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18 May 1998

Volume 72, Issue 20, pp. 2499-2618

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Improved performance of a wavelength converter based on dual pump four-wave mixing in a bulk semiconductor optical amplifier

I. Tomkos, I. Zacharopoulos, D. Syvridis, T. Sphicopoulos, C. Caroubalos, and E. Roditi

Appl. Phys. Lett. 72, 2499 (1998); http://dx.doi.org/10.1063/1.121399 (3 pages) | Cited 10 times

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Very high conversion efficiency (6.5 dB for 23.4 nm down-wavelength shift and 4.5 dB for 16 nm up-wavelength shift) is reported, using four-wave mixing in a bulk semiconductor optical amplifier. Based on a dual pump configuration where wavelength conversion is achieved by shifting one of the pumps, superior performance has been achieved in terms of both efficiency and the converted signal-to-background amplified spontaneous emission noise ratio, especially for very large wavelength shifts. Simple theoretical considerations are also discussed for the explanation of the improved performance of the converter. © 1998 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.55.Px Semiconductor lasers; laser diodes
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Nv Optical frequency converters

Unusual polarization dependent optical erasure of surface relief gratings on azobenzene polymer films

X. L. Jiang, L. Li, J. Kumar, D. Y. Kim, and S. K. Tripathy

Appl. Phys. Lett. 72, 2502 (1998); http://dx.doi.org/10.1063/1.121400 (3 pages) | Cited 36 times

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Direct formation of surface relief gratings at modest intensities on azobenzene polymers has recently been accomplished. Unusual optical erasure of these surface relief gratings was observed. It is found that the optical erasure is dependent on the polarization state of the erasing beam as well as that of the recording beams used to form the gratings. Thus, gratings when formed memorize the polarization states which created them and influence their erasure behaviors accordingly. Direct transfer of patterns by photoprinting through a phase mask has been achieved. © 1998 American Institute of Physics.
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42.70.Jk Polymers and organics
42.40.Eq Holographic optical elements; holographic gratings
42.70.Ln Holographic recording materials; optical storage media
42.79.Vb Optical storage systems, optical disks
42.40.Ht Hologram recording and readout methods

Signs of nonlinear refraction in chloroaluminum phthalocyanine solution

Tai-Huei Wei, Tzer-Hsiang Huang, and Mu-Shih Lin

Appl. Phys. Lett. 72, 2505 (1998); http://dx.doi.org/10.1063/1.121401 (3 pages) | Cited 24 times

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Opposite signs of nonlinear refraction in chloroaluminum (ClAl) phthalocyanine (Pc) dissolved in methanol are observed using the Z-scan technique with two output modes of a frequency-doubled, Q-switched, mode-locked Nd:YAG laser operating at 10 Hz. Using the single picosecond (ps) pulses switched out of the pulse trains, positive nonlinear refraction is observed and attributed to population transitions among ClAlPc’s singlet states. Using the full nanosecond pulse trains, a sign change of nonlinear refraction relative to that of single ps-pulse excitation is observed, and is attributed to the heat-induced temperature rise and the population relaxing to ClAlPc’s triplet states. © 1998 American Institute of Physics.
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42.65.-k Nonlinear optics
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.47.-p Spectroscopy of solid state dynamics

Nonreciprocal TE-mode phase shift by domain walls in magnetooptic rib waveguides

A. F. Popkov, M. Fehndrich, M. Lohmeyer, and H. Dötsch

Appl. Phys. Lett. 72, 2508 (1998); http://dx.doi.org/10.1063/1.121402 (3 pages) | Cited 14 times

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The nonreciprocal wave number shift of a TE-like mode propagating along a normally magnetized gyrotropic rib waveguide supporting a domain lattice is predicted theoretically using perturbation theory. The electromagnetic fields are calculated by the effective index method and by a more rigorous numerical method. Preliminary estimations for Bi-substituted iron garnets show that the maximum nonreciprocal phase shift of a TE-like mode may be comparable to that of a TM-like mode in a tangentially magnetized waveguide. © 1998 American Institute of Physics.
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42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
78.20.Ls Magneto-optical effects
75.70.Kw Domain structure (including magnetic bubbles and vortices)
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Influence of boundary conditions on time-reversal focusing through heterogeneous media

