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5 Jan 2004

Volume 84, Issue 1, pp. 1-157

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 151 (2004); http://dx.doi.org/10.1063/1.1637950 (3 pages)

M. Feng, N. Holonyak, and W. Hafez
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Linewidth enhancement factor and optical gain in (GaIn)(NAs)/GaAs lasers

N. C. Gerhardt, M. R. Hofmann, J. Hader, J. V. Moloney, S. W. Koch, and H. Riechert

Appl. Phys. Lett. 84, 1 (2004); http://dx.doi.org/10.1063/1.1638628 (3 pages) | Cited 23 times

Online Publication Date: 30 December 2003

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Experimental results on the linewidth enhancement factor α of 1.3 μm (GaIn)(NAs) lasers are presented and analyzed on the basis of a comparison with theoretical data obtained from a microscopic model. Our experimental data are obtained from the shift of the Fabry–Perot modes with injection current using an approach to eliminate temperature-dependent artifacts. At the emission wavelength at threshold we find a value of 2.5 for α which clamps for varying injection current. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes

Low-divergence coherent soft x-ray source at 13 nm by high-order harmonics

Eiji J. Takahashi, Yasuo Nabekawa, and Katsumi Midorikawa

Appl. Phys. Lett. 84, 4 (2004); http://dx.doi.org/10.1063/1.1637949 (3 pages) | Cited 54 times

Online Publication Date: 30 December 2003

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We have generated a few tens of nanojoules of coherent soft x-ray pulses at a wavelength around 13 nm with high-order harmonics. Output energy was estimated to be 25 nJ/pulse at the 59th harmonic (13.5 nm), and the beam divergence was measured to be 0.35 mrad full width at half maximum. Since a Mo/Si mirror covers two harmonics in the high reflectivity region, we can use ∼ 50 nJ harmonic energy per pulse in the 13 nm wavelength. This high-coherent low-emittance x-ray source is useful for the characterization and inspection of an optical system for extreme-ultraviolet lithography. © 2004 American Institute of Physics.
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42.25.Kb Coherence
42.79.Bh Lenses, prisms and mirrors
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors

Time-resolved photoluminescence measurements of InAs self-assembled quantum dots grown on misorientated substrates

L. Ya. Karachinsky, S. Pellegrini, G. S. Buller, A. S. Shkolnik, N. Yu. Gordeev, V. P. Evtikhiev, and V. B. Novikov

Appl. Phys. Lett. 84, 7 (2004); http://dx.doi.org/10.1063/1.1637962 (3 pages) | Cited 18 times

Online Publication Date: 30 December 2003

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Time-resolved photoluminescence decay measurements have been performed on samples with varying-sized self-assembled InAs/GaAs quantum dot ensembles, formed by substrate misorientation. Ground-state radiative recombination lifetimes from 0.8 to 5.3 ns in the incident power density range of 0.05–3400 W cm−2 at a temperature of 77 K have been obtained. It was found that a reduction of the quantum dot size led to a corresponding reduction of the radiative lifetime. The evident biexponential decay was obtained for the ground state emission of the quantum dot array, with the slower second component attributed to a carrier recapturing process. © 2004 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
73.21.La Quantum dots
81.07.Ta Quantum dots
78.47.-p Spectroscopy of solid state dynamics

Coulomb explosion-induced formation of highly oriented nanoparticles on thin films of 3C–SiC by the femtosecond pulsed laser

Yuanyuan Dong and Pal Molian

Appl. Phys. Lett. 84, 10 (2004); http://dx.doi.org/10.1063/1.1637948 (3 pages) | Cited 53 times

Online Publication Date: 30 December 2003

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We report the formation of highly oriented, uniform, and spherical nanoparticles of 3C–SiC as a result of Coulomb explosion during the interaction of near-infrared ultrafast laser pulses with 3C–SiC thin films grown on Si substrate. Experiments were performed at laser fluences well below the single shot, thermal modification threshold. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena

Observation of the discrete transition of optically trapped particle position in the vicinity of an interface

