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Optical nanorod antennas as dispersive one-dimensional Fabry–Pérot resonators for surface plasmons

Ertugrul Cubukcu

and Federico Capasso

Appl. Phys. Lett. 95, 201101 (2009) (3 pages)

Online Publication Date: 16 November 2009

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Resonant optical nanoantennas exhibit a different length scaling due to the surface plasmons compared to their radio frequency counterparts. In this letter, we address this difference by calculating the wavelength-dependent effective mode index n_eff for a cylindrical one-dimensional gold nanowire waveguide. Our results show that nanorod optical antennas act as dispersive and lossy Fabry–Pérot resonators for surface plasmons.

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42.82.-m	Integrated optics
42.79.Gn	Optical waveguides and couplers

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Blue light-emitting diodes with a roughened backside fabricated by wet etching

Chia-Feng Lin ,

Chun-Min Lin ,

Kuei-Ting Chen ,

Wan-Chun Huang ,

Ming-Shiou Lin ,

Jing-Jie Dai ,

Ren-Hao Jiang ,

Yu-Chieh Huang ,

and Chung-Ying Chang

Appl. Phys. Lett. 95, 201102 (2009) (3 pages)

Online Publication Date: 16 November 2009

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The InGaN-based light-emitting diodes (LEDs) with a roughened patterned backside on the N-face GaN surface were fabricated through a crystallographic etching process to increase light-extraction efficiency. After laser decomposition, laser scribing, and a lateral crystallographic wet etching process at the GaN/Al₂O₃ interface, stable crystallographic etching planes were formed as the GaN {10 math

} planes that included an angle with the top GaN (0001) plane measured at 58°. The GaN buffer layer acted as the sacrificial layer for the laser decomposition process and the lateral wet etching process with a 26 μm/min etching rate. The LED with the inverted pyramidal N-face GaN surface close to the GaN/Al₂O₃ interface has a larger light-scattering process than the conventional LED. The light-output power of the LED with the backside roughened surface had a 47% enhancement when measured in LED chip form.

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85.60.Jb

Light-emitting devices

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Extended depth of focus in a particle field measurement using a single-shot digital hologram

Wen Chen ,

Chenggen Quan ,

and Cho Tay

Appl. Phys. Lett. 95, 201103 (2009) (3 pages)

Online Publication Date: 16 November 2009

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We propose a method to extend the depth of focus in a particle field measurement using a single-shot digital hologram. A focal plane is obtained for each pixel based on an entropy method, and a depth map is subsequently extracted. A synthesized extended focused image is determined correspondingly using the extracted depth map. In addition, a wavelet modulus maxima algorithm and Canny algorithm are further employed to detect the edges of each particle, and the sizes and a three-dimensional localization of the particles are also estimated. Preliminary results are presented to show the feasibility and effectiveness of the proposed technique.

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42.40.Kw	Holographic interferometry; other holographic techniques
07.60.Ly	Interferometers
42.30.Sy	Pattern recognition

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Randomly packed n-SnO₂ nanorods/p-SiC heterojunction light-emitting diodes

H. Yang ,

S. Yu ,

C. Cheng ,

S. Tsang ,

H. Liang ,

and H. Fan

Appl. Phys. Lett. 95, 201104 (2009) (3 pages)

Online Publication Date: 17 November 2009

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A layer of randomly packed n-SnO₂ nanorods is grown by vapor transport method on the p-SiC(4H) substrate to realize heterojunction light-emitting diodes. Diodelike rectifying current-voltage characteristics, with a turn-on voltage of ∼ 4.5 V and reverse leakage current density of <0.25 A/m², are obtained at room temperature. Furthermore, electroluminescent spectra with emission peaks at around 395, 434, and 497 nm are observed from the heterojunction under forward bias. This is due to the relaxation of electrons in the conduction band of SnO₂ to the surface defect states and subsequent radiative recombination with holes injected from the p-SiC substrate.

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85.60.Jb

Light-emitting devices

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Electrically switchable multiple volume hologram recording in polymer-dispersed liquid-crystal films

Hongyue Gao ,

Haihui Pu ,

Bin Gao ,

Dejin Yin ,

Jianhua Liu ,

and Fuxi Gan

Appl. Phys. Lett. 95, 201105 (2009) (3 pages)

Online Publication Date: 17 November 2009

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Multiple Bragg hologram recording was investigated in trimethylolpropane triacrylate based polymer-dispersed liquid-crystal thin films. Ten volume holograms were stored at a single location of less than 0.8 mm² area with the diffraction efficiencies of 6%–15%, by a simplified method of peristrophic multiplexing, and the formation process of multiple volume holograms was presented. Furthermore, volume hologram capacity was studied both experimentally and theoretically in this film. Based on the maximum of Δn, ∼ 2×10⁻², the theoretical capacity of a location could be improved to 25 Bragg holograms with the relatively high diffraction efficiency of 1%, and the holographic storage density of more than 20 Gbits/in.² was achieved just by peristrophic multiplexing. Finally, electrically switchability for multiple holograms with a low threshold voltage of ∼ 3 V/μm was realized, which demonstrates that this material is a potential medium for electrically controlled holographic storage or diffraction device.