Mickaël Tanter, Jean-Louis Thomas, and Mathias Fink

Appl. Phys. Lett. 72, 2511 (1998); http://dx.doi.org/10.1063/1.121403 (3 pages) | Cited 5 times

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This letter presents a way to overcome ultrasonic focusing degradations through strongly diffracting nondissipative layers. A first set of experiments shows that, using finite aperture transducer arrays, neither the time-reversal technique, nor other focusing techniques are able to achieve proper focusing through this kind of aberrator. These experimental results show the limits of a finite aperture time-reversal mirror compared to the theoretical behavior of a time-reversal cavity. To simulate a time-reversal cavity, totally reflecting walls are set between the time-reversal mirror and the aberrator. The experiments and numerical simulations presented in this letter show that as soon as we introduce these reflecting boundaries, the time-reversal focusing becomes optimal and the spatial resolution is strongly improved. © 1998 American Institute of Physics.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.38.Ar Transducing principles, materials, and structures: general

A sonochemical approach to the surface synthesis of cadmium sulfide nanoparticles on submicron silica

N. Arul Dhas and A. Gedanken

Appl. Phys. Lett. 72, 2514 (1998); http://dx.doi.org/10.1063/1.120624 (3 pages) | Cited 42 times

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A sonochemical procedure for the preparation of cadmium sulfide (CdS) nanoparticles coated on submicron spherical silica particles has been described. Ultrasonic irradiation of a slurry of silica microspheres, cadmium sulfate, and thiourea in an aqueous medium for 3 h under ambient air yields cadmium sulfide–silica (CSS) composite. Heating the initial amorphous CSS nanocomposite at 150 °C for 1 h under a N2 atmosphere yields diffraction peaks assignable to the CdS phase. The transmission electron microscopy image of CSS shows that the CdS nanoparticles homogeneously coated on the silica (SiO2) carrier. The infrared spectroscopy illustrated the structural changes that occur when the amorphous SiO2 is coated with CdS nanoparticles ultrasonically. The photoluminescence spectrum of the CdS and CSS shows a broadband with a maximum centered around 560 nm, which is similar to that of quantum CdS particles. The sharp onset of a CSS emission band compared to that of the CdS emission band in the red region indicates that the SiO2 carrier provides a medium for controlling the aggregation of CdS nanoparticles. © 1998 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.05.Dz II-VI semiconductors
62.65.+k Acoustical properties of solids
81.07.-b Nanoscale materials and structures: fabrication and characterization
78.30.Fs III-V and II-VI semiconductors
78.55.Et II-VI semiconductors
81.20.-n Methods of materials synthesis and materials processing
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
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Nanosize diamond formation promoted by direct current glow discharge process: Synchrotron radiation and high resolution electron microscopy studies

I. Gouzman, A. Hoffman, G. Comtet, L. Hellner, G. Dujardin, and M. Petravic

Appl. Phys. Lett. 72, 2517 (1998); http://dx.doi.org/10.1063/1.121404 (3 pages) | Cited 20 times

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Diamond nucleation on Si(100) surfaces can be promoted by a dc-glow discharge process, using a CH4/H2 gas mixture. However, the phase composition and structure of the carbon film deposited during the dc-glow discharge pretreatment are still unclear. In the present work, we report on a combined study of near edge x-ray absorption fine structure (NEXAFS), and high resolution scanning electron microscopy (HR-SEM) of this film as a function of substrate temperature. NEXAFS measurements of the films deposited by the dc-glow discharge process render unambiguous evidence of diamond phase formation in the 880–900 °C substrate temperature range. It is determined from HR-SEM measurements that in this temperature range, nanosize diamond particles are formed. At lower and higher substrate temperatures the NEXAFS results indicate the predominant formation of graphitic carbon. The changes in the film composition as a function of substrate temperature during the dc-glow discharge process is expressed in terms of relative graphitic character (RGC) of the precursor film. © 1998 American Institute of Physics.
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81.05.ub Fullerenes and related materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
78.70.Dm X-ray absorption spectra
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology

