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  • 101.
    Xie, Mengyao
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Schubert, M.
    Department of Electrical Engeneering, University of Nebraska, Lincoln, Nebraska 68588.
    Lu, Jun
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Silva, A. G.
    Departamento de Fíısica, Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa Campus da Caparica, Caparica, Portugal.
    Santos, A.
    Departamento de Fíısica, Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa Campus da Caparica, Caparica, Portugal.
    Bundaleski, N.
    Departamento de Fíısica, Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa Campus da Caparica, Caparica, Portugal.
    Persson, Per O A
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hsiao, Ching-Lien
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Schaff, W.J.
    Department of Electrical and computer Engineering, Cornel University, Ithaca, New York, USA.
    Darakchieva, Vanya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Structural, free-charge carrier and phonon properties of zinc-blende and wurtizte polymorphs in InN epitaxial layersManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    We present a comprehensive study of the structural, phonon and free electron properties of zincblende InN films containing inclusion of wurtzite InN. Appropriate methods based on X-ray diffraction and Infrared spectroscopic ellipsometry to identify wurtizte and zinc-blende InN and quantify their phase ratio are developed and discussed. Thorough analysis on the formation of the cubic and wurtzite phases is presented and their evolution with film thickness is discussed in detail. The freecharge carrier and phonon properties of the two phases are discussed together with the determination of electron accumulation at the zinc-blende InN (001) and wurtzite (10̅11) surfaces.

  • 102.
    Xie, Mengyao
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Sedrine, Ben
    IST/ITN Instituto Superior Técnico, Universidade Técnica de Lisboa, Portugal.
    Hong, L.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Schöche, S.
    Department of Electrical Engineering, Center for Nanohybrid Functional Materials, University of Nebraska-Lincoln, U.S.A.
    Hofmann, T.
    Department of Electrical Engeneering, University of Nebraska, Lincoln, Nebraska 68588.
    Schubert, M.
    Department of Electrical Engeneering, University of Nebraska, Lincoln, Nebraska 68588.
    Wang, X
    Graduate School of electrical and Electronics Engineering and InN-Project as a CREST program of JST, Chiba University, Japan.
    Yoshikawa, A.
    Graduate School of electrical and Electronics Engineering and InN-Project as a CREST program of JST, Chiba University, Japan.
    Wang, K.
    Research Organization of Science and Engineering, Ritsumeikan University, Japan.
    Araki, T.
    Department of Photonics, Ritsumeikan University, Japan.
    Darakchieva, Vanya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Nanishi, Y.
    Department of Photonics, Ritsumeikan University, Japan/WCU Hybrid Materials Program, Department of Materials Science and Engineering, Seoul National University, Republic of Korea.
    Effect of Mg doping on the structural and free-charge carrier properties of InN2014Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, nr 16, s. 163504-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the structural and free-charge carrier properties of two sets of InN films grown by molecular beam epitaxy doped with different Mg concentrations from 1x1018 cm-3 to 3.9x1021 cm-3. We determine the effect of Mg doping on surface morphology, lattice parameters, structural characteristics and carrier properties. We show that infrared spectroscopic ellipsometry can be used to evidence successful p-type doping in InN, which is an important issue in InN. High resolution X-ray diffraction, combined with atomic force microscopy measurements reveals a drastic decrease in structural quality of the film for Mg concentrations above 1020 cm-3, accompanied with a significant increase in surface roughness. In addition, a decrease of the c-lattice parameter and an increase of the a-lattice parameter are found with increasing Mg concentration. Different contributions to the strain are discussed and it is suggested that the incorporation of Mg leads to a change of growth mode and generation of tensile growth strain. At high Mg concentrations zinc-blende InN inclusions appear which are suggested to originate from higher densities of stacking faults. Infrared spectroscopic ellipsometry analysis shows a reduced LPP-coupling, manifested as a characteristic dip in the IRSE data, and qualitatively different broadening behavior for Mg concentrations between 1.1x1018 cm−3 and 2.9x1019 cm−3 indicate the existence of a p-type conducting bulk InN layer for these Mg concentrations.