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42.70.Ln	Holographic recording materials; optical storage media
42.79.Vb	Optical storage systems, optical disks
42.70.Df	Liquid crystals
42.40.Lx	Diffraction efficiency, resolution, and other hologram characteristics
42.40.Ht	Hologram recording and readout methods
42.40.Pa	Volume holograms

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Intensity modulation of terahertz quantum cascade lasers under external light injection

Norihiko Sekine

and Iwao Hosako

Appl. Phys. Lett. 95, 201106 (2009) (3 pages)

Online Publication Date: 17 November 2009

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We investigated the light-current characteristics of terahertz (THz) quantum cascade lasers under external light injection, which excites interband transitions in the active materials. It was found that the amount of reduction in the THz power was constant for all injection currents above threshold, and the dependence of the reduction amount on the wavelength of the external light was observed to show a resonancelike feature. The dominant intensity modulation mechanism was found to be the loss change caused by interband transitions in the active region. Further, the effective coupling efficiency plays an important role in the intensity modulation.

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42.55.Px	Semiconductor lasers; laser diodes
42.60.Fc	Modulation, tuning, and mode locking
42.60.Jf	Beam characteristics: profile, intensity, and power; spatial pattern formation

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Transient optical response of quantum well excitons to intense narrowband terahertz pulses

A. Jameson ,

J. Tomaino ,

Yun-Shik Lee ,

J. Prineas ,

J. Steiner ,

M. Kira ,

and S. Koch

Appl. Phys. Lett. 95, 201107 (2009) (3 pages)

Online Publication Date: 17 November 2009

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Intense narrowband terahertz pulses are used to modify excitonic transitions in semiconductor quantum wells and to study the dephasing properties of the optically dark 2p states. Time-resolved terahertz-pump and optical-probe measurements exhibit strong nonlinear optical transients of the 1s heavy-hole and light-hole exciton resonances when the terahertz radiation is tuned near the 1s to 2p intraexciton transition. A microscopic theory attributes the observed nonlinearities to Rabi sidebands showing that the 2p-dephasing time is three times that of the 1s-state.

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73.21.Fg	Quantum wells
71.35.-y	Excitons and related phenomena
78.47.J-	Ultrafast spectroscopy (<1 psec)
78.47.D-	Time resolved spectroscopy (>1 psec)
81.07.St	Quantum wells
78.70.Gq	Microwave and radio-frequency interactions

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Direct measurement of auger recombination in In_0.1Ga_0.9N/GaN quantum wells and its impact on the efficiency of In_0.1Ga_0.9N/GaN multiple quantum well light emitting diodes

M. Zhang ,

P. Bhattacharya ,

J. Singh ,

and J. Hinckley

Appl. Phys. Lett. 95, 201108 (2009) (3 pages)

Online Publication Date: 18 November 2009

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The Auger recombination coefficient in In_0.1Ga_0.9N/GaN quantum wells, emitting at 407 nm has been determined from large signal modulation measurements on lasers in which these quantum wells form the gain region. A value of 1.5×10⁻³⁰ cm⁶ s⁻¹ is determined for the Auger coefficient at room temperature, which is used to analyze the reported efficiency characteristics of 410 nm In_0.1Ga_0.9N/GaN quantum wells light emitting diodes. The calculated efficiencies agree remarkably well with the measured ones. It is apparent that Auger recombination is largely responsible for limiting device efficiencies at high injection currents.

