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2 Aug 2010

Volume 97, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 97, 051101 (2010); http://dx.doi.org/10.1063/1.3470591 (3 pages)

Pascal Böhi, Max F. Riedel, Theodor W. Hänsch, and Philipp Treutlein
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Control of interface abruptness of polar MgZnO/ZnO quantum wells grown by pulsed laser deposition

Matthias Brandt, Martin Lange, Marko Stölzel, Alexander Müller, Gabriele Benndorf, Jan Zippel, Jörg Lenzner, Michael Lorenz, and Marius Grundmann

Appl. Phys. Lett. 97, 052101 (2010); http://dx.doi.org/10.1063/1.3475402 (3 pages) | Cited 17 times

Online Publication Date: 2 August 2010

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A strong quantum confined Stark effect (QCSE) was observed in wedge shaped MgZnO/ZnO quantum wells (QWs) grown by pulsed laser deposition. A reduced laser fluence of 1.8 J/cm2 was used. Reference samples grown at higher standard fluence 2.4 J/cm2 showed only a negligible QCSE. Using off-axis deposition without substrate rotation, a constant composition of the barriers was maintained while varying the well width in a wedge shaped QW. A redshift of the QW luminescence with increasing QW thickness up to 230 meV below the ZnO emission was found, accompanied by an increase in the exciton lifetime from 0.3 ns up to 4.2 μs.
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78.20.Jq Electro-optical effects
78.67.De Quantum wells
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
71.35.-y Excitons and related phenomena

Enhanced thermoelectricity in composites by electronic structure modifications and nanostructuring

A. Popescu and L. M. Woods

Appl. Phys. Lett. 97, 052102 (2010); http://dx.doi.org/10.1063/1.3464288 (3 pages) | Cited 12 times

Online Publication Date: 4 August 2010

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The thermoelectric performance of nanocomposites with locally distorted density of states is investigated. The analytical expressions we have derived allow us to explore the effects of localized states modeled as Lorentzians on the materials transport properties in terms of their sharpness and locations relative to the Fermi level. Further optimization of the transport through nanostructuring design is also explored. We show that composites with both locally distorted density of states and nanostructure integration open the possibility for significant enhancement of the thermoelectric performance at room temperature.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.63.Bd Nanocrystalline materials
73.22.-f Electronic structure of nanoscale materials and related systems
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.At Surface states, band structure, electron density of states

Electrochemical hydrogen termination of boron-doped diamond

René Hoffmann, Armin Kriele, Harald Obloh, Jakob Hees, Marco Wolfer, Waldemar Smirnov, Nianjun Yang, and Christoph E. Nebel

Appl. Phys. Lett. 97, 052103 (2010); http://dx.doi.org/10.1063/1.3476346 (3 pages) | Cited 11 times

Online Publication Date: 4 August 2010

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Boron-doped diamond is a promising transducer material for numerous devices which are designed for contact with electrolytes. For optimized electron transfer the surface of diamond needs to be hydrogen terminated. Up to now H-termination of diamond is done by plasma chemical vapor deposition techniques. In this paper, we show that boron-doped diamond can be H-terminated electrochemically by applying negative voltages in acidic solutions. Electrochemical H-termination generates a clean surface with virtually no carbon–oxygen bonds (x-ray photoelectron spectroscopy), a reduced electron affinity (scanning electron microscopy), a highly hydrophobic surface (water contact angle), and a fast electron exchange with Fe(CN)6−3/−4 (cyclic voltammetry).
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81.65.Cf Surface cleaning, etching, patterning
82.80.Fk Electrochemical methods
81.05.ug Diamond
07.07.Mp Transducers
82.45.Gj Electrolytes
68.03.Cd Surface tension and related phenomena
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Vertical low-voltage oxide transistors gated by microporous SiO2/LiCl composite solid electrolyte with enhanced electric-double-layer capacitance

Jie Jiang, Jia Sun, Bin Zhou, Aixia Lu, and Qing Wan

Appl. Phys. Lett. 97, 052104 (2010); http://dx.doi.org/10.1063/1.3477949 (3 pages) | Cited 2 times

Online Publication Date: 4 August 2010

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Vertical low-voltage indium-tin oxide field-effect transistors (FETs) gated by microporous SiO2-based solid electrolyte are fabricated at room temperature. Our results indicate that Li ions can enhance the electric-double-layer capacitance of the microporous SiO2 solid electrolyte and reduce the operation voltage of the vertical FETs from 1.5 to 0.8 V. Such vertical low-voltage FETs exhibited a good performance with a high current output ( ∼ 1.0 A/cm2), a low subthreshold swing (<80 mV/decade), and a large on-off ratio (>106), respectively. An operation mechanism which provides a better insight into the oxide-based vertical FETs is discussed.
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85.30.Tv Field effect devices

Transparent p-type SnOx thin film transistors produced by reactive rf magnetron sputtering followed by low temperature annealing

Elvira Fortunato, Raquel Barros, Pedro Barquinha, Vitor Figueiredo, Sang-Hee Ko Park, Chi-Sun Hwang, and Rodrigo Martins

Appl. Phys. Lett. 97, 052105 (2010); http://dx.doi.org/10.1063/1.3469939 (3 pages) | Cited 22 times

Online Publication Date: 4 August 2010

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P-type thin-film transistors (TFTs) using room temperature sputtered SnOx (x<2) as a transparent oxide semiconductor have been produced. The SnOx films show p-type conduction presenting a polycrystalline structure composed with a mixture of tetragonal β-Sn and α-SnOx phases, after annealing at 200 °C. These films exhibit a hole carrier concentration in the range of ≈ 1016–1018 cm−3; electrical resistivity between 101–102 Ω cm; Hall mobility around 4.8 cm2/V s; optical band gap of 2.8 eV; and average transmittance ≈85% (400 to 2000 nm). The bottom gate p-type SnOx TFTs present a field-effect mobility above 1 cm2/V s and an ON/OFF modulation ratio of 103.
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85.30.Tv Field effect devices

