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19 Aug 2002

Volume 81, Issue 8, pp. 1369-1534

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High-responsivity, normal-incidence long-wave infrared (λ ∼ 7.2 μm) InAs/In0.15Ga0.85As dots-in-a-well detector

S. Raghavan, P. Rotella, A. Stintz, B. Fuchs, S. Krishna, C. Morath, D. A. Cardimona, and S. W. Kennerly

Appl. Phys. Lett. 81, 1369 (2002); http://dx.doi.org/10.1063/1.1498009 (3 pages) | Cited 69 times

Online Publication Date: 9 August 2002

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Normal incidence InAs/In0.15Ga0.85As dots-in-a-well detectors operating at T = 78 K with λp ∼ 7.2 μm and a spectral width (Δλ/λ) of 35% are reported. The peak at 7.2 μm is attributed to the bound-to-bound transitions between the ground state of the dot and the states within the InGaAs well. A broad shoulder around 5 μm, which is attributed to the bound-to-continuum transition, is also observed. Calibrated blackbody measurements at a device temperature of 78 K yield a peak responsivity of 3.58 A/W (Vb = −1 V), peak detectivity = 2.7×109 cm Hz1/2/W (Vb = −0.3 V), conversion efficiency of 57% and a gain ∼25. © 2002 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
78.67.Hc Quantum dots

Thin-film lasers based on dye-deoxyribonucleic acid-lipid complexes

Y. Kawabe, L. Wang, T. Nakamura, and N. Ogata

Appl. Phys. Lett. 81, 1372 (2002); http://dx.doi.org/10.1063/1.1501164 (3 pages) | Cited 34 times

Online Publication Date: 9 August 2002

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Amplified spontaneous emission (laser action without cavities) from deoxyribonucleic acid (DNA) derivative films was achieved by doping with a hemicyanine dye which is well known as a nonlinear optical molecule. The amplification confirmed by spectral narrowing and superlinear dependence of the emission intensity on the pumping was observed from the complex films when the film samples were irradiated with a nanosecond laser at the intensity above a threshold value ( ∼ 20 μJ). The durability and low threshold values suggest the possibility of DNA complexes as a practical candidate for thin-film dye lasers. © 2002 American Institute of Physics.
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42.55.Mv Dye lasers
42.70.Hj Laser materials
87.14.G- Nucleic acids
42.65.-k Nonlinear optics

Ferroelectric BaTiO3 thin-film optical waveguide modulators

A. Petraru, J. Schubert, M. Schmid, and Ch. Buchal

Appl. Phys. Lett. 81, 1375 (2002); http://dx.doi.org/10.1063/1.1498151 (3 pages) | Cited 47 times

Online Publication Date: 9 August 2002

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High-quality BaTiO3 epitaxial thin films on MgO substrates have been grown by pulsed-laser deposition. Both, c-axis and a-axis BaTiO3 orientations were studied. Mach–Zehnder optical waveguide modulators with a fork angle of 1.7° have been fabricated by ion-beam etching. The waveguides are of the ridge type, the BaTiO3 thickness is 1 μm, the ridge step 50 nm, and the width 2 μm. Light was coupled into the waveguides from optical fibers. The BaTiO3 waveguide propagation losses are 2–3 dB/cm. Electrodes of 3 mm length were deposited besides the waveguides. Electro-optic modulation has been demonstrated with Vπ = 6.3 V at 632 nm wavelength and Vπ = 9.5 V at 1550 nm wavelength for the a-axis samples, and with Vπ = 8 V at 632 nm wavelength and Vπ = 15 V at 1550 nm for the c-axis samples. Theoretical modelling of the Mach–Zehnder modulators for both crystalline orientations of the BaTiO3 films gave the Pockels coefficients r51 = 80 pm/V for the c-axis film and an effective Pockels coefficient reff = 734 pm/V for the a-axis films at 632 nm wavelength. © 2002 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
42.82.Et Waveguides, couplers, and arrays
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
78.20.Jq Electro-optical effects
77.55.-g Dielectric thin films
81.15.Fg Pulsed laser ablation deposition
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Intervalley scattering in GaAs–AlAs quantum cascade lasers

