eV m as well as expected electron effective masses of m*/m0 ∼0.033-0.042 for each bilayer 2DEG spin sub-band. Moreover, the enhancement of α with decrease of tQW is found. The corresponding self-consistent calculation, which suggests the interaction between the bilayer 2DEGs, is carried out and the origin of α enhancement is discussed.

  • 13. Alfieri, G.
    et al.
    Monakhov, E. V.
    Svensson, B. G.
    Hallén, Anders.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Defect energy levels in hydrogen-implanted and electron-irradiated n-type 4H silicon carbide2005In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 98, no 11Article in journal (Refereed)
    Abstract [en]

    Using deep level transient spectroscopy (DLTS), we have studied the energy position and thermal stability of deep levels in nitrogen doped 4H-SiC epitaxial layers after 1.2 MeV proton implantation and 15 MeV electron irradiation. Isochronal annealing was performed at temperatures from 100 to 1200 degrees C in steps of 50 degrees C. The DLTS measurements, which were carried out in the temperature range from 120 to 630 K after each annealing step, reveal the presence of ten electron traps located in the energy range of 0.45-1.6 eV below the conduction band edge (E-c). Of these ten levels, three traps at 0.69, 0.73, and 1.03 eV below E-c, respectively, are observed only after proton implantation. Dose dependence and depth profiling studies of these levels have been performed. Comparing the experimental data with computer simulations of the implantation and defects profiles, it is suggested that these three new levels, not previously reported in the literature, are hydrogen related. In particular, the E-c-0.73 eV level displays a very narrow depth distribution, confined within the implantation profile, and it originates most likely from a defect involving only one H atom.

  • 14. Alfieri, G.
    et al.
    Monakhov, E. V.
    Svensson, B. G.
    Linnarsson, Margareta K.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Annealing behavior between room temperature and 2000 degrees C of deep level defects in electron-irradiated n-type 4H silicon carbide2005In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 98, no 4Article in journal (Refereed)
    Abstract [en]

    The annealing behavior of irradiation-induced defects in 4H-SiC epitaxial layers grown by chemical-vapor deposition has been systematically studied by means of deep level transient spectroscopy (DLTS). The nitrogen-doped epitaxial layers have been irradiated with 15-MeV electrons at room temperature and an isochronal annealing series from 100 to 2000 degrees C has been performed. The DLTS measurements, which have been carried out in the temperature range from 120 to 630 K after each annealing step, revealed the presence of six electron traps located in the energy range of 0.45-1.6 eV below the conduction-band edge (E-c). The most prominent and stable ones occur at E-c-0.70 eV (labeled Z(1/2)) and E-c-1.60 eV(EH6/7). After exhibiting a multistage annealing process over a wide temperature range, presumably caused by reactions with migrating defects, a significant fraction of both Z(1/2) and EH6/7 (25%) still persists at 2000 degrees C and activation energies for dissociation in excess of 8 and similar to 7.5 eV are estimated for Z(1/2) and EH6/7, respectively. On the basis of these results, the identity of Z(1/2) and EH6/7 is discussed and related to previous assignments in the literature.

  • 15.
    Al-Zoubi, Noura
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Nilson, G.
    Uddeholms AB, Hagfors, Sweden.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    The bain path of paramagnetic Fe-Cr based alloys2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 1, 013708- p.Article in journal (Refereed)
    Abstract [en]

    Employing the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation, we calculated the total energy and local magnetic moments of paramagnetic Fe-Cr-M (M = Cr, Mn, Fe, Co, Ni) alloys along the tetragonal distortion (Bain) path connecting the body centered cubic (bcc) and the face centered cubic (fcc) structures. The paramagnetic phase is modeled by the disordered local magnetic moment scheme. For all alloys, the local magnetic moments on Fe atoms decrease from the maximum value corresponding to the bcc phase toward the minimum value realized for the fcc phase. Cobalt atoms have non-vanishing local magnetic moments only for tetragonal lattices with c/a < 1.30, whereas the local magnetic moments of Mn show weak crystal structure dependence. We find that Cr stabilizes the bcc lattice and increases the energy barrier as going from the bcc toward the fcc phase. Both Co and Ni favor the fcc lattice and decrease the energy barrier relative to the bcc phase. On the other hand, the tetragonal distortion around the fcc phase is facilitated by Cr and to a somewhat lesser extent also by Ni, but strongly impeded by Co. Manganese has negligible effect on the structural energy difference as well as on the energy barrier along the Bain path. Our findings on the alloying induced softening or hardening of Fe-Cr based alloys against tetragonal distortions are important for understanding the interstitial driven martensitic transformations in alloy steels.

  • 16.
    Andersson, Sebastian
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Exchange coupling and magnetoresistance in CoFe/NiCu/CoFe spin valves near the Curie point of the spacer2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 107, no 9, 09D711- p.Article in journal (Refereed)
    Abstract [en]

    Thermal control of exchange coupling between two strongly ferromagnetic layers through a weakly ferromagnetic Ni-Cu spacer and the associated magnetoresistance is investigated. The spacer, having a Curie point slightly above room temperature, can be cycled between its paramagnetic and ferromagnetic states by varying the temperature externally or using joule heating. It is shown that the giant magnetoresistance vanishes due to a strong reduction in the mean free path in the spacer at above similar to 30% Ni concentration-before the onset of ferromagnetism. Finally, a device is proposed which combines thermally controlled exchange coupling and large magnetoresistance by separating the switching and the readout elements.

  • 17. Asplund, C.
    et al.
    Mogg, S.
    Plaine, G.
    Salomonsson, F.
    Chitica, N.
    Hammar, Mattias
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Doping-induced losses in AlAs/GaAs distributed Bragg reflectors2001In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 90, no 2, 794-800 p.Article in journal (Refereed)
    Abstract [en]

    We have studied n- and p-type doping-induced performance degradation of AlAs/GaAs distributed Bragg reflectors (DBRs) for applications in vertical cavity lasers (VCLs). Based on high-accuracy optical reflectance and triple-axis x-ray diffraction measurements on a variety of differently doped DBR structures grown by metalorganic vapor-phase epitaxy, a fitting procedure was employed to extract the doping-dependent optical loss. A striking observation is that the reflectance of these DBRs is much more sensitive to n- than p-type doping incorporation. While in the latter case the loss can be well accounted for by intervalence-band and free-carrier absorption, additional loss mechanisms must be considered for n-type DBRs. We relate the losses to doping-enhanced interdiffusion effects resulting in increased interface scattering. These findings should have important consequences for the design of VCLs, demonstrating the importance of reduced n-type doping concentrations and/or growth temperatures, or the application of alternative device concepts, e.g., employing intracavity contacts.