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73.63.Hs	Quantum wells
85.60.Jb	Light-emitting devices
78.67.De	Quantum wells
72.20.Jv	Charge carriers: generation, recombination, lifetime, and trapping

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Shape-dependent nonlinear absorption and relaxation in CuInS₂ nanocrystals

N. Venkatram ,

Sudip Batabyal ,

Lu Tian ,

Jagadese Vittal ,

and Wei Ji

Appl. Phys. Lett. 95, 201109 (2009) (3 pages)

Online Publication Date: 18 November 2009

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We report the observation of nonlinear-optical response and relaxation in copper indium sulfide (CuInS₂) crystalline nanoparticles and nanorods with femtosecond Z-scans and transient absorption measurements. Dependent on the size and shape, two-photon absorption and saturation in the one-photon absorption manifest themselves in these measurements as laser excitation wavelength of 780 nm is in the proximity of the lowest-lying excitonic energy, particularly for the nanorods. The transient absorption measurements by both one-photon and two-photon excitation reveal that electron-hole recombination is faster in smaller nanoparticles, or in nanorods with smaller aspect ratio. However, the decay to trapping states is independent of the size and aspect-ratio.

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78.67.Bf	Nanocrystals, nanoparticles, and nanoclusters
73.63.Bd	Nanocrystalline materials
72.20.Jv	Charge carriers: generation, recombination, lifetime, and trapping
78.47.jb	Transient absorption
78.40.Fy	Semiconductors
61.46.Df	Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
71.35.-y	Excitons and related phenomena

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Terahertz lasing from silicon by infrared Raman scattering on bismuth centers

S. Pavlov ,

U. Böttger ,

R. Eichholz ,

N. Abrosimov ,

H. Riemann ,

V. Shastin ,

B. Redlich ,

and H.-W. Hübers

Appl. Phys. Lett. 95, 201110 (2009) (3 pages)

Online Publication Date: 18 November 2009

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Stimulated emission at terahertz frequencies (4.5–5.8 THz) has been realized by electronic Raman scattering of infrared radiation on bismuth donor centers in silicon at low temperatures. The Stokes shift of the observed laser emission is 40.53 meV which corresponds to the bismuth intracenter transition between the 1s(A₁) ground state and the excited 1s(E) state. The laser has a low optical threshold and the largest frequency coverage in comparison with other Raman silicon lasers based on shallow donor centers. Time-resolved pump spectra enable the separation of donor and Raman lasing.

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42.55.Px	Semiconductor lasers; laser diodes
42.55.Ye	Raman lasers
78.30.-j	Infrared and Raman spectra
42.65.Dr	Stimulated Raman scattering; CARS
42.65.Es	Stimulated Brillouin and Rayleigh scattering

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Reflection-mode sensing using optical microresonators

Barry Koch ,

Yasha Yi ,

Jun-Ying Zhang ,

Stephen Znameroski ,

and Terry Smith

Appl. Phys. Lett. 95, 201111 (2009) (3 pages)

Online Publication Date: 19 November 2009

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The authors present an approach for applying optical microring resonators to sensing. The approach relies on the interaction of the resonator with a nanoparticle taggant, which can induce coupling between forward and backward propagating traveling-wave resonant modes of the device. In the conventional four-port Add/Drop filter configuration, such coupling results in significant build-up of output intensity at ports that would normally be “dark.” Because the increased intensity occurs across a wide range of device resonances, the sensor may be interrogated using broadband excitation and with a broadband detector, enabling a low-cost, robust system.

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07.07.Df	Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.82.Et	Waveguides, couplers, and arrays

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Control of free space propagation of Airy beams generated by quadratic nonlinear photonic crystals

Ido Dolev ,

Tal Ellenbogen ,

Noa Voloch-Bloch ,

and Ady Arie

Appl. Phys. Lett. 95, 201112 (2009) (3 pages)

Online Publication Date: 20 November 2009

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We present experimentally the control of free space propagation of an Airy beam. This beam is generated by a nonlinear wave mixing process in an asymmetrically poled nonlinear photonic crystal. Changing the quasi-phase matching conditions, e.g., the crystal temperature or pump wavelength, alters the location of the Airy beam peak intensity along the same curved trajectory. We explain that the variation in the beam shape is caused by noncollinear interactions. Owing to the highly asymmetric shape of nonlinear crystal in the Fourier space, these noncollinear interactions are still relatively efficient for positive (nonzero) phase mismatch.