L. R. Wilson, D. A. Carder, J. W. Cockburn, R. P. Green, D. G. Revin, M. J. Steer, M. Hopkinson, G. Hill, and R. Airey

Appl. Phys. Lett. 81, 1378 (2002); http://dx.doi.org/10.1063/1.1500775 (3 pages) | Cited 18 times

Online Publication Date: 9 August 2002

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We have investigated the importance of intervalley (Γ–Χ) electron transfer between Γ-point quantum well states and X-point barrier states in GaAs-based quantum cascade lasers with indirect band gap AlAs barriers. A series of samples has been studied in which the energy separation between the coupled injector/upper laser levels and the lowest confined X state in the injection barrier is varied. We demonstrate that for lasing to occur, electron injection into the upper laser level must proceed via Γ states confined below the lowest X state in the injection barrier. The limit this places on the minimum operating wavelength (λ ≈ 8 μm) for the present laser design is overcome by utilizing a double injection barrier to achieve lasing at λ = 7.2 μm. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.Fg Quantum wells

Low-threshold terahertz quantum-cascade lasers

Michel Rochat, Lassaad Ajili, Harald Willenberg, Jérôme Faist, Harvey Beere, Giles Davies, Edmund Linfield, and David Ritchie

Appl. Phys. Lett. 81, 1381 (2002); http://dx.doi.org/10.1063/1.1498861 (3 pages) | Cited 100 times

Online Publication Date: 9 August 2002

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A quantum-cascade laser operating at λ = 66 μm is demonstrated. It consists of a three-quantum-well chirped-superlattice active region embedded in a waveguide based on a single interface plasmon and a buried contact. A threshold current density of 210 A/cm2 at T = 12 K, a maximum peak optical power of 4 mW, and operation up to T = 44 K are achieved in a 2.7 mm long device with a high reflectivity backfacet coating. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
73.21.Fg Quantum wells
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Highly nondegenerate femtosecond four-wave mixing in tapered microstructure fiber

Kazi S. Abedin, Juliet T. Gopinath, Erich P. Ippen, Charles E. Kerbage, Robert S. Windeler, and Benjamin J. Eggleton

Appl. Phys. Lett. 81, 1384 (2002); http://dx.doi.org/10.1063/1.1501440 (3 pages) | Cited 11 times

Online Publication Date: 9 August 2002

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We demonstrate efficient, highly nondegenerate four-wave mixing of femtosecond pulses, with a frequency shift of ∼6000 cm−1, in an 18 cm tapered microstructure fiber. Using a pump at 810 nm and a signal at 1540 nm, light is generated at wavelengths between 535 nm and 570 nm with 10% efficiency. Due to the walk-off between pump and signal pulses in the fiber, the interaction length in the tapered fiber is only 1.4 cm. Ten percent efficiency is achieved in this short length because of the enhanced nonlinearity of the tapered fiber and its unique dispersion characteristics. © 2002 American Institute of Physics.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.81.Dp Propagation, scattering, and losses; solitons

Shrinkage- and refractive-index shift-corrected volume holograms for optical interconnects

Jing-Heng Chen, Der-Chin Su, and Jung-Chieh Su

Appl. Phys. Lett. 81, 1387 (2002); http://dx.doi.org/10.1063/1.1502022 (3 pages) | Cited 4 times

Online Publication Date: 9 August 2002

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The Bragg mismatching condition for volume holograms occurs because of the changes in the thickness and the refractive index of holographic recording materials during the recording and reconstruction procedures. We propose an improved compensation method to physically correct these effects in the fabrications of volume holograms for optical interconnects. In order to show the validity of this method, Slavich photographic plate VRP-M is used to fabricate optical interconnects. The correction of the Bragg diffraction angle shift of about 2.10°, which is induced by 6.14% film shrinkage and 0.06 refractive index shift, is successfully demonstrated with the surface-normal configuration. A shrinkage- and refractive-index shift-corrected volume hologram with 23% diffraction efficiency is experimentally confirmed. The methodology proposed is applicable to other phase media when the associated film shrinkage and refractive-index shift data are experimentally determined. © 2002 American Institute of Physics.
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42.40.Ht Hologram recording and readout methods
42.40.Lx Diffraction efficiency, resolution, and other hologram characteristics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.82.Ds Interconnects, including holographic interconnects

