physica status solidi (RRL) - Rapid Research Letters

Cover image for Vol. 6 Issue 4

April 2012

Volume 6, Issue 4

Pages A37–A49, 145–186

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      Cover Picture: Properties of nitride-based photovoltaic cells under concentrated light illumination (Phys. Status Solidi RRL 4/2012)

      Shota Yamamoto, Mikiko Mori, Yosuke Kuwahara, Takahiro Fujii, Tatsuo Nakao, Shinichiro Kondo, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki and Hiroshi Amano

      Version of Record online: 29 MAR 2012 | DOI: 10.1002/pssr.201290006

      Thumbnail image of graphical abstract

      One of the disadvantages of compound semiconductor solar cells is their high cost compared with silicon or organic solar cells. This problem can be solved by using a condenser lens system. Thus, if the solar cells can operate at 200 suns, the cost per chip would be reduced considerably. In their Letter on pp. 145–147, Yamamoto et al. report on the focusing properties of nitride-based solar cells up to 200 suns and also discuss the dependence of solar cell characteristics on concentration ratio. The structure of the devices prepared in this study consists of 50 pairs of unintentionally doped Ga0.83In0.17N/Ga0.93In0.07N superlattice layers as active layers on freestanding GaN substrate. Another 10 pairs of Si-doped Ga0.90In0.10N/GaN superlattice layers were inserted beneath the active layers in order to reduce the dislocation density. These nitride-based solar cells operate effectively even at 200 suns, their conversion efficiency of 3.4% is the highest ever reported value for nitride solar cells.

  2. Issue Information

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    4. Inside Back Cover
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  3. Inside Back Cover

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      Inside Back Cover: Design and maskless fabrication of ultrathin suspended membranes of GaN (Phys. Status Solidi RRL 4/2012)

      I. M. Tiginyanu, V. Popa, M. A. Stevens-Kalceff, D. Gerthsen, P. Brenner and D. Pavlidis

      Version of Record online: 29 MAR 2012 | DOI: 10.1002/pssr.201290008

      Thumbnail image of graphical abstract

      In their Rapid Research Letter on pp. 148–150, Ion Tiginyanu et al. demonstrate that focused ion beam (FIB) processing in combination with photo- electrochemical (PEC) etching is a versatile tool for the design and maskless fabrication of ultra-thin GaN membranes suspended over micro/nanocolumns and micro/nanowalls. The proposed novel approach represents a technological breakthrough in the fabrication of ultrathin suspended membranes of non-layered crystalline semiconductor solids. The drawing shows a collage of a bridge-like GaN membrane, the spatial architecture of both the ultrathin membrane and the supporting micro/nanowalls being fully defined by the features of FIB direct writing and PEC etching. These findings pave the way for the fabrication of ultrathin suspended GaN membranes for various MEMS/NEMS applications, and open the unique possibility for 3D nanostructuring of gallium nitride in a controlled fashion.

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      Back Cover: High-temperature thermoelectric properties of Cu2In4Te7 (Phys. Status Solidi RRL 4/2012)

      Theerayuth Plirdpring, Ken Kurosaki, Atsuko Kosuga, Manabu Ishimaru, Yuji Ohishi, Hiroaki Muta and Shinsuke Yamanaka

      Version of Record online: 29 MAR 2012 | DOI: 10.1002/pssr.201290009

      Thumbnail image of graphical abstract

      Thermoelectric (TE) generators have served as long-term reliable power supplies (e.g. in space missions) for many years. On the other hand, they can play an important role in converting waste heat into electrical energy, thus making a significant contribution to alternative energy supply. The efficiency of such power-generation devices depends on the TE properties of the materials and the temperature gradient across the device. Recently, Cu2Ga4Te7 has been reported to have a relatively high thermoelectric figure of merit (ZT). However, the TE properties of Cu2In4Te7, which has the same defect zinc-blende structure, have been hardly investigated. They are addressed by Ken Kurosaki and co-workers in their Letter on pp. 154–156. In the Cu2In4Te7 structure, a seventh of the cation sites are structural vacancies. As a result of phonon scattering by these vacancies, Cu2In4Te7 exhibits a low lattice thermal conductivity and thus relatively high ZT values.

  5. Contents

    1. Top of page
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    3. Issue Information
    4. Inside Back Cover
    5. Back Cover
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    7. NEW IN pss
    8. Rapid Research Letters
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  6. NEW IN pss

    1. Top of page
    2. Cover Picture
    3. Issue Information
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    5. Back Cover
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  7. Rapid Research Letters

    1. Top of page
    2. Cover Picture
    3. Issue Information
    4. Inside Back Cover
    5. Back Cover
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    7. NEW IN pss
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    1. Solar cells

      Properties of nitride-based photovoltaic cells under concentrated light illumination (pages 145–147)

      Shota Yamamoto, Mikiko Mori, Yosuke Kuwahara, Takahiro Fujii, Tatsuo Nakao, Shinichiro Kondo, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki and Hiroshi Amano

      Version of Record online: 13 MAR 2012 | DOI: 10.1002/pssr.201206038

      Thumbnail image of graphical abstract

      In this Letter the properties of nitride-based solar cells under concentrated light illumination from 1 to 200 suns are investigated. The conversion efficiency of solar cells increased with increasing concentration up to 200 suns. The short-circuit current density, open-circuit voltage, fill factor, and conversion efficiency were 510 mA/cm2, 1.9 V, 70%, and 3.4%, respectively, under an air mass filter of 1.5G at 200 suns and room temperature.