Photoluminescence and electronic density of states in a-C:H films

F. Giorgis, F. Giuliani, C. F. Pirri, A. Tagliaferro, and E. Tresso

Appl. Phys. Lett. 72, 2520 (1998); http://dx.doi.org/10.1063/1.121405 (3 pages) | Cited 22 times

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The density of states in the energy region near Fermi level for hydrogenated amorphous carbon thin films is presented. The different types of states are identified in their origin and the problem of their detection is considered. It is shown that only some of these states are accessible to detection by electron spin resonance. A quantitative correlation between their density and the quantum efficiency of the room temperature photoluminescence process is achieved. Such correlation applies to films having a wide range of physical properties deposited by different techniques. © 1998 American Institute of Physics.
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78.66.Jg Amorphous semiconductors; glasses
78.55.Hx Other solid inorganic materials
71.23.Cq Amorphous semiconductors, metallic glasses, glasses

Pressure dependence of the negative bias voltage for stabilization of cubic boron nitride thin films deposited by sputtering

Wilfredo Otaño-Rivera, Lawrence J. Pilione, and Russell Messier

Appl. Phys. Lett. 72, 2523 (1998); http://dx.doi.org/10.1063/1.121407 (3 pages) | Cited 8 times

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Thin films of boron nitride were deposited by unbalanced magnetron sputtering at pressures between 0.065 and 1.32 Pa in order to study the effects of pressure and negative substrate bias on the energy of the bombarding plasma ions and subsequent stabilization of the cubic phase. It was found that the threshold bias voltage for nucleation of films with a high percentage of the cubic phase increases with the product of the pressure and sheath thickness. This trend is explained in terms of the changes in the average energy of the particles bombarding the growing film produced by pressure-dependent charge-exchange collisions in the plasma/substrate sheath. This energy modification process has predictable consequences in complex deposition processes. © 1998 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology

Piezoelectric actuator generating torsional displacement from piezoelectric d15 shear response

A. E. Glazounov, Q. M. Zhang, and C. Kim

Appl. Phys. Lett. 72, 2526 (1998); http://dx.doi.org/10.1063/1.121408 (3 pages) | Cited 7 times

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A torsional actuator generating angular displacement from piezoelectric shear strain was developed. The actuator is a tube consisting of an even number of segments poled along the length, which are adhesively bonded together, and the joints act as electrodes to apply the driving voltage. The experimental data measured on the prototype actuator: (i) prove the proposed concept of the torsional actuator, (ii) show that the actuator functions well under the torque load, and (iii) demonstrate that it has superior characteristics compared to previously reported designs of torsional actuators. © 1998 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Studies of metallic species and oxygen incorporation during sputter-deposition of SrBi2Ta2O9 films, using mass spectroscopy of recoiled ions

J. Im, A. R. Krauss, A. M. Dhote, D. M. Gruen, O. Auciello, R. Ramesh, and R. P. H. Chang

Appl. Phys. Lett. 72, 2529 (1998); http://dx.doi.org/10.1063/1.121409 (3 pages) | Cited 9 times

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We have recently developed a mass spectroscopy of recoiled ions technique which is suitable for monolayer-specific surface analysis of thin films during growth. We present initial results using this technique to study the effect of different bottom electrode layers on metallic species and oxygen incorporation in the early stages of SrBi2Ta2O3 (SBT) film growth via ion beam-sputter deposition. The work discussed here has been focused on studying the incorporation of Sr, Bi, and Ta during growth of SBT on Pt/Ti/SiO2/Si, Pt/MgO, Ti, and Si substrates. We found that the incorporation of Bi in sputter-deposited SBT films depends critically on the bottom electrode surface composition and the growth temperature. © 1998 American Institute of Physics.
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81.15.Cd Deposition by sputtering
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.35.Fx Diffusion; interface formation

