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6 Jun 2011

Volume 98, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 233101 (2011); http://dx.doi.org/10.1063/1.3597211 (3 pages)

Yu-Jung Lu (呂宥蓉), Hon-Way Lin (林弘偉), Hung-Ying Chen (陳虹穎), Yu-Chen Yang (楊右丞), and Shangjr Gwo (果尚志)
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Observation of phase shifts in a vertical cavity quantum dot switch

C. Y. Jin, O. Kojima, T. Kita, O. Wada, and M. Hopkinson

Appl. Phys. Lett. 98, 231101 (2011); http://dx.doi.org/10.1063/1.3596704 (3 pages) | Cited 4 times

Online Publication Date: 6 June 2011

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We have studied the possibility to utilize semiconductor quantum dots (QDs) as an optical phase shifter within a vertical geometry for ultrafast information processing. From theoretical analyses, an optical phase nonlinearity in QD structures has been predicted which can be enhanced through the use of an vertical optical cavity. Asymmetric cavity structures with 16/30 periods of GaAs/AlGaAs layers for the front/back mirrors have been fabricated to demonstrate a practical device with significant nonlinear characteristics for optical switching. A phase shift of 18° has been initially observed with a tilted pump scheme. This observation paves the way toward a Mach–Zehnder optical switch using QDs inside a vertical cavity.
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42.79.-e Optical elements, devices, and systems
42.79.Bh Lenses, prisms and mirrors
42.82.-m Integrated optics
78.67.Hc Quantum dots

High-performance quantum cascade lasers with wide electroluminescence ( ∼ 600 cm−1), operating in continuous-wave above 100 °C

Kazuue Fujita, Shinichi Furuta, Atsushi Sugiyama, Takahide Ochiai, Akio Ito, Tatsuo Dougakiuchi, Tadataka Edamura, and Masamichi Yamanishi

Appl. Phys. Lett. 98, 231102 (2011); http://dx.doi.org/10.1063/1.3596706 (3 pages) | Cited 4 times

Online Publication Date: 7 June 2011

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The authors report high temperature continuous-wave (cw) operations of broad-gain quantum cascade lasers based on the anticrossed dual-upper-state to multiple-lower-state design. The devices exhibit extremely wide electroluminescence (>600 cm−1) and subthreshold amplified spontaneous emission ( ∼ 570 cm−1) spectra at room temperature. Despite showing such broad electroluminescence spectra, the high-reflection coated, buried heterostructure lasers operating at 6.8 μm demonstrate a low threshold current density of ∼ 1.5 kA/cm2 and a high power of >500 mW with a high slope efficiency of ∼ 1.6 W/A in cw mode at 300 K. The maximum cw operating temperature of above 100 °C is achieved.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Real time demonstration of high bitrate quantum random number generation with coherent laser light

T. Symul, S. M. Assad, and P. K. Lam

Appl. Phys. Lett. 98, 231103 (2011); http://dx.doi.org/10.1063/1.3597793 (3 pages) | Cited 6 times

Online Publication Date: 7 June 2011

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We present a random number generation scheme that uses broadband measurements of the vacuum field contained in the radio-frequency sidebands of a single-mode laser. Even though the measurements may contain technical noise, we show that suitable algorithms can transform the digitized photocurrents into a string of random numbers that can be made arbitrarily correlated with a subset of the quantum fluctuations (high quantum correlation regime) or arbitrarily immune to environmental fluctuations (high environmental immunity). We demonstrate up to 2 Gbps of real time random number generation that were verified using standard randomness tests.
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03.67.Hk Quantum communication

Resilience of gated avalanche photodiodes against bright illumination attacks in quantum cryptography

Z. L. Yuan, J. F. Dynes, and A. J. Shields

Appl. Phys. Lett. 98, 231104 (2011); http://dx.doi.org/10.1063/1.3597221 (3 pages) | Cited 6 times

