physica status solidi (RRL) - Rapid Research Letters

Cover image for Vol. 7 Issue 3

March 2013

Volume 7, Issue 3

Pages 3–233

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      Cover Picture: Look fast: Crystallization of conjugated molecules during solution shearing probed in-situ and in real time by X-ray scattering (Phys. Status Solidi RRL 3/2013)

      Detlef-M. Smilgies, Ruipeng Li, Gaurav Giri, Kang Wei Chou, Ying Diao, Zhenan Bao and Aram Amassian

      Article first published online: 6 MAR 2013 | DOI: 10.1002/pssr.201390007

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      Solution shearing and related coating techniques such as knife coating or doctor blading are developing into versatile tools to finely control thin-film morphology to a much higher extent than has been possible with traditional deposition methods like drop casting and spin coating. By judicious choice of the coating pa-rameters – shearing speed and gap as well as solution concentration and substrate temperature – not only high-quality deposits can be prepared, but also laterally oriented films. Smilgies et al. show on pp. 177–179 that a detailed picture of the crystallization process can be obtained in-situ, in real time, and with high spatial resolution using a combi-nation of grazing-incidence X-ray scattering and optical microscopy. A high-precision miniature coater was developed and com-bined with X-ray microbeam optics and a fast-acquisition X-ray pixel-array detector. The developed set-up will be used to study crystallization under viscoelastic shear and to identify critical pa-rameters for future roll-to-roll processing of organic electronics materials.

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      Issue Information: Phys. Status Solidi RRL 3/2013

      Article first published online: 6 MAR 2013 | DOI: 10.1002/pssr.201390008

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      Back Cover: Flexible semi-transparent silicon (100) fabric with high-k/metal gate devices (Phys. Status Solidi RRL 3/2013)

      Jhonathan P. Rojas and Muhammad Mustafa Hussain

      Article first published online: 6 MAR 2013 | DOI: 10.1002/pssr.201390009

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      Can we build a truly high-performance computer that is both flexible and transparent? It is not simple to answer this ques-tion. Today's computers have microprocessors where the billions of transistors have 3.1 GHz speed. To achieve this unprecedented speed the transistors are scaled down to 25 nm length, have high-k/metal gate stacks instead of classical silicon oxide/poly silicon gate. A foldable computer will be ultra-portable, will have ultra-speed computation capability, and will be ultra-low-power, affordable and multi-functional. Therefore, as a logical first step, high-k/metal gate capacitors are fabricated on semiconductor industry's first choice bulk silicon (100), then they are released using conventional micro-fabrication processes to achieve a flexible and transparent chipset on silicon fabric. This process, as outlined by J. P. Rojas and M. M. Hussain on pp. 187–191, opens up opportunity for flexible inorganic electronics, transforming conventional electronics into flexible and transparent inorganic electronics without compromising their traditional performance, reliability, multi-functionality and affordability.

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      Contents: Phys. Status Solidi RRL 3/2013 (pages 3–9)

      Article first published online: 6 MAR 2013 | DOI: 10.1002/pssr.201350507

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      Frontispiece: Evidence of two-photon absorption in strain-free quantum dot GaAs/AlGaAs solar cells (Phys. Status Solidi RRL 3/2013)

      Andrea Scaccabarozzi, Silvia Adorno, Sergio Bietti, Maurizio Acciarri and Stefano Sanguinetti

      Article first published online: 6 MAR 2013 | DOI: 10.1002/pssr.201350509

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      To accommodate the need of energy-related research for quality publications that keep the pace, pss (RRL) expands its coverage of photovoltaics and solar cells in a new regular section rrl solar, see the Rapid Research Letter by Andrea Scaccabarozzi et al. in this issue (pp. 173–176).

      rrl solar calls for Rapid Research Letter and Review@RRL contributions in the following areas:

      • Photovoltaic materials preparation, optimization, characterization and physics

      • Significant solar cell advances, modeling or characterization results and techniques