Resistive switching transition induced by a voltage pulse in a Pt/NiO/Pt structure

Inrok Hwang, Myung-Jae Lee, Gyoung-Ho Buh, Jieun Bae, Jinsik Choi, Jin-Soo Kim, Sahwan Hong, Yeon Soo Kim, Ik-Su Byun, Seung-Woong Lee, Seung-Eon Ahn, Bo Soo Kang, Sung-Oong Kang, and Bae Ho Park

Appl. Phys. Lett. 97, 052106 (2010); http://dx.doi.org/10.1063/1.3477953 (3 pages) | Cited 13 times

Online Publication Date: 5 August 2010

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We have observed a switching transition between bistable memory switching and monostable threshold switching in Pt/NiO/Pt structure. Bistable memory switching could be changed to monostable threshold switching by applying a positive electrical pulse with height of 2 V and width between 10−2 and 10−4 s. The change is reversible by applying a negative electrical pulse with the same height and width. By considering polarity- and width-dependence of the switching transition and compositional difference on electrical properties in NiOx, we have proposed a model in which the migration of oxygen ions (O2−) is responsible for the switching transition in Pt/NiO/Pt structures.
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73.40.Rw Metal-insulator-metal structures
72.60.+g Mixed conductivity and conductivity transitions
71.30.+h Metal-insulator transitions and other electronic transitions

Effect of n+GaN cap polarization field on Cs-free GaN photocathode characteristics

N. Tripathi, L. D. Bell, S. Nikzad, and F. Shahedipour-Sandvik

Appl. Phys. Lett. 97, 052107 (2010); http://dx.doi.org/10.1063/1.3476341 (3 pages) | Cited 2 times

Online Publication Date: 6 August 2010

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We report on a Cs-free GaN photocathode structure in which band engineering at the photocathode surface caused by Si delta doping eliminates the need for use of cesium for photocathode activation. The structure is capped with a highly doped n+GaN layer. We have identified that n+GaN cap thickness plays an important role in limiting the effect of polarization induced charges at the GaN surface on the photocathode emission threshold. Physics based device simulations is used for further analysis of the experimental results. Our findings clearly illustrate the impact of polarization induced surface charges on the device properties including its emission threshold.
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85.60.Ha Photomultipliers; phototubes and photocathodes
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.uj III-V and II-VI semiconductors

Minority carrier lifetime in type-2 InAs–GaSb strained-layer superlattices and bulk HgCdTe materials

Dmitry Donetsky, Gregory Belenky, Stefan Svensson, and Sergei Suchalkin

Appl. Phys. Lett. 97, 052108 (2010); http://dx.doi.org/10.1063/1.3476352 (3 pages) | Cited 24 times

Online Publication Date: 6 August 2010

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Minority carrier lifetime, τ, in type-2 strained-layer superlattices (SLSs) and in long-wave Hg0.78Cd0.22Te (MCT) was measured by optical modulation response technique. It was shown that at 77 K radiative recombination can contribute to the measured τ values. The Shockley–Read–Hall (SRH) lifetimes were attained as 100 ns, 31 ns, and more than 1 μs for midwave infrared superlattices, long-wave infrared (LWIR) superlattices, and MCT correspondingly. The nature of the difference between the SRH lifetimes in LWIR superlattice and MCT is discussed.
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81.05.Ea III-V semiconductors
81.05.Dz II-VI semiconductors
73.63.-b Electronic transport in nanoscale materials and structures
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Cr III-V semiconductors

Enhancement of thermoelectric efficiency in (Ca,Dy)MnO3–(Ca,Yb)MnO3 solid solutions

Yang Wang, Yu Sui, Xianjie Wang, and Wenhui Su

Appl. Phys. Lett. 97, 052109 (2010); http://dx.doi.org/10.1063/1.3477959 (3 pages) | Cited 1 time

Online Publication Date: 6 August 2010

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Transport and thermoelectric (TE) properties have been investigated for the (Ca,Dy)MnO3–(Ca,Yb)MnO3 solid solutions. Resistivity is found to be closely correlated with the structural distortions in this system. The enhanced TE efficiency in the solid solutions can be well attributed to the distortion of electronic density of states along with a strong point defect scattering. Such band structure engineering and phonon engineering have resulted in an effective improvement of the TE performance in these solid solutions and could be applied to more systems.
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72.20.Pa Thermoelectric and thermomagnetic effects
71.20.Ps Other inorganic compounds
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
61.72.J- Point defects and defect clusters
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Subgrain size inhomogeneities in the luminescence spectra of thin film chalcopyrites

Levent Gütay, Christoph Lienau, and Gottfried Heinrich Bauer

Appl. Phys. Lett. 97, 052110 (2010); http://dx.doi.org/10.1063/1.3475018 (3 pages) | Cited 9 times

Online Publication Date: 6 August 2010

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We report near-field photoluminescence (PL) spectra of Cu(InGa)Se2 thin films recorded with a lateral optical resolution of ≈200 nm and simultaneous detection of the sample topography. Our results reveal significant local variations in the PL spectra, specifically the PL yield, on length scales of 0.2–1.5 μm. Local variations in both the splitting of quasi-Fermi levels μ and the band gap energy are quantitatively extracted from the PL spectra by applying Planck’s generalized law. We show pronounced fluctuations of μ and the band gap on length scales below the grain size. These fluctuations are only weakly correlated with the topographic film structure.
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78.55.Hx Other solid inorganic materials
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties
78.66.Li Other semiconductors
68.55.ag Semiconductors
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