    2. Nanomembranes

      Design and maskless fabrication of ultrathin suspended membranes of GaN (pages 148–150)

      I. M. Tiginyanu, V. Popa, M. A. Stevens-Kalceff, D. Gerthsen, P. Brenner and D. Pavlidis

      Version of Record online: 13 FEB 2012 | DOI: 10.1002/pssr.201206020

      Thumbnail image of graphical abstract

      In this Letter, a breakthrough in the fabrication of ultrathin suspended membranes of non-layered crystalline solids is presented. On the example of GaN, it is shown that focused ion beam direct “writing” in combination with photoelectrochemical etching represents a versatile tool for the design and maskless fabrication of ultrathin membranes suspended over micro/nanocolumns, the spatial architecture of the obtained structures being fully defined by the ion energy/dose and etching conditions.

    3. Flexible electronics

      Excellent organic/inorganic transparent thin film moisture barrier entirely made by hot wire CVD at 100 °C (pages 151–153)

      Diederick Spee, Karine van der Werf, Jatin Rath and Ruud Schropp

      Version of Record online: 20 FEB 2012 | DOI: 10.1002/pssr.201206035

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      Electronic devices made on plastic substrates can easily be damaged by water and oxygen permeating into their active layers. The authors present a simple three-layer barrier structure consisting of two silicon nitride layers with a polymer layer in between, all made by hot wire CVD. This is pinhole free and has a water vapor transmission rate low enough even for organic electronic devices.

    4. Thermoelectrics

      High-temperature thermoelectric properties of Cu2In4Te7 (pages 154–156)

      Theerayuth Plirdpring, Ken Kurosaki, Atsuko Kosuga, Manabu Ishimaru, Yuji Ohishi, Hiroaki Muta and Shinsuke Yamanaka

      Version of Record online: 7 MAR 2012 | DOI: 10.1002/pssr.201206058

      Thumbnail image of graphical abstract

      Cu2In4Te7 has a defect zinc-blende structure in which a seventh of the cation sites are structural vacancies. As a result of phonon scattering by structural vacancies, Cu2In4Te7 exhibits low lattice thermal conductivity and thus a relatively high thermoelectric figure of merit.

    5. Nitride semiconductors

      Photoluminescence properties of selectively grown InN microcrystals (pages 157–159)

      Jumpei Kamimura, Katsumi Kishino and Akihiko Kikuchi

      Version of Record online: 3 FEB 2012 | DOI: 10.1002/pssr.201105532

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      This Letter reports on the photoluminescence (PL) properties of regularly arranged InN microcrystals with m -plane sidewall facets. Narrow PL emission at 0.678 eV with a linewidth of ∼14 meV at 4 K and normal red shift of the PL peak energy with increasing temperature were observed. InN microcrystals were found to have a low carrier density and excellent optical properties without being adversely affected by surface electron accumulation, despite their relatively high surface area.

    6. Double resonance Raman effects in InN nanowires (pages 160–162)

      N. Domènech-Amador, R. Cuscó, R. Calarco, T. Yamaguchi, Y. Nanishi and L. Artús

      Version of Record online: 8 MAR 2012 | DOI: 10.1002/pssr.201206057

      Thumbnail image of graphical abstract

      This Letter reports on the observation of the excitation wavelength dependence of the LO frequency in InN nanowires due to impurity-induced Raman double-resonance effects. The large frequency shifts (∼8 cm–1) found when the excitation wavelength is increased from 488 to 780 nm are related to the selective excitation of large wave-vector phonons. This allows to probe the LO-phonon dispersion in InN nanowires.

    7. Nitride devices

      The effect of barrier strain on the reliability of Inx Al1–xN/AlN/GaN heterostructure field-effect transistors (pages 163–165)

      Cemil Kayis, Romualdo A. Ferreyra, Congyong Zhu, Vitaliy Avrutin, Ümit Özgür and Hadis Morkoç

      Version of Record online: 12 MAR 2012 | DOI: 10.1002/pssr.201206024

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      In this Letter the authors show that a nearly lattice-matched (In0.17Al0.83N) HFET barrier exhibits very low degradation along with current density remaining high compared with devices having barriers with lower or higher indium contents. The results suggest that lattice-matched InAlN can be a good candidate for power transistors due to its relatively better reliability while maintaining a high current density.