Stress development during deposition of CNx thin films

E. Broitman, W. T. Zheng, H. Sjöström, I. Ivanov, J. E. Greene, and J.-E. Sundgren

Appl. Phys. Lett. 72, 2532 (1998); http://dx.doi.org/10.1063/1.121410 (3 pages) | Cited 30 times

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We have investigated the influence of deposition parameters on stress generation in CNx (0.3<x<0.5) thin films deposited onto Si(001) substrates by reactive magnetron sputtering of C in pure N2 discharges. Film stress, σ, which in all cases is compressive, decreases with an increase in the N2 pressure, PN2, due to structural changes induced by the pressure-dependent variation in the average energy of particles bombarding the film during deposition. The film stress σ is also a function of the film growth temperature, Ts, and exhibits a maximum value of ∼ 5 GPa at 350 °C. Under these conditions, the films have a distorted microstructure consisting of a three-dimensional, primarily sp2 bonded, network. In contrast, films deposited at Ts<200 °C with a low stress are amorphous. At 350 °C<Ts<600 °C, σ gradually decreases as Ts is increased and the microstructure becomes more graphitic and contains fewer defects. Nanoindentation measurements show that the films grown at 350 °C exhibit the highest hardness and elasticity. © 1998 American Institute of Physics.
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81.15.Cd Deposition by sputtering
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
61.43.Er Other amorphous solids
68.35.Gy Mechanical properties; surface strains
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

Long-range ferroelectric interactions in KTaO3/KNbO3 superlattice structures

H.-M. Christen, E. D. Specht, D. P. Norton, M. F. Chisholm, and L. A. Boatner

Appl. Phys. Lett. 72, 2535 (1998); http://dx.doi.org/10.1063/1.121411 (3 pages) | Cited 53 times

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Symmetric superlattice structures consisting of alternating atomic-scale layers of KTaO3 and KNbO3 with variable periodicity were grown on KTaO3 substrates by pulsed laser deposition. The in-plane structure of KNbO3 closely matches that of the KTaO3 substrate, resulting in KTaO3/KNbO3 heterostructures that are uniformly strained in-plane without misfit dislocations. This strain imposes an in-plane KNbO3 lattice spacing identical to that of the KTaO3 substrate for the temperature range 30 °C<T<700 °C, and a tetragonal-to-tetragonal transition is observed whose phase transition temperature Tc depends on the KNbO3 layer thickness. The in-plane strain results in a significant increase in this ferroelectric-paraelectric Tc for superlattices with relatively thick KNbO3 layers (Tc = 535 °C for a 17 nm thick layer, as compared to 435 °C for bulk KNbO3) and for K(Nb0.5Ta0.5)O3 random-alloy thin films. As the superlattice period decreases, a reduction of Tc is observed. For superlattices with periodicities of 50 Å or less, the Curie temperature is identical to that of the K(Ta0.5Nb0.5)O3 random-alloy film, indicating significant long-range ferroelectric coupling across the KTaO3 layers. © 1998 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.B- Phase transitions and Curie point
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Fg Pulsed laser ablation deposition

Oxygen and the thermal stability of thin CoSi2 layers

R. T. Tung

Appl. Phys. Lett. 72, 2538 (1998); http://dx.doi.org/10.1063/1.120625 (3 pages) | Cited 10 times

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The thermal stability of thin CoSi2 layers is demonstrated to improve with the use of oxygen-containing annealing ambients. Pinhole formation observed in 11–27 nm thick CoSi2 layers after anneals at 800 °C in nitrogen and vacuum is found to be eliminated when oxygen is used as the annealing ambient. A thin SiO2 layer grown during oxygen anneals, which curbs surface diffusion and reduces the rates of kinetic processes, is thought to be the primary reason for the retardation of layer agglomeration. The beneficial effect of air exposure and wet etches to the integrity of thin CoSi2 layers is also shown. These findings suggest the inclusion of oxygen in certain Co salicide processing steps.
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68.60.Dv Thermal stability; thermal effects
73.40.Ns Metal-nonmetal contacts
85.40.Ls Metallization, contacts, interconnects; device isolation
61.72.Cc Kinetics of defect formation and annealing
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Improvement of Ge self-organized quantum dots by use of Sb surfactant

