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15 May 2011

Volume 109, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 109, 102408 (2011); http://dx.doi.org/10.1063/1.3577609 (5 pages)

A. S. Samardak, A. Nogaret, N. B. Janson, A. Balanov, I. Farrer, and D. A. Ritchie
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Preface to Special Topic: Plenary and Invited Papers from the 30th International Conference on the Physics of Semiconductors, Seoul, South Korea, 2010

Hyeonsik Cheong and Jisoon Ihm

J. Appl. Phys. 109, 102301 (2011); http://dx.doi.org/10.1063/1.3579399 (1 page)

Online Publication Date: 31 May 2011

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Abstract Unavailable
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis

Zero-mode anomalies of massless Dirac electron in graphene

Tsuneya Ando

J. Appl. Phys. 109, 102401 (2011); http://dx.doi.org/10.1063/1.3575639 (7 pages)

Online Publication Date: 31 May 2011

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A brief review is given on singularities appearing in electronic properties of monolayer graphene at the Dirac point from a theoretical point of view. The topics include effective-mass description of electronic states, singular behavior of the conductivity including the Hall effect and nonuniversality of the minimum conductivity, and the singular diamagnetic response to uniform and spatially varying magnetic field.
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73.22.Pr Electronic structure of graphene
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
61.48.Gh Structure of graphene
72.80.Vp Electronic transport in graphene
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Wave function engineering: Other phases of Si for photovoltaic applications

Marvin L. Cohen and Brad D. Malone

J. Appl. Phys. 109, 102402 (2011); http://dx.doi.org/10.1063/1.3575641 (5 pages)

Online Publication Date: 31 May 2011

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We present first-principles electronic structural calculations of the quasiparticle and optical spectra of two silicon phases, Si-XII and the recently predicted phase of Si in the body-centered-tetragonal structure. The quasiparticle spectra calculated within the GW approximation predict that both of these materials are indirect bandgap semiconductors with small bandgaps. The optical spectra of these materials are obtained by solving the Bethe-Salpeter equation taking into account electron-hole interactions. Comparison is made to other phases of silicon commonly used in photovoltaic applications. The results suggest the possible utility of these materials as photovoltaics.
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88.40.jj Silicon solar cells
73.20.At Surface states, band structure, electron density of states
71.20.Mq Elemental semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Magnetotransport in a wide parabolic well superimposed with a superlattice

Yu.A. Pusep, G. M. Gusev, A. K. Bakarov, A. I. Toropov, and J. C. Portal

J. Appl. Phys. 109, 102403 (2011); http://dx.doi.org/10.1063/1.3576134 (3 pages)

Online Publication Date: 31 May 2011

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The electron properties of artificially disordered superlattices embedded in a wide AlGaAs parabolic well were investigated in a strong magnetic field. We demonstrated that in the extreme quantum limit the interlayer disorder results in formation of a new correlated phase. A nearly uniform electron distribution over the superlattice wells was found in a weak magnetic field. However, a nonuniform phase with partially localized electrons, representing well-developed fractional quantum Hall effect features, was observed in high magnetic field (at the filling factor ν < 1). A distinct magnetic field–induced transition separates these two phases.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.43.-f Quantum Hall effects
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.21.Cd Superlattices
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Nonresonant feeding of photonic crystal nanocavity modes by quantum dots

A. Laucht, N. Hauke, A. Neumann, T. Günthner, F. Hofbauer, A. Mohtashami, K. Müller, G. Böhm, M. Bichler, M.-C. Amann, M. Kaniber, and J. J. Finley