  • 18. Ayedh, H. M.
    et al.
    Bobal, V.
    Nipoti, R.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Svensson, B. G.
    Formation of carbon vacancy in 4H silicon carbide during high-temperature processing2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 1, 012005- p.Article in journal (Refereed)
    Abstract [en]

    As-grown and pre-oxidized silicon carbide (SiC) samples of polytype 4H have been annealed at temperatures up to 1950 degrees C for 10 min duration using inductive heating, or at 2000 degrees C for 30 s using microwave heating. The samples consisted of a n-type high-purity epitaxial layer grown on 4 degrees off-axis < 0001 > n(+)-substrate and the evolution of the carbon vacancy (V-C) concentration in the epitaxial layer was monitored by deep level transient spectroscopy via the characteristic Z(1/2) peak. Z(1/2) appears at similar to 0.7 eV below the conduction band edge and arises from the doubly negative charge state of V-C. The concentration of V-C increases strongly after treatment at temperatures >= 1600 degrees C and it reaches almost 10(15)cm(-3) after the inductive heating at 1950 degrees C. A formation enthalpy of similar to 5.0 eV is deduced for V-C, in close agreement with recent theoretical predictions in the literature, and the entropy factor is found to be similar to 5 k (k denotes Boltzmann's constant). The latter value indicates substantial lattice relaxation around V-C, consistent with V-C being a negative-U system exhibiting considerable Jahn-Teller distortion. The microwave heated samples show evidence of non-equilibrium conditions due to the short duration used and display a lower content of V-C than the inductively heated ones. Finally, concentration-versus-depth profiles of V-C favour formation in the "bulk" of the epitaxial layer as the prevailing process and not a Schottky type process at the surface.

  • 19. Ayedh, H. M.
    et al.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Svensson, B. G.
    Elimination of carbon vacancies in 4H-SiC epi-layers by near-surface ion implantation: Influence of the ion species2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, no 17, 175701Article in journal (Refereed)
    Abstract [en]

    The carbon vacancy (VC) is a prevailing point defect in high-purity 4H-SiC epitaxial layers, and it plays a decisive role in controlling the charge carrier lifetime. One concept of reducing the VC-concentration is based on carbon self-ion implantation in a near surface layer followed by thermal annealing. This leads to injection of carbon interstitials (Ci's) and annihilation of VC's in the epi-layer "bulk". Here, we show that the excess of C atoms introduced by the self-ion implantation plays a negligible role in the VC annihilation. Actually, employing normalized implantation conditions with respect to displaced C atoms, other heavier ions like Al and Si are found to be more efficient in annihilating VC's. Concentrations of VC below ∼2 × 1011 cm-3 can be reached already after annealing at 1400 °C, as monitored by deep-level transient spectroscopy. This corresponds to a reduction in the VC-concentration by about a factor of 40 relative to the as-grown state of the epi-layers studied. The negligible role of the implanted species itself can be understood from simulation results showing that the concentration of displaced C atoms exceeds the concentration of implanted species by two to three orders of magnitude. The higher efficiency for Al and Si ions is attributed to the generation of collision cascades with a sufficiently high energy density to promote Ci-clustering and reduce dynamic defect annealing. These Ci-related clusters will subsequently dissolve during the post-implant annealing giving rise to enhanced Ci injection. However, at annealing temperatures above 1500 °C, thermodynamic equilibrium conditions start to apply for the VC-concentration, which limit the net effect of the Ci injection, and a competition between the two processes occurs.

  • 20. Ayedh, H. M.
    et al.
    Nipoti, R.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Svensson, B. G.
    Thermodynamic equilibration of the carbon vacancy in 4H-SiC: A lifetime limiting defect2017In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 122, no 2, 025701Article in journal (Refereed)
    Abstract [en]

    The carbon vacancy (V-C) is a prominent defect in as-grown 4H-SiC epitaxial layers for high power bipolar devices. V-C is electrically active with several deep levels in the bandgap, and it is an efficient "killer" of the minority carrier lifetime in n-type layers, limiting device performance. In this study, we provide new insight into the equilibration kinetics of the thermodynamic processes governing the V-C concentration and how these processes can be tailored. A slow cooling rate after heat treatment at similar to 2000 degrees C, typically employed to activate dopants in 4H-SiC, is shown to yield a strong reduction of the V-C concentration relative to that for a fast rate. Further, post-growth heat treatment of epitaxial layers has been conducted over a wide temperature range (800-1600 degrees C) under C-rich surface conditions. It is found that the thermodynamic equilibration of V-C at 1500 degrees C requires a duration less than 1 h resulting in a V-C concentration of only similar to 10(11) cm(-3), which is, indeed, beneficial for high voltage devices. In order to elucidate the physical processes controlling the equilibration of V-C, a defect kinetics model is put forward. The model assumes Frenkel pair generation, injection of carbon interstitials (C-i's) from the C-rich surface (followed by recombination with V-C's), and diffusion of V-C's towards the surface as the major processes during the equilibration, and it exhibits good quantitative agreement with experiment.