Continuous-wave 1664.7 nm fiber source utilizing four-wave mixing and stimulated Raman scattering

C. J. S. de Matos, D. A. Chestnut, and J. R. Taylor

Appl. Phys. Lett. 81, 1390 (2002); http://dx.doi.org/10.1063/1.1501454 (3 pages) | Cited 1 time

Online Publication Date: 9 August 2002

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We present a continuous-wave light source based on four-wave mixing and first- and second-order stimulated Raman scattering in a 9 km dispersion-shifted optical fiber. The source operates at 1664.7 nm with a 1.7 nm linewidth and a power up to 371 mW. Applications could be found in spectroscopy. © 2002 American Institute of Physics.
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42.55.Wd Fiber lasers
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.60.By Design of specific laser systems

Near-infrared holographic recording with quasi-nonvolatile readout in LiNbO3:In,Fe

Guoquan Zhang, Yasuo Tomita, Xinzheng Zhang, and Jingjun Xu

Appl. Phys. Lett. 81, 1393 (2002); http://dx.doi.org/10.1063/1.1503408 (3 pages) | Cited 4 times

Online Publication Date: 9 August 2002

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We investigate near-infrared photorefractivity and the dynamics of refractive index grating buildup and readout processes in reduced LiNbO3:In,Fe. High asymmetry in grating buildup and readout erasure rates is observed. This remarkable property makes the recorded grating quasinonvolatile during readout. The reason for the high asymmetry is explained qualitatively in terms of a multiple-defect-center model. © 2002 American Institute of Physics.
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42.40.Ht Hologram recording and readout methods
42.40.Eq Holographic optical elements; holographic gratings
42.70.Ln Holographic recording materials; optical storage media
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.79.Vb Optical storage systems, optical disks
71.38.Mx Bipolarons
42.70.Gi Light-sensitive materials

Waveguiding effects in the measurement of optical gain in a layer of Si nanocrystals

J. Valenta, I. Pelant, and J. Linnros

Appl. Phys. Lett. 81, 1396 (2002); http://dx.doi.org/10.1063/1.1502195 (3 pages) | Cited 66 times

Online Publication Date: 9 August 2002

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We discuss applicability of the variable stripe length method to experimental investigation of optical gain in a luminescent layer that behaves like a planar waveguide. We show that an interplay between the output direction of guided light modes and the numerical aperture of the collection optics may lead to an artifact manifesting itself as an apparent but false gain. We propose a way to circumvent this inconvenience by using a “shifting excitation spot” complementary measurement. The method is demonstrated on a layer of Si nanocrystals embedded into a synthetic silica plate. © 2002 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Ap Elemental semiconductors
42.70.Hj Laser materials
81.07.Bc Nanocrystalline materials

Multi-prism x-ray lens

Björn Cederström, Mats Lundqvist, and Carolina Ribbing

Appl. Phys. Lett. 81, 1399 (2002); http://dx.doi.org/10.1063/1.1501443 (3 pages) | Cited 12 times

Online Publication Date: 9 August 2002

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Refractive x-ray lenses with a triangular surface profile have been used to focus a synchrotron beam to sub-μm line width. These lenses are free from spherical aberration and work in analogy with one-dimensional focusing parabolic compound refractive lenses. However, the focal length can be easily varied by changing the gap between the two jaws. Silicon lenses were fabricated by wet anisotropic etching, and epoxy replicas were molded from the silicon masters. The lenses provided intensity gains up to a factor of 32 and the smallest focal line width was 0.87 μm. The simplified geometry and associated fabrication technique open possibilities for low-Z materials such as beryllium, which should greatly enhance the performance of refractive x-ray optics. © 2002 American Institute of Physics.
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41.50.+h X-ray beams and x-ray optics
42.79.Bh Lenses, prisms and mirrors
07.85.-m X- and γ-ray instruments