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42.70.Qs	Photonic bandgap materials
42.25.Bs	Wave propagation, transmission and absorption
42.70.Mp	Nonlinear optical crystals
42.65.Jx	Beam trapping, self-focusing and defocusing; self-phase modulation
42.30.Kq	Fourier optics

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On carrier spillover in c- and m-plane InGaN light emitting diodes

J. Lee ,

X. Li ,

X. Ni ,

Ü. Özgür ,

H. Morkoç ,

T. Paskova ,

G. Mulholland ,

and K. Evans

Appl. Phys. Lett. 95, 201113 (2009) (3 pages)

Online Publication Date: 20 November 2009

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The internal quantum efficiency (IQE) and relative external quantum efficiency (EQE) in InGaN light-emitting diodes (LEDs) emitting at 400 nm with and without electron blocking layers (EBLs) on c-plane GaN and m-plane GaN were investigated in order to shed some light on any effect of polarization charge induced field on efficiency killer carrier spillover. Without an EBL the EQE values suffered considerably (by 80%) for both orientations, which is clearly attributable to carrier spillover. Substantial carrier spillover in both polarities, therefore, suggests that the polarization charge is not the major factor in efficiency degradation observed, particularly at high injection levels. Furthermore, the m-plane variety with EBL did not show any discernable efficiency degradation up to a maximum current density of 2250 A cm⁻² employed while that on c-plane showed a reduction by ∼ 40%. In addition, IQE of m-plane LED structure determined from excitation power dependent photoluminescence was ∼ 80% compared to 50% in c-plane LEDs under resonant and moderate excitation condition. This too is indicative of the superiority of m-plane LED structures, most probably due to relatively larger optical matrix elements for m-plane orientation.

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85.60.Jb	Light-emitting devices
78.55.Cr	III-V semiconductors

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Surface-plasmon mode hybridization in subwavelength microdisk lasers

R. Perahia ,

T. Alegre ,

A. Safavi-Naeini ,

and O. Painter

Appl. Phys. Lett. 95, 201114 (2009) (3 pages)

Online Publication Date: 20 November 2009

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Hybridization of surface-plasmon and dielectric waveguide whispering-gallery modes are demonstrated in a semiconductor microdisk laser cavity of subwavelength proportions. A metal layer is deposited on top of the semiconductor microdisk, the radius of which is systematically varied to enable mode hybridization between surface-plasmon and dielectric modes. The anticrossing behavior of the two cavity mode types is experimentally observed via photoluminescence spectroscopy and optically pumped lasing action at a wavelength of λ ∼ 1.3 μm is achieved at room temperature.

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42.55.Sa	Microcavity and microdisk lasers
42.55.Px	Semiconductor lasers; laser diodes
42.60.Da	Resonators, cavities, amplifiers, arrays, and rings

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Study of an organic-inorganic hybrid columinescence system by photoacoustic method

Yue-tao Yang ,

Xiao-jun Liu ,

and Shu-yi Zhang

Appl. Phys. Lett. 95, 201115 (2009) (3 pages)

Online Publication Date: 20 November 2009

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In this work, a columinescence system is found for lanthanide complexes Ln(p-ABA)₃⋅H₂O (p-ABA: p-aminobenzoic acid) incorporated in silica matrix. It is found that the luminescence quantum yield of Tb³⁺ emissions increases remarkably when partly replacing Tb(p-ABA)₃⋅H₂O by Gd(p-ABA)₃⋅H₂O in silica glass. Moreover, through the ratio of the fast to the slow heat components derived from a photoacoustic method, the intrinsic luminescence quantum yield of Tb³⁺ and the ligand sensitization efficiency are determined for the samples. The luminescence quenching effect for Tb–Er(p-ABA)₃⋅H₂O complexes in silica matrix is also discussed.

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78.20.Pa	Photoacoustic effects
62.65.+k	Acoustical properties of solids
78.55.-m	Photoluminescence, properties and materials

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Resonant nanometric cross-shaped apertures: Single apertures versus periodic arrays

L. Lin ,

L. Hande ,

and A. Roberts

Appl. Phys. Lett. 95, 201116 (2009) (3 pages)

Online Publication Date: 20 November 2009

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Here localized surface plasmon (LSP) resonances occurring inside cross-shaped apertures arranged in thin metallic films are investigated. It is shown that these resonances can be controlled by altering the geometry of the apertures, whereas surface plasmon polariton excitation and Wood anomalies arising as a consequence of the periodicity distorts the spectrum produced by isolated LSP resonances. Simulations showing the behavior of single apertures versus periodic arrays of apertures are compared with experimental results for periodic arrays.

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73.22.Lp	Collective excitations
68.55.jd	Thickness
71.36.+c	Polaritons (including photon-phonon and photon-magnon interactions)
78.66.Bz	Metals and metallic alloys

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Extremely broadened high-order harmonics generated by the femtosecond pulses propagating through the filaments in air

R. Ganeev

and H. Kuroda

Appl. Phys. Lett. 95, 201117 (2009) (3 pages)

Online Publication Date: 20 November 2009

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We demonstrate a considerable broadening of the harmonics generating in laser plasma using the laser pulses propagating through the filaments in air. A fourfold increase of harmonic bandwidth was achieved in the case of phase-modulated laser pulses, alongside with an increase in harmonic conversion efficiency (from 5×10⁻⁶ to 1.2×10⁻⁵). We also present the studies of harmonic generation using phase-modulated pulses at different ranges of ellipticity of the polarization of laser beam.