Online Publication Date: 8 June 2011

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Semiconductor avalanche photodiodes (APDs) are commonly used for single photon detection in quantum key distribution. Recently, many attacks using bright illumination have been proposed to manipulate gated InGaAs APDs. In order to devise effective countermeasures, careful analysis of these attacks must be carried out to distinguish between incorrect operation and genuine loopholes. Here, we show that correctly operated, gated APDs are immune to continuous-wave illumination attacks, while monitoring the photocurrent for anomalously high values is a straightforward countermeasure against attacks using temporally tailored light.
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85.60.Dw Photodiodes; phototransistors; photoresistors
03.67.Dd Quantum cryptography and communication security

Tuneable polaritonics at room temperature with strongly coupled Tamm plasmon polaritons in metal/air-gap microcavities

C. Grossmann, C. Coulson, G. Christmann, I. Farrer, H. E. Beere, D. A. Ritchie, and J. J. Baumberg

Appl. Phys. Lett. 98, 231105 (2011); http://dx.doi.org/10.1063/1.3597304 (3 pages) | Cited 2 times

Online Publication Date: 8 June 2011

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We report strong coupling between Tamm plasmons and excitons in III–V quantum wells at room temperature in ultracompact sample designs. A high refractive index contrast air-gap mirror together with optical Tamm states at a metal/semiconductor interface tightly confines the intracavity field leading to substantial local field enhancements. Angular-resolved reflectivity spectra give clear evidence for anticrossing in the dispersion relation. Room temperature Rabi splittings of 10 meV are found in excellent agreement with simulations. Electrical control of the polariton modes is realized without need for doped mirror layers. Such air-gap microcavities open innovative possibilites for electrically tunable microcavities and polaritonic microelectromechanics.
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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)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.35.-y Excitons and related phenomena

81 fJ/bit energy-to-data ratio of 850 nm vertical-cavity surface-emitting lasers for optical interconnects

P. Moser, W. Hofmann, P. Wolf, J. A. Lott, G. Larisch, A. Payusov, N. N. Ledentsov, and D. Bimberg

Appl. Phys. Lett. 98, 231106 (2011); http://dx.doi.org/10.1063/1.3597799 (3 pages) | Cited 5 times

Online Publication Date: 8 June 2011

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Extremely energy-efficient oxide-confined high-speed 850 nm vertical-cavity surface-emitting lasers for optical interconnects are presented. Error-free performance at 17 and 25 Gb/s via a 100 m multimode fiber link is demonstrated at record high dissipation-power-efficiencies of up to 69 fJ/bit (<0.1 mW/Gbps) and 99 fJ/bit, respectively. These are the most power efficient high-speed directly modulated light sources reported to date. The total energy-to-data ratio is 83 fJ/bit at 25 °C and reduces to 81 fJ/bit at 55 °C. These results were obtained without adjustment of driving conditions. A high D-factor of 12.0 GHz/(mA)0.5 and a K-factor of 0.41 ns are measured.
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42.62.-b Laser applications
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.81.Uv Fiber networks
42.82.Ds Interconnects, including holographic interconnects
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Type-II core/shell nanoparticle induced photorefractivity

Xiangping Li, Joel Van Embden, Richard A. Evans, and Min Gu

Appl. Phys. Lett. 98, 231107 (2011); http://dx.doi.org/10.1063/1.3596437 (3 pages)

Online Publication Date: 8 June 2011

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We demonstrate engineering the photocharge generation efficiency of nanoparticles on the nanometer scale by using a type-II band-gap structure. Compared to bare CdSe cores, the dispersion of type-II core/shell nanoparticles in photorefractive polymer led to an average 100% increase in photocurrents. An improvement to the refractive-index construction time, and a near 100% enhancement to the two beam coupling net-gain coefficients and four-wave mixing internal diffraction efficiencies have been achieved at moderate biases.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.Hc Quantum dots
78.20.Mg Photorefractive effects
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Electrical injection, continuous wave operation of subwavelength-metallic-cavity lasers at 260 K