Triple-optical autocorrelation for direct optical pulse-shape measurement

Tzu-Ming Liu, Yin-Chieh Huang, Gia-Wei Chern, Kung-Hsuan Lin, Chih-Jie Lee, Yu-Chueh Hung, and Chi-Kuang Sun

Appl. Phys. Lett. 81, 1402 (2002); http://dx.doi.org/10.1063/1.1501453 (3 pages) | Cited 2 times

Online Publication Date: 9 August 2002

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Triple optical autocorrelation of femtosecond optical pulses was realized simply with third-harmonic-generation technique. This optical technique provides complete knowledge of transient pulse intensity variation directly in time domain. Only analytic calculation is needed to obtain the pulse-shape from data without direction-of-time ambiguity. Combined with a spectral measurement and the Gerchberg–Saxton algorithm, except for pulses with complete temporal and spectral symmetry that will cause a twofold ambiguity, exact phase variation in time can also be retrieved through an iterative calculation with an O(n) complexity. © 2002 American Institute of Physics.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
02.60.-x Numerical approximation and analysis
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
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Evidence of ionized metal clusters in ion plating discharges

A. D. Wilson, A. Davison, A. Leyland, A. Matthews, and K. S. Fancey

Appl. Phys. Lett. 81, 1405 (2002); http://dx.doi.org/10.1063/1.1501449 (3 pages) | Cited 1 time

Online Publication Date: 9 August 2002

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A quadropole mass-energy analyzer has been used to detect positively charged metal ions at the substrate (cathode) of an ion plating system. By studying titanium, evaporated into thermionically supported argon glow discharges at pressures of 1–4 Pa, we have detected the presence of ionized clusters of the vapor material up to the analyzer mass limit of 2500 a.m.u. In contrast, a similar analysis from an equivalent titanium-only discharge has revealed a relatively insignificant cluster detection rate. The results support an earlier prognosis that these clusters may nucleate and grow through vapor cooling, caused by collisions with gas atoms in the discharge. © 2002 American Institute of Physics.
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52.70.Nc Particle measurements
07.75.+h Mass spectrometers
52.77.Dq Plasma-based ion implantation and deposition
81.15.Jj Ion and electron beam-assisted deposition; ion plating

Temporally resolved cavity ring-down spectroscopy in a pulsed nitrogen plasma

A. P. Yalin, R. N. Zare, C. O. Laux, and C. H. Kruger

Appl. Phys. Lett. 81, 1408 (2002); http://dx.doi.org/10.1063/1.1500427 (3 pages) | Cited 14 times

Online Publication Date: 9 August 2002

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Cavity ring-down spectroscopy (CRDS) has enabled temporally resolved measurements of the N2+ ion concentration in a pulsed atmospheric pressure nitrogen plasma. A 10 ns voltage pulse is applied to a dc-sustained plasma to change the ionization fraction rapidly. Our measurements show that the pulse increases the N2+ ion concentration from 3.9×1012 to more than 1.5×1013 cm−3, and that the N2+ concentration returns to the dc level in about 10 μs. We also determine the electron density by measuring the electrical conductivity of the plasma. Because N2+ is the dominant ion, the good agreement between electrical and CRDS measurements provides validation of the temporally resolved CRDS technique. © 2002 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.-b Plasma properties
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment
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Molar volumes of molten indium at high pressures measured in a diamond anvil cell

Guoyin Shen, Nagayoshi Sata, Mathew Newville, Mark L. Rivers, and Stephen R. Sutton

Appl. Phys. Lett. 81, 1411 (2002); http://dx.doi.org/10.1063/1.1499737 (3 pages) | Cited 11 times

Online Publication Date: 9 August 2002

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Molar volumes of molten indium have been measured in an isothermal compression up to 8.5 GPa at 710(3) K in an externally heated diamond anvil cell. The measurement is based on the x-ray diffraction and x-ray absorption of materials using a synchrotron monochromatic x-ray microbeam. The fit to the results with the Birch–Murnaghan equation of state gives parameters of V0 = 16.80 cm3, K0 = 23.9(6) GPa, assuming that K′ = 4. This method should be applicable for measuring molar volumes of liquids and other amorphous materials in the diamond anvil cell. © 2002 American Institute of Physics.
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61.25.Mv Liquid metals and alloys
78.70.Dm X-ray absorption spectra
64.30.-t Equations of state of specific substances
62.50.-p High-pressure effects in solids and liquids
62.10.+s Mechanical properties of liquids