C. S. Peng, Q. Huang, W. Q. Cheng, J. M. Zhou, Y. H. Zhang, T. T. Sheng, and C. H. Tung

Appl. Phys. Lett. 72, 2541 (1998); http://dx.doi.org/10.1063/1.121412 (3 pages) | Cited 26 times

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A Sb-mediated growth technique is developed to deposit Ge quantum dots (QDs) of small size, high density, and free of dislocations. These QDs were grown at low growth temperature by molecular beam epitaxy. The photoluminescence and absorption properties of these Ge QDs suggest an indirect-to-direct conversion, which is in good agreement with a theoretical calculation. © 1998 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
78.40.Fy Semiconductors

Two-dimensional network of dislocations and nanocavities in hydrogen-implanted and two-step annealed silicon

Min Gao, X. F. Duan, Fenglian Wang, and Jianming Li

Appl. Phys. Lett. 72, 2544 (1998); http://dx.doi.org/10.1063/1.121413 (3 pages) | Cited 5 times

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Conventional transmission electron microscopy and energy-filtering were used to study the dislocations and nanocavities in proton-implanted (001) silicon. A two-dimensional network of dislocations and nanocavities was found after a two-step annealing, while only isolated cavities were present in single-step annealed Si. In addition, two-step annealing increased materially the size and density of the nanocavities. The Burgers vector of the dislocations was mainly the 1/2〈110〉 type. The gettering of oxygen at the nanocavities was demonstrated. © 1998 American Institute of Physics.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Cy Elemental semiconductors
81.40.Gh Other heat and thermomechanical treatments
61.72.Cc Kinetics of defect formation and annealing
61.72.Yx Interaction between different crystal defects; gettering effect
81.65.Tx Gettering

Cross-sectional transmission electron microscopy analysis of {311} defects from Si implantation into silicon

K. Moller, Kevin S. Jones, and Mark E. Law

Appl. Phys. Lett. 72, 2547 (1998); http://dx.doi.org/10.1063/1.120623 (3 pages) | Cited 20 times

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Transient enhanced diffusion (TED) below the amorphization dose threshold is thought to be caused by the release of interstitials from {311} defects. The interstitials are annihilated by diffusion to and then recombination with the surface of the wafer. This would suggest that the layer of {311} defects formed from an implantation and anneal would dissolve from the surface down. Cross-section transmission electron microscopy (TEM) was used to investigate this hypothesis. It is shown that the {311} defects dissolve uniformly across the layer, and the width of the layer does not change until the {311} defects nearly completely dissolve. The total population was also measured using plan-view TEM, so that the dissolution and distribution functions could be plotted from the same annealing conditions. These data suggest that surface is not the limiting factor in the interstitial removal from {311} defects. © 1998 American Institute of Physics.
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61.72.uf Ge and Si
61.72.J- Point defects and defect clusters
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Cc Kinetics of defect formation and annealing
81.05.Cy Elemental semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Phase noise of a resonant-tunneling relaxation oscillator

S. Verghese, C. D. Parker, and E. R. Brown

Appl. Phys. Lett. 72, 2550 (1998); http://dx.doi.org/10.1063/1.121414 (3 pages) | Cited 6 times