Kang Ding, Zhicheng Liu, Leijun Yin, Hua Wang, Ruibin Liu, Martin T. Hill, Milan J. H. Marell, Peter J. van Veldhoven, Richard Nötzel, and C. Z. Ning

Appl. Phys. Lett. 98, 231108 (2011); http://dx.doi.org/10.1063/1.3598961 (3 pages) | Cited 5 times

Online Publication Date: 8 June 2011

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We report continuous wave lasing operation at T = 260 K of subwavelength-metallic-cavities with semiconductor core encapsulated in silver under electric injection. The physical cavity volumes of the two lasers presented are 0.96λ3 (λ = 1563.4 nm) and 0.78λ3 (λ = 1488.7 nm), respectively. Longitudinal modes observed in one of lasers correspond to the Fabry–Perot cavity in the length direction. Such record high temperature operation of a subwavelength laser is of great importance for the development of small light sources in future integrated photonic circuits and other on-chip applications.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers
42.60.By Design of specific laser systems

High-resolution heterodyne spectroscopy using a tunable quantum cascade laser around 3.5 THz

Y. Ren, J. N. Hovenier, R. Higgins, J. R. Gao, T. M. Klapwijk, S. C. Shi, B. Klein, T.-Y. Kao, Q. Hu, and J. L. Reno

Appl. Phys. Lett. 98, 231109 (2011); http://dx.doi.org/10.1063/1.3599518 (3 pages) | Cited 7 times

Online Publication Date: 9 June 2011

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A frequency tunable terahertz heterodyne spectrometer, based on a third-order distributed feedback quantum cascade laser as a local oscillator, has been demonstrated by measuring molecular spectral lines of methanol (CH3OH) gas at 3.5 THz. By varying the bias voltage of the laser, we achieved a tuning range of ∼ 1 GHz of the lasing frequency, within which the molecular spectral lines were recorded. The measured spectra show excellent agreement with modeled ones. By fitting we derived the lasing frequency for each bias voltage accurately. The ultimate performance of the receiver including the resolution of noise temperature and frequency is also addressed.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
33.20.Bx Radio-frequency and microwave spectra

Cascaded third harmonic generation in lithium niobate nanowaveguides

Alexander S. Solntsev, Andrey A. Sukhorukov, Dragomir N. Neshev, Rumen Iliew, Reinhard Geiss, Thomas Pertsch, and Yuri S. Kivshar

Appl. Phys. Lett. 98, 231110 (2011); http://dx.doi.org/10.1063/1.3597627 (3 pages) | Cited 1 time

Online Publication Date: 9 June 2011

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We predict highly efficient third harmonic generation through simultaneous phase-matching of second-harmonic generation and sum-frequency generation in lithium niobate nanowaveguides, enabled due to strong modal dispersion. We demonstrate that the waveguide size which corresponds to phase-matching is also optimal for highest mode confinement and therefore for strongly enhanced conversion efficiency.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Gn Optical waveguides and couplers

To realize the optimal probe pulse length for detection of pulsed terahertz signal with spectral-encoding technique

Xiao-Yu Peng, Xin-Hai Zhang, Jing-Hua Teng, Hong-Cheng Guo, and Yong-Lim Foo

Appl. Phys. Lett. 98, 231111 (2011); http://dx.doi.org/10.1063/1.3598405 (3 pages)

Online Publication Date: 9 June 2011

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The approach to realize the optimal chirped probe pulse length for an arbitrary pulsed terahertz (THz) signal measured with the spectral-encoding technique was investigated by simulation. It was found that either the maximum positive peak or the absolute value of the strongest negative peak of the normalized difference between the probe spectrum modulated by THz signal and the background probe spectrum tended to be maximized when the probe pulse duration approached to the optimal value. The probe pulse length can be adjusted continuously with a pair of triangular dispersive prisms. THz signals from high-voltage biased air plasmas induced by femtosecond laser pulse were measured with minimum distortion using our simple method.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
84.40.-x Radiowave and microwave (including millimeter wave) technology