Silver as a sensitizer for erbium

C. Strohhöfer and A. Polman

Appl. Phys. Lett. 81, 1414 (2002); http://dx.doi.org/10.1063/1.1499509 (3 pages) | Cited 48 times

Online Publication Date: 9 August 2002

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The photoluminescence of Er3+in borosilicate glass is strongly enhanced by the presence of silver. Samples prepared by a combination of erbium ion implantation and Na+↔Ag+ ion exchange show an increase of the Er3+excitation efficiency of up to a factor 70 when excited at 488 nm. Excitation of Er3+ is possible over a broad wavelength range in the near ultraviolet and visible. Our data suggest that absorption of light occurs at a silver ion/atom pair or similar defect, followed by energy transfer to Er3+. We can exclude that silver nanocrystals are part of the dominant excitation mechanism, neither via local field enhancement effects due to their surface plasmon resonance nor via absorption and subsequent energy transfer to Er3+. © 2002 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.40.Ha Other nonmetallic inorganics
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
61.72.up Other materials
61.80.Jh Ion radiation effects
61.82.Ms Insulators

Thermal stability of polycrystalline silicon electrodes on ZrO2 gate dielectrics

Charles M. Perkins, Baylor B. Triplett, Paul C. McIntyre, Krishna C. Saraswat, and Eric Shero

Appl. Phys. Lett. 81, 1417 (2002); http://dx.doi.org/10.1063/1.1499513 (3 pages) | Cited 34 times

Online Publication Date: 9 August 2002

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Thermal stability of gate stack structures composed of ZrO2 gate dielectrics and silicon electrodes was investigated. The ZrO2 films were deposited by atomic layer deposition, while the polycrystalline silicon electrodes were deposited using different variants of chemical (CVD) and physical vapor deposition (PVD). Zirconium silicide formation was noted in all CVD-electroded samples after subsequent annealing treatments at temperatures above 750 °C, but not in the room temperature PVD-electroded samples, even after gate annealing at 1050 °C. The dependence of zirconium silicide formation on the Si deposition process was explained using thermodynamic arguments which explicitly include the effects of oxygen deficiency of the metal oxide films. © 2002 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
68.35.Ct Interface structure and roughness
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Cd Deposition by sputtering
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.37.Lp Transmission electron microscopy (TEM)

Spectroscopic ellipsometry study of optical transitions in Zn1−xCoxO alloys

Kwang Joo Kim and Young Ran Park

Appl. Phys. Lett. 81, 1420 (2002); http://dx.doi.org/10.1063/1.1501765 (3 pages) | Cited 111 times

Online Publication Date: 9 August 2002

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Zn1−xCoxO (x ⩽ 0.22) films were prepared on (0001)-oriented Al2O3 substrates by rf magnetron sputtering. The alloys show wurtzite crystal structure with the c-axis lattice constant increasing with increasing x. The optical properties of the samples were measured by spectroscopic ellipsometry at room temperature in the 1.5–5 eV photon energy region. As x increases, the optical band gap absorption edge (E0) of the alloys shows a redshift from that of pure ZnO, reaching 350 meV for x = 0.22. The excitonic character of the E0 edge is gradually reduced as x increases and is replaced by the three-dimensional critical-point shape. Optical absorption structures are also observed below the E0 edge near 2 eV and interpreted as due to the transitions between the crystal-field-split 3d levels of tetrahedral Co2+ ions substituting Zn2+ ions. © 2002 American Institute of Physics.
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78.40.Fy Semiconductors
78.66.Hf II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds
61.66.Fn Inorganic compounds
68.55.-a Thin film structure and morphology
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Lateral indium–indium pair correlations within the wetting layers of buried InAs/GaAs quantum dots