Hideki Fujiwara, Hidehisa Takasaki, Jun-ichi Hotta, and Keiji Sasaki

Appl. Phys. Lett. 84, 13 (2004); http://dx.doi.org/10.1063/1.1637947 (3 pages) | Cited 15 times

Online Publication Date: 30 December 2003

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Discrete transitions in the position of a particle optically trapped in the vicinity of an interface are observed using a nanometer position sensing system. These discrete transitions in the position with distance from the interface are attributed to interference effects due to reflection and scattering of the trapping laser beam from the interface and the particle. The discrete transitions occurred at uniform intervals of ∼ 400 nm, corresponding to the spacing of standing wave nodes of the trapping laser beam. © 2004 American Institute of Physics.
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37.10.Vz Mechanical effects of light on atoms, molecules, and ions

Self-frequency tripling from two cascaded second-order nonlinearities in GdAl3(BO3)4:Nd3+

Alain Brenier, Chaoyang Tu, Zhaojie Zhu, Jianfu Li, Yan Wang, Zhenyu You, and BaiChang Wu

Appl. Phys. Lett. 84, 16 (2004); http://dx.doi.org/10.1063/1.1637941 (3 pages) | Cited 20 times

Online Publication Date: 30 December 2003

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We combine inside a single noncentrosymmetric laser crystal, GdAl3(BO3)4:Nd3+, a stimulated emission and two second-order nonlinearities in cascade. The first one self-doubles the 1062.8 nm Nd3+ laser emission corresponding to the 4F3/2→4I11/2 channel, despite the fact that it is not phase-matched. The second one can be phase-matched or not and mixes the laser wave and its second harmonic (SH) in order to produce the third harmonic (TH) at 354.3 nm. © 2004 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.45.+h Stimulated emission

Refractive index perturbations in optical fibers resulting from frozen-in viscoelasticity

A. D. Yablon, M. F. Yan, P. Wisk, F. V. DiMarcello, J. W. Fleming, W. A. Reed, E. M. Monberg, D. J. DiGiovanni, J. Jasapara, and M. E. Lines

Appl. Phys. Lett. 84, 19 (2004); http://dx.doi.org/10.1063/1.1638883 (3 pages) | Cited 31 times

Online Publication Date: 30 December 2003

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We show that frozen-in viscoelasticity has a significant impact on the refractive index profile of optical fibers. Viscoelastic strains can be frozen into an optical fiber during draw, or by cooling down a drawn fiber from its fictive temperature while under tension. The resulting refractive index perturbation is concentrated in the highest viscosity region of the fiber, exhibits minimal birefringence, and can significantly alter critical performance characteristics. Our quantitative theory for the refractive index perturbation is in excellent agreement with measured data. Frozen-in viscoelasticity can also be harnessed to serve as the basis for optical fiber devices. © 2004 American Institute of Physics.
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42.81.Qb Fiber waveguides, couplers, and arrays
83.60.Df Nonlinear viscoelasticity
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Near-term aging and thermal behavior of polyfluorene in various aggregation states

H. Cheun, B. Tanto, W. Chunwaschirasiri, B. Larson, and M. J. Winokur

Appl. Phys. Lett. 84, 22 (2004); http://dx.doi.org/10.1063/1.1637431 (3 pages) | Cited 26 times

Online Publication Date: 30 December 2003

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Steady-stage photoluminescence and photoabsorption have been used to characterize the impact of aggregation in various poly(di-n-alkylfluorene) thin films. Highly aggregated films exhibit systematic changes in the photoluminescence while aging. These are indicative of a gradual increase in interchain interactions. Nonaggregated films do not exhibit this behavior. However the mesomorphic properties are altered and these films undergo irreversible changes on thermal cycling. All these properties appear to be correlated with changes in the local short-range molecular packing. © 2004 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
78.66.Qn Polymers; organic compounds
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
78.55.Kz Solid organic materials
78.40.Me Organic compounds and polymers

Time-resolved analysis of the white photoluminescence from SiO2 films after Si and C coimplantation