J. Appl. Phys. 109, 102404 (2011); http://dx.doi.org/10.1063/1.3576137 (5 pages)

Online Publication Date: 31 May 2011

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We experimentally probe the nonresonant feeding of photons into the optical mode of a two dimensional photonic crystal nanocavity from the discrete emission from a quantum dot. For a strongly coupled system of a single exciton and the cavity mode, we track the detuning-dependent photoluminescence intensity of the exciton-polariton peaks at different lattice temperatures. At low temperatures we observe a clear asymmetry in the emission intensity depending on whether the exciton is at higher or lower energy than the cavity mode. At high temperatures this asymmetry vanishes when the probabilities to emit or absorb a phonon become similar. For a different dot-cavity system where the cavity mode is detuned by ΔE>5 meV to lower energy than the single exciton transitions emission from the mode remains correlated with the quantum dot as demonstrated unambiguously by cross-correlation photon counting experiments. By monitoring the temporal evolution of the photoluminescence spectrum, we show that feeding of photons into the mode occurs from multi-exciton transitions. We observe a clear anti-correlation of the mode and single exciton emission; the mode emission quenches as the population in the system reduces toward the single exciton level while the intensity of the mode emission tracks the multi-exciton transitions.
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42.70.Qs Photonic bandgap materials
78.67.Hc Quantum dots
71.35.-y Excitons and related phenomena
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.55.Cr III-V semiconductors

Injection, detection and gate voltage control of spins in the spin field effect transistor

Joonyeon Chang, Hyun Cheol Koo, Jonghwa Eom, Suk Hee Han, and Mark Johnson

J. Appl. Phys. 109, 102405 (2011); http://dx.doi.org/10.1063/1.3576140 (5 pages)

Online Publication Date: 31 May 2011

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We demonstrate electrical spin injection and gate voltage control of spin precession in an InAs quantum well channel that has Permalloy injector and detector, and is covered by a gate oxide and a Au gate electrode. The electrical injection and detection of ballistic spin-polarized electrons are characterized using conventional lateral spin valve techniques. An external magnetic field is used to overcome the shape anisotropy of the magnetizations of injector and detector. We can then inject spins that have both spin orientation and velocity along the axis of the channel, and we observe an oscillatory channel conductance as a function of monotonically increasing gate voltage. This conductance oscillation is the hallmark of a spin field effect transistor. After presenting the basic results, we discuss issues associated with (1) the Hanle effect in a two-dimensional electron gas with high spin-orbit interaction and (2) the observation of a conductance oscillation in a multimode (two-dimensional) channel.
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85.30.Tv Field effect devices

Vortex stability and permanent flow in nonequilibrium polariton condensates

G. Tosi, D. Sanvitto, M. Baudisch, E. Karimi, B. Piccirillo, L. Marrucci, A. Lemaître, J. Bloch, and L. Viña

J. Appl. Phys. 109, 102406 (2011); http://dx.doi.org/10.1063/1.3576151 (4 pages)

Online Publication Date: 31 May 2011

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We study the effects of imprinting a single-quantized vortex on the steady state of a microcavity exciton-polariton condensate generated via parametric scattering. Interestingly we observe two distinct regimes: In the first case, at low polariton densities, the effect of the pulsed probe, containing the vortex state, is to generate a gain response in the condensate lasting for tens of picoseconds during which no dissipation of the circulating currents is detected. In the second regime, at higher densities, the gain lasts much less and the circulation is imprinted directly into the steady state, which acquires permanent rotation for as long as the vortex remains within the condensate. We use two different ways of measuring the circulation of the condensate and demonstrate that in both cases, polariton condensation in the parametric scattering regime can sustain permanent supercurrents.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
71.35.-y Excitons and related phenomena

Loss mechanisms of quantum cascade lasers operating close to optical phonon frequencies

F. Castellano, A. Bismuto, M. I. Amanti, R. Terazzi, M. Beck, S. Blaser, A. Bächle, and J. Faist

J. Appl. Phys. 109, 102407 (2011); http://dx.doi.org/10.1063/1.3576153 (5 pages)

Online Publication Date: 31 May 2011

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The extension of the operating frequency of Quantum Cascade Lasers (QCL) into the 20−50 μm regime is a desirable goal as it would bridge the gap between mid-infrared and THz devices. Coherent light emitters in this spectral range are also needed for spectroscopy and radio astronomy applications. Since little attention has been devoted to the subject in the past, we investigate the dominant loss mechanisms of QCLs in this spectral range. We report on an InGaAs/InAlAs QCL in an InP dielectric waveguide emitting at 23 μm wavelength whose electroluminescence spectrum shows an anomalous low-frequency cut which prevents laser action at low electric field. We also observe similar line shape in other GaAs/AlGaAs devices. The spectral features are analyzed and explained in terms of refractive index anomalies induced by phonon resonances.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.82.Et Waveguides, couplers, and arrays

