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1 Oct 2007

Volume 91, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 143101 (2007); http://dx.doi.org/10.1063/1.2789812 (3 pages)

Hyun S. Kim, Hua Qin, and Robert H. Blick
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Medium resolution off-axis electron holography with millivolt sensitivity

David Cooper, Robert Truche, Pierrette Rivallin, Jean-Michel Hartmann, Frederic Laugier, Francois Bertin, Amal Chabli, and Jean-Luc Rouviere

Appl. Phys. Lett. 91, 143501 (2007); http://dx.doi.org/10.1063/1.2794006 (3 pages) | Cited 22 times

Online Publication Date: 1 October 2007

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Focused ion beam prepared silicon calibration specimens with boron doped layers have been examined using off-axis electron holography. By using a state-of-the-art FEI Titan microscope with unprecedented stability, we have been able to record holograms for time periods of 128 s with contrast levels of almost 40% and an average signal on the charge coupled device camera of 30 000 counts. A consequence of this is a significant improvement of the signal-to-noise ratio in the phase images allowing steps in potential of less than 0.030±0.003 V to be measured if sufficient care is taken during specimen preparation.
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42.40.Lx Diffraction efficiency, resolution, and other hologram characteristics
41.85.-p Beam optics

Tuning the photoresponse of quantum dot infrared photodetectors across the 8–12 μm atmospheric window via rapid thermal annealing

P. Aivaliotis, E. A. Zibik, L. R. Wilson, J. W. Cockburn, M. Hopkinson, and R. J. Airey

Appl. Phys. Lett. 91, 143502 (2007); http://dx.doi.org/10.1063/1.2794014 (3 pages) | Cited 11 times

Online Publication Date: 1 October 2007

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We report on wide spectral tunability of narrow-band (Δλ/λ ∼ 12%) InAs/In0.15Ga0.85As/GaAs quantum dot-in-a-well infrared photodetectors using postgrowth rapid thermal annealing. The well resolved absorption and photocurrent peaks shift from 8 to 11.6 μm by annealing the devices at 800 °C for up to 4 min. Upon annealing, the dot confinement potential becomes shallower and the tunneling probability increases, resulting not only in an increased responsivity but also in an increased dark current. The combined effect is to reduce detector detectivity from 1.1×1010 cm Hz1/2 W−1 at 8 μm to 3×109 cm Hz1/2 W−1 at 11 μm (T = 77 K). Our results demonstrate that spectral tunability from 8 to 12 μm can be achieved while maintaining good detector performance.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Ultraviolet-oxidized mercaptan-terminated organosilane nanolayers as diffusion barriers at Cu-silica interfaces

D. D. Gandhi, U. Tisch, B. Singh, M. Eizenberg, and G. Ramanath

Appl. Phys. Lett. 91, 143503 (2007); http://dx.doi.org/10.1063/1.2760164 (3 pages) | Cited 5 times

Online Publication Date: 2 October 2007

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We demonstrate the use of UV-exposed molecular nanolayers (MNLs) of 3-mercaptan-propyl-trimethoxysilane to inhibit copper-transport across Cu–SiO2 interfaces more efficiently than the pristine MNLs. Bias-thermal-annealing tests of Cu/MNL/SiO2/Si(001)/Al capacitors, with MNLs exposed to 254 nm UV radiation, exhibit enhanced barrier properties to Cu diffusion, when compared with capacitors with MNLs not exposed to UV light. X-ray photoelectron spectroscopy reveals that UV exposure converts the mercaptan termini to sulfonates, which are more effective in inhibiting Cu diffusion. Our findings are of importance for tailoring the chemical and mechanical integrity of interfaces for use in applications such as nanodevice wiring and molecular electronics.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
66.30.H- Self-diffusion and ionic conduction in nonmetals
79.60.-i Photoemission and photoelectron spectra
84.32.Tt Capacitors

Spectrally narrowed edge emission from organic light-emitting diodes

Yun Tian, Zhengqing Gan, Zhaoqun Zhou, David W. Lynch, Joseph Shinar, Ji-hun Kang, and Q-Han Park

Appl. Phys. Lett. 91, 143504 (2007); http://dx.doi.org/10.1063/1.2778358 (3 pages) | Cited 6 times