P. Pellegrino, A. Pérez-Rodriguez, B. Garrido, O. González-Varona, J. R. Morante, S. Marcinkevicius, A. Galeckas, and J. Linnros

Appl. Phys. Lett. 84, 25 (2004); http://dx.doi.org/10.1063/1.1634692 (3 pages) | Cited 17 times

Online Publication Date: 30 December 2003

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The analysis of the white photoluminescence (PL) from Si+ and C+ coimplanted SiO2 is reported as a function of the implanted dose. By both steady and time-resolved measurements, the presence of several components in the emission between 2 and 3.3 eV has been resolved. The decays of the PL transients are characterized by short lifetimes, below 2 ns. For the emission at 2.1–2.3 eV, photoluminescence decay transients have been measured, obtaining a fast relaxation component of about 50–70 ps, followed by a slower component of the order of 1 ns. These values contrast with the very slow behavior, characteristic for the light emission from Si nanocrystals, and make carbon-related emitting centers interesting for optoelectronic applications where fast switching behavior is important. © 2004 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.47.-p Spectroscopy of solid state dynamics
78.66.Nk Insulators
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.up Other materials

Thermal stability and decomposition of the HfO2–Al2O3 laminate system

Hyo Sik Chang, Hyunsang Hwang, Mann-Ho Cho, Dae Won Moon, Seok Joo Doh, Jong Ho Lee, and Nae-In Lee

Appl. Phys. Lett. 84, 28 (2004); http://dx.doi.org/10.1063/1.1637955 (3 pages) | Cited 8 times

Online Publication Date: 30 December 2003

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The thermal stability of the HfO2–Al2O3 laminate gate stack grown by atomic layer chemical vapor deposition was investigated using medium-energy ion scattering spectroscopy and high-resolution x-ray photoelectron spectroscopy. The laminate structure was maintained up to 800 °C under ultrahigh vacuum conditions, while it was drastically degraded at 850 °C, resulting in silicide formation on the film surface. Dissociated oxygen in the Hf–Al-oxide preferentially diffuses out through the film and desorbing at the surface. Volatile SiO species and Al–O components desorb through the sample surface, while HfO2 contributes to Hf silicide formation on the film surface. © 2004 American Institute of Physics.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.60.Dp Adsorbed layers and thin films

Temperature memory effect of a nickel–titanium shape memory alloy

Yanjun Zheng, Lishan Cui, and Jan Schrooten

Appl. Phys. Lett. 84, 31 (2004); http://dx.doi.org/10.1063/1.1637958 (3 pages) | Cited 35 times

Online Publication Date: 30 December 2003

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An incomplete transformation cycle induces a kinetic stop in the following complete transformation cycle in shape memory alloys. Therefore, the kinetic stop can be regarded as a memory of the previous arrest temperature. Herein, we show that the temperature memory effect of a nickel–titanium shape memory alloy can be expanded to be operational in a very wide temperature range by prestraining and constraining, which may be exploited for various practical applications. © 2004 American Institute of Physics.
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81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep

Structural stability of BeH2 at high pressures

P. Vajeeston, P. Ravindran, A. Kjekshus, and H. Fjellvåg

Appl. Phys. Lett. 84, 34 (2004); http://dx.doi.org/10.1063/1.1637967 (3 pages) | Cited 17 times

Online Publication Date: 30 December 2003

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The electronic structure and structural stability of BeH2 are studied using first-principles density-functional calculation. The calculated structural parameters for α-BeH2 at the equilibrium volume are in very good agreement with experiments. At higher pressures α-BeH2 successively undergoes four structural transitions: (i) α- to β-BeH2 at 7.07 GPa; (ii) β- to γ-BeH2 at 51.41 GPa; (iii) γ- to δ-BeH2 at 86.56 GPa; and (iv) δ- to ϵ-BeH2 at 97.55 GPa [an effective two-phase (γ and δ) region is found at 73.71–86.56 GPa]. Density of states studies reveal that BeH2 remains insulating up to 100 GPa whereupon anomalous changes are seen in the band-gap region with increasing pressure. © 2004 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Ps Other inorganic compounds