Spiking computation and stochastic amplification in a neuron-like semiconductor microstructure

A. S. Samardak, A. Nogaret, N. B. Janson, A. Balanov, I. Farrer, and D. A. Ritchie

J. Appl. Phys. 109, 102408 (2011); http://dx.doi.org/10.1063/1.3577609 (5 pages)

Online Publication Date: 31 May 2011

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We have demonstrated the proof of principle of a semiconductor neuron, which has dendrites, axon, and a soma and computes information encoded in electrical pulses in the same way as biological neurons. Electrical impulses applied to dendrites diffuse along microwires to the soma. The soma is the active part of the neuron, which regenerates input pulses above a voltage threshold and transmits them into the axon. Our concept of neuron is a major step forward because its spatial structure controls the timing of pulses, which arrive at the soma. Dendrites and axon act as transmission delay lines, which modify the information, coded in the timing of pulses. We have finally shown that noise enhances the detection sensitivity of the neuron by helping the transmission of weak periodic signals. A maximum enhancement of signal transmission was observed at an optimum noise level known as stochastic resonance. The experimental results are in excellent agreement with simulations of the FitzHugh-Nagumo model. Our neuron is therefore extremely well suited to providing feedback on the various mathematical approximations of neurons and building functional networks.
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84.35.+i Neural networks
85.30.-z Semiconductor devices
84.30.Sk Pulse and digital circuits

The quantum spin Hall effect

Hartmut Buhmann

J. Appl. Phys. 109, 102409 (2011); http://dx.doi.org/10.1063/1.3577612 (6 pages)

Online Publication Date: 31 May 2011

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In a two-dimensional system the quantum spin Hall effect (QSHE) state is characterized by an insulating bulk and two counter-propagating helical edge states. These edge channels are protected by time reversal symmetry and spin currents propagate without dissipation. It was shown that HgTe-based quantum well structures are the most suitable candidates for its experimental realization. Here, the experimental requirements are discussed which lead to the observation of quantized edge channel transport which is one of the main signatures of the QSHE. Experiments will be presented which demonstrate the stability of the quantized conductance and its nonlocal character. Furthermore, evidence for the spin polarization of the QSHE edge channels is shown in an all-electrical measurement which demonstrates the potential of the QSHE for spin injection and detection applications in spintronics.
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73.43.-f Quantum Hall effects
72.25.-b Spin polarized transport

Blue light emission from strongly photoexcited and electron-doped SrTiO3

Yasuhiro Yamada and Yoshihiko Kanemitsu

J. Appl. Phys. 109, 102410 (2011); http://dx.doi.org/10.1063/1.3577613 (4 pages)

Online Publication Date: 31 May 2011

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We studied photoluminescence (PL) spectrum and dynamics of undoped and electron-doped SrTiO3. At low temperatures below 100 K, we observed two band-edge PL peaks and a broad PL band in strongly photoexcited SrTiO3 and electron-doped SrTiO3 samples. In electron-doped samples, the peak energy of the broad PL band depends on the excitation photon energy at low temperatures: it changes from 2.5 to 2.9 eV with the excitation photon energy. On the other hand, the PL dynamics is independent of the excitation photon energy and is explained by a simple model involving single-carrier trapping and Auger recombination. From the PL spectrum and dynamics under different excitation photon energies, the PL processes in SrTiO3 are discussed.
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78.55.Hx Other solid inorganic materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Optically-detected NMR of optically-hyperpolarized 31P neutral donors in 28Si

M. Steger, T. Sekiguchi, A. Yang, K. Saeedi, M. E. Hayden, M. L. W. Thewalt, K. M. Itoh, H. Riemann, N. V. Abrosimov, P. Becker, and H.-J. Pohl