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52.38.Hb	Self-focussing, channeling, and filamentation in plasmas
52.50.Jm	Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
42.65.Ky	Frequency conversion; harmonic generation, including higher-order harmonic generation

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Spectrally resolved confocal microscopy for laser mode imaging and beam characteristic investigations

W. Brezna

and J. Smoliner

Appl. Phys. Lett. 95, 201118 (2009) (3 pages)

Online Publication Date: 20 November 2009

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In this letter, confocal optical microscopy is used to investigate the intensity patterns of an infrared vertical cavity surface emitting laser in three dimensions with high spectral resolution. The measurements were performed between the near field (Fresnel) regime and the far field (Fraunhofer) regime. The calculated intensity patterns were found to be in good agreement with the measured intensity distribution. The calculations together with the measurements can be used to determine the phase relation between different positions inside the gain medium.

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42.60.Jf	Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Da	Resonators, cavities, amplifiers, arrays, and rings
42.55.Px	Semiconductor lasers; laser diodes
07.60.Pb	Conventional optical microscopes

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Hybrid InP-based photonic crystal lasers on silicon on insulator wires

Y. Halioua ,

T. Karle ,

F. Raineri ,

P. Monnier ,

I. Sagnes ,

G. Roelkens ,

D. Van Thourhout ,

and R. Raj

Appl. Phys. Lett. 95, 201119 (2009) (3 pages)

Online Publication Date: 20 November 2009

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We report on InP-based photonic crystal lasers operating at 1.585 μm at room temperature, integrated with and evanescently coupled to silicon on insulator (SOI) waveguides. By optically pumping at 1.18 μm through the SOI wires, pulsed laser emission from line defect photonic crystal waveguides accurately aligned (<30 nm) to the silicon circuitry is demonstrated.

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42.55.Px	Semiconductor lasers; laser diodes
42.55.Tv	Photonic crystal lasers and coherent effects
42.60.By	Design of specific laser systems

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Characteristics of kilohertz-ignited, radio-frequency atmospheric-pressure dielectric barrier discharges in argon

Pei-Si Le ,

Guo Li ,

Sen Wang ,

He-Ping Li ,

and Cheng-Yu Bao

Appl. Phys. Lett. 95, 201501 (2009) (3 pages)

Online Publication Date: 17 November 2009

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In this letter, ignited by a kilohertz atmospheric-pressure dielectric-barrier discharge (APDBD), the stable and uniform argon radio-frequency (rf) APDBDs are generated with lower rf ignition voltages compared to the conventional rf APDBDs without the aid of the kilohertz filamentary discharges. The experimental studies on the mechanisms of this dual-frequency APDBD method indicate that it is the filaments extending from the kilohertz electrode region to the rf electrode region that provide the seed electrons for the ignition of the rf APDBDs at the lower applied rf voltages. A 12-mm-long stable and uniform argon plasma jet is obtained using the coaxial-type plasma generator.

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52.80.Pi	High-frequency and RF discharges
52.75.-d	Plasma devices

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Measurement of the electron density in a microwave plasma torch at atmospheric pressure

Qing Zhang ,

Guixin Zhang ,

Liming Wang ,

Xinxin Wang ,

Shumin Wang ,

and Yan Chen

Appl. Phys. Lett. 95, 201502 (2009) (3 pages)

Online Publication Date: 20 November 2009

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The electron density in a microwave plasma torch at atmospheric pressure was measured with a Mach–Zehnder interferometer. The electron density is on the order of 10¹⁷/cm³, one order higher than that deduced from the Stark broadening of spectral lines, and increases with the increase in the microwave power. The spatial distribution of the electron density was obtained. The highest electron density locates at the symmetrical axis of the plasma torch and decreases radially. It was found that the electron density fluctuates within a range of 0.3 with the time under the same experimental conditions.