  • 21. Azarov, A. Yu
    et al.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Du, X. L.
    Rauwel, P.
    Kuznetsov, A. Yu.
    Svensson, B. G.
    Effect of implanted species on thermal evolution of ion-induced defects in ZnO2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 7, 073512- p.Article in journal (Refereed)
    Abstract [en]

    Implanted atoms can affect the evolution of ion-induced defects in radiation hard materials exhibiting a high dynamic annealing and these processes are poorly understood. Here, we study the thermal evolution of structural defects in wurtzite ZnO samples implanted at room temperature with a wide range of ion species (from B-11 to Bi-209) to ion doses up to 2 x 10(16) cm(-2). The structural disorder was characterized by a combination of Rutherford backscattering spectrometry, nuclear reaction analysis, and transmission electron microscopy, while secondary ion mass spectrometry was used to monitor the behavior of both the implanted elements and residual impurities, such as Li. The results show that the damage formation and its thermal evolution strongly depend on the ion species. In particular, for F implanted samples, a strong out-diffusion of the implanted ions results in an efficient crystal recovery already at 600 degrees C, while co-implantation with B (via BF2) ions suppresses both the F out-diffusion and the lattice recovery at such low temperatures. The damage produced by heavy ions (such as Cd, Au, and Bi) exhibits a two-stage annealing behavior where efficient removal of point defects and small defect clusters occurs at temperatures similar to 500 degrees C, while the second stage is characterized by a gradual and partial annealing of extended defects. These defects can persist even after treatment at 900 degrees C. In contrast, the defects produced by light and medium mass ions (O, B, and Zn) exhibit a more gradual annealing with increasing temperature without distinct stages. In addition, effects of the implanted species may lead to a nontrivial defect evolution during the annealing, with N, Ag, and Er as prime examples. In general, the obtained results are interpreted in terms of formation of different dopant-defect complexes and their thermal stability.

  • 22. Azarov, A. Yu
    et al.
    Jensen, J.
    Hallén, Anders.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Aggerstam, T.
    Dopant distribution in high fluence Fe implanted GaN2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 104, no 5Article in journal (Refereed)
    Abstract [en]

    Undoped wurtzite GaN epilayers implanted at room temperature with 50-325 keV Fe+ ions in the fluence range of 10(15)-10(17) ions/cm(2) are studied by a combination of Rutherford backscattering/channeling spectrometry and time-of-flight elastic recoil detection analysis. The results show an enhanced Fe concentration close to the surface for high ion fluences (>1 X 10(16) cm(-2)), which increases with the ion fluence. Annealing at 800 degrees C for 30 min has a negligible effect on the Fe distribution in the material bulk, but further increases the Fe concentration near the surface. Our findings can be understood by radiation enhanced diffusion during ion implantation and an increased Fe diffusivity in the near surface region with distorted stoichiometry, or formation of secondary phases and precipitates for the highest doses. The simulation shows that, if enhanced diffusion is the reason for Fe buildup at the surface, both radiation enhanced diffusion and the thermal diffusion of Fe atoms near the surface, need to be at least five times larger than ordinary bulk diffusion to explain the increased Fe surface concentration.

  • 23. Azarov, A. Yu.
    et al.
    Svensson, B. G.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Du, X. L.
    Kuznetsov, A. Yu.
    Effect of composition on damage accumulation in ternary ZnO-based oxides implanted with heavy ions2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 3, 033509- p.Article in journal (Refereed)
    Abstract [en]

    Thin films of wurtzite MgxZn1-xO (x <= 0.3) grown by molecular beam epitaxy and wurtzite CdxZn1-xO (x <= 0.05) grown by metal organic chemical vapor deposition were implanted at room temperature with 150 keV Er+ ions and 200 keV Au+ ions in a wide dose range. Damage accumulation was studied by Rutherford backscattering/channeling spectrometry. Results show that the film composition affects the damage accumulation behavior in both MgZnO and CdZnO dramatically. In particular, increasing the Mg content in MgZnO results in enhanced damage accumulation in the region between the bulk and surface damage peaks characteristically distinguished in the pure ZnO. However, the overall damage accumulation in MgZnO layers, as well as in pure ZnO, exhibits saturation with increasing ion dose and MgZnO cannot be amorphized even at the highest ion dose used (3 X 10(16) Er/cm(2)). Increasing the Cd content in CdZnO affects the saturation stage of the damage accumulation and leads to an enhancement of damage production in both Cd and Zn sublattices. (C) 2010 American Institute of Physics. [doi:10.1063/1.3467532]

  • 24. B. Araujo, R.
    et al.
    S. De Almeida, J.
    Ferreira Da Silva, A.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala University, Sweden.
    Insights in the electronic structure and redox reaction energy in LiFePO4 battery material from an accurate Tran-Blaha modified Becke Johnson potential2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, no 12, 125107Article in journal (Refereed)
    Abstract [en]

    The main goals of this paper are to investigate the accuracy of the Tran-Blaha modified Becke Johnson (TB-mBJ) potential to predict the electronic structure of lithium iron phosphate and the related redox reaction energy with the lithium deintercalation process. The computed electronic structures show that the TB-mBJ method is able to partially localize Fe-3d electrons in LiFePO<inf>4</inf> and FePO<inf>4</inf> which usually is a problem for the generalized gradient approximation (GGA) due to the self interaction error. The energy band gap is also improved by the TB-mBJ calculations in comparison with the GGA results. It turned out, however, that the redox reaction energy evaluated by the TB-mBJ technique is not in good agreement with the measured one. It is speculated that this disagreement in the computed redox energy and the experimental value is due to the lack of a formal expression to evaluate the exchange and correlation energy. Therefore, the TB-mBJ is an efficient method to improve the prediction of the electronic structures coming form the standard GGA functional in LiFePO<inf>4</inf> and FePO<inf>4</inf>. However, it does not appear to have the same efficiency for evaluating the redox reaction energies for the investigated system.

  • 25.
    Baldissera, Gustavo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. University of Oslo, Norway.
    Understanding the optical properties of ZnO1-xSx and ZnO1-xSex alloys2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 4, 045704Article in journal (Refereed)
    Abstract [en]

    ZnO1-xYx with chalcogen element Y exhibits intriguing optoelectronic properties as the alloying strongly impacts the band-gap energy E-g(x). In this work, we analyze and compare the electronic structures and the dielectric responses of Zn(O,S) and Zn(O, Se) alloys by means of the density functional theory and the partially self-consistent GW approach. We model the crystalline stability from the total energies, and the results indicate that Zn(O, S) is more stable as alloy than Zn(O, Se). We demonstrate also that ion relaxation strongly affects total energies, and that the band-gap bowing depends primarily on local relaxation of the bonds. Moreover, we show that the composition dependent band-gap needs to be analyzed by the band anti-crossing model for small alloying concentration, while the alloying band-bowing model is accurate for strong alloying. We find that the Se-based alloys have a stronger change in the band-gap energy (for instance, Delta E-g(0.50) = E-g(ZnO) -(E)g(x = 0.50) approximate to 2.2 eV) compared with that of the S-based alloy (Delta E-g(0.50) = 1.2 eV), mainly due to a stronger relaxation of the Zn-anion bonds that affects the electronic structure near the band edges. The optical properties of the alloys are discussed in terms of the complex dielectric function epsilon(omega) = epsilon(1)(omega) + i epsilon(2)(omega) and the absorption coefficient alpha(omega). While the large band-gap bowing directly impacts the low-energy absorption spectra, the high-frequency dielectric constant epsilon(infinity) is correlated to the intensity of the dielectric response at energies above 4 eV. Therefore, the dielectric constant is only weakly affected by the non-linear band-gap variation. Despite strong structural relaxation, the high absorption coefficients of the alloys demonstrate that the alloys have well-behaved optoelectronic properties.