J. Appl. Phys. 109, 102411 (2011); http://dx.doi.org/10.1063/1.3577614 (6 pages) | Cited 1 time

Online Publication Date: 31 May 2011

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The electron and nuclear spins of the shallow donor 31P are promising qubit candidates invoked in many proposed Si-based quantum computing schemes. We have recently shown that the near-elimination of inhomogeneous broadening in highly isotopically enriched 28Si enables an optical readout of both the donor electron and nuclear spins by resolving the donor hyperfine splitting in the near-gap donor bound exciton transitions. We have also shown that pumping these same transitions can very quickly produce large electron and nuclear hyperpolarizations at low magnetic fields, where the equilibrium electron and nuclear polarizations are very small. Here we show preliminary results of the measurement of 31P neutral donor NMR parameters using this optical nuclear hyperpolarization mechanism for preparation of the 31P nuclear spin system, followed by optical readout of the resulting nuclear spin population after manipulation with NMR pulse sequences. This allows for the observation of single-shot NMR signals with very high signal-to-noise ratio under conditions where conventional NMR is not possible, due to the low concentration of 31P and the small equilibrium polarization.
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33.25.+k Nuclear resonance and relaxation
31.30.Gs Hyperfine interactions and isotope effects
03.67.Lx Quantum computation architectures and implementations

An electron jet pump: The Venturi effect of a Fermi liquid

D. Taubert, G. J. Schinner, C. Tomaras, H. P. Tranitz, W. Wegscheider, and S. Ludwig

J. Appl. Phys. 109, 102412 (2011); http://dx.doi.org/10.1063/1.3577959 (5 pages)

Online Publication Date: 31 May 2011

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A three-terminal device based upon a two-dimensional electron system is investigated in the regime of nonequilibrium transport. Excited electrons scatter with the cold Fermi sea and transfer energy and momentum to other electrons. A geometry analogous to a water jet pump is used to create a jet pump for electrons. Because of its phenomenological similarity we name the observed behavior the “electronic Venturi effect.”
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85.30.-z Semiconductor devices

Shape control of quantum dots studied by cross-sectional scanning tunneling microscopy

J. G. Keizer, M. Bozkurt, J. Bocquel, T. Mano, T. Noda, K. Sakoda, E. C. Clark, M. Bichler, G. Abstreiter, J. J. Finley, W. Lu, T. Rohel, H. Folliot, N. Bertru, and P. M. Koenraad

J. Appl. Phys. 109, 102413 (2011); http://dx.doi.org/10.1063/1.3577960 (6 pages)

Online Publication Date: 31 May 2011

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In this cross-sectional scanning tunneling microscopy study we investigated various techniques to control the shape of self-assembled quantum dots (QDs) and wetting layers (WLs). The result shows that application of an indium flush during the growth of strained InGaAs/GaAs QD layers results in flattened QDs and a reduced WL. The height of the QDs and WLs could be controlled by varying the thickness of the first capping layer. Concerning the technique of antimony capping we show that the surfactant properties of Sb result in the preservation of the shape of strained InAs/InP QDs during overgrowth. This could be achieved by both a growth interrupt under Sb flux and capping with a thin GaAsSb layer prior to overgrowth of the uncapped QDs. The technique of droplet epitaxy was investigated by a structural analysis of strain free GaAs/AlGaAs QDs. We show that the QDs have a Gaussian shape, that the WL is less than 1 bilayer thick, and that minor intermixing of Al with the QDs takes place.
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81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)

Photon-to-electron quantum information transfer

Hideo Kosaka

J. Appl. Phys. 109, 102414 (2011); http://dx.doi.org/10.1063/1.3577962 (5 pages)

Online Publication Date: 31 May 2011

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Spin is a fundamental property of electrons and plays an important role in information storage. For spin-based quantum information technology, preparation and read-out of the electron spin state must be spin coherent, but both the traditional preparation and read-out of the spin state are projective to up/down spin states, which do not have spin coherence. We have recently demonstrated that the polarization coherence of light can be coherently transferred to the spin coherence of electrons in a semiconductor. We have also developed a new scheme named tomographic Kerr rotation (TKR) by generalizing the traditional KR to directly readout the spin coherence of optically prepared electrons without the need for the spin dynamics, which allows the spin projection measurement in an arbitrary set of basis states. These demonstrations were performed using g-factor-controlled semiconductor quantum wells with precessing and nonprecessing electrons. The developed scheme offers a tool for performing basis-independent preparation and read-out of a spin quantum state in a solid. These results encourage us to make a quantum media converter between flying photon qubits and stationary electron spin qubits in semiconductors.
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72.25.Dc Spin polarized transport in semiconductors
73.21.Fg Quantum wells
72.40.+w Photoconduction and photovoltaic effects
73.21.La Quantum dots
73.63.Kv Quantum dots
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Effect of detuning on the phonon induced dephasing of optically driven InGaAs/GaAs quantum dots