  • 103.
    Xie, Mengyao
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Tasnadi, Ferenc
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Darakchieva, Vanya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Elastic constants, composition, and piezolectric polarization in InxAl1-xN: From ab initio calculations to experimental implications for the applicability of Vegards rule2012Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, nr 15, s. 155310-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a theoretical analysis on the applicability of Vegards linear rule in InxAl1-xN alloys in relation to strain related elastic and piezoelectric properties. We derive the elastic stiffness constants and biaxial coefficients, as well as the respective deviations from linearity (Vegards rule) by using ab initio calculations. The stress-strain relationships to extract composition from the lattice parameters are derived in different coordinate systems for InxAl1-xN with an arbitrary surface orientation. The error made in the composition extracted from the lattice parameters if the deviations from linearity are not taken into account is discussed for different surface orientations, compositions and degrees of strain in the InxAl1-xN films. The strain induced piezoelectric polarization is analyzed for InxAl1-xN alloys grown pseudomorphically on GaN. The polarization values are compared with those obtained from our experimental data for the lattice parameters. We establish the importance of the deviation from linearity to correctly determine the piezoelectric polarization and also a smooth, not particular piezoelectric response at GaN lattice matched conditions.

  • 104.
    Xie, Mengyao
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Tasnádi, Ferenc
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Abrikossov, I. A.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Darakchieva, Vanya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Effect of impurities on the lattice parameters of InNManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    We study the effect of the most common impurities and dopants on the lattice parameters of InN by using ab-initio calculations. We have considered both the size and deformation potential effect and report results for H, O, Si andMg. The incorporation of H on interstitial site and substitutional O leads to expansion of the lattice. On the other hand, incorporation of Si or Mg leads to contraction of the lattice. The most pronounced effect is observed for Si. Our results indicate that the increase of the in-plane lattice parameter of Mg doped InN cannot be explained neither by the size nor by the deformation potential effect and suggest that the growth strain is changed in this case.a)Electronic mail: vanya@ifm.liu.se.

  • 105.
    Xie, Mengyao
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Xie, Mengyao
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Darakchieva, Vanya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Darakchieva, Vanya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Kamimura, J.
    Kamimura, J.
    Kishino, K.
    Kishino, K.
    Lattice parameters and optical phonons2008Inngår i: IWN 2008,2008, 2008Konferansepaper (Fagfellevurdert)
  • 106.
    Yakimova, Rositsa
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Iakimov, Tihomir
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Yazdi, Gholamreza
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Bouhafs, Chamseddine
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Eriksson, J.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Zakharov, A.
    MaxLab, Sweden .
    Boosalis, A.
    University of Nebraska, NE 68588 USA University of Nebraska, NE 68588 USA .
    Schubert, M.
    University of Nebraska, NE 68588 USA University of Nebraska, NE 68588 USA .
    Darakchieva, Vanya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Morphological and electronic properties of epitaxial graphene on SiC2014Inngår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 439, s. 54-59Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on the structural and electronic properties of graphene grown on SiC by high-temperature sublimation. We have studied thickness uniformity of graphene grown on 4H-SiC (0 0 0 1), 6H-SiC (0 0 0 1), and 3C-SiC (1 1 1) substrates and investigated in detail graphene surface morphology and electronic properties. Differences in the thickness uniformity of the graphene layers on different SiC polytypes is related mainly to the minimization of the terrace surface energy during the step bunching process. It is also shown that a lower substrate surface roughness results in more uniform step bunching and consequently better quality of the grown graphene. We have compared the three SiC polytypes with a clear conclusion in favor of 3C-SiC. Localized lateral variations in the Fermi energy of graphene are mapped by scanning Kelvin probe microscopy It is found that the overall single-layer graphene coverage depends strongly on the surface terrace width, where a more homogeneous coverage is favored by wider terraces, It is observed that the step distance is a dominating, factor in determining the unintentional doping of graphene from the SiC substrate. Microfocal spectroscopic ellipsometry mapping of the electronic properties and thickness of epitaxial graphene on 3C-SiC (1 1 1) is also reported. Growth of one monolayer graphene is demonstrated on both Si- and C-polarity of the 3C-SiC substrates and it is shown that large area homogeneous single monolayer graphene can be achieved on the Si-face substrates. Correlations between the number of graphene monolayers on one hand and the main transition associated with an exciton enhanced van Hove singularity at similar to 4.5 eV and the free-charge carrier scattering time, on the other are established It is shown that the interface structure on the Si- and C-polarity of the 3C-SiC (1 1 1) differs and has a determining role for the thickness and electronic properties homogeneity of the epitaxial graphene.