  • 26. Ban, S.
    et al.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Pattern storage and recognition using ferrofluids2006In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 99, no 8Article in journal (Refereed)
    Abstract [en]

    An implementation of an associative memory based on a ferromagnetic nanocolloid is proposed. The design contains inductive input and output units for training the ferrofluid as well as sensors incorporated into the output units for performing recall. Using Monte Carlo simulations of the system we demonstrate the possibility of creating nanoparticle configurations that can serve to associate input/output pattern pairs.

  • 27. Barrios, C. A.
    et al.
    Lourdudoss, Sebastian
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Martinsson, H.
    Analysis of leakage current in GaAs/AlGaAs buried-heterostructure lasers with a semi-insulating GaInP: Fe burying layer2002In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 92, no 5, 2506-2517 p.Article in journal (Refereed)
    Abstract [en]

    The leakage current in recently demonstrated GaAs/AlGaAs buried heterostructure (BH) lasers with a semi-insulating (SI) GaInP:Fe burying layer has been theoretically and experimentally analyzed. Calculated current-voltage characteristics of n-GaAs/SI-GaInP/n-GaAs and p-GaAs/SI-GaInP/p-GaAs planar configurations have been studied specially to assess the behavior of SI-GaInP:Fe under electron and hole injection. Two-dimensional potential profiles have been used to explain the leakage current mechanism in the SI-GaInP-buried lasers. Simulations reveal that the total leakage current decreases as the active trap concentration in the SI-GaInP:Fe burying layer is increased as expected, but the leakage current is strongly confined in the vicinity of the active region where the local leakage current density increases significantly as the trap density increases. It is found that the insertion of a n-GaInP hole blocking layer between the p-metal and the SI-GaInP layer decreases the total leakage current. Experimental light-current and current-voltage characteristics of fabricated lasers with and without an additional n-GaInP layer, and electroluminescence (EL) emitted from the burying GaInP:Fe layers corroborate qualitatively the simulations and demonstrate the benefits of using a n-GaInP layer for reducing leakage current in these type of lasers.

  • 28. Baruah, S.
    et al.
    Sinha, S. S.
    Ghosh, B.
    Pal, S. K.
    Raychaudhuri, A. K.
    Dutta, Joydeep
    School of Engineering and Technology, Asian Institute of Technolo, Thailand.
    Photoreactivity of ZnO nanoparticles in visible light: Effect of surface states on electron transfer reaction2009In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 105, no 7Article in journal (Refereed)
    Abstract [en]

    Wide band gap metal oxide semiconductors such as zinc oxide (ZnO) show visible band photolysis that has been employed, among others, to degrade harmful organic contaminants into harmless mineral acids. Metal oxides show enhanced photocatalytic activity with the increase in electronic defects in the crystallites. By introducing defects into the crystal lattice of ZnO nanoparticles, we observe a redshift in the optical absorption shifting from the ultraviolet region to the visible region (400-700 nm), which is due to the creation of intermediate defect states that inhibit the electron hole recombination process. The defects were introduced by fast nucleation and growth of the nanoparticles by rapid heating using microwave irradiation and subsequent quenching during the precipitation reaction. To elucidate the nature of the photodegradation process, picosecond resolved time correlated single photon count (TCSPC) spectroscopy was carried out to record the electronic transitions resulting from the de-excitation of the electrons to their stable states. Photodegradation and TCSPC studies showed that defect engineered ZnO nanoparticles obtained through fast crystallization during growth lead to a faster initial degradation rate of methylene blue as compared to the conventionally synthesized nanoparticles.

  • 29. Batlle, X.
    et al.
    Hattink, B. J.
    Labarta, A.
    Åkerman, Johan
    Escudero, R.
    Schuller, I. K.
    Quantitative x-ray photoelectron spectroscopy study of Al/AlOx bilayers2002In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 91, no 12, 10163-10168 p.Article in journal (Refereed)
    Abstract [en]

    An x-ray photoelectron spectroscopy (XPS) analysis of Nb/Al wedge bilayers, oxidized by both plasma and natural oxidation, is reported. The main goal is to show that the oxidation state-i.e., O:(oxidize)Al ratio-, structure and thickness of the surface oxide layer, as well as the thickness of the metallic Al leftover, as functions of the oxidation procedure, can be quantitatively evaluated from the XPS spectra. This is relevant to the detailed characterization of the insulating barriers in (magnetic) tunnel junctions.

  • 30. Bergqvist, A.
    et al.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A phenomenological differential #x2010;relation #x2010;based vector hysteresis model1994In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 75, 5484-5486 p.Article in journal (Refereed)
    Abstract [en]

    A phenomenological inherently vector hysteresis model employing simple differentials as a means of keeping track of the past history of the magnetic field is proposed. This results in a simple and computationally fairly efficient formulation for vector hysteresis of any dimension. An expression for determining model parameters from experimental data or from the Preisach function is given. The model exhibits rotational hysteresis and reduction of remanent magnetization by an orthogonal field and reduces to the classical Preisach model in one dimension. Details concerning the numerical implementation are discussed and computational examples demonstrating model properties are presented.

  • 31. Bergqvist, A.
    et al.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A phenomenological magnetomechanical hysteresis model1994In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 75, no 10, 5496-5498 p.Article in journal (Refereed)
    Abstract [en]

    To obtain accurate design tools for applications involving giant magnetostrictive materials, magnetomechanical hysteresis effects should be taken into account. The problem consists of determining the magnetization and mechanical strain from the combined past history of magnetic field and mechanical stress. In this work, coupled magnetomechanical hysteresis has been modeled by using simple path #x2010;dependent differentials to accumulate the past history in functions related to the magnetization and strain through material #x2010;dependent parameters. By using anhysteretic curves and a few additional parameters to characterize a material, major, and minor loops with respect to both field and stress have been calculated for Terfenol #x2010;D and have shown good agreement with experiments.