Low temperature near-field scanning optical microscopy on infrared and terahertz photonic-crystal quantum cascade lasers

I. C. Moldovan-Doyen, G. Xu, L. Greusard, G. Sevin, E. Strupiechonski, G. Beaudoin, I. Sagnes, S. P. Khanna, E. H. Linfield, A. G. Davies, R. Colombelli, and Y. De Wilde

Appl. Phys. Lett. 98, 231112 (2011); http://dx.doi.org/10.1063/1.3597411 (3 pages) | Cited 2 times

Online Publication Date: 10 June 2011

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We report the development of a scattering-type near-field scanning optical microscope (sNSOM) which operates at temperatures down to 100 K with a scanning range of up to 400 μm. We have used this sNSOM to map the electromagnetic near-field on mid-IR and terahertz (THz) surface emitting quantum cascade lasers with photonic-crystal resonators. Mid-IR devices operate at λ = 7.5 μm (40 THz) while THz devices operate at λ ≈ 110 μm (2.7 THz). The near-field images—in agreement with numerical calculations—demonstrate an instrument resolution of 100's nm.
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07.79.Fc Near-field scanning optical microscopes
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.70.Qs Photonic bandgap materials
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

The transition from a TEM-like mode to a plasmonic mode in parallel-plate waveguides

Jingbo Liu, Rajind Mendis, and Daniel M. Mittleman

Appl. Phys. Lett. 98, 231113 (2011); http://dx.doi.org/10.1063/1.3598404 (3 pages) | Cited 10 times

Online Publication Date: 10 June 2011

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We describe subwavelength-resolved measurements of the broadband terahertz field propagating inside a finite-width parallel-plate waveguide. We observe a transition in the spatial mode of the waveguide, in which the energy distribution shifts from the waveguide center to the edges with increasing frequency. This transition is surprisingly abrupt, and depends sensitively on the gap between the waveguide plates. These results may have important implications for a variety of terahertz experiments as well as in the design of optical systems and components in the visible and near-infrared regimes, which rely on plasmonic wave guiding.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Transition from strong to ultrastrong coupling regime in mid-infrared metal-dielectric-metal cavities

P. Jouy, A. Vasanelli, Y. Todorov, A. Delteil, G. Biasiol, L. Sorba, and C. Sirtori

Appl. Phys. Lett. 98, 231114 (2011); http://dx.doi.org/10.1063/1.3598432 (3 pages) | Cited 3 times

Online Publication Date: 10 June 2011

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We have investigated the transition from strong to ultrastrong coupling regime between a mid-infrared intersubband excitation and the fundamental mode of a metal-dielectric-metal microcavity. The ultrastrong coupling regime is demonstrated up to room temperature for a wavelength of 11.7 μm by using 260 nm thick cavities, which impose an extreme subwavelength confinement. By varying the doping of our structures we show that the experimental signature of the transition to the ultrastrong coupling regime is the opening of a photonic gap in the polariton dispersion. The width of this gap depends quadratically on the ratio between the Rabi and intersubband transition energies.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
82.70.-y Disperse systems; complex fluids
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)
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Reduction in thermal boundary conductance due to proton implantation in silicon and sapphire

Patrick E. Hopkins, Khalid Hattar, Thomas Beechem, Jon F. Ihlefeld, Douglas L. Medlin, and Edward S. Piekos

Appl. Phys. Lett. 98, 231901 (2011); http://dx.doi.org/10.1063/1.3592822 (3 pages) | Cited 2 times

Online Publication Date: 6 June 2011

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We measure the thermal boundary conductance across Al/Si and Al/Al2O3 interfaces that are subjected to varying doses of proton ion implantation with time domain thermoreflectance. The proton irradiation creates a major reduction in the thermal boundary conductance that is much greater than the corresponding decrease in the thermal conductivities of both the Si and Al2O3 substrates into which the ions were implanted. Specifically, the thermal boundary conductances decrease by over an order of magnitude, indicating that proton irradiation presents a unique method to systematically decrease the thermal boundary conductance at solid interfaces.
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61.72.up Other materials
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
66.70.Df Metals, alloys, and semiconductors
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
78.20.N- Thermo-optic effects