      • Important and verified advances in PV efficiency

      • Novel and urgent results in photovoltaics concepts, physics and technology

      • All materials and device systems

  7. rrl solar

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    1. Intermediate band solar cells

      Evidence of two-photon absorption in strain-free quantum dot GaAs/AlGaAs solar cells (pages 173–176)

      Andrea Scaccabarozzi, Silvia Adorno, Sergio Bietti, Maurizio Acciarri and Stefano Sanguinetti

      Article first published online: 7 JAN 2013 | DOI: 10.1002/pssr.201206518

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      An intermediate band solar cell containing high-density, strain-free quantum dots grown by droplet epitaxy is demonstrated to produce photocurrent when two sub-bandgap energy photons are absorbed simultaneously. The quality of the quantum dot/barrier pair – allowed by the absence of strain-related defects, the good confinement, and the capability of droplet epitaxy to grow high-density and large aspect ratio quantum dots – opens new opportunities for quantum dot based solar cells.

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    1. Organic semiconductors

    2. Fast thermoelectricity

      Ultrafast transverse thermoelectric response in c-axis inclined epitaxial La0.5Sr0.5CoO3 thin films (pages 180–183)

      Lan Yu, Yong Wang, Pengxiang Zhang and Hanns-Ulrich Habermeier

      Article first published online: 29 JAN 2013 | DOI: 10.1002/pssr.201307002

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      The transverse thermoelectric (TTE) effect, with electrical and thermal flows perpendicular to each other, enables to manage the particular heat flux by adjusting the dimensions of the specimens. The authors observe an ultrafast TTE voltage with a rise time of 7 ns in inclined La0.5Sr0.5CoO 3 thin films, and low resistivity is thought to be responsible for this ultrafast response.

    3. Magnetocalorics

      Precursor state of skyrmions in MnSi: a heat capacity study (pages 184–186)

      S. Shanmukharao Samatham and V. Ganesan

      Article first published online: 21 JAN 2013 | DOI: 10.1002/pssr.201206523

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      The skyrmion lattice is classified as a typical topological excitation, and the precursor state of skyrmions is equally interesting. In this Letter, the authors explore this exotic phase in MnSi through heat capacity. They utilize the option of varying magnetic fields under isothermal conditions in a precise fashion in addition to the usual routines and could establish the phase diagram.

    4. Flexible electronics

      Flexible semi-transparent silicon (100) fabric with high-k/metal gate devices (pages 187–191)

      Jhonathan P. Rojas and Muhammad Mustafa Hussain

      Article first published online: 7 JAN 2013 | DOI: 10.1002/pssr.201206490

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      Thousands of semiconductor industry's advanced high-k/metal gate stacks based metal-oxide-semiconductor capacitors (MOSCAPs) are fabricated on mechanically flexible, optically semi-transparent mono-crystalline bulk silicon (100) using a generic micro-fabrication flow for cost-effective batch processing of flexible electronics for truly high-performance ultra-mobile computation and communication.

    5. Organic LEDs

      High color rendering index and chromatic stability of top-emitting white organic light-emitting diodes capped with a supplementary green color conversion layer (pages 192–195)

      Jiaheng Li, Wenqing Zhu, Linghao Xiong, Wenbing Sun, Xiaoliang Wu and Jin Cao

      Article first published online: 6 DEC 2012 | DOI: 10.1002/pssr.201206482

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      This Letter reports high color rendering index (CRI) and chromatic stability of top-emitting white organic light-emitting diodes (TEWOLEDs) by capping a supplementary green color conversion layer on the cathode of single blue emitter-based TEWOLEDs. This method provides a new avenue to improve the color rendering of organic LEDs.