  • 32. Bergqvist, A.
    et al.
    Tiberg, H.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Application of a vector Preisach model in a magnetic circuit1993In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 73, 5839-5841 p.Article in journal (Refereed)
    Abstract [en]

    Magnetic hysteresis effects have been included in a finite #x2010;element description of a magnetic circuit by using the classical vector Preisach model for the constitutive relation between H and B. The influence of an external electric circuit is taken into account by adding equations derived from Faraday #x2019;s law. Computational results are presented for a magnetic circuit used in a magnetostrictive device.

  • 33.
    Berrier, Audrey
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Ferrini, R.
    Ecole Polytech Fed Lausanne, Lab Optoelect & Mat Mol.
    Talneau, A.
    CNRS, LPN.
    Houdré, R.
    Ecole Polytech Fed Lausanne, Inst Photon Elect Quant.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Impact of feature-size dependent etching on the optical properties of photonic crystal devices2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 9, 096106-1-096106-3 p.Article in journal (Refereed)
    Abstract [en]

    Feature size dependence in Ar/Cl-2 chemically assisted ion beam etching of InP-based photonic crystals (PhCs) and its influence on the optical properties of PhC devices operating in the band gap are investigated. The analysis of the measured quality factors, the determined mirror reflectivities, and losses of one-dimensional Fabry-Perot cavities clearly demonstrates the importance of feature-size dependent etching. The optical properties show a dramatic improvement up to a hole depth of about 3.5 mu m that is primarily due to a significant reduction in extrinsic losses. However, beyond this hole depth, the improvement is at a lower rate, which suggests that extrinsic losses, although present, are not dominant.

  • 34.
    Berrier, Audrey
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Mulot, Mikaël
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Malm, Gunnar
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Carrier transport through a dry-etched InP-based two-dimensional photonic crystal2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 12, 123101-1-123101-6 p.Article in journal (Refereed)
    Abstract [en]

    The electrical conduction across a two-dimensional photonic crystal (PhC) fabricated by Ar/Cl-2 chemically assisted ion beam etching in n-doped InP is influenced by the surface potential of the hole sidewalls, modified by dry etching. Carrier transport across photonic crystal fields with different lattice parameters is investigated. For a given lattice period the PhC resistivity increases with the air fill factor and for a given air fill factor it increases as the lattice period is reduced. The measured current-voltage characteristics show clear ohmic behavior at lower voltages followed by current saturation at higher voltages. This behavior is confirmed by finite element ISE TCAD (TM) simulations. The observed current saturation is attributed to electric-field-induced saturation of the electron drift velocity. From the measured and simulated conductance for the different PhC fields we show that it is possible to determine the sidewall depletion region width and hence the surface potential. We find that at the hole sidewalls the etching induces a Fermi level pinning at about 0.12 eV below the conduction band edge, a value much lower than the bare InP surface potential. The results indicate that for n-InP the volume available for conduction in the etched PhCs approaches the geometrically defined volume as the doping is increased.

  • 35. Bertini, L
    et al.
    Stiewe, C
    Toprak, Muhammet S.
    KTH, Superseded Departments, Materials Science and Engineering.
    Williams, S
    Platzek, D
    Mrotzek, A
    Zhang, Y
    Gatti, C
    Muller, E
    Muhammed, Mamoun
    KTH, Superseded Departments, Materials Science and Engineering.
    Rowe, M
    Nanostructured Co1-xNixSb3 skutterudites: Synthesis, thermoelectric properties, and theoretical modeling2003In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 93, no 1, 438-447 p.Article in journal (Refereed)
    Abstract [en]

    Nanostructured skutterudite Co1-xNixSb3 has been synthesized by chemical alloying with Ni substitution for Co up to 27.5 at. %. High concentration of grain boundaries provided by nanostructuring is expected to lower the thermal conductivity of thermoelectric materials and could thus increase their thermoelectric dimensionless figure-of-merit ZT. Material preparation comprises two key stages, coprecipitation of the precursor, and thermal processing to produce the skutterudite. By modeling the chemistry of the metal ions in aqueous solution, optimum coprecipitation conditions were achieved. The precipitated precursor consists of a solid solution of the different intermediate compounds, and exhibits high reactivity. Calcination and reduction of the precursor resulted in the alloying of these elements and in the formation of skutterudite at a temperature as low as 723-773 K. Unfilled CoSb3 skutterudites were prepared by chemical precipitation from aqueous solutions to achieve powders with a very small grain size (similar to40 nm). Compacted samples were produced from this powder by uniaxial pressing under various conditions. Thermal conductivity, electrical resistivity and Seebeck coefficient of the resulting compacts were measured in a temperature range from 150 to 575 K. Measurement procedures were standardized for absolute accuracy and reproducibility between the DLR, Cologne and NEDO, Cardiff Laboratories. It was found that the thermal conductivity can be decreased by almost an order of magnitude at the highest concentration of grain boundaries compared to highly annealed CoSb3. Scanning Seebeck microthermoprobe examination, facilitated spatially resolved measurement of Seebeck coefficient S, providing information on samples' homogeneity and on its effect on local S. Indications on the formation of an additional Ni containing phase were found. The electronic structure of Ni-doped skutterudites has been investigated by means of fully periodic density functional theory calculations and a topological analysis of the resulting electron densities. Ni substitution for Co doubles the electronic charge transfer from the pnicogen ring to the metal frame and fills the region of the CoSb3 band gap with occupied states, thus explaining the increase of electrical conductivity observed experimentally. The effect of the Ni substitution on the thermal conductivity is analyzed. The computed changes of the cell parameter with rising Ni content differ with those found by x-ray powder diffraction, thereby suggesting that the structural hypothesis of Ni replacing Co in the cubic frame of the skutterudite is only approximate or possibly incorrect.