The surface boundary conditions in GaN/AlGaN/GaN transistor heterostructures

M. Gladysiewicz, R. Kudrawiec, J. Misiewicz, G. Cywinski, M. Siekacz, P. Wolny, and C. Skierbiszewski

Appl. Phys. Lett. 98, 231902 (2011); http://dx.doi.org/10.1063/1.3592801 (3 pages) | Cited 5 times

Online Publication Date: 7 June 2011

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The distribution of electric field in GaN(cap)/AlGaN/GaN(buffer) transistor heterostructures with various AlGaN layer thicknesses (10, 20, and 30 nm) has been studied by contactless electroreflectance and compared with theoretical calculations performed for various positions of the Fermi-level on GaN surface. For the three samples the best agreement between experimental data and theoretical calculations has been found at the same position of the Fermi-level on GaN surface (i.e., 0.55±0.05 eV below the conduction band). It means that the Fermi-level is pinned on GaN surface and this pinning can be treated as the boundary condition for the distribution of polarization-related fields in this heterostructure.
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85.30.-z Semiconductor devices

Induced magnetic anisotropy in lifted (Ga,Mn)As thin films

F. Greullet, L. Ebel, F. Münzhuber, S. Mark, G. V. Astakhov, T. Kießling, C. Schumacher, C. Gould, K. Brunner, W. Ossau, and L. W. Molenkamp

Appl. Phys. Lett. 98, 231903 (2011); http://dx.doi.org/10.1063/1.3597301 (3 pages)

Online Publication Date: 7 June 2011

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We demonstrate the ability to release the growth-induced strain in (Ga,Mn)As layers and (In,Ga)As/(Ga,Mn)As bilayers by lifting them from the GaAs substrate. The lifted (bi)layers are then deposited back onto various substrates. The change in strain before and after processing has been studied by means of x-ray diffraction. Magnetic characterization demonstrates the efficiency of our lift-off process to reorient the magnetization to the direction normal to the layer plane.
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75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Surface damage on diamond membranes fabricated by ion implantation and lift-off

V. S. Drumm, A. D. C. Alves, B. A. Fairchild, K. Ganesan, J. C. McCallum, D. N. Jamieson, S. Prawer, S. Rubanov, R. Kalish, and L. C. Feldman

Appl. Phys. Lett. 98, 231904 (2011); http://dx.doi.org/10.1063/1.3597223 (3 pages) | Cited 4 times

Online Publication Date: 8 June 2011

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Thin membranes with excellent optical properties are essential elements in diamond based photonic systems. Due to the chemical inertness of diamond, ion beam processing must be employed to carve photonic structures. One method to realize such membranes is ion-implantation graphitization followed by chemical removal of the sacrificial graphite. The interface revealed when the sacrificial layer is removed has interesting properties. To investigate this interface, we employed the surface sensitive technique of grazing angle channeled Rutherford backscattering spectroscopy. Even after high temperature annealing and chemical etching a thin layer of damaged diamond remains, however, it is removed by hydrogen plasma exposure.
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81.65.Cf Surface cleaning, etching, patterning
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
61.05.Np Atom, molecule, and ion scattering (for structure determination only)
52.77.Dq Plasma-based ion implantation and deposition
61.72.Cc Kinetics of defect formation and annealing

In situ synchrotron based x-ray fluorescence and scattering measurements during atomic layer deposition: Initial growth of HfO2 on Si and Ge substrates

K. Devloo-Casier, J. Dendooven, K. F. Ludwig, G. Lekens, J. D’Haen, and C. Detavernier

Appl. Phys. Lett. 98, 231905 (2011); http://dx.doi.org/10.1063/1.3598433 (3 pages) | Cited 2 times

