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3 Dec 2012

Volume 101, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 233101 (2012); http://dx.doi.org/10.1063/1.4749281 (3 pages)

S. A. Studenikin, J. Thorgrimson, G. C. Aers, A. Kam, P. Zawadzki, Z. R. Wasilewski, A. Bogan, and A. S. Sachrajda
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Enhanced infrared photo-response from GaSb/GaAs quantum ring solar cells

P. J. Carrington, M. C. Wagener, J. R. Botha, A. M. Sanchez, and A. Krier

Appl. Phys. Lett. 101, 231101 (2012); http://dx.doi.org/10.1063/1.4768942 (5 pages) | Cited 1 time

Online Publication Date: 3 December 2012

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GaAs-based solar cells containing stacked layers of nanostructured type II GaSb quantum ring solar cells are reported which show significantly enhanced infrared photo-response extending out to 1400 nm. The ring formation reduces the net strain energy associated with the large lattice mismatch making it possible to stack multi-layers without the need for strain balancing. The (1 sun) short-circuit current for a 10 layer sample is enhanced by ∼6% compared to a GaAs control cell. The corresponding open-circuit voltage of 0.6 V is close to the theoretical maximum expected from such structures.
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88.40.jm Thin film III-V and II-VI based solar cells
88.40.hj Efficiency and performance of solar cells

Microwave frequency comb attributed to the formation of dipoles at the surface of a semiconductor by a mode-locked ultrafast laser

M. J. Hagmann, S. Pandey, A. Nahata, A. J. Taylor, and D. A. Yarotski

Appl. Phys. Lett. 101, 231102 (2012); http://dx.doi.org/10.1063/1.4768952 (3 pages) | Cited 1 time

Online Publication Date: 3 December 2012

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The generation of terahertz radiation by focusing a mode-locked ultrafast laser on the surface of a semiconductor was demonstrated by Zhang in 1990, and others have made numerous measurements and analyses of this effect. We have measured the surge current which causes this radiation, showing that this current, and presumably the radiation, are frequency combs with harmonics at integer multiples of the pulse repetition rate of the laser. The harmonics in the current are enhanced by placing the semiconductor in a tunneling junction, where the fundamental is increased by 8 dB with a DC tunneling current of 100 pA.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking

Experimental verification of the 3-step model of photoemission for energy spread and emittance measurements of copper and CsBr-coated copper photocathodes suitable for free electron laser applications

Juan R. Maldonado, Piero Pianetta, David H. Dowell, Jeff Corbett, Sam Park, John Schmerge, Ann Trautwein, and William Clay

Appl. Phys. Lett. 101, 231103 (2012); http://dx.doi.org/10.1063/1.4769220 (4 pages) | Cited 1 time

Online Publication Date: 4 December 2012

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This paper presents measurements and analysis of the quantum efficiency (QE) and intrinsic emittance of Cu and CsBr coated Cu photocathodes. The data analysis uses expressions for the quantum efficiency and the intrinsic emittance for metal cathodes previously derived from Spicer's three-step model of photoemission. Data taken with a 257 nm CW laser on (100) Cu crystals indicate an emittance of 0.77 (μm/mm-rms) for CsBr coated and 0.42 (μm/mm-rms) for uncoated cathodes. The high quantum efficiency and low emittance observed for CsBr coated cathodes have applications in free electron laser and other devices requiring high brightness electron beams.
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
85.60.Ha Photomultipliers; phototubes and photocathodes
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Controlled energy shuttling in terpolymers enabling independent optimization of absorption and transport properties in organic solar cell materials

Hannah Mangold, Ian A. Howard, Silvia Janietz, and Frédéric Laquai

Appl. Phys. Lett. 101, 231104 (2012); http://dx.doi.org/10.1063/1.4769249 (5 pages)

Online Publication Date: 4 December 2012

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The optimization of current materials for organic solar cells is complicated by the fact that individual modifications concurrently affect several efficiency-limiting factors. For example, in donor-acceptor copolymers, the chemical optimization of the light absorption properties concurrently alters the charge transport properties and not necessarily in the desired direction. This interdependency frustrates step-wise optimization of materials for maximum power conversion efficiency. In this letter, we introduce a terpolymer which we demonstrate effectively decouples the light absorption and charge transport properties onto separate monomeric units, allowing each desired property to be independently tuned in the material and opening an avenue for step-wise, material-design-based optimization of organic solar cell quantum efficiency.
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72.40.+w Photoconduction and photovoltaic effects
72.80.Ng Disordered solids
78.30.Jw Organic compounds, polymers
78.40.Kc Metals, semimetals, and alloys
78.40.Me Organic compounds and polymers
61.41.+e Polymers, elastomers, and plastics