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52.70.Kz	Optical (ultraviolet, visible, infrared) measurements
52.75.Hn	Plasma torches
52.25.Os	Emission, absorption, and scattering of electromagnetic radiation

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Measurement of anharmonicity of phonons in the negative thermal expansion compound Zn(CN)₂ by high pressure inelastic neutron scattering

R. Mittal ,

S. Chaplot ,

and H. Schober

Appl. Phys. Lett. 95, 201901 (2009) (3 pages)

Online Publication Date: 16 November 2009

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Zn(CN)₂ is known to have an isotropic negative thermal expansion (NTE) coefficient (about −51×10⁻⁶ K⁻¹) over 10–370 K that is twice as large as that of ZrW₂O₈. We have measured the pressure dependence of the phonon spectra up to 30 meV from a polycrystalline sample of Zn(CN)₂ at pressures of 0, 0.3, 1.9, and 2.8 kbar at temperatures of 165 and 225 K. The measurements enabled us to estimate the energy dependence of the ratios Γ_i/B (Γ_i are Grüneisen parameters as a function of phonon energy E_i at ambient pressure and B is the bulk modulus), which reflect the anharmonicity of phonons. We conclude that the phonon modes of low energy below 15 meV play an important role in the understanding of the NTE behavior in Zn(CN)₂ and the measured anharmonicity can quantitatively explain the NTE.

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63.20.-e	Phonons in crystal lattices
65.40.De	Thermal expansion; thermomechanical effects
63.70.+h	Statistical mechanics of lattice vibrations and displacive phase transitions
81.40.Jj	Elasticity and anelasticity, stress-strain relations
62.20.de	Elastic moduli

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Synthesis and characterization of nanoporous Pt–Ni alloys

Hongqi Li ,

Amit Misra ,

Jon Baldwin ,

and S. Picraux

Appl. Phys. Lett. 95, 201902 (2009) (3 pages)

Online Publication Date: 16 November 2009

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Two nanoporous Pt–Ni alloys were synthesized by dealloying ternary amorphous Si–Pt–Ni precursors. Both foams have nearly the same composition, ligament diameter size, and density. However, their ligament patterns are different, depending on the microstructure of precursors. The difference in morphology is shown to have a profound effect on mechanical properties. The structure with well-aligned long nanoligaments exhibited over 50% higher hardness and stiffness than the structure with short random-oriented nanoligaments. These nanoporous Pt–Ni structures are thermally stable at 300 °C.

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81.16.-c	Methods of micro- and nanofabrication and processing
61.43.Gt	Powders, porous materials
62.20.Qp	Friction, tribology, and hardness
81.40.Np	Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.46.-w	Structure of nanoscale materials
81.20.-n	Methods of materials synthesis and materials processing

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Dynamical and quasistatic structural relaxation paths in Pd₄₀Ni₄₀P₂₀ glass

A. Kahl ,

T. Koeppe ,

D. Bedorf ,

R. Richert ,

M. Lind ,

M. Demetriou ,

W. Johnson ,

W. Arnold ,

and K. Samwer

Appl. Phys. Lett. 95, 201903 (2009) (3 pages)

Online Publication Date: 19 November 2009

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By sequential heat treatment of a Pd₄₀Ni₄₀P₂₀ metallic glass at temperatures and durations for which α-relaxation is not possible, dynamic, and quasistatic relaxation paths below the glass transition are identified via ex situ ultrasonic measurements following each heat treatment. The dynamic relaxation paths are associated with hopping between nonequilibrium potential energy states of the glass, while the quasistatic relaxation path is associated with reversible β-relaxation events toward quasiequilibrium states. These quasiequilibrium states are identified with secondary potential energy minima that exist within the inherent energy minimum of the glass, thereby supporting the concept of the sub-basin/metabasin organization of the potential-energy landscape.

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61.43.Fs	Glasses
64.70.pe	Metallic glasses
62.65.+k	Acoustical properties of solids
81.40.Gh	Other heat and thermomechanical treatments

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Photoluminescence enhancement of Er-doped silica containing Ge nanoclusters

J. Guzman ,

S. Shin ,

C. Liao ,

C. Yuan ,

P. Stone ,

O. Dubón ,

K. Yu ,

J. Beeman ,

M. Watanabe ,

J. Ager ,

D. Chrzan ,

and E. Haller

Appl. Phys. Lett. 95, 201904 (2009) (3 pages)

Online Publication Date: 19 November 2009

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The photoluminescence (PL) of Er-doped silica films containing Ge nanoclusters synthesized by ion implantation was investigated. The area of the 1540 nm Er³⁺ PL peak was enhanced by up to a factor of 200 by the addition of Ge nanoclusters. The PL enhancement was found to be proportional to the concentration of Ge atoms. Control experiments with argon ion implantation were used to show that the enhancement is due to the presence of Ge and not radiation damage. Furthermore, the Er³⁺ PL was found to be strongly influenced by the postgrowth annealing and the crystallinity of the Ge nanoclusters.