CaAl-based bulk metallic glasses with high thermal stability

F. Q. Guo, S. J. Poon, and G. J. Shiflet

Appl. Phys. Lett. 84, 37 (2004); http://dx.doi.org/10.1063/1.1637940 (3 pages) | Cited 63 times

Online Publication Date: 30 December 2003

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We report that binary Ca–Al alloys can be readily cast into amorphous rods of 1 mm in diameter. Upon further alloying to depress the liquidus temperature, the amorphous rod diameter is increased to 3 mm. The high glass transition temperature Tg ∼ 210 °C and crystallization onset temperature Tonset ∼ 240 °C or higher observed are attributed to the covalent bonding trend noted in Ca–Al alloys that exhibit complex network structures. Along with a high microhardness value of 200–235 DPH (diamond pyramid hardness) and low mass densities of 2 gm/cm3, these thermally stable light-metal alloys are recognized as potential structural amorphous metals. © 2004 American Institute of Physics.
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81.05.Kf Glasses (including metallic glasses)
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.43.Fs Glasses
68.35.Gy Mechanical properties; surface strains

Fast electro-optic switching in nematic liquid crystals

Anca-Luiza Alexe-Ionescu, Andrei Th. Ionescu, Emil S. Barna, Valentin Barna, and Nicola Scaramuzza

Appl. Phys. Lett. 84, 40 (2004); http://dx.doi.org/10.1063/1.1637961 (3 pages) | Cited 1 time

Online Publication Date: 30 December 2003

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The switching between on and off states of nematic liquid crystal pixels can be controlled with the well-known electro-optic effect. This effect however presents a fast response at switching on the electric field but a slow response at switching it off. Here we show a suitable choice of materials, cell geometries, surface preparations, and time dependence of the applied voltage that leads to a switch off response as fast as that at switch on. This is due to the particular conductivity mechanism in polymers with aromatic rings leading to rectifying properties when deposited on top of indium tin oxide surface. A transient negative charge at polymer–liquid crystal interface favors a faster and stronger planar orientation of the nematic molecules diminishing drastically the switch off time and increasing the contrast ratio. These facts, interesting enough from a fundamental point of view, could also lead to important technological consequences. © 2004 American Institute of Physics.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
78.20.Jq Electro-optical effects
78.66.Qn Polymers; organic compounds
42.70.Df Liquid crystals
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.79.Kr Display devices, liquid-crystal devices
61.30.Vx Polymer liquid crystals

High-gain photorefractive reflection gratings in layered photoconductive polymers

O-Pil Kwon, Germano Montemezzani, Peter Günter, and Suck-Hyun Lee

Appl. Phys. Lett. 84, 43 (2004); http://dx.doi.org/10.1063/1.1638900 (3 pages) | Cited 12 times

Online Publication Date: 30 December 2003

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Large two-wave mixing gain in reflection grating geometry is obtained in layered organic photorefractive polymers doped with the chromophore piperidinodicyanostyrene. With an applied field of 60 V/μm and for a grating spacing of 0.205 μm, one measures a two-wave mixing gain coefficient of 104 cm−1 and a diffraction efficiency of 4.8% in 100-μm-thick samples. Our photorefractive and electrochemical investigations suggest that the excellent material performance in reflection grating geometry is associated with an increased effective number of trapping sites. © 2004 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.40.Eq Holographic optical elements; holographic gratings
72.80.Le Polymers; organic compounds (including organic semiconductors)

Observation of backflow in the switch-on dynamics of a hybrid aligned nematic

S. A. Jewell and J. R. Sambles

Appl. Phys. Lett. 84, 46 (2004); http://dx.doi.org/10.1063/1.1638903 (3 pages) | Cited 9 times

Online Publication Date: 30 December 2003

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The optical convergent-beam technique is used to measure, in 0.3 ms steps, the response of the director in a 4.6-μm-thick ZLI-2293 filled hybrid aligned nematic cell when a 10 kHz, 7 Vrms ac voltage is applied to the cell. The total time taken for the reorientation process is 2.4 ms, with backflow observed during the first 1.5 ms after the application of the voltage. The measured director profiles show excellent agreement with theoretical profiles produced from the Leslie–Eriksen–Parodi theory using typical values for the viscosity coefficients. Fluid velocity profiles within the cell are also modeled. © 2004 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
83.80.Xz Liquid crystals: nematic, cholesteric, smectic, discotic, etc.