Dynamics and pulse-package oscillations in broad-area semiconductor lasers with short optical feedback

Akira Takeda, Rui Shogenji, and Junji Ohtsubo

Appl. Phys. Lett. 101, 231105 (2012); http://dx.doi.org/10.1063/1.4769181 (3 pages)

Online Publication Date: 4 December 2012

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Pulse-package oscillations in broad-area semiconductor lasers subjected to short optical feedback are experimentally observed. The pulse-package oscillation consists of a frequency component that corresponds to an external optical feedback loop with an envelop of periodic low-frequency fluctuations. However, the periodicity induced by optical feedback does not always improve the time-averaged beam profiles of the laser oscillations. We also investigated time-averaged near-field beam profiles in relation with the optical feedback dynamics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Dynamic axial mode tuning in a rolled-up optical microcavity

Shilong Li, Libo Ma, Honglou Zhen, Matthew R. Jorgensen, Suwit Kiravittaya, and Oliver G. Schmidt

Appl. Phys. Lett. 101, 231106 (2012); http://dx.doi.org/10.1063/1.4769371 (4 pages)

Online Publication Date: 5 December 2012

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We demonstrate a dynamic axial mode tuning method by means of near-field probe in a rolled-up optical microcavity. The spatially selective nature of the tuning has been explored through both the lateral and transversal probing processes. A series of perturbation calculations based on the axial confinement model are performed to prove and improve the understanding of experimental results.
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42.79.-e Optical elements, devices, and systems

Interplay of polarization fields and Auger recombination in the efficiency droop of nitride light-emitting diodes

Emmanouil Kioupakis, Qimin Yan, and Chris G. Van de Walle

Appl. Phys. Lett. 101, 231107 (2012); http://dx.doi.org/10.1063/1.4769374 (4 pages)

Online Publication Date: 5 December 2012

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We use theoretical modeling to investigate the effect of polarization fields and non-radiative Auger recombination on the efficiency-droop and green-gap problems of polar and nonpolar nitride light-emitting diodes. The dependence of radiative and nonradiative recombination rates on electron-hole wave-function overlap is analyzed. Device designs that minimize the polarization fields lead to higher efficiency, not because the internal quantum efficiency is improved at a given carrier density but because they can be operated at a lower carrier density for a given current density.
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85.60.Jb Light-emitting devices
79.60.Jv Interfaces; heterostructures; nanostructures

Room temperature direct-bandgap electroluminescence from n-type strain-compensated Ge/SiGe multiple quantum wells

Zhi Liu, Weixuan Hu, Chong Li, Yaming Li, Chunlai Xue, Chuanbo Li, Yuhua Zuo, Buwen Cheng, and Qiming Wang

Appl. Phys. Lett. 101, 231108 (2012); http://dx.doi.org/10.1063/1.4769834 (4 pages) | Cited 1 time

Online Publication Date: 5 December 2012

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N-type strain-compensated Ge/Si0.15Ge0.85 multiple quantum wells (MQWs) were grown on a Si0.1Ge0.9 virtual substrate using ultrahigh vacuum chemical vapor deposition on a n+-Si(001) substrate. Under low forward bias voltage ranging from 0.6 to 1.2 V, narrow direct-bandgap electroluminescence (EL) peak from MQWs light emitting diode was observed at room temperature. The quantum confinement effect of the direct-bandgap transitions and the temperature dependent EL peak redshift are in good agreement with the calculated results.
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78.60.Fi Electroluminescence
78.67.De Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.65.Fg Quantum wells

Competitive carrier interactions influencing the emission dynamics of GaAsSb-capped InAs quantum dots

N. Pavarelli, T. J. Ochalski, H. Y. Liu, K. Gradkowski, M. Schmidt, D. P. Williams, D. J. Mowbray, and G. Huyet

Appl. Phys. Lett. 101, 231109 (2012); http://dx.doi.org/10.1063/1.4769431 (4 pages)