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78.66.-w	Optical properties of specific thin films
78.55.Hx	Other solid inorganic materials
42.70.-a	Optical materials
81.40.Gh	Other heat and thermomechanical treatments
81.40.Tv	Optical and dielectric properties related to treatment conditions
68.55.Ln	Defects and impurities: doping, implantation, distribution, concentration, etc.

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Electronic structure of substitutional Mn in epitaxial In_0.965Mn_0.035Sb film

N. Parashar ,

D. Keavney ,

and B. Wessels

Appl. Phys. Lett. 95, 201905 (2009) (3 pages)

Online Publication Date: 19 November 2009

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The magnetic and electronic structure of Mn in In_0.965Mn_0.035Sb ferromagnetic semiconductor thin film was studied by x-ray absorption spectroscopy and x-ray magnetic circular dichroism. Comparison with atomic multiplet calculations suggests that manganese substitutes on sites with tetrahedral symmetry. Strong magnetic dichroism was observed from 5 to 300 K, at an applied field of 2 T. The temperature dependence of dichroism indicates presence of two magnetic Mn species having very similar spectral features. A high temperature species dominates the dichroic response over 50–300 K and a low temperature species is observed below 50 K.

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71.20.Nr	Semiconductor compounds
75.50.Pp	Magnetic semiconductors
75.50.Dd	Nonmetallic ferromagnetic materials
75.70.Ak	Magnetic properties of monolayers and thin films
81.05.Ea	III-V semiconductors
78.20.Ls	Magneto-optical effects
75.60.Ej	Magnetization curves, hysteresis, Barkhausen and related effects
78.70.Dm	X-ray absorption spectra

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Effects of well width and growth temperature on optical and structural characteristics of AlN/GaN superlattices grown by metal-organic chemical vapor deposition

C. Bayram ,

N. Péré-laperne ,

and M. Razeghi

Appl. Phys. Lett. 95, 201906 (2009) (3 pages)

Online Publication Date: 20 November 2009

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AlN/GaN superlattices (SLs) employing various well widths (from 1.5 to 7.0 nm) are grown by metal-organic chemical vapor deposition technique at various growth temperatures (T_S) (from 900 to 1035 °C). The photoluminescence (PL), x-ray diffraction, and intersubband (ISB) absorption characteristics of these SLs and their dependency on well width and growth temperature are investigated. Superlattices with thinner wells (grown at the same T_S) or grown at lower T_S (employing the same well width) are shown to demonstrate higher strain effects leading to a higher PL energy and ISB absorption energy. Simulations are employed to explain the experimental observations. ISB absorptions from 1.04 to 2.15 μm are demonstrated via controlling well width and growth temperature.

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68.65.Cd	Superlattices
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Cr	III-V semiconductors
81.05.Ea	III-V semiconductors
78.67.Pt	Multilayers; superlattices; photonic structures; metamaterials

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Transfer of graphene layers grown on SiC wafers to other substrates and their integration into field effect transistors

Sakulsuk Unarunotai ,

Yuya Murata ,

Cesar Chialvo ,

Hoon-sik Kim ,

Scott MacLaren ,

Nadya Mason ,

Ivan Petrov ,

and John Rogers

Appl. Phys. Lett. 95, 202101 (2009) (3 pages)

Online Publication Date: 16 November 2009

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This letter presents a simple method for transferring epitaxial sheets of graphene on silicon carbide to other substrates. The graphene was grown on the (0001) face of 6H-SiC by thermal annealing at 1550 °C in a hydrogen atmosphere. Transfer was accomplished using a peeling process with a bilayer film of gold/polyimide, to yield graphene with square millimeters of coverage on the target substrate. Raman spectroscopy provided evidence that the transferred material is single layer. Back gated field-effect transistors fabricated on oxidized silicon substrates with Cr/Au as source-drain electrodes exhibited ambipolar characteristics with hole mobilities of ∼ 100 cm²/V-s, and negligible influence of resistance at the contacts.