  • 36. Bertram, F.
    et al.
    Zhang, Fan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Evertsson, J.
    Carla, F.
    Pan, Jinshan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Messing, M. E.
    Mikkelsen, A.
    Nilsson, J-O
    Lundgren, E.
    In situ anodization of aluminum surfaces studied by x-ray reflectivity and electrochemical impedance spectroscopy2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, no 3, 034902- p.Article in journal (Refereed)
    Abstract [en]

    We present results from the anodization of an aluminum single crystal [Al(111)] and an aluminum alloy [Al 6060] studied by in situ x-ray reflectivity, in situ electrochemical impedance spectroscopy and ex situ scanning electron microscopy. For both samples, a linear increase of oxide film thickness with increasing anodization voltage was found. However, the slope is much higher in the single crystal case, and the break-up of the oxide film grown on the alloy occurs at a lower anodization potential than on the single crystal. The reasons for these observations are discussed as are the measured differences observed for x-ray reflectivity and electrochemical impedance spectroscopy.

  • 37. Bethge, O.
    et al.
    Zimmermann, C.
    Lutzer, B.
    Simsek, S.
    Smoliner, J.
    Stoeger-Pollach, M.
    Henkel, Christoph
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Bertagnolli, E.
    Effective reduction of trap density at the Y2O3/Ge interface by rigorous high-temperature oxygen annealing2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, no 21, 214111- p.Article in journal (Refereed)
    Abstract [en]

    The impact of thermal post deposition annealing in oxygen at different temperatures on the Ge/Y2O3 interface is investigated using metal oxide semiconductor capacitors, where the yttrium oxide was grown by atomic layer deposition from tris(methylcyclopentadienyl) yttrium and H2O precursors on n-type (100)-Ge substrates. By performing in-situ X-ray photoelectron spectroscopy, the growth of GeO during the first cycles of ALD was proven and interface trap densities just below 1 x 10(11) eV(-1) cm(-2) were achieved by oxygen annealing at high temperatures (550 degrees C-600 degrees C). The good interface quality is most likely driven by the growth of interfacial GeO2 and thermally stabilizing yttrium germanate.

  • 38. Bohnenkamp, U.
    et al.
    Sandström, Rolf
    KTH, Superseded Departments, Materials Science and Engineering.
    Grimvall, G.
    Electrical resistivity of steels and face-centered-cubic iron2002In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 92, no 8, 4402-4407 p.Article in journal (Refereed)
    Abstract [en]

    Literature data for the electrical resistivity of austenitic and ferritic steels are analyzed in a model that takes into account their composition and microstructure. The resistivity in these systems is so high that one must allow for its saturation. That effect is described with the shunt-resistor model, and saturation at 1.68 muOmegam. Our analysis yields the contributions to the resistivity of austenite per weight percent from the solute elements N, C, Nb, Si, Ti, Cu, Ni, Cr, and Mo, with the contribution decreasing in this order. For ferrite, the contribution of the solute elements Si, Mn, Cu, Ni, Mo, and Cr was determined, with the contribution decreasing in this order. The data allow us to obtain the previously unknown resistivity of metastable pure gamma-iron (fcc Fe) near room temperature, and find an interpolation formula for the resistivity up to 1183 K where the gamma phase becomes stable. The resistivity in metastable gamma-iron is significantly larger than the resistivity in stable alpha-Fe (bcc Fe) below 1000 K. This difference is attributed to a strong electron scattering due to spin disorder in gamma-iron at intermediate temperatures.

  • 39.
    Canalias, Carlota
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Hirohashi, Junji
    KTH, School of Engineering Sciences (SCI), Physics.
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Physics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Physics.
    Polarization switching characteristics of flux grown KTiOPO4 and RbTiOPO4 at room temperature2005In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 97, no 12, 124105- p.Article in journal (Refereed)
    Abstract [en]

    A study of polarization-switching characteristics under an applied electrical field at room temperature is presented for flux-grown KTiOPO4 and RbTiOPO4. By optimizing the experimental conditions, we determined the coercive field and the domain-switching time quantitatively by direct observation of the switching current. For both isomorphs, the inverse of the polarization-switching time, 1/t(s), follows an exponential dependence on the applied field E in low-field regime, and a linear dependence on E in the high-field regime. Domain morphology of KTiOPO4 based on selective etching reveals laminar structures elongated in the b crystallographic direction. An estimation of the domain-wall velocity shows that the domain speed in the polar direction is, at least, two orders of magnitude larger than in the a-b plane. The velocity along the b direction is similar to 30 times larger than along the a axis.

  • 40. Carmody, C.
    et al.
    Tan, H. H.
    Jagadish, C.
    Douhéret, Olivier
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Maknys, Kestutis
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Anand, Srinivasan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Zou, J.
    Dao, L.
    Gal, M.
    Structural, electrical, and optical analysis of ion implanted semi-insulating InP2004In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 95, no 2, 477-482 p.Article in journal (Refereed)
    Abstract [en]

    Semi-insulating InP was implanted with MeV P, As, Ga, and In ions, and the resulting evolution of structural properties with increased annealing temperature was analyzed using double crystal x-ray diffractometry and cross sectional transmission electron microscopy. The types of damage identified are correlated with scanning spreading resistance and scanning capacitance measurements, as well as with previously measured Hall effect and time resolved photoluminescence results. We have identified multiple layers of conductivity in the samples which occur due to the nonuniform damage profile of a single implant. Our structural studies have shown that the amount and type of damage caused by implantation does not scale with implant ion atomic mass.

  • 41. Carmody, C.
    et al.
    Tan, H. H.
    Jagadish, C.
    Gaarder, A.
    Marcinkevicius, Saulius
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Ultrafast carrier trapping and recombination in highly resistive ion implanted InP2003In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 94, no 2, 1074-1078 p.Article in journal (Refereed)
    Abstract [en]

    MeV P+ implanted and annealed p-InP, and Fe+ implanted and annealed semi-insulating InP have both been shown to produce the high resistivity, good mobility, and ultrafast optical response desired for ultrafast photodetectors. Hall effect measurements and time resolved photoluminescence were used to analyze the electrical and optical features of such implanted materials. Low temperature annealing was found to yield the fastest response times-130 fs for Fe+ implanted and 400 fs for P+ implanted InP, as well as resistivities of the order similar to10(6) Omega/square. It was found that the electrical activation of Fe-related centers, useful for achieving high resistivities in Fe+ implanted semi-insulating InP, was not fully realized at the annealing temperatures chosen to produce the fastest optical response. Implanting p-InP in the dose regime where type conversion occurs, and subsequent annealing at 500degreesC, produces high resistivities and ultrafast carrier trapping times that are only marginally dose dependent.