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Experimental results are presented for the phase noise of a relaxation oscillator consisting of a resonant-tunneling diode in series connection with a transmission line, one end of which is shorted. Unlike constant-wave negative-resistance oscillators, the resonant-tunneling relaxation oscillator (RTRO) emits a sequence of sharp current pulses that are mode locked to the fundamental mode of the cavity formed by the short-circuited transmission line. The phase noise in the RTRO was investigated with and without injection locking by a weak sinusoidal source. Injection-locking gain of 51 dB was measured for fundamental injection locking. Subharmonic injection locking was demonstrated out to the 12th subharmonic. Also, timing jitter as low as 200 fs was measured for an RTRO that emitted ∼ 30 ps pulses at a repetition rate of 1.1 GHz. © 1998 American Institute of Physics.
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84.30.Ng Oscillators, pulse generators, and function generators
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Diffusion of Pt in molecular beam epitaxy grown ZnSe

J. Slotte, R. Salonen, T. Ahlgren, J. Räisänen, E. Rauhala, and P. Uusimaa

Appl. Phys. Lett. 72, 2553 (1998); http://dx.doi.org/10.1063/1.121415 (3 pages) | Cited 3 times

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Diffusion of platinum in zinc selenide has been studied by the use of the 4He and 12C ion backscattering techniques. The samples were thin films grown by molecular beam epitaxy on GaAs (100) epitaxial layers followed by evaporation of platinum and annealing in the temperature range 500–800 °C. The diffusion coefficients were determined by the fitting of a concentration independent solution of the diffusion equation to the experimental depth profiles. The activation energy and the pre-exponential factor of the diffusion process were found to be 1.7 eV and 6.4×10−6 cm2/s, respectively. © 1998 American Institute of Physics.
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66.30.J- Diffusion of impurities
68.60.Wm Other nonelectronic physical properties
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.70.Jb Chemical composition analysis, chemical depth and dopant profiling
61.72.S- Impurities in crystals

Excitation of size selected nanocrystallites in porous silicon

Zain Yamani, Nicholaos Rigakis, and Munir H. Nayfeh

Appl. Phys. Lett. 72, 2556 (1998); http://dx.doi.org/10.1063/1.121416 (3 pages) | Cited 8 times

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We prepared silicon that exhibits green-to-red rainbow luminescence along the sample, reflecting gradients in the crystallite size. The excitation has a size-dependent feature, riding a smooth bulklike continuum. For the size-dependent contribution, we measured absorption band edges of 3.75 and 3.0–3.25 eV at the meniscus and opposite end. Excitation in the meniscus, monitored at the edge of the blue emission, isolates ultrasmall sizes, with “excitation coefficients” quadratic with energy, and emission encompassing much of the visible spectrum. Results are discussed in terms of quantum-confinement-induced restructuring of the diamondlike bonds to form radiative Si–Si surface states. © 1998 American Institute of Physics.
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78.55.Mb Porous materials
78.55.Ap Elemental semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.46.-w Structure of nanoscale materials

Raman analysis of short-range clustering in laser-deposited CdSxTe1−x films

A. Fischer, L. Anthony, and A. D. Compaan

Appl. Phys. Lett. 72, 2559 (1998); http://dx.doi.org/10.1063/1.121417 (3 pages) | Cited 14 times

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Raman line shapes of the longitudinal optical phonon have been analyzed for the pseudobinary alloy system CdSxTe1−x over the full alloy range. The polycrystalline thin films were grown by pulsed laser deposition at, typically, 370 °C including films with x values throughout the miscibility gap (0.06<x<0.97). Peak shift, broadening, and asymmetry arising from spatial correlation effects yield details of the microstructural clustering. The dependence of phonon coherence length on the x value cannot be explained simply from a random occupancy of the anion sublattice. We employed a linear chain model with site probabilities modified by the Warren–Cowley short-range order parameter to infer coherence lengths versus x. The data are best fit with a short-range order parameter of 0.73 at x = 1/2. © 1998 American Institute of Physics.
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68.55.-a Thin film structure and morphology
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
78.30.Fs III-V and II-VI semiconductors
78.66.Hf II-VI semiconductors

Temperature dependence of impact ionization in AlGaN–GaN heterostructure field effect transistors