Online Publication Date: 2 October 2007

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A dramatic spectrally narrowed edge emission (SNEE) from small molecular organic light-emitting diodes at room temperature, with a full width at half maximum of 5–10 nm, is described. The results show that this emission is due to irregular waveguide modes that leak from the indium tin oxide anode to the glass substrate at a grazing angle. Measurements of variable stripe length devices exhibit an apparent weak optical gain, but there is no observable threshold bias associated with this SNEE. Hence this apparent “optical gain” is suspected to result from misalignment of the propagating leaky waveguide mode and the collecting optics.
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85.60.Jb Light-emitting devices

In situ silicon oxide based intermediate reflector for thin-film silicon micromorph solar cells

P. Buehlmann, J. Bailat, D. Dominé, A. Billet, F. Meillaud, A. Feltrin, and C. Ballif

Appl. Phys. Lett. 91, 143505 (2007); http://dx.doi.org/10.1063/1.2794423 (3 pages) | Cited 45 times

Online Publication Date: 2 October 2007

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We show that SiO-based intermediate reflectors (SOIRs) can be fabricated in the same reactor and with the same process gases as used for thin-film silicon solar cells. By varying input gas ratios, SOIR layers with a wide range of optical and electrical properties are obtained. The influence of the SOIR thickness in the micromorph cell is studied and current gain and losses are discussed. Initial micromorph cell efficiency of 12.2% (Voc = 1.40 V, fill factor = 71.9%, and Jsc = 12.1 mA/cm2) is achieved with top cell, SOIR, and bottom cell thicknesses of 270, 95, and 1800 nm, respectively.
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84.60.Jt Photoelectric conversion

Enhancement of the allowed gradient in a dielectric-loaded superconducting cavity

Baleegh Abdo and Levi Schächter

Appl. Phys. Lett. 91, 143506 (2007); http://dx.doi.org/10.1063/1.2794432 (3 pages)

Online Publication Date: 2 October 2007

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It is shown that by incorporating a nonisotropic conductive thin film in a dielectric loaded super-conductive structure, it is possible to design an accelerator cavity wherein the maximum magnetic field at the surface of the superconductive material is below the critical value, although the gradient on axis may exceed 50 MV/m.
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29.20.-c Accelerators

Beryllium compensation doping of InAs/GaSb infrared superlattice photodiodes

Darin Hoffman, Binh-Minh Nguyen, Pierre-Yves Delaunay, Andrew Hood, Manijeh Razeghi, and Joe Pellegrino

Appl. Phys. Lett. 91, 143507 (2007); http://dx.doi.org/10.1063/1.2795086 (3 pages) | Cited 18 times

Online Publication Date: 2 October 2007

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Capacitance-voltage measurements in conjunction with dark current measurements on InAs/GaSb long wavelength infrared superlattice photodiodes grown by molecular-beam epitaxy on GaSb substrates are reported. By varying the beryllium concentration in the InAs layer of the active region, the residually n-type superlattice is compensated to become slightly p type. By adjusting the doping, the dominant dark current mechanism can be varied from diffusion to Zener tunneling. Minimization of the dark current leads to an increase of the zero-bias differential resistance from less than 4 to 32 Ω cm2 for a 100% cutoff of 12.05 μm
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Nonlinear thermal properties of three-terminal mesoscopic dielectric systems

Y. Ming, Z. X. Wang, Q. Li, and Z. J. Ding

Appl. Phys. Lett. 91, 143508 (2007); http://dx.doi.org/10.1063/1.2794799 (3 pages) | Cited 13 times

Online Publication Date: 3 October 2007

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This paper studies the thermal properties of three-terminal mesoscopic dielectric systems in the nonlinear response regime at low temperature. For a symmetric three-terminal system, when the temperature is finitely different between the left and right thermal reservoirs, the temperature of the central thermal reservoir is always higher than the averaging temperature of the others. This nonlinear thermal phenomenon is also observed for asymmetric three-terminal systems. At the end, a model of thermal rectification is presented.
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44.10.+i Heat conduction
73.23.Ad Ballistic transport
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Current-voltage characteristics of LiNbO3/La0.69Ca0.31MnO3 heterojunction and its tunability