B. Shin, B. Lita, R. S. Goldman, J. D. Phillips, and P. K. Bhattacharya

Appl. Phys. Lett. 81, 1423 (2002); http://dx.doi.org/10.1063/1.1501760 (3 pages) | Cited 11 times

Online Publication Date: 9 August 2002

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We have investigated lateral In–In pair correlations within the wetting layers of buried InAs/GaAs quantum dots imaged with cross-sectional scanning tunneling microscopy. We quantified the number of In–In pairs along the [110] direction as a function of the spacing between them. Since the number of In–In pairs exceeds that of a randomly generated distribution of In atoms, significant lateral In clustering within the wetting layers is apparent. A comparison of the experimentally determined and randomly generated In–In pair distributions reveals nearest-neighbor In–In pair interaction energies similar to those calculated for InGaAs alloy surfaces [J. -H. Cho, S. B. Zhang, and A. Zunger, Phys. Rev. Lett. 84, 3654 (2000)]. The In–In pair correlations increase with high temperature annealing, indicating that vertical In–Ga interdiffusion occurs simultaneously with lateral In segregation. Together, these results suggest that initial In clustering in the wetting layer may be frozen at the surface during growth, and that annealing increases the effective sizes of these clusters, driving the system toward its segregated equilibrium state. © 2002 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
61.72.Cc Kinetics of defect formation and annealing
68.35.Fx Diffusion; interface formation

Deformation potentials of the E2(high) phonon mode of AlN

A. Sarua, M. Kuball, and J. E. Van Nostrand

Appl. Phys. Lett. 81, 1426 (2002); http://dx.doi.org/10.1063/1.1501762 (3 pages) | Cited 29 times

Online Publication Date: 9 August 2002

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AlN layers grown on (111)-oriented silicon substrates were studied by Raman spectroscopy. The deformation potentials of the nonpolar E2(high) phonon mode of hexagonal AlN were derived from phonon frequency shifts under biaxial stress applied to the layer. Stress was applied by mechanical bending of the wafer with resulting in-plane biaxial stress in AlN. The technique allows one to avoid the uncertainty of x-ray diffraction strain determination inherent to experimental methods commonly used for deformation potentials determination in III–V nitrides. The obtained values for the phonon deformation potentials are in reasonably good agreement with previous theoretical calculations. For pure biaxial stress, we determine a phonon frequency shift of 3 cm−1/GPa. © 2002 American Institute of Physics.
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78.66.Fd III-V semiconductors
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.30.Fs III-V and II-VI semiconductors
68.60.Bs Mechanical and acoustical properties
62.20.F- Deformation and plasticity

Healing kinetics of interfacial voids in GaAs wafer bonding

YewChung Sermon Wu and Guo-Zen Hu

Appl. Phys. Lett. 81, 1429 (2002); http://dx.doi.org/10.1063/1.1502194 (3 pages) | Cited 2 times

Online Publication Date: 9 August 2002

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A periodic structure of bonded GaAs wafers has been proposed for quasi-phase-matched second-harmonic generation. After bonding, voids were formed at the interface due to the natural topographical irregularities and contamination on the wafer surface. Within the voids, crystallites with diamond-shaped and dendritic geometries were found, which corresponded to the bonded regions. In this study, artificial voids were introduced at the bonded interface to study the growth kinetics of these crystallites, that is the healing kinetics of these voids. It was found that the crystallite geometries and the growth rates are controlled by the nucleation of new surface layers on the bonded planes, which was the slowest stage during the healing process. © 2002 American Institute of Physics.
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68.35.Dv Composition, segregation; defects and impurities
61.72.Qq Microscopic defects (voids, inclusions, etc.)
68.35.Ct Interface structure and roughness
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
68.35.Md Surface thermodynamics, surface energies
81.65.-b Surface treatments
81.05.Ea III-V semiconductors

Anisotropic liquid crystal gels for switchable polarizers and displays

Hongwen Ren and Shin-Tson Wu

Appl. Phys. Lett. 81, 1432 (2002); http://dx.doi.org/10.1063/1.1502021 (3 pages) | Cited 14 times