Online Publication Date: 6 December 2012

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The optical properties of InAs/GaAs quantum dots capped with a GaAsSb quantum well are investigated by means of power-dependent and time-resolved photoluminescence. The structure exhibits the coexistence of a type-I ground state and few type-II excited states, the latter characterized by a simultaneous carrier density shift of the peak position and wavelength-dependent carrier lifetimes. Complex emission dynamics are observed under a high-power excitation regime, with the different states undergoing shifts during specific phases of the measurement. These features are satisfactorily explained in terms of band structure and energy level modifications induced by two competitive carrier interactions inside the structure.
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78.67.Hc Quantum dots
71.20.Nr Semiconductor compounds
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.21.La Quantum dots
73.63.Kv Quantum dots
78.55.Cr III-V semiconductors

Size-dependent efficiency and efficiency droop of blue InGaN micro-light emitting diodes

Pengfei Tian, Jonathan J. D. McKendry, Zheng Gong, Benoit Guilhabert, Ian M. Watson, Erdan Gu, Zhizhong Chen, Guoyi Zhang, and Martin D. Dawson

Appl. Phys. Lett. 101, 231110 (2012); http://dx.doi.org/10.1063/1.4769835 (4 pages)

Online Publication Date: 6 December 2012

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The mechanisms of size-dependent efficiency and efficiency droop of blue InGaN micro-pixel light emitting diodes (μLEDs) have been investigated experimentally and by simulation. Electrical characterisation confirms the improvement of current spreading for smaller μLEDs, which enables the achievement of the higher efficiency at high injection current densities. Owing to the higher ratio of sidewall perimeter to mesa area of smaller μLEDs, a lower efficiency was observed at a low injection current density, resulting from defect-related Shockley-Read-Hall non-radiative recombination. We demonstrate that such sidewall etch defects can be partially recovered by increased thermal annealing time, consequently improving the efficiency at low current densities.
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85.60.Jb Light-emitting devices
81.65.Cf Surface cleaning, etching, patterning

Z-microscopy for parallel axial imaging with micro mirror array

Chuan Yang, Kebin Shi, Mingda Zhou, Siyang Zheng, Shizhuo Yin, and Zhiwen Liu

Appl. Phys. Lett. 101, 231111 (2012); http://dx.doi.org/10.1063/1.4768677 (5 pages)

Online Publication Date: 7 December 2012

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We propose and demonstrate a method of “z-microscopy” by utilizing an array of 45°-tilted micro mirrors arranged along the axial direction. Image signals emitted from different axial positions can be orthogonally reflected by the corresponding micro mirrors and spatially separated for parallel detection, essentially converting the more challenging axial imaging to a lateral imaging problem. Each micro mirror also provides optical sectioning capability due to its finite dimension. Numerical analysis shows that nearly diffraction limited axial resolution can be achieved. Experimental demonstration of z-imaging of fluorescent microspheres is also presented.
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07.60.Pb Conventional optical microscopes
42.30.Va Image forming and processing
42.79.Bh Lenses, prisms and mirrors

Internal frequency mixing in a single optomechanical resonator

Chenguang Huang, Jiahua Fan, Ruoyu Zhang, and Lin Zhu

Appl. Phys. Lett. 101, 231112 (2012); http://dx.doi.org/10.1063/1.4769838 (4 pages) | Cited 2 times

Online Publication Date: 7 December 2012

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In this letter, we observe that both the fundamental radial breathing mode and the flapping mode couple to a high Q optical mode and generate frequency mixing through the nonlinear optical transfer function in a single nitride optomechanical resonator. The harmonic generation of the flapping mode produces a comb-like frequency mixing spectrum. Instead of using the external pump modulation, we show that the regenerative oscillation of an internal mechanical mode can be used as a modulation source for optomechanical RF mixing.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Yj Optical parametric oscillators and amplifiers
42.79.-e Optical elements, devices, and systems
42.30.Lr Modulation and optical transfer functions
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Atomic layer deposition of Al2O3 on GaSb using in situ hydrogen plasma exposure

Laura B. Ruppalt, Erin R. Cleveland, James G. Champlain, Sharka M. Prokes, J. Brad Boos, Doewon Park, and Brian R. Bennett

Appl. Phys. Lett. 101, 231601 (2012); http://dx.doi.org/10.1063/1.4768693 (5 pages) | Cited 2 times