  • 42. Carville, N. C.
    et al.
    Manzo, Michele
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Denning, D.
    Gallo, Katia
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Rodriguez, B. J.
    Growth mechanism of photoreduced silver nanostructures on periodically proton exchanged lithium niobate: Time and concentration dependence2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 18, 187212-1-187212-7 p.Article in journal (Refereed)
    Abstract [en]

    Photodeposition of metallic nanostructures onto ferroelectric surfaces, which have been chemically patterned using a proton exchange process, has recently been demonstrated. By varying the molar concentration of the AgNO 3 solution and the illumination time, one can determine the initial nucleation sites, control the rate of nucleation and the height of silver nanostructures formed, and study the mechanisms by which these processes occurs. The nanoparticles are found to deposit preferentially in the boundary between ferroelectric and proton exchanged regions, in an area proton exchanged via lateral diffusion under the masking layer used for chemical patterning, consistent with our previous results. Using a short illumination time (3 min), we are able to determine that the initial nucleation of the silver nanostructure, having a width of 0.17 ± 0.02 μm and a height of 1.61 ± 0.98 nm, occurs near the edge of the reactive ion etched area within this lateral diffusion region. Over longer illumination times (15 min), we find that the silver deposition has spread to a width of 1.29 ± 0.06 μm, extending across the entire lateral diffusion region. We report that at a high molar concentration of AgNO3 (10-2 M), the amount of silver deposition for 5 min UV illumination is greater (2.88 ± 0.58 nm) compared to that at low (10-4 M) concentrations (0.78 ± 0.35 nm), however, this is not the case for longer time periods. With increasing illumination time (15 min), experiments at 10-4 M had greater overall deposition, 6.90 ± 1.52 nm, compared to 4.50 ± 0.76 nm at 10 -2 M. For longer exposure times (30 min) at 10-2 M, the nanostructure height is 4.72 ± 0.59 nm, suggesting a saturation in the nanostructure height. The results are discussed in terms of the electric double layer that forms at the crystal surface. There is an order of magnitude difference between the Debye lengths for 10-2 and 10-4 M solutions, i.e., 3.04 vs. 30.40 nm, which suggests the Debye length plays a role in the availability of Ag ions at the surface.

  • 43. Carville, N. Craig
    et al.
    Neumayer, Sabine M.
    Manzo, Michele
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Baghban, Mohammad-Amin
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Ivanov, Ilia N.
    Gallo, Katia
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Rodriguez, Brian J.
    Influence of annealing on the photodeposition of silver on periodically poled lithium niobate2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 5, 054102Article in journal (Refereed)
    Abstract [en]

    The preferential deposition of metal nanoparticles onto periodically poled lithium niobate surfaces, whereby photogenerated electrons accumulate in accordance with local electric fields and reduce metal ions from solution, is known to depend on the intensity and wavelength of the illumination and the concentration of the solution used. Here, it is shown that for identical deposition conditions (wavelength, intensity, concentration), post-poling annealing for 10 h at 200 degrees C modifies the surface reactivity through the reorientation of internal defect fields. Whereas silver nanoparticles deposit preferentially on the +z domains on unannealed crystals, the deposition occurs preferentially along 180 degrees domain walls for annealed crystals. In neither case is the deposition selective; limited deposition occurs also on the unannealed -z domain surface and on both annealed domain surfaces. The observed behavior is attributed to a relaxation of the poling-induced defect frustration mediated by Li+ ion mobility during annealing, which affects the accumulation of electrons, thereby changing the surface reactivity. The evolution of the defect field with temperature is corroborated using Raman spectroscopy.

  • 44. Castro Meira, M. V.
    et al.
    Ferreira da Silva, A.
    Baldissera, Gustavo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Freitas, J. A., Jr.
    Gutman, N.
    Sa'ar, A.
    Nur, O.
    Willander, M.
    Optical characterization of ZnO nanopillars on Si and macroporous periodic Si structure2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, no 12, 123527- p.Article in journal (Refereed)
    Abstract [en]

    ZnO nanopillars were successfully grown using both the vapor-liquid-solid and the aqueous chemical growth methods on different substrates, such as quartz, n-, and p-type non-porous Si wafer (flat) and microporous periodic Si structure (MPSiS). Scanning electron microscopy was employed to compare sample morphologies. The absorption was calculated employing the GW(0) method, based on the local density approximation, and with the projector augmented wave approach. Experiment and theory show a reasonable agreement when the shape of the optical absorption is considered. The measured absorption of ZnO nanopillars, on different substrates, is lower than that observed for ZnO films on quartz substrate, in the energy gap spectral range. A strong effect of MPSiS substrates on ZnO nanopillar properties is observed. The photoluminescence technique was also employed as an optical characterization.

  • 45. Chawla, Amit Kumar
    et al.
    Singhal, Sonal
    Nagar, Sandeep
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Gupta, Hari Om
    Chandra, Ramesh
    Study of composition dependent structural, optical, and magnetic properties of Cu-doped Zn1-xCdxS nanoparticles2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 12, 123519- p.Article in journal (Refereed)
    Abstract [en]

    Cu-doped Zn1-xCdxS nanoparticles were synthesized by coprecipitation technique in ice bath at 280 K. The band gap energy of Zn1-xCdxS:Cu nanoparticles can be tuned to a lower energy by increasing the Cd content, indicating the formation of the alloyed nanoparticles. The alloy structure is further supported by the systematic shifting of characteristic x-ray diffraction peaks to lower angles with increase in Cd content. Systematic copper doping induces a red shift in the energy band gap of Zn0.9Cd0.1S:Cu nanoparticles with increase in copper concentration. Cu-doped Zn0.9Cd0.1S nanoparticles were found to have ferromagnetic nature at 5 K whereas undoped particles were found to be diamagnetic. Green luminescence further proves proper doping of Cu into the ZnCdS matrix. It is believed that the green luminescence originates from the recombination between the shallow donor level (sulfur vacancy) and the t(2) level of Cu2+. This method provides an inexpensive and simple procedure to produce ternary ZnCdS: Cu nanoparticles with tunable optical properties via changing Cd and/or Cu concentrations.