A. J. Ramsay, T. M. Godden, S. J. Boyle, E. M. Gauger, A. Nazir, B. W. Lovett, Achanta Venu Gopal, A. M. Fox, and M. S. Skolnick

J. Appl. Phys. 109, 102415 (2011); http://dx.doi.org/10.1063/1.3577963 (5 pages)

Online Publication Date: 31 May 2011

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Recently, longitudinal acoustic phonons have been identified as the main source of the intensity damping observed in Rabi rotation measurements of the ground-state exciton of a single InAs/GaAs quantum dot. Here we report experiments of intensity damped Rabi rotations in the case of detuned laser pulses. The results have implications for the coherent optical control of both excitons and spins using detuned laser pulses.
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81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
78.67.Hc Quantum dots
71.35.-y Excitons and related phenomena
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Magnetotransport in adsorbate-induced two-dimensional electron systems on cleaved InAs surfaces

Tohru Okamoto, Toshimitsu Mochizuki, Masaaki Minowa, Kazunari Komatsuzaki, and Ryuichi Masutomi

J. Appl. Phys. 109, 102416 (2011); http://dx.doi.org/10.1063/1.3578263 (4 pages)

Online Publication Date: 31 May 2011

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This article reviews recent low-temperature magnetotransport measurements on two-dimensional electron systems (2DESs) formed at in situ cleaved InAs(110) surfaces by deposition of other materials. The surface donor level, at which the Fermi level of the 2DES is pinned, is determined from the saturation electron density for different kinds of adatoms. It decreases with increasing atomic ionization energy. For the case of Cs-deposition, the 2D electron density and mobility are studied over a wide coverage range. A clear increase in electron mobility appears above half monolayer coverage. For a surface covered with a submonolayer of Fe, hysteresis in the magnetoresistance is observed. It is associated with spin-glass ordering in the Fe film.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Ee Mobility edges; hopping transport
72.20.Fr Low-field transport and mobility; piezoresistance
71.20.Nr Semiconductor compounds

Defects in SiC for quantum computing

J. R. Weber, W. F. Koehl, J. B. Varley, A. Janotti, B. B. Buckley, C. G. Van de Walle, and D. D. Awschalom

J. Appl. Phys. 109, 102417 (2011); http://dx.doi.org/10.1063/1.3578264 (5 pages)

Online Publication Date: 31 May 2011

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The successful implementation of the nitrogen-vacancy (NV) center in diamond as a qubit has spawned a great deal of interest in this defect. In principle, similar defects suitable for quantum computing should exist in other material systems; however, very little work has been done on identifying NV-like centers in other materials. We discuss the key properties of the NV center in diamond in the context of uncovering similar defects in other materials, with the specific example of SiC. Using first-principles calculations, we compare the properties of the NV center in diamond to the analogous defect in 4H-SiC. We also compare the properties of the bare vacancies. We calculate defect formation energies and charge-state transition levels to determine which defects are likely to form. Then, by analyzing the defect-induced electronic states, we determine whether stable defects in 4H-SiC may have properties similar to those of the NV center in diamond.
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61.72.jd Vacancies
71.55.Ht Other nonmetals

Switching ultrastrong light–matter coupling on a subcycle scale

R. Huber, A. A. Anappara, G. Günter, A. Sell, S. De Liberato, C. Ciuti, G. Biasiol, L. Sorba, A. Tredicucci, and A. Leitenstorfer

J. Appl. Phys. 109, 102418 (2011); http://dx.doi.org/10.1063/1.3578341 (5 pages)

Online Publication Date: 31 May 2011

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Intersubband cavity polaritons in a quantum well waveguide structure are optically generated within less than one cycle of light by a 12-femtosecond near-infrared pulse. Mid-infrared probe transients trace the nonadiabatic switch-on of ultrastrong light-matter coupling and the conversion of bare photons into cavity polaritons directly in the time domain. Future perspectives of room-temperature subcycle control of ultrastrong electron–photon interaction are discussed.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.79.Gn Optical waveguides and couplers