N. Dyakonova, A. Dickens, M. S. Shur, R. Gaska, and J. W. Yang

Appl. Phys. Lett. 72, 2562 (1998); http://dx.doi.org/10.1063/1.121418 (3 pages) | Cited 33 times

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We report on the studies of the impact ionization in AlGaN–GaN heterostructure field effect transistors in the temperature range 17–43 °C. The results show that the breakdown voltage and the characteristic electrical field Ei of the impact ionization have a positive temperature coefficient. The value of Ei at room temperature is estimated to be approximately 2.6 MV/cm, which agrees with recent theoretical prediction [J. Kolnik et al., J. Appl. Phys. 82, 726 (1997)]. © 1998 American Institute of Physics.
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85.30.Tv Field effect devices

Capacitance measurements of junction formation and structure in polymer light-emitting electrochemical cells

I. H. Campbell, D. L. Smith, C. J. Neef, and J. P. Ferraris

Appl. Phys. Lett. 72, 2565 (1998); http://dx.doi.org/10.1063/1.121419 (3 pages) | Cited 32 times

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We present capacitance–voltage and current–voltage measurements of polymer light-emitting electrochemical cells and compare these results with steady state device model calculations. The capacitance–voltage characteristic is used to assess the formation and structure of the electrochemical junction in the device. The cell capacitance and current both increase sharply above a threshold voltage as the bias is increased. The threshold voltage for the rapid increase in capacitance is lower than that for the increase in current, indicating that the electrochemical junction begins to form prior to significant current flow. The electrochemical junction width, estimated from the capacitance measurements, is about 15 nm at a current density of 0.1 A/cm2. The steady state device model calculations are in reasonable agreement with these observations. © 1998 American Institute of Physics.
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85.60.Jb Light-emitting devices
82.47.-a Applied electrochemistry
82.45.-h Electrochemistry and electrophoresis
42.70.Jk Polymers and organics
78.60.Ps Chemiluminescence

Evidence of hydrogen–carbon interactions in plasma hydrogenated carbon-doped n-InP

B. Theys, J. L. Benchimol, E. V. K. Rao, J. Chevallier, and M. Juhel

Appl. Phys. Lett. 72, 2568 (1998); http://dx.doi.org/10.1063/1.121420 (3 pages) | Cited 4 times

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Unlike GaAs which is p type, InP, when doped with the amphoteric C, is known to exhibit n-type conduction but with a low carrier-to-dopant ratio. To learn more about C behavior, we have intentionally introduced atomic H in C-doped n-InP by exposing the samples to a radio-frequency deuterium plasma. We show here that C, unlike other n dopants (S, Sn, and Si), strongly interacts with H in InP. First, the distribution of deliberately introduced H closely follows that of C. Second, for all C dopings studied here, the H concentration is nearly equal to that of C. Finally, and most importantly, the electrical properties of the material are also significantly altered, for instance, the free-electron concentration increases by more than an order of magnitude in certain samples. © 1998 American Institute of Physics.
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72.80.Ey III-V and II-VI semiconductors
71.55.Eq III-V semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
61.72.S- Impurities in crystals

Silicon-based organic-inorganic microcavity and its dispersion curve from angle-resolved photoluminescence

A. Arena, S. Patanè, G. Saitta, S. Savasta, R. Girlanda, and R. Rinaldi

Appl. Phys. Lett. 72, 2571 (1998); http://dx.doi.org/10.1063/1.121421 (3 pages) | Cited 10 times

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We report an experimental study of a planar organic-inorganic microcavity consisting of a porous silicon distributed Bragg reflector, a single layer of acridina orange as active material and a top aluminum reflector. By tuning the cavity resonance energy around the maximum of the organic material photoluminescence, we found an intense emission and a spectral narrowing of the emission band to about 45 meV. The angle-resolved photoluminescence spectra enable us to determine the microcavity dispersion curve. The very good agreement with the theoretical dispersion provides a precise determination of the refractive index of the organic material. © 1998 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds
78.66.Db Elemental semiconductors and insulators
78.55.Mb Porous materials
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