Online Publication Date: 3 December 2012

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In this report, we study the effectiveness of hydrogen plasma surface treatments for improving the electrical properties of GaSb/Al2O3 interfaces. Prior to atomic layer deposition of an Al2O3 dielectric, p-GaSb surfaces were exposed to hydrogen plasmas in situ, with varying plasma powers, exposure times, and substrate temperatures. Good electrical interfaces, as indicated by capacitance-voltage measurements, were obtained using higher plasma powers, longer exposure times, and increasing substrate temperatures up to 250 °C. X-ray photoelectron spectroscopy reveals that the most effective treatments result in decreased SbOx, decreased Sb, and increased GaOx content at the interface. This in situ hydrogen plasma surface preparation improves the semiconductor/insulator electrical interface without the use of wet chemical pretreatments and is a promising approach for enhancing the performance of Sb-based devices.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.65.-b Surface treatments
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.60.Jv Interfaces; heterostructures; nanostructures
79.60.Bm Clean metal, semiconductor, and insulator surfaces
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TiO2 nanofibrous interface development for Raman detection of environmental pollutants

D. Maznichenko, P. R. Selvaganapathy, K. Venkatakrishnan, and B. Tan

Appl. Phys. Lett. 101, 231602 (2012); http://dx.doi.org/10.1063/1.4769112 (5 pages)

Online Publication Date: 3 December 2012

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Sensor development has been reliant on planar Au and Ag nanoparticle research. The current findings explored a unique 3-D network of crystalline TiO2 nanoparticles linked as nanofibers. In addition to the favorability of using TiO2 for chemical and bio-molecular sensing, the nanofiber network provides molecular diffusion control and an increased confocal volume signal. Controlled femtosecond laser synthesis is also demonstrated that directly impacts surface-enhanced Raman spectroscopy detection of two common environmentally harmful chemicals: bisphenol A and diclofenac sodium salt. These findings assert that 3-D nanofibrous network porosity optimization is crucial for Raman monitoring of drinking water.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.55.Px Semiconductor lasers; laser diodes
82.80.-d Chemical analysis and related physical methods of analysis
92.60.Sz Air quality and air pollution

Chemical and structural investigations of the incorporation of metal manganese into ruthenium thin films for use as copper diffusion barrier layers

A. P. McCoy, P. Casey, J. Bogan, J. G. Lozano, P. D. Nellist, and G. Hughes

Appl. Phys. Lett. 101, 231603 (2012); http://dx.doi.org/10.1063/1.4769229 (4 pages) | Cited 1 time

Online Publication Date: 4 December 2012

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The incorporation of manganese into a 3 nm ruthenium thin-film is presented as a potential mechanism to improve its performance as a copper diffusion barrier. Manganese (∼1 nm) was deposited on an atomic layer deposited Ru film, and the Mn/Ru/SiO2 structure was subsequently thermally annealed. X-ray photoelectron spectroscopy studies reveal the chemical interaction of Mn with the SiO2 substrate to form manganese-silicate (MnSiO3), implying the migration of the metal through the Ru film. Electron energy loss spectroscopy line profile measurements of the intensity of the Mn signal across the Ru film confirm the presence of Mn at the Ru/SiO2 interface.
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81.05.Bx Metals, semimetals, and alloys
81.40.Gh Other heat and thermomechanical treatments
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.20.Uv Electron energy loss spectroscopy
79.60.Dp Adsorbed layers and thin films

Evolution of variable range hopping in strongly localized two dimensional electron gas at NdAlO3/SrTiO3 (100) heterointerfaces

A. Annadi, A. Putra, A. Srivastava, X. Wang, Z. Huang, Z. Q. Liu, T. Venkatesan, and Ariando

Appl. Phys. Lett. 101, 231604 (2012); http://dx.doi.org/10.1063/1.4768932 (4 pages)

Online Publication Date: 4 December 2012

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We report evolution of the two-dimensional electron gas behavior at the NdAlO3/SrTiO3 heterointerfaces with varying thicknesses of the NdAlO3 overlayer. The samples with a thicker NdAlO3 show strong localizations at low temperatures and the degree of localization is found to increase with the NdAlO3 thickness. The T−1/3 temperature dependence of the sheet resistance at low temperatures and the magnetoresistance study reveal that the conduction is governed by a two-dimensional variable range hopping mechanism in this strong localized regime. We attribute this thickness dependence of the transport properties of the NdAlO3/SrTiO3 interfaces to the interface strain induced by the overlayers.
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73.63.-b Electronic transport in nanoscale materials and structures
72.20.Ee Mobility edges; hopping transport
72.20.My Galvanomagnetic and other magnetotransport effects