Carrier dynamics of high-efficiency green light emission in graded-indium-content InGaN/GaN quantum wells: An important role of effective carrier transfer

Yuanping Sun, Yong-Hoon Cho, E.-K. Suh, H. J. Lee, R. J. Choi, and Y. B. Hahn

Appl. Phys. Lett. 84, 49 (2004); http://dx.doi.org/10.1063/1.1637959 (3 pages) | Cited 15 times

Online Publication Date: 30 December 2003

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Optical properties and carrier dynamics of high-efficiency green-light-emitting InGaN/GaN multiple quantum wells (MQWs) with graded-In-content were studied by photoluminescence (PL), PL excitation, and time-resolved PL techniques. Two separated InGaN-related peaks were clearly found in PL spectra due to strong phase separation in the well of the graded-In-content InGaN MQWs. The integrated intensity of the main InGaN green emission ( ∼ 510 nm) decreased by only about a factor of 7 with increasing temperature from 10 to 300 K, indicating strong carrier localization and high quantum efficiency. Strong carrier transfer from low-In-content region with weak carrier localization to high-In-content part with strong carrier localization was observed by time-resolved PL. Therefore, we conclude that the effective carrier transfer from weakly to strongly localized states plays an important role to enhance brightness and quantum efficiency in the green-light-emitting InGaN MQWs with graded-In content. © 2004 American Institute of Physics.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
73.63.Hs Quantum wells
68.65.Fg Quantum wells
78.47.-p Spectroscopy of solid state dynamics

Optical properties of metallic nanoparticles in Ni-ion-implanted α-Al2O3 single crystals

X. Xiang, X. T. Zu, S. Zhu, and L. M. Wang

Appl. Phys. Lett. 84, 52 (2004); http://dx.doi.org/10.1063/1.1636817 (3 pages) | Cited 20 times

Online Publication Date: 30 December 2003

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64 keV Ni ion implantation was performed at room temperature up to a dose of 1×1017 cm−2 in α-Al2O3 single crystals. The charge states, structure, and optical properties of metallic embedded Ni nanoparticles were studied by using x-ray photoelectron spectroscopy (XPS), transmission electron microscopy, and optical spectroscopy, respectively. XPS analysis showed that implanted Ni ions are mainly in charge state of metallic Ni0. Nanoparticles distributed from the surface to 30 nm below the surface were observed in a high-angle annular dark-field image. The size of nanoparticles ranges from 1 to 5 nm in diameter. A high-resolution electron microscopy image indicated the Ni-implanted area had been entirely amorphized. A new broad absorption band centered at 400 nm appeared in the optical absorption spectrum of the as-implanted crystal, due to surface plasma resonance of Ni nanoparticles. We did not find any emission band in the as-implanted sample under a Xe lamp excitation wavelength of 250–430 nm in a spectrophotometer. © 2004 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.72.up Other materials
61.46.-w Structure of nanoscale materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Spectral investigation for phosphorescent polymer light-emitting devices with doubly doped phosphorescent dyes

Fangzhong Shen, Hong Xia, Chengbo Zhang, Dong Lin, Xiaodong Liu, and Yuguang Ma

Appl. Phys. Lett. 84, 55 (2004); http://dx.doi.org/10.1063/1.1629795 (3 pages) | Cited 13 times