  • 46.
    Chen, Rongzhen
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Band-edge density-of-states and carrier concentrations in intrinsic and p-type CuIn1-xGaxSe22012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 112, no 10, 103708- p.Article in journal (Refereed)
    Abstract [en]

    The electronic structures of chalcopyrite CuIn1-xGaxSe2 have recently been reported to have strongly anisotropic and non-parabolic valence bands (VBs) even close to the Gamma-point VB maximum. Also, the lowest conduction band (CB) is non-parabolic for energies 50-100 meV above the CB minimum. The details in the band-edge dispersion govern the material's electrical properties. In this study, we, therefore, analyze the electronic structure of the three uppermost VBs and the lowest CB in CuIn1-xGaxSe2 (x = 0, 0.5, and 1). The parameterized band dispersions are explored, and the density-of-states (DOS) as well as the constant energy surfaces are calculated and analyzed. The carrier concentration and the Fermi energy E-F in the intrinsic alloys as functions of the temperature is determined from the DOS. The carrier concentration in p-type materials is modeled by assuming the presence of Cu vacancies as the acceptor type defect. We demonstrate that the non-parabolicity of the energy bands strongly affects the total DOS. Therefore, it is important to take into account full band dispersion of the VBs and CB when analyzing the free carrier concentration, like for instance, in studies of electronic transport and/or measurements that involve strong excitation conditions.

  • 47.
    Chen, Rongzhen
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. University of Oslo, Norge.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. University of Oslo, Norge.
    Electronic and optical properties of Cu2 X SnS4 (X = Be, Mg, Ca, Mn, Fe, and Ni) and the impact of native defect pairs2017In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 121, no 20, 203104Article in journal (Refereed)
    Abstract [en]

    Reducing or controlling cation disorder in Cu2ZnSnS4 is a major challenge, mainly due to low formation energies of the anti-site pair (Cu Zn - + Zn Cu +) and the compensated Cu vacancy (V Cu - + Zn Cu +). We study the electronic and optical properties of Cu2XSnS4 (CXTS, with X = Be, Mg, Ca, Mn, Fe, and Ni) and the impact of defect pairs, by employing the first-principles method within the density functional theory. The calculations indicate that these compounds can be grown in either the kesterite or stannite tetragonal phase, except Cu2CaSnS4 which seems to be unstable also in its trigonal phase. In the tetragonal phase, all six compounds have rather similar electronic band structures, suitable band-gap energies Eg for photovoltaic applications, as well as good absorption coefficients α(ω). However, the formation of the defect pairs (C u X + X Cu) and (V Cu + X Cu) is an issue for these compounds, especially considering the anti-site pair which has formation energy in the order of ∼0.3 eV. The (C u X + X Cu) pair narrows the energy gap by typically ΔEg ≈ 0.1-0.3 eV, but for Cu2NiSnS4, the complex yields localized in-gap states. Due to the low formation energy of (C u X + X Cu), we conclude that it is difficult to avoid disordering from the high concentration of anti-site pairs. The defect concentration in Cu2BeSnS4 is however expected to be significantly lower (as much as ∼104 times at typical device operating temperature) compared to the other compounds, which is partly explained by larger relaxation effects in Cu2BeSnS4 as the two anti-site atoms have different sizes. The disadvantage is that the stronger relaxation has a stronger impact on the band-gap narrowing. Therefore, instead of trying to reduce the anti-site pairs, we suggest that one shall try to compensate (C u X + X Cu) with (V Cu + X Cu) or other defects in order to stabilize the gap energy.

  • 48. Chen, X. W.
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Choy, W. C. H.
    Highly efficient and tunable fluorescence of a nanofluorophore in silica/metal dual shells with plasmonic resonance2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 2Article in journal (Refereed)
    Abstract [en]

    A dual-shell structure consisting of a silica buffer shell and a metallic outer shell is studied and designed for highly efficient and tunable fluorescence. The enhanced Purcell effect due to the plasmonic resonance and the dependence of the resonance on the structural parameters are analyzed and discussed through a classical electromagnetic approach. With the present dual-shell structure a fivefold enhancement of the fluorescence efficiency can be achieved for a nanofluorophore comprised of multiple tetramethylrhodamine isothiocyanate dye molecules, as compared to the nanofluorophore within a single silica shell. Furthermore, the peak wavelength of the fluorescence spectrum can be tuned easily (due to the variation of the surface plasmon resonance) by over 50 nm when the refractive index of the ambient material varies from 1.3 to 1.6.

  • 49. Chen, Xue-Wen
    et al.
    Choy, Wallace C. H.
    He, Sailing
    Chui, P. C.
    Comprehensive analysis and optimal design of top-emitting organic light-emitting devices2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 11Article in journal (Refereed)
  • 50. Cho, C. R.
    et al.
    Grishin, Alexander M.
    KTH, Superseded Departments, Physics.
    Background oxygen effects on pulsed laser deposited Na0.5K0.5NbO3 films: From superparaelectric state to ferroelectricity2000In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 87, no 9, 4439-4448 p.Article in journal (Refereed)
    Abstract [en]

    Ambient oxygen pressure in a pulsed laser deposition process has been observed to have a critical influence on the compositional, crystalline, and electrical properties of Na0.5K0.5NbO3 (NKN) thin films grown onto polycrystalline Pt80Ir20 and SiO2 (native oxide)/Si(111) substrates. Films prepared at high oxygen pressure (similar to 400 mTorr) were found to be single phase and highly c-axis oriented. X-ray diffraction theta-2 theta scans and rocking curve data show a strong effect of NKN film self-assembling along the [001] direction regardless of the substrate texture. The high dielectric permittivity of 550, low dissipation factor of less than 3%, and high remanent polarization of 12 mu C/cm(2) indicate the high ferroelectric quality of the fabricated film. The role of the high-energy component of the erosion products has been proven to be crucial to film performance. On the other hand, films grown at low oxygen pressure (similar to 10 mTorr) have been found to be mixed phases of ferroelectric NKN and paraelectric potassium niobates. These films have shown superparaelectric behavior: 5% tunability at an electric field of 100 kV/cm, losses as low as 0.3%, and excellent stability to temperature and frequency changes.

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