    6. Oxide thin-film transistors

      High performance Zn–Sn–O thin film transistors with Cu source/drain electrode (pages 196–198)

      Chul-Kyu Lee, Se Yeob Park, Hong Yoon Jung, Chang-Kyu Lee, Byeong-Geun Son, Hyo Jin Kim, Young-Joo Lee, Young-Chang Joo and Jae Kyeong Jeong

      Article first published online: 10 JAN 2013 | DOI: 10.1002/pssr.201206486

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      In this Letter, the authors describe the fabrication of high performance zinc tin oxide thin film transistors with copper source/drain. Direct contact between channel layer and Cu electrode results in the degradation of transistor properties due to the Cu migration during thermal annealing. The Ta diffusion barrier prevents copper atoms from migrating into the channel layer during thermal annealing, leading to a high mobility of 17.8 cm2/Vs and gate swing of 0.48 V/decade.

    7. Transition metal oxides

      Dual behavior of excess electrons in rutile TiO2 (pages 199–203)

      A. Janotti, C. Franchini, J. B. Varley, G. Kresse and C. G. Van de Walle

      Article first published online: 7 JAN 2013 | DOI: 10.1002/pssr.201206464

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      First-principles calculations reveal that localized small polarons and delocalized free electrons coexist in TiO2, with polarons being slightly lower in energy. This explains why electronic transport measurements probe mobile, delocalized free electrons, while optical absorption spectra provide signatures of small polarons. Binding of polarons to shallow donors such as oxygen vacancies explains the rich spectrum of Ti3+ species observed in electron spin resonance experiments.

    8. Anomalous Hall effect

      Hall effect of tetragonal and orthorhombic SrRuO3 films (pages 204–206)

      Francis Bern, Michael Ziese, Kathrin Dörr, Andreas Herklotz and Ionela Vrejoiu

      Article first published online: 18 DEC 2012 | DOI: 10.1002/pssr.201206500

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      SrRuO3 films were grown on Ba0.75Sr0.25TiO3 buffered LaAlO3 substrates in tetragonal, and on SrTiO3 substrates in orthorhombic symmetry, respectively. The Hall resistivity ρyx of tetragonal and orthorhombic SrRuO3 films is strikingly different. This symmetry dependence shows that the anomalous Hall effect is dominated by a Berry-phase mechanism.

    9. Growth of InN on cubic ZrO2

      Theoretical study of the initial stage of InN growth on cubic zirconia (111) substrates (pages 207–210)

      Yao Guo, Shigeru Inoue, Atsushi Kobayashi, Jitsuo Ohta and Hiroshi Fujioka

      Article first published online: 14 DEC 2012 | DOI: 10.1002/pssr.201206465

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      This Letter reports the initial stage of InN growth on cubic zirconia (111) substrates using first-principles calculations based on density functional theory. It is found that the nitrogen atoms tend to stay at the stable site with the largest adsorption energy, suggesting that the first layer of InN films is the nitrogen layer. In addition, it is shown that the energetically favorable arrangement is comprised of InN(0001)//cubic zirconia(111) and InN equation image//cubic zirconia equation image, which is quite consistent with previously obtained experimental data.

    10. In situ X-ray diffraction

      Analysis of strain relaxation process in GaInN/GaN heterostructure by in situ X-ray diffraction monitoring during metalorganic vapor-phase epitaxial growth (pages 211–214)

      Daisuke Iida, Yasunari Kondo, Mihoko Sowa, Toru Sugiyama, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama and Isamu Akasaki

      Article first published online: 30 JAN 2013 | DOI: 10.1002/pssr.201307023

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      The authors analyze strain relaxation in a GaInN/GaN heterostructure by combining in situ X-ray diffraction (XRD) monitoring and ex situ observations. These in situ XRD measurements enable to clearly observe the critical thicknesses corresponding to strain relaxation in the GaInN/GaN heterostructure, which are caused by the formation of surface pits with bent threading dislocations, and the generation of misfit dislocations on GaInN during growth.