Online Publication Date: 8 June 2011

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The initial growth of HfO2 was studied by means of synchrotron based in situ x-ray fluorescence (XRF) and grazing incidence small angle x-ray scattering (GISAXS). HfO2 was deposited by atomic layer deposition (ALD) using tetrakis(ethylmethylamino)hafnium and H2O on both oxidized and H-terminated Si and Ge surfaces. XRF quantifies the amount of deposited material during each ALD cycle and shows an inhibition period on H-terminated substrates. No inhibition period is observed on oxidized substrates. The evolution of film roughness was monitored using GISAXS. A correlation is found between the inhibition period and the onset of surface roughness.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.70.Ck X-ray scattering
78.70.En X-ray emission spectra and fluorescence
78.55.Hx Other solid inorganic materials
68.55.aj Insulators
81.65.Mq Oxidation

Medium-range icosahedral order in quasicrystal-forming Zr2Pd binary metallic glass

Li Huang, X. W. Fang, C. Z. Wang, M. J. Kramer, Z. J. Ding, and K. M. Ho

Appl. Phys. Lett. 98, 231906 (2011); http://dx.doi.org/10.1063/1.3597302 (3 pages) | Cited 4 times

Online Publication Date: 9 June 2011

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Medium-range order in Zr2Pd metallic glass was studied using a combination of x-ray diffraction experiment and atomistic simulations. We show that, in contrast to earlier experimental interpretations, the icosahedral-like polyhedron is centered around Pd, rather than Zr. Furthermore, we find that the ordered icosahedral packing around Pd extends to the third shell in the way similar to that in the Bergman-type clusters. The existence of Bergman-type clusters sheds interesting light into the formation of nanoquasicrystal phase during crystallization process of Zr2Pd metallic glass.
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61.43.Fs Glasses
61.44.Br Quasicrystals
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
71.23.Ft Quasicrystals
81.05.Kf Glasses (including metallic glasses)
64.70.dg Crystallization of specific substances

Effect of doping on global and local order in crystalline GeTe

Xavier Biquard, Milos Krbal, Alexander V. Kolobov, Paul Fons, Robert E. Simpson, Bérangère Hyot, Bernard André, Junji Tominaga, and Tomoya Uruga

Appl. Phys. Lett. 98, 231907 (2011); http://dx.doi.org/10.1063/1.3598384 (3 pages) | Cited 2 times

Online Publication Date: 9 June 2011

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Effect of nitrogen and carbon doping on the structure of GeTe has been investigated using x-ray diffraction and extended x-ray absorption fine structure (EXAFS) spectroscopies. While Bragg diffraction which probes the global structure exhibits a clear transition upon doping from the rhombohedral phase to the cubic (rocksalt) phase, the local structure probed by EXAFS remains rhombohedrally distorted across the compositions studied. The apparent inconsistency between the results of the two techniques used is attributed to disordering upon doping and the resulting order-disorder transition that is “seen” by site-averaging diffraction as a displacive rhombohedral-to-cubic transition.
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61.72.U- Doping and impurity implantation
78.70.Dm X-ray absorption spectra
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
64.60.Cn Order-disorder transformations

Ultrathin (1×2)-Sn layer on GaAs(100) and InAs(100) substrates: A catalyst for removal of amorphous surface oxides

P. Laukkanen, M. P. J. Punkkinen, J. Lång, M. Tuominen, M. Kuzmin, V. Tuominen, J. Dahl, J. Adell, J. Sadowski, J. Kanski, V. Polojärvi, J. Pakarinen, K. Kokko, M. Guina, M. Pessa, et al.