Intrinsic charge transport of conjugated organic molecules in electromigrated nanogap junctions

Hyunwook Song, Youngsang Kim, Heejun Jeong, Mark A. Reed, and Takhee Lee

J. Appl. Phys. 109, 102419 (2011); http://dx.doi.org/10.1063/1.3578345 (4 pages) | Cited 1 time

Online Publication Date: 31 May 2011

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We present the measurement of charge transport through phenylene conjugated molecules using electromigrated nanogap junctions. To elucidate the intrinsic transport properties of the conjugated molecular junctions, a variety of molecular transport techniques were performed at low temperature, including inelastic electron tunneling spectroscopy, temperature- and length-variable transport measurements, and transition voltage spectroscopy. Such a self-consistent characterization of the molecular junction demonstrates the observation of intrinsic molecular properties in these junctions.
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73.40.Rw Metal-insulator-metal structures

Anisotropic strain effects on the photoluminescence emission from heteroepitaxial and homoepitaxial nonpolar (Zn,Mg)O/ZnO quantum wells

J.-M. Chauveau, M. Teisseire, H. Kim-Chauveau, C. Morhain, C. Deparis, and B. Vinter

J. Appl. Phys. 109, 102420 (2011); http://dx.doi.org/10.1063/1.3578636 (6 pages) | Cited 1 time

Online Publication Date: 31 May 2011

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We report on the properties of nonpolar a-plane (Zn,Mg)O/ZnO quantum wells (QW) grown by molecular beam epitaxy on r plane sapphire and a plane ZnO substrates. For the QWs grown on sapphire, the anisotropy of the lattice parameters of the (Zn,Mg)O barrier gives rise to an unusual in-plane strain state in the ZnO QWs, which induces a strong blue-shift of the excitonic transitions, in addition to the confinement effects. We observe this blue-shift in photoluminescence excitation experiments. The photoluminescence excitation energies of the QWs are satisfactorily simulated when taking into account the variation of the exciton binding energy with the QW width and the residual anisotropic strain. Then we compare the photoluminescence properties of homoepitaxial QWs grown on ZnO bulk substrate and heteroepitaxial QWs grown on sapphire. We show that the reduction of structural defects and the improvement of surface morphology are correlated with a strong enhancement of the photoluminescence properties: reduction of full width at half maximum, strong increase of the luminescence intensities. The comparison convincingly demonstrates the interest of homoepitaxial nonpolar QWs for bright UV emission applications.
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81.07.St Quantum wells
78.67.De Quantum wells
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.Fg Quantum wells

The invention and early history of the CCD

George E. Smith

J. Appl. Phys. 109, 102421 (2011); http://dx.doi.org/10.1063/1.3578638 (6 pages)

Online Publication Date: 31 May 2011

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As the first practical solid state imaging device, the invention of the charge coupled device has profoundly affected image sensing technology. They are used in a wide range of applications both as area and linear imaging devices starting with the replacement of imaging tubes used in commercial TV cameras and cam-corders. The rapid rise of their use in digital cameras has initiated the demise of film photography and created vast new markets with great economic benefit for many. Other uses include a wide variety of scientific, surveillance, and scanning applications. The inception of the device at Bell Labs by W. S. Boyle and G. E. Smith, Bell Syst. Tech. J. 49, 587 (1970);G. F. Amelio, M. F. Tompsett, and G. E. Smith, Bell Syst. Tech. J. 49, 593 (1970); W. S. Boyle and G. E. Smith, U.S. patent 3,792,322 (12 February 1974) was strongly influenced by several unique factors existing both within Bell Labs and the current world state of technology. These factors and their relevance will be discussed along with the train of thought leading to the invention. Early experimental devices and their initial applications were vigorously pursued and will be described. Mention of current applications will be given.
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85.30.Tv Field effect devices