  • 107.
    Yakimova, Rositsa
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Yazdi, Gholamreza
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Iakimov, Tihomir
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Eriksson, Jens
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad sensorvetenskap. Linköpings universitet, Tekniska fakulteten.
    Darakchieva, Vanya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Challenges of Graphene Growth on Silicon Carbide2013Inngår i: ECS Transactions, Vol. 53, nr 1, s. 9-16Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    One of the main challenges in the fabrication of device quality graphene is the achievement of large area monolayer graphene that is processing compatible. Here, the impact of the substrate properties on the thickness uniformity and electronic characteristics for epitaxial graphene on SiC produced by high temperature sublimation has been evidenced and discussed. Several powerful techniques have been used to collect data, among them large scale ellipsometry mapping has been demonstrated for the first time. The study is covering all three SiC polytype, e.g. 4H-, 6H- and 3C-SiC in order to reveal eventual peculiarities that have to be controlled during graphene growth. The advantage of the cubic polytype is unambiguously demonstrated.

  • 108.
    Zhou, Mi
    et al.
    University of N Texas.
    Pasquale, Frank L
    University of N Texas.
    Dowben, Peter A
    University of Nebraska Lincoln.
    Boosalis, Alex
    University of Nebraska Lincoln.
    Schubert, Mathias
    University of Nebraska Lincoln.
    Darakchieva, Vanya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Kong, Lingmei
    University of Nebraska Lincoln.
    Kelber, Jeffry A
    University of N Texas.
    Direct graphene growth on Co3O4(111) by molecular beam epitaxy2012Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 24, nr 7, s. 072201-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Direct growth of graphene on Co3O4(111) at 1000 K was achieved by molecular beam epitaxy from a graphite source. Auger spectroscopy shows a characteristic sp(2) carbon lineshape, at average carbon coverages from 0.4 to 3 ML. Low energy electron diffraction (LEED) indicates (111) ordering of the sp2 carbon film with a lattice constant of 2.5(+/-0.1) angstrom characteristic of graphene. Sixfold symmetry of the graphene diffraction spots is observed at 0.4, 1 and 3 ML. The LEED data also indicate an average domain size of similar to 1800 angstrom, and show an incommensurate interface with the Co3O4(111) substrate, where the latter exhibits a lattice constant of 2.8(+/-0.1) angstrom. Core level photoemission shows a characteristically asymmetric C(1s) feature, with the expected pi to pi* satellite feature, but with a binding energy for the 3 ML film of 284.9(+/-0.1) eV, indicative of substantial graphene-to-oxide charge transfer. Spectroscopic ellipsometry data demonstrate broad similarity with graphene samples physically transferred to SiO2 or grown on SiC substrates, but with the pi to pi* absorption blue-shifted, consistent with charge transfer to the substrate. The ability to grow graphene directly on magnetically and electrically polarizable substrates opens new opportunities for industrial scale development of charge- and spin-based devices.

  • 109.
    Žukauskaitė, Agnė
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Tholander, Christopher
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Pališaitis, Justinas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Persson, Per O. Å.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Darakchieva, Vanya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Ben Sedrine, Nebiha
    Instituto Tecnológico e Nuclear, 2686-953 Sacavém and CFNUL, Lisbon 1649-003, Portugal.
    Tasnádi, Ferenc
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Birch, Jens
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    YxAl1-xN Thin Films2012Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, nr 42, s. 422001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reactive magnetron sputtering was used to deposit YxAl1-xN thin films, 0≤x≤0.22, onto Al2O3(0001) and Si(100) substrates. X-ray diffraction and analytical electron microscopy show that the films are solid solutions. Lattice constants are increasing with Y concentration, in agreement with ab initio calculations. Spectroscopic ellipsometry measurements reveal a band gap decrease from 6.2 eV (x=0) down to 4.9 eV (x=0.22). Theoretical investigations within the special quasirandom structure approach show that the wurtzite structure has the lowest mixingenthalpy for 0≤x≤0.75.

123 101 - 109 of 109
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