Online Publication Date: 30 December 2003

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The photoluminescence and electroluminescence (EL) spectral characteristics of two phosphorescent dyes, green fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)3] and red tris-(4,7-diphenyl-1,10-phenanthroline)rhenium dications [Ru(4,7-Ph2-phen)3]2+, doubly doped poly(N-vinylcarbazol) (PVK) films were investigated. The efficient energy transfers from PVK host to both Ir(ppy)3 and [Ru(4,7-Ph2-phen)3]2+ dopants were observed in photoexcitation and EL devices. The intensity ratio (Ri) of red emission versus green emission as function of doping ratio (Rc) of [Ru(4,7-Ph2-phen)3]2+ and Ir(ppy)3 in PVK host is found according to a power-law function with the slopes of 2.28±0.2 for PL which obey the power-law with Ri–Rc2 predicated by Förster energy transfer model. EL spectra show a driving voltage depentent power law of Ri–Rc1.53±0.14 at low voltage and Ri–Rc1.16±0.08 at high voltage, respectively. The shift in the power law of Förster energy transfer is likely due to additional emission mechanisms such as carrier trapping and triplet exciton saturation at high current density. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Localization versus field effects in single InGaN quantum wells

A. Bell, J. Christen, F. Bertram, F. A. Ponce, H. Marui, and S. Tanaka

Appl. Phys. Lett. 84, 58 (2004); http://dx.doi.org/10.1063/1.1638880 (3 pages) | Cited 17 times

Online Publication Date: 30 December 2003

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The optical properties of InxGa1−xN quantum wells (x = 0.13) have been studied by cathodoluminescence (CL) spectroscopy. A blueshift of the quantum well emission is observed with increasing excitation density, which can be explained by considering (a) band filling of in-plane potential fluctuations caused by compositional inhomogeneities, or (b) screening of piezoelectric fields inside the well. We have used time-resolved CL spectroscopy to distinguish between the two effects. The onset and decay of the relaxation and recombination kinetics are measured by using rectangular excitation pulses with ultrafast on and off switching and with pulse lengths sufficiently long to ensure excitation into quasi-steady-state conditions. For well widths of Lz ⩽ 6 nm, a redshift is observed after the electron beam is switched on and a further redshift occurs after the electron beam is switched off. For Lz ≥ 8 nm, a blueshift is observed after the electron beam is switched on and a redshift is observed after the electron beam is switched off. We attribute the different behaviors to the dominance of localization effects for Lz ⩽ 6 nm and the dominance of field effects for Lz ≥ 8 nm. © 2004 American Institute of Physics.
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78.67.De Quantum wells
78.60.Hk Cathodoluminescence, ionoluminescence
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Effect of acidic and basic surface dipoles on the depletion layer of indium tin oxide as measured by in-plane conductance

A. L. Swint and P. W. Bohn

Appl. Phys. Lett. 84, 61 (2004); http://dx.doi.org/10.1063/1.1638630 (3 pages) | Cited 7 times

Online Publication Date: 30 December 2003

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Four-point probe measurements of indium tin oxide (ITO) films demonstrate the ability to decrease or increase in-plane resistance by surface treatment with acids or bases, respectively. Treatment of ITO surfaces with solutions of varying pH indicates that the degree of protonation or hydroxylation of basic or acidic surface sites, respectively, alters the n-type depletion layer depth and consequently affects the in-plane conductance. Modifying the ITO surface with a series of nearly constant-pH tetraalkylammonium hydroxide species reveals that the in-plane conductance is also modulated by the size of the adsorbed surface dipole layer. The overall change in in-plane conductance upon acid or base treatment is attributed to the net effect of surface charge and adsorbed dipole layer magnitude. Due to the intrinsically high signal–to–noise ratio of the in-plane resistance, these observations have implications for the use of ITO in condensed phase sensing applications. © 2004 American Institute of Physics.
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82.30.Nr Association, addition, insertion, cluster formation
73.61.Ng Insulators

Pulse-induced quantum interference of intersubband transitions in coupled quantum wells

T. Müller, W. Parz, G. Strasser, and K. Unterrainer

Appl. Phys. Lett. 84, 64 (2004); http://dx.doi.org/10.1063/1.1638881 (3 pages) | Cited 22 times