    8. Titania nanotubes

      Experimental observation of two-layer TiO2 nanotube arrays prepared by stepping-voltage anodization (pages 166–168)

      Jietao Ding, Zhanwen Xiao and Hongsong Fan

      Version of Record online: 27 FEB 2012 | DOI: 10.1002/pssr.201206047

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      This Letter presents the formation of two-layer TiO2 nanotube arrays by in situ stepping down the anodic voltage, and proposes a possible growth mechanism. Scanning electron microscopy observations show a transition of the interface structures induced by the variation of the anodic voltage, demonstrating that the second tube layer can grow both at the cell boundary and right beneath the bottom of the first tube layer.

    9. Ru-doped TiO2 nanotubes: Improved performance in dye-sensitized solar cells (pages 169–171)

      Seulgi So, Kiyoung Lee and Patrik Schmuki

      Version of Record online: 7 MAR 2012 | DOI: 10.1002/pssr.201105600

      Thumbnail image of graphical abstract

      Ruthenium doping of TiO2 nanotube layers enhances their conductivity – this leads to a considerable beneficial effect when the layers are used as dye carriers in Grätzel-type solar cells. The authors achieved in situ doping of the oxide nanotubes by using Ru alloys in a self-organizing anodization process. There is an optimum Ru content of ≈0.02 at% that leads to improved conductivity while maintaining a well-defined tube geometry.

    10. Titania

      Electronic structure and enhanced visible-light absorption of N,B-codoped TiO2 (pages 172–174)

      Meili Guo, Xiao-Dong Zhang and Jiulin Du

      Version of Record online: 2 MAR 2012 | DOI: 10.1002/pssr.201206029

    11. Phononic structures

      Hypersonic surface waves in 2D titanium nanostructure on silicon (pages 175–177)

      Slawomir Mielcarek, Aleksandra Trzaskowska, Bartlomiej Graczykowski and Jayanta Sarkar

      Version of Record online: 6 MAR 2012 | DOI: 10.1002/pssr.201206039

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      This Letter presents experimental and theoretical evidence for a phononic frequency gap in the hypersonic range for thermally activated surface acoustic waves. Two-dimensional phononic crystals have been studied by surface Brillouin light scattering. The spectra have revealed the presence of a new type of surface modes, which are related to phononic effects and mechanical eigenmodes of nanoislands. The experimental data were compared with results of theoretical modelling performed by the finite element method.

    12. Germanium surfaces

      Ge(100) surfaces prepared in vapor phase epitaxy process ambient (pages 178–180)

      Sebastian Brückner, Enrique Barrigón, Oliver Supplie, Peter Kleinschmidt, Anja Dobrich, Claas Löbbel, Ignacio Rey-Stolle, Henning Döscher and Thomas Hannappel

      Version of Record online: 29 FEB 2012 | DOI: 10.1002/pssr.201206028

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      Ge(100) substrates are the common template for III–V multijunction solar cells grown by metalorganic vapor phase epitaxy (MOVPE). The authors study chemical and structural surface properties of vicinal Ge(100) after preparation in H2 ambient. Correlation of in situ reflection anisotropy (RA) spectra to results from various surface science instruments enables the authors to establish the in situ RA spectrum of the monohydride terminated Ge(100) surface.

    13. Oxide interfaces

      Nondestructive investigation of interface states in high-k oxide films on Ge substrate using X-ray absorption spectroscopy (pages 181–183)

      Deok-Yong Cho, Hyung-Suk Jung, Il-Hyuk Yu, Won Goo Park, Suyeon Cho, Useong Kim, Se-Jung Oh, Byeong-Gyu Park, Fan-Hsiu Chang, Hong-Ji Lin and Cheol Seong Hwang

      Version of Record online: 12 MAR 2012 | DOI: 10.1002/pssr.201206059

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      The possible formation of Ge oxides at the interfaces between high-permittivity oxide films and the germanium substrate is investigated nondestructively using O K-edge X-ray absorption spectroscopy (XAS). The XAS study shows evidently that GeO2 forms naturally at Al2O3/Ge and SiO2/Ge interfaces, which can block the Ge diffusion and suppress the formation of germanates. In contrast, the absence of such passivation layers at HfO2/Ge and ZrO2/Ge interfaces results in the formation of unwanted germanates in the oxide films.

    14. Nanocarbon

      Controllable fabrication and characterization of conical nanocarbon structures on polymer substrate for transparent and flexible field emission displays (pages 184–186)

      Pradip Ghosh, Shunsaku Satou, Takuma Tsuchiya, Yasuhiko Hayashi and Masaki Tanemura

      Version of Record online: 20 FEB 2012 | DOI: 10.1002/pssr.201206037

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      This Letter presents a fabrication routine for field electron emitters based on highly transparent (transparency around 90%) conical nanocarbon structures (CNCS) directly grown on a flexible nafion substrate at room temperature using a versatile ion irradiation method without the aid of a catalyst. This room-temperature grown CNCS-based emitter is expected to provide opportunities for the fabrication of new-generation transparent, flexible and light-weight field emission displays for use in everyday life.

  8. Information for authors

    1. Top of page
    2. Cover Picture
    3. Issue Information
    4. Inside Back Cover
    5. Back Cover
    6. Contents
    7. NEW IN pss
    8. Rapid Research Letters
    9. Information for authors
    1. You have free access to this content

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