Single- and few-electron dynamic quantum dots in a perpendicular magnetic field

S. J. Wright, A. L. Thorn, M. D. Blumenthal, S. P. Giblin, M. Pepper, T. J. B. M. Janssen, M. Kataoka, J. D. Fletcher, G. A. C. Jones, C. A. Nicoll, Godfrey Gumbs, and D. A. Ritchie

J. Appl. Phys. 109, 102422 (2011); http://dx.doi.org/10.1063/1.3578685 (5 pages)

Online Publication Date: 31 May 2011

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We present experimental studies of the current pumped through a dynamic quantum dot over a wide range of magnetic fields. At low fields we observe a repeatable structure indicating increased confinement of the electrons in the dynamic dot. At higher fields (B>5T), we observe a structure which changes markedly from device to device suggesting that in this regime the transport is sensitive to local disorder. The results are significant for the development of dynamic quantum dot pumps as quantum standards of electrical current.
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85.30.Tv Field effect devices

Next-generation multijunction solar cells: The promise of II-VI materials

J. W. Garland, T. Biegala, M. Carmody, C. Gilmore, and S. Sivananthan

J. Appl. Phys. 109, 102423 (2011); http://dx.doi.org/10.1063/1.3582902 (10 pages)

Online Publication Date: 31 May 2011

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High concentration photovoltaic (HCPV) systems offer the highest photovoltaic (PV) conversion efficiencies. Also, as production is beginning to ramp up, HCPV is becoming cost competitive with thin-film poly-CdTe and crystalline Si systems in high solar insolation regions. High solar concentrations, X ∼ 500, are used to increase cell efficiencies and greatly reduce the cell area per unit of incident solar radiation, thereby greatly reducing the cell cost per watt. The monolithic three-junction (3J) solar cells presently used in HCPV systems typically consist of two epitaxial III-V homojunctions, such as GaInP and GaInAs, grown on an active Ge substrate by metal-organic chemical vapor deposition (MOCVD). The III-V bandgaps are chosen to match the currents generated in each junction and minimize the energy lost to thermalization of the electron-hole pairs generated, subject to the constraint of approximate lattice matching. We propose using cells consisting of one or more CdTe-based II-VI homojunctions grown on large-area active Si substrates by high-throughput MBE or a less expensive high-vacuum deposition technique as an alternative to III-V based multijunction cells grown by MOCVD. The bandgap of Si is more optimal than that of Ge for two-junction (2J) or 3J cells, and lattice mismatches affect the efficiencies of such cells only slightly, which allows greater freedom in the choice of bandgaps, and thus the potential for higher efficiencies. Also, such cells could be manufactured at a much lower cost due to the larger area, much lower cost and superior mechanical properties of Si substrates as compared to Ge substrates. The much lower cell cost also would enable medium concentration PV systems that would require more cell area, but with simplified, less expensive tracking and optics, resulting in lower overall system costs. Promising initial results from material-property measurements and single-junction and 2J CdZnTe/Si cell characterization results are given. Both the promise of the proposed technology and the challenges it faces are discussed.
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88.40.H- Solar cells (photovoltaics)

Silicon colloids: A new enabling nanomaterial

F. Meseguer, R. Fenollosa, I. Rodriguez, E. Xifré-Pérez, F. Ramiro-Manzano, M. Garín, and M. Tymczenko

J. Appl. Phys. 109, 102424 (2011); http://dx.doi.org/10.1063/1.3581880 (6 pages)

Online Publication Date: 31 May 2011

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We have recently developed a new type of silicon structure that we refer to as a silicon colloid. This new material consists of almost perfectly spherical silicon micro- and nanoparticles with a very smooth surface. They are able to trap light very efficiently in a large-span frequency range covering the visible to the far infrared regions. Silicon colloids can be thought of as a completely new material for scientific and technological purposes, with manifold applications covering electronics, photonics, cosmetics, or paints, among others. Here, we report on the synthesis of polycrystalline, amorphous, and porous silicon colloids, as well as their optical properties, some applications concerning light filters, and photonic bonding.
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81.07.Bc Nanocrystalline materials
78.30.Am Elemental semiconductors and insulators
78.40.Fy Semiconductors
78.66.Jg Amorphous semiconductors; glasses
82.70.Dd Colloids
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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