S. M. Guo, Y. G. Zhao, C. M. Xiong, W. G. Huang, Z. H. Cheng, and X. X. Xi

Appl. Phys. Lett. 91, 143509 (2007); http://dx.doi.org/10.1063/1.2785113 (3 pages) | Cited 4 times

Online Publication Date: 4 October 2007

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The authors have fabricated LiNbO3/La0.69Ca0.31MnO3 heterojunctions by growing LiNbO3 on La0.69Ca0.31MnO3 single crystals. Rectifying behavior was found in these junctions, which can be tuned by applied magnetic field. A band diagram is proposed to account for the junction behavior. A voltage pulse-induced resistive switching was also observed, which can be understood by considering the ferroelectric polarization at the junction interface. The ability to tune transport properties of ferroelectric-ferromagnetic heterojunctions by magnetic field and electric polarization is potentially significant for their electronic applications.
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75.47.Lx Magnetic oxides
77.22.Ej Polarization and depolarization
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

13 GHz direct modulation of terahertz quantum cascade lasers

Stefano Barbieri, Wilfried Maineult, Sukhdeep S. Dhillon, Carlo Sirtori, Jesse Alton, Nicolas Breuil, Harvey E. Beere, and David A. Ritchie

Appl. Phys. Lett. 91, 143510 (2007); http://dx.doi.org/10.1063/1.2790827 (3 pages) | Cited 13 times

Online Publication Date: 4 October 2007

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By directly modulating the bias voltage of a double-metal waveguide, 2.8 THz quantum cascade laser, we observe the appearance of multiple gigahertz sidebands in the emission spectrum, with a spacing that can be continuously tuned up to 13 GHz. By using an upconversion technique, the terahertz spectrum is shifted at 1.57 μm, and displayed on an optical spectrum analyzer. A marked increase in the number of sidebands is observed when the modulation frequency approaches the round-trip frequency ( ∼ 12.3 GHz). The laser packaging high frequency response has been measured using a microwave rectification technique, and is limited by the bond-wire parasitic inductance.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
42.79.Gn Optical waveguides and couplers

Delayed-switch-on effect in metal-insulator-metal organic memories

M. L. Wang, J. Zhou, X. D. Gao, B. F. Ding, Z. Shi, X. Y. Sun, X. M. Ding, and X. Y. Hou

Appl. Phys. Lett. 91, 143511 (2007); http://dx.doi.org/10.1063/1.2794434 (3 pages) | Cited 13 times

Online Publication Date: 4 October 2007

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We report a delayed-switch-on effect in organic memories; i.e., the organic memory devices can automatically switch from off state to on state after a certain period of time when biased at voltages below the threshold voltage. Meanwhile, the lower the voltage is, the longer the switching time will be. The time scales from milliseconds to about 104 s with decreasing voltage. Moreover, by applying a certain voltage between threshold voltage and Vmax, intermediate states are also obtained. The existence of filamentary microconducting channels in the organic layer is proposed to be responsible for the observed switching phenomenon.
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85.30.Tv Field effect devices

A waveguide slit array antenna fabricated with subwavelength periodic grooves

Cheng Huang, Chunlei Du, and Xiangang Luo

Appl. Phys. Lett. 91, 143512 (2007); http://dx.doi.org/10.1063/1.2794727 (3 pages) | Cited 10 times

Online Publication Date: 4 October 2007

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This paper presents a waveguide slit array antenna with high gain and narrow beamwidth. This antenna is formed by subwavelength slits surrounded with periodic grooves. The far field radiation characteristics of the improved antenna are investigated. Simulation results show that the gain of the antenna with a designed working frequency is improved by 11 dB and a strong beam can be obtained. The physical mechanism for the performance improvement is governed by the resonance excitation of surface electromagnetic waves and can be well described by the coherent superposition of power radiated from the grooves and central slits.
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84.40.Ba Antennas: theory, components and accessories
84.40.Az Waveguides, transmission lines, striplines

Dielectric and piezoelectric properties of (K0.5Na0.5)NbO3–Ba(Zr0.05Ti0.95)O3 lead-free ceramics

Dunmin Lin, K. W. Kwok, and H. W. L. Chan

Appl. Phys. Lett. 91, 143513 (2007); http://dx.doi.org/10.1063/1.2794798 (3 pages) | Cited 22 times