Online Publication Date: 30 December 2003

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We report the measurement of the transient intersubband absorption in a coupled quantum well semiconductor structure. Pulsed interband excitation is used to prepare a coherent population in the two lowest states of a three level system of electronic subbands. The time-dependent absorption to the upper state is probed by midinfrared time-domain spectroscopy. For certain pump–probe delay times we observe in the intersubband absorption spectra typical signatures of quantum interference: regions with reduced or enhanced absorption. © 2004 American Institute of Physics.
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73.23.-b Electronic transport in mesoscopic systems
71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states
73.21.Fg Quantum wells
78.47.-p Spectroscopy of solid state dynamics
78.30.Fs III-V and II-VI semiconductors

Pressure dependence of the fundamental band-gap energy of CdSe

W. Shan, W. Walukiewicz, J. W. Ager, K. M. Yu, J. Wu, and E. E. Haller

Appl. Phys. Lett. 84, 67 (2004); http://dx.doi.org/10.1063/1.1638879 (3 pages) | Cited 18 times

Online Publication Date: 30 December 2003

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Pressure-dependent photomodulation spectroscopic studies of the optical transition associated with the fundamental bandgap of single-crystal bulk CdSe are presented. Photomodulated transmission (PT) measurements were performed at room temperature as a function of applied hydrostatic pressure using the diamond-anvil-cell technique. The sharp, derivative-like PT spectral features corresponding to the band-gap transition in CdSe were found to shift linearly toward higher energy with increasing pressure. By examining the pressure dependence of the PT spectra, the pressure coefficient for the direct band gap of wurtzite CdSe was determined to be 43.1 meV/GPa. The hydrostatic deformation potential of the band gap was found to be −2.3 eV. © 2004 American Institute of Physics.
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71.20.Nr Semiconductor compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Millimeter wave emission from GaN high electron mobility transistor

Yanqing Deng, Roland Kersting, Jingzhou Xu, Ricardo Ascazubi, Xi-Cheng Zhang, Michael S. Shur, Remis Gaska, Grigory S. Simin, M. Asif Khan, and Victor Ryzhii

Appl. Phys. Lett. 84, 70 (2004); http://dx.doi.org/10.1063/1.1638625 (3 pages) | Cited 25 times

Online Publication Date: 30 December 2003

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We report on millimeter wave electromagnetic radiation from a GaN high electron mobility transistor with the gate length of 1.5 μm at 8 K. The emission takes place at gate and drain voltages in the linear regime of operation but close to the saturation voltage with the principal emission peak at approximately 75 GHz, which is much higher than the device cut-off frequency. An explanation of this effect involves the “shallow water” plasma wave instability, with the frequency of the plasma waves decreased by the ungated regions of the device. © 2004 American Institute of Physics.
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85.30.Tv Field effect devices
84.40.-x Radiowave and microwave (including millimeter wave) technology
73.50.Mx High-frequency effects; plasma effects

Photoemission study of hole-injection enhancement in organic electroluminescent devices with Au/CFx anode

J. X. Tang, Y. Q. Li, L. S. Hung, and C. S. Lee

Appl. Phys. Lett. 84, 73 (2004); http://dx.doi.org/10.1063/1.1637945 (3 pages) | Cited 14 times

Online Publication Date: 30 December 2003

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We demonstrate hole-injection enhancement from Au into N,N′-bis-(1-naphyl)-N,N′diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) by inserting between them a plasma-polymerized fluorocarbon (CFx) buffer layer. Ultraviolet and x-ray photoemission spectroscopic study indicates that chemically tailoring the Au surface with CFx can reduce the hole-injection barrier to ∼1 eV with respect to bare Au. This effect is ascribed to the buildup of an interfacial electric field, arising from the molecular dipolar characteristic of CFx. The present results suggest that CFx can function as a hole-injection enhancement layer for organic optoelectronic/electronic devices which use a metallic anode. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
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