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85.30.Tv	Field effect devices
73.40.Cg	Contact resistance, contact potential
78.30.Na	Fullerenes and related materials
73.63.-b	Electronic transport in nanoscale materials and structures
78.67.Wj	Optical properties of graphene
61.72.Cc	Kinetics of defect formation and annealing

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Charge sensing in enhancement mode double-top-gated metal-oxide-semiconductor quantum dots

E. Nordberg ,

H. Stalford ,

R. Young ,

G. Ten Eyck ,

K. Eng ,

L. Tracy ,

K. Childs ,

J. Wendt ,

R. Grubbs ,

J. Stevens ,

M. Lilly ,

M. Eriksson ,

and M. Carroll

Appl. Phys. Lett. 95, 202102 (2009) (3 pages)

Online Publication Date: 17 November 2009

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Laterally coupled charge sensing of quantum dots is highly desirable because it enables measurement even when conduction through the quantum dot itself is suppressed. In this work, we demonstrate such charge sensing in a double-top-gated metal-oxide-semiconductor system. The current through a point contact constriction integrated near a quantum dot shows sharp 2% changes corresponding to charge transitions between the dot and a nearby lead. We extract the coupling capacitance between the charge sensor and the quantum dot, and we show that it agrees well with a three-dimensional capacitance model of the integrated sensor and quantum dot system.

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73.40.Qv	Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.63.Kv	Quantum dots

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Electron accumulation at nonpolar and semipolar surfaces of wurtzite InN from generalized infrared ellipsometry

V. Darakchieva ,

M. Schubert ,

T. Hofmann ,

B. Monemar ,

Ching-Lien Hsiao ,

Ting-Wei Liu ,

Li-Chyong Chen ,

W. Schaff ,

Y. Takagi ,

and Y. Nanishi

Appl. Phys. Lett. 95, 202103 (2009) (3 pages)

Online Publication Date: 17 November 2009

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The free electron properties of nonpolar (11 math

0)-oriented and semipolar (10 math

1)-oriented wurtzite InN films are studied by generalized infrared ellipsometry (GIRSE). We demonstrate the sensitivity of GIRSE to the surface charge accumulation layer and find a distinct surface electron accumulation to occur at all surfaces. The obtained surface electron sheet densities are found to vary from 0.9×10¹³ to 2.3×10¹⁴ cm⁻² depending on the surface orientation and bulk electron concentration. The upper limits of the surface electron mobility parameters of 417–644 cm²/V s are determined and discussed in the light of electron confinement at the surface.

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73.61.Ey	III-V semiconductors
72.20.Fr	Low-field transport and mobility; piezoresistance
73.40.Qv	Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.05.Ea	III-V semiconductors
68.55.jd	Thickness

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Photoluminescence studies of arsenic-doped Hg_1−xCd_xTe epilayers

I. Robin ,

M. Taupin ,

R. Derone ,

A. Solignac ,

P. Ballet ,

and A. Lusson

Appl. Phys. Lett. 95, 202104 (2009) (3 pages)

Online Publication Date: 17 November 2009

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Arsenic incorporation in HgCdTe epilayers has been achieved with a nonconventional radio frequency plasma source during molecular beam epitaxial growth. Photoluminescence studies were carried out on HgCdTe arsenic-doped samples. Measurements were done on the as-grown sample, after a Hg vacancy filling annealing and after a 400 °C activation annealing under Hg pressure. A comparison with extended x-ray absorption fine structure results allows us to assign the observed optical transitions to the Hg vacancies, As₂Te₃ glass and AsHg dopants. An optical signature of the arsenic site transfer upon activation annealing is found.

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78.55.Et	II-VI semiconductors
78.70.Dm	X-ray absorption spectra
68.55.A-	Nucleation and growth
61.72.Cc	Kinetics of defect formation and annealing

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Spin-polarization dynamics in InGaAs quantum dots during pulsed electrical spin-injection

Pablo Asshoff ,

Wolfgang Löffler ,

Jochen Zimmer ,

Heiko Füser ,

Harald Flügge ,

Heinz Kalt ,

and Michael Hetterich

Appl. Phys. Lett. 95, 202105 (2009) (3 pages)

Online Publication Date: 17 November 2009

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We investigate the fidelity of electron spin initialization in quantum dots utilizing nanosecond-pulsed electrical spin injection through a semimagnetic spin aligner in a spin light-emitting diode. At the onset of the electroluminescence signal, the circular polarization degree of the emitted light, corresponding to the spin polarization degree, is distinctively higher than under constant-current excitation. The observed spin-polarization dynamics are attributed to state filling effects. Additional contributions due to spin-flip mechanisms within the optically active region are identified.

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85.75.-d	Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.60.Jb	Light-emitting devices
85.35.Be	Quantum well devices (quantum dots, quantum wires, etc.)
72.25.-b	Spin polarized transport
73.63.Kv	Quantum dots

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Charge transport in polypyrrole:ZnO-nanowires composite films

A. Singh ,

Aditee Joshi ,

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November 2009

Volume 95, Issue 20, Articles (20xxxx)