Manipulation of giant Faraday rotation in graphene metasurfaces

Arya Fallahi and Julien Perruisseau-Carrier

Appl. Phys. Lett. 101, 231605 (2012); http://dx.doi.org/10.1063/1.4769095 (4 pages)

Online Publication Date: 4 December 2012

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Faraday rotation is a fundamental magneto-optical phenomenon used in various optical control and magnetic field sensing techniques. Recently, it was shown that a giant Faraday rotation can be achieved in the low-THz regime by a single monoatomic graphene layer. Here, we demonstrate that this exceptional property can be manipulated through adequate nano-patterning, notably achieving giant rotation up to 6THz with features no smaller than 100 nm. The effect of the periodic patterning on the Faraday rotation is predicted by a simple physical model, which is then verified and refined through accurate full-wave simulations.
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78.67.Wj Optical properties of graphene
81.16.Rf Micro- and nanoscale pattern formation
78.20.Ls Magneto-optical effects

An accurate determination of the surface energy of solid selenium

G. Guisbiers, S. Arscott, and R. Snyders

Appl. Phys. Lett. 101, 231606 (2012); http://dx.doi.org/10.1063/1.4769358 (3 pages)

Online Publication Date: 5 December 2012

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Selenium is currently a key element for developing nano and micro-technologies. Nevertheless, the surface energy of solid selenium (γSe) reported in the literature is still questionable. In this work, we have measured γSe = 0.291 ± 0.025 J/m2 at 293 K using the sessile drop technique with different probe liquids, namely ethylene glycol, de-ionized water, mercury, and gallium. This value is in excellent agreement with theoretical predictions.
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68.35.Md Surface thermodynamics, surface energies

Significant increase in conduction band discontinuity due to solid phase epitaxy of Al2O3 gate insulator films on GaN semiconductor

S. Toyoda, T. Shinohara, H. Kumigashira, M. Oshima, and Y. Kato

Appl. Phys. Lett. 101, 231607 (2012); http://dx.doi.org/10.1063/1.4769818 (4 pages)

Online Publication Date: 5 December 2012

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We have investigated band discontinuities and chemical structures of Al2O3 gate insulator films on n-type GaN semiconductor by photoemission and x-ray absorption spectroscopy. It is found that the solid phase epitaxy at the GaN crystal during annealing procedures at 800 °C leads to phase transformation of Al2O3 films from amorphous to crystalline. Changes in crystallographic structures closely correlate with the significant increase in conduction band discontinuity at the Al2O3/GaN interface, which suggests that epitaxial Al2O3 films on GaN semiconductor, free from grain boundaries of Al2O3 polycrystalline, hold the potential for high insulation performance.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Nk Insulators
79.60.Bm Clean metal, semiconductor, and insulator surfaces
64.70.dg Crystallization of specific substances
68.55.-a Thin film structure and morphology

Determination of the deep donor-like interface state density distribution in metal/Al2O3/n-GaN structures from the photocapacitance–light intensity measurement

M. Matys, B. Adamowicz, and T. Hashizume

Appl. Phys. Lett. 101, 231608 (2012); http://dx.doi.org/10.1063/1.4769815 (4 pages) | Cited 1 time

Online Publication Date: 6 December 2012

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We developed a method for determining of the deep donor-like interface state density distribution Dit(E) at the insulator/wide bandgap semiconductor interface in metal/insulator/semiconductor structures from the measurements of photocapacitance vs. ultraviolet light intensity CL(Φ). From the comparison of theoretical and experimental CL(Φ) curves we obtained the continuous donor Dit(E) in the energy range between 0.15 eV and 1 eV from the valence band top for a metal/Al2O3/n-GaN device. In addition, the acceptor-like interface state Dit(E) in the upper part of the bandgap was determined from the capacitance-voltage method.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.40.+w Photoconduction and photovoltaic effects

Quantum capacitance in topological insulators under strain in a tilted magnetic field

M. Tahir and U. Schwingenschlögl

Appl. Phys. Lett. 101, 231609 (2012); http://dx.doi.org/10.1063/1.4770000 (4 pages)