Online Publication Date: 4 October 2007

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Lead-free ceramics (1−x)(K0.5Na0.5)NbO3–xBa(Zr0.05Ti0.95)O3 doped with 1 mol % MnO2 have been fabricated by pressureless sintering. With the MnO2 doping, all the ceramics can be well sintered at 1100–1160 °C and exhibit a dense and pure perovskite structure. After the addition of Ba(Zr0.05Ti0.95)O3, a relax behavior is induced and both the cubic-tetragonal and tetragonal-orthorhombic phase transitions shift to lower temperatures. Coexistence of the orthorhombic and tetragonal phases is hence formed in the ceramics with 0.04<x<0.07 at room temperature. It is suggested that owing to the more possible polarization states resulting from the coexistence of the two phases, the piezoelectric and dielectric properties of the ceramics are enhanced significantly. The ceramic with x = 0.06 exhibits the following optimum properties: d33 = 234 pC/N, kp = 0.49, kt = 0.48, εr = 1191, tan δ = 1.20%, and TC = 318 °C.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.-j Piezoelectricity and electromechanical effects
64.70.K- Solid-solid transitions
77.22.Ej Polarization and depolarization

Voltage-controlled variable light emissions from GaN codoped with Eu, Er, and Tm

L. Zhang, F. Q. Liu, and C. Liu

Appl. Phys. Lett. 91, 143514 (2007); http://dx.doi.org/10.1063/1.2795791 (3 pages) | Cited 4 times

Online Publication Date: 4 October 2007

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In this letter, a model to calculate the emission intensities of different rare-earth (RE) dopants in GaN is proposed based on the quantum collision theory and Judd-Ofelt approximation. The possible white light emission from Eu-, Er-, and Tm-codoped GaN is predicted according to the Commission International de I’Eclairage chromaticity diagram. Variable-wavelength emissions can be realized by adjusting the relative concentrations of different RE dopants in GaN and the bias voltage of the applied electric field. The availability of voltage-controlled light emissions and white light emission of the RE-doped GaN electroluminescent devices may have great potential for application in displays.
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78.55.Cr III-V semiconductors
78.60.Fi Electroluminescence
61.72.uj III-V and II-VI semiconductors
71.55.Eq III-V semiconductors
61.72.S- Impurities in crystals

Analysis of plasma oscillations in high-electron mobility transistorlike structures: Distributed circuit approach

I. Khmyrova and Yu. Seijyou

Appl. Phys. Lett. 91, 143515 (2007); http://dx.doi.org/10.1063/1.2794772 (3 pages) | Cited 6 times

Online Publication Date: 5 October 2007

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We develop simple distributed circuit model of the high-electron mobility transistor (HEMT)-like structure for the analysis of the effects associated with plasma oscillations excited in its two-dimensional electron gas (2DEG) channel. Circuit components of the model are related to physical and geometrical parameters of the structure. Developed model accounts for dependence of resistance and inductance of 2DEG channel gated region on gate voltage. Such an approach facilitates and improves understanding of HEMT-like structures’ behavior in the regime of excitation of plasma oscillation and is applicable for their performance evaluation and optimization as well.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
85.30.Tv Field effect devices
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Sensing electron transport in a blue-emitting copolymer by transient electroluminescence

Sebastian Bange, Andriy Kuksov, and Dieter Neher

Appl. Phys. Lett. 91, 143516 (2007); http://dx.doi.org/10.1063/1.2797991 (3 pages) | Cited 8 times

Online Publication Date: 5 October 2007

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A variation of the transient electroluminescence technique is introduced which allows us to selectively study the electron transport in a thin polymer layer. It relies on the formation of an insoluble interlayer from a formerly solvable polymer and enables probing of unipolar electron transport despite of injection barriers. It opens up possibilities to gain insight into the operation of light-emitting diodes. Applicability to a blue-emitting spirobifluorene-based copolymer is shown by comparison to time-of-flight results for electron and hole transport and evidence supplied for an intermixing of electron and hole dynamics through blocking of electrons at the polymer/anode interface.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Ee Mobility edges; hopping transport
72.25.Hg Electrical injection of spin polarized carriers
78.60.Fi Electroluminescence
64.75.-g Phase equilibria
82.45.Wx Polymers and organic materials in electrochemistry
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