Appl. Phys. Lett. 98, 231908 (2011); http://dx.doi.org/10.1063/1.3596702 (3 pages)

Online Publication Date: 10 June 2011

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Amorphous surface oxides of III–V semiconductors are harmful in many contexts of device development. Using low-energy electron diffraction and photoelectron spectroscopy, we demonstrate that surface oxides formed at Sn-capped GaAs(100) and InAs(100) surfaces in air are effectively removed by heating. This Sn-mediated oxide desorption procedure results in the initial well-defined Sn-stabilized (1×2) surface even for samples exposed to air for a prolonged time. Based on ab initio calculations we propose that the phenomenon is due to indirect and direct effects of Sn. The Sn-induced surface composition weakens oxygen adsorption.
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68.43.Mn Adsorption kinetics
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.40.Gh Other heat and thermomechanical treatments
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.43.Nr Desorption kinetics
68.35.Dv Composition, segregation; defects and impurities

Enhancement of the magneto-optical performance of Sr(Ti0.6−xGaxFe0.4)O3 perovskite films by Ga substitution

Peng Jiang, Lei Bi, Dong Hun Kim, G. F. Dionne, and C. A. Ross

Appl. Phys. Lett. 98, 231909 (2011); http://dx.doi.org/10.1063/1.3595337 (3 pages) | Cited 2 times

Online Publication Date: 10 June 2011

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Epitaxial films of ferromagnetic single-phase perovskite (Ti0.6−xGaxFe0.4)O3 (x ≤ 0.6) were grown on (001) oriented (La,Sr)(Al,Ta)O3 substrates by pulsed laser deposition. The films had an out-of-plane magnetic easy axis which is attributed to magnetoelastic effects. Ga lowered the optical absorption of the film, the Faraday rotation, and the magnetization but increased the magneto-optical figure of merit. The figure of merit for x = 0.4 was 3.5±0.3 deg/dB, at least approximately three times greater than the value at x = 0, and the optical loss at 1550 nm wavelength was 0.012–0.015 dB/μm.
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78.20.Ls Magneto-optical effects
78.66.Nk Insulators
81.15.Fg Pulsed laser ablation deposition
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
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Phase change behavior in titanium-doped Ge2Sb2Te5 films

S. J. Wei, H. F. Zhu, K. Chen, D. Xu, J. Li, F. X. Gan, X. Zhang, Y. J. Xia, and G. H. Li

Appl. Phys. Lett. 98, 231910 (2011); http://dx.doi.org/10.1063/1.3597617 (3 pages) | Cited 4 times

Online Publication Date: 10 June 2011

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The titanium-doped Ge2Sb2Te5 films were deposited on Si(100) substrates by comagnetron sputtering method. The titanium concentrations in those films were determined by x-ray photoelectron spectroscopy. The influence of Ti doping upon phase change characteristics of the samples has been investigated by x-ray diffraction and a temperature-regulable UVISEL™ typed spectroscopic ellipsometry. With the augmentation of Ti doping concentration, the crystalline temperatures of the films went up while annealing, and the face-centered-cubic phase of them had high thermal stability because of the bond making between Ti and Te elements partly.
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68.55.ag Semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Cd Deposition by sputtering
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Determination of the anisotropic elastic properties of Ge1Sb2Te4

Arnaud Marmier, Krisztian Kohary, and C. David Wright

Appl. Phys. Lett. 98, 231911 (2011); http://dx.doi.org/10.1063/1.3598934 (3 pages) | Cited 1 time

Online Publication Date: 10 June 2011

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The elastic properties of Ge–Sb–Te (GST) alloys are important for phase-change devices (such as CD-RW, DVD-RW, Blu-ray, or phase-change random access memory) because the transition between the crystalline and amorphous phases involves a volume change accommodated by a strain estimated to be between 150 MPa and 10 GPa. However, the elastic properties of GST alloys are poorly characterized and the experimental and theoretical values show large discrepancies. We carry out a careful analysis of the elastic properties of a model system, crystalline Ge1Sb2Te4, using density functional theory and elastic anisotropy considerations. We show that Ge1Sb2Te4 exhibits significant anisotropy in its elastic properties.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.kg Semiconductors
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