    11. III-nitride photosensors

      Nitride-based hetero-field-effect-transistor-type photosensors with extremely high photosensitivity (pages 215–217)

      Mami Ishiguro, Kazuya Ikeda, Masataka Mizuno, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama and Isamu Akasaki

      Article first published online: 22 JAN 2013 | DOI: 10.1002/pssr.201206483

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      The authors fabricated AlGaN/GaN hetero-field-effect-transistor-type (HFET-type) photosensors with a p-GaInN optical gate for the detection of visible light. By changing the InN molar fraction in the p-GaInN optical gate, the wavelength range of the photosensitivity of the HFET-type photosensors can be controlled. The photosensitivity of the HFET-type photosensors greatly surpassed those of commercially available Si pin and Si avalanche photodiodes, and was comparable to those of photomultiplier tubes.

    12. Iron-based superconductors

      Effect of external pressure on Tc of as-grown and thermally treated superconducting Rbx Fe2–ySe2 single crystals (pages 218–220)

      M. Kanagaraj, A. Krzton-Maziopa, G. Kalai Selvan, E. Pomjakushina, K. Conder, S. Weyeneth, R. Puzniak and S. Arumugam

      Article first published online: 10 DEC 2012 | DOI: 10.1002/pssr.201206426

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      The external pressure effect on the superconducting transition temperature Tc of as-grown and thermally treated single crystals of superconducting iron chalcogenide Rb0.85Fe1.9Se2 has been studied performing magnetisation measurements under pressure. The maximum Tc was found at 33.2 K for the crystal annealed for 3 h at 215 °C at zero pressure. Under external pressure, the as-grown crystal shows a clear enhancement of Tc (maximum Tc ∼ 28.2 K at 0.83 GPa). However, a negative pressure effect on Tc observed in annealed samples (at 215 °C and 265 °C) subjected to external pressure indicates that some relaxation of excess Fe magnetic moments into the Fe2Se2 layers might have happened.

    13. Piezoelectric ceramics

      Dielectric and piezoelectric properties of manganese-modified PbHfO3–PbTiO3–Pb(Mg1/3Nb2/3)O3 ternary ceramics with morphotropic phase boundary compositions (pages 221–223)

      Dawei Wang, Maosheng Cao, Quanliang Zhao, Yan Cui and Shujun Zhang

      Article first published online: 28 JAN 2013 | DOI: 10.1002/pssr.201206508

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      In this Letter, the “hardening” effects of MnO2 doping on the (1–x)Pb(Hf1–yTiy)O3x Pb(Mg1/3Nb2/3)O3 ternary piezoelectric ceramics (PHT–PMN) with morphotropic phase boundary compositions were investigated. Compared with the commercial hard PZT ceramics, the PHT–PMN ceramics doped with 0.2 wt% and 0.5–0.8 wt% MnO2 possess better piezoelectric and electromechanical properties than PZT4 and PZT8, respectively, which is attractive for high-power applications.

    14. Oxide phosphors

      Solvothermal synthesis and luminescent properties of Y2Ti2O7:Eu3+ spheres (pages 224–227)

      E. Pavitra, G. Seeta Rama Raju and Jae Su Yu

      Article first published online: 11 DEC 2012 | DOI: 10.1002/pssr.201206484

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      In this Letter, facile solvothermal synthesis of pyrochlore Y2Ti2O7 (YT):Eu3+ spheres was demonstrated. These spheres showed an efficient excitation in the YAG:Ce3+ emission region. When the YT:Eu3+ spheres were mixed with YAG:Ce3+ yellow phosphor, the emission of YAG: Ce3+ served as an excitation source to the YT:Eu3+, hence it provided natural white light.

    15. Scintillators

      Delayed recombination and excited state ionization of the Ce3+ activator in the SrHfO3 host (pages 228–231)

      Eva Mihóková, Vítězslav Jarý, Lawrence S. Schulman and Martin Nikl

      Article first published online: 17 DEC 2012 | DOI: 10.1002/pssr.201206499

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      Loss of fast scintillation light deteriorates scintillator performance. Its cause can be assessed through the temperature dependence of delayed recombination decay following ultraviolet excitation. There are two components: The high temperature contribution is due to thermal ionization of the emitting center and its analysis enables determination of the ionization energy, while the low temperature contribution is likely due to quantum tunneling between the recombination center and nearby traps.

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