Online Publication Date: 9 August 2002

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An anisotropic liquid crystal gel with low operating voltage, high contrast ratio, broad bandwidth, wide viewing angle, and fast response time was demonstrated. In the voltage-off state, the gel is highly transparent. When the gel is activated by an electric field, light scattering occurs for the polarization along the molecular axis. By incorporating a λ/4 film between the gel and a reflector, this reflective device is useful for modulating unpolarized light. Potential applications of such anisotropic gel as a broadband switchable polarizer, reflective display, and transflective display are emphasized. © 2002 American Institute of Physics.
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42.70.Df Liquid crystals
82.70.Gg Gels and sols
42.79.Kr Display devices, liquid-crystal devices
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Carbon site switching in carbon-doped GaAs

J. Mimila-Arroyo, S. W. Bland, and A. Lusson

Appl. Phys. Lett. 81, 1435 (2002); http://dx.doi.org/10.1063/1.1502005 (3 pages)

Online Publication Date: 9 August 2002

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Carbon thermal stability in carbon-doped GaAs layers is studied. Epitaxial layers were grown by low-pressure metalorganic chemical vapor deposition extrinsically doped with an atomic carbon concentration around 1×1020 cm−3. The hole concentration is found to be a complex function of the annealing time, increasing from an initial value ∼ 7.2×1019 cm−3, to some intermediate value whereupon the hole concentration decreases before resuming its increase to a value consistent with the atomic concentration. The observed carrier loss and its subsequent recovery is explained by a double-site switch of one carbon from the CAs–Ga–CAs dimer. First, the carbon moves to an interstitial site Ci, where it behaves like a double donor, followed by a move to a more distant As substitutional site where it behaves as a normal shallow acceptor. This process allows to recover an additional hole concentration equal to the initial carbon dimer concentration. Both processes follow a first-order kinetics with different kinetic coefficients. © 2002 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
61.72.uj III-V and II-VI semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.J- Point defects and defect clusters
68.60.Dv Thermal stability; thermal effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Measurement of the thermo-optic coefficients in sol-gel derived inorganic–organic hybrid material films

Eun-Seok Kang, Tae-Ho Lee, and Byeong-Soo Bae

Appl. Phys. Lett. 81, 1438 (2002); http://dx.doi.org/10.1063/1.1501448 (3 pages) | Cited 26 times

Online Publication Date: 9 August 2002

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Thermo-optic coefficients (dn/dT) of inorganic–organic hybrid material films prepared by sol-gel process of organoalkylsilanes are measured using the prism coupler equipped with autocontrolled hot stage. In order to validate the reliability of this method, dn/dT of polymethylmethacrylate film is measured. dn/dT of inorganic–organic hybrid material films are negative and as high as the order of 10−4, which are comparable to those of optical polymers. Their dn/dT increase with increasing organic content in the film and mainly depend on their thermal expansion. © 2002 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
68.55.-a Thin film structure and morphology
61.41.+e Polymers, elastomers, and plastics
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
68.60.Dv Thermal stability; thermal effects
42.70.Jk Polymers and organics
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Theoretical and experimental investigation of boron diffusion in polycrystalline HfO2 films

Chun-Li Liu, Z. X. Jiang, R. I. Hegde, D. D. Sieloff, R. S. Rai, D. C. Gilmer, C. C. Hobbs, P. J. Tobin, and Shifeng Lu

Appl. Phys. Lett. 81, 1441 (2002); http://dx.doi.org/10.1063/1.1501766 (3 pages) | Cited 11 times

Online Publication Date: 9 August 2002

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We present ab initio modeling results including formation, migration, and activation energies for B diffusion through bulk and grain boundaries in polycrystalline HfO2 films. Modeling results clearly indicate that B can penetrate through a 40 Å HfO2 film via grain boundary diffusion, but not by bulk diffusion. Secondary ion mass spectroscopy analysis of B concentration profiles for polysilicon/HfO2/Si gate stacks after different anneals showed double B peaks at the interfaces and thus confirmed the modeling prediction. © 2002 American Institute of Physics.
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68.60.Wm Other nonelectronic physical properties
66.30.J- Diffusion of impurities
61.72.S- Impurities in crystals
61.72.Mm Grain and twin boundaries
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
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