Online Publication Date: 6 December 2012

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Topological insulators exhibit unique properties due to surface states of massless Dirac fermions with conserved time reversal symmetry. We consider the quantum capacitance under strain in an external tilted magnetic field and demonstrate a minimum at the charge neutrality point due to splitting of the zeroth Landau level. We also find beating in the Shubnikov de Haas oscillations due to strain, which originate from the topological helical states. Varying the tilting angle from perpendicular to parallel washes out these oscillations with a strain induced gap at the charge neutrality point. Our results explain recent quantum capacitance and transport experiments.
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71.70.Di Landau levels
72.20.My Galvanomagnetic and other magnetotransport effects
73.20.At Surface states, band structure, electron density of states
05.30.Fk Fermion systems and electron gas
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Lattice strains and polarized luminescence in homoepitaxial growth of a-plane ZnO

Hiroaki Matsui and Hitoshi Tabata

Appl. Phys. Lett. 101, 231901 (2012); http://dx.doi.org/10.1063/1.4769036 (4 pages)

Online Publication Date: 3 December 2012

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In-plane lattice strains in a-plane zinc oxide (ZnO) homoepitaxial layers were selectively introduced by changing substrate type and growth conditions. Strain-free layers were observed when using a Crystec ZnO substrate, which resulted in atomically flat surfaces with nano-facets consisting of the m-plane (10-10) at atomic scale. In contrast, ZnO layers on Goodwill ZnO substrates possessed in-plane lattice strains due to generation of basal-plane stacking faults. The degree of lattice strains was systematically changed by the oxygen pressure, which clarified the close correlation between photoluminescence (PL) polarization and lattice strains. The polarization ratio of PL enhanced with the lattice strains.
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78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors

Nanosecond pulsed laser blackening of copper

Guang Tang, Andrew C. Hourd, and Amin Abdolvand

Appl. Phys. Lett. 101, 231902 (2012); http://dx.doi.org/10.1063/1.4769215 (4 pages) | Cited 2 times

Online Publication Date: 4 December 2012

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Nanosecond (12 ns) pulsed laser processing of copper at 532 nm resulted in the formation of homogenously distributed, highly organized microstructures. This led to the fabrication of large area black copper substrates with absorbance of over 97% in the spectral range from 250 nm to 750 nm, and a broadband absorbance of over 80% between 750 nm and 2500 nm. Optical and chemical analyses of the fabricated black metal are presented and discussed. The employed laser is an industrially adaptable source and the presented technique for fabrication of black copper could find applications in broadband thermal radiation sources, solar energy absorbers, irradiative heat transfer devices, and thermophotovoltaics.
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81.65.-b Surface treatments
78.47.J- Ultrafast spectroscopy (<1 psec)
42.62.Cf Industrial applications

Applied stress controls the production of nano-twins in coarse-grained metals

Y. Cao, Y. B. Wang, X. Z. Liao, M. Kawasaki, S. P. Ringer, T. G. Langdon, and Y. T. Zhu

Appl. Phys. Lett. 101, 231903 (2012); http://dx.doi.org/10.1063/1.4769216 (5 pages) | Cited 2 times

Online Publication Date: 4 December 2012

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We present evidence that the level of the applied stress plays a critical role in deformation twinning in face-centred cubic alloys. While conventional cold rolling of a face-centred cubic structure produces a microstructure with a high-density of extended dislocations, increasing the applied stress using high-pressure torsion gives a nano-twinned coarse-grained structure. This suggests the existence of a critical stress for deformation twinning which thereby delineates an approach for the production of nano-twinned microstructures in coarse-grained materials with superior mechanical properties.
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61.72.Mm Grain and twin boundaries
61.72.Nn Stacking faults and other planar or extended defects
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
62.50.-p High-pressure effects in solids and liquids

Competing nonlinearities with metamaterials

Polina V. Kapitanova, Alexey P. Slobozhnanyuk, Ilya V. Shadrivov, Pavel A. Belov, and Yuri S. Kivshar

Appl. Phys. Lett. 101, 231904 (2012); http://dx.doi.org/10.1063/1.4768945 (4 pages)

Online Publication Date: 4 December 2012

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We suggest an approach for creating metamaterials with sign-varying nonlinear response. We demonstrate that microwave metamaterials with such competing nonlinearities can be created by loading split-ring resonators (“meta-atoms” of the structure) with pairs of varactor diodes and photodiodes exhibiting nonmonotonic resonance frequency shift with changing incident microwave power. Additionally, the nonlinear response of such metamaterials can be controlled by illuminating the meta-atoms by light.
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42.70.-a Optical materials
42.65.-k Nonlinear optics
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