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19 Jun 2000

Volume 76, Issue 25, pp. 3673-3830

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Detection of single photons using a field-effect transistor gated by a layer of quantum dots

A. J. Shields, M. P. O’Sullivan, I. Farrer, D. A. Ritchie, R. A. Hogg, M. L. Leadbeater, C. E. Norman, and M. Pepper

Appl. Phys. Lett. 76, 3673 (2000); http://dx.doi.org/10.1063/1.126745 (3 pages) | Cited 60 times

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We demonstrate that the conductance of a field-effect transistor (FET) gated by a layer of nanometer-sized quantum dots is sensitive to the absorption of single photons. Rather than relying upon an avalanche process, as in conventional semiconductor single-photon detectors, the gain in this device derives from the fact that the conductivity of the FET channel is very sensitive to the photoexcited charge trapped in the dots. This phenomenon may allow a type of three-terminal single-photon detector to be developed based upon FET technology. © 2000 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.Tv Field effect devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.61.Ey III-V semiconductors

Generation of wavelength-tunable single-mode picosecond pulses from a self-seeded gain-switched Fabry–Perot laser diode with a high-birefringence fiber loop mirror

Shenping Li, K. S. Chiang, and W. A. Gambling

Appl. Phys. Lett. 76, 3676 (2000); http://dx.doi.org/10.1063/1.126746 (3 pages) | Cited 9 times

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We demonstrate a simple self-seeding scheme for generating wavelength-tunable single-mode picosecond pulses at a fixed repetition rate with a Fabry–Perot (FP) laser diode. In this scheme, the FP laser diode is self-seeded from a high-birefringence (HiBi) fiber loop mirror that acts as a periodic multichannel wavelength filter. By setting the channel spacing of the filter properly, stepwise wavelength tuning over a wide range can be achieved by either changing the FP cavity roundtrip phase shift or tuning the fiber loop mirror filter. With this scheme, fast electrical tuning is also possible by incorporating a phase-control section into the FP cavity. Using a HiBi fiber loop mirror with a channel spacing of 1.56 nm and a FP laser diode with a mode spacing of 1.45 nm, we were able to generate picosecond pulses at a repetition rate of approximately 2 GHz, whose wavelength could be tuned stepwise over ten successive laser cavity modes by either changing the temperature of the laser diode or tensioning/pressing a section of the HiBi fiber in the loop mirror. A side-mode suppression ratio over 15 dB over the entire tuning range was achieved. © 2000 American Institute of Physics.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
42.79.Ci Filters, zone plates, and polarizers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Cavity-Q-driven spectral shift in a cylindrical whispering-gallery-mode microcavity laser

Hee-Jong Moon, Young-Tak Chough, Jung Bog Kim, Kyungwon An, Jonghoon Yi, and Jongmin Lee

Appl. Phys. Lett. 76, 3679 (2000); http://dx.doi.org/10.1063/1.126747 (3 pages) | Cited 17 times

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Cavity-Q-driven spectral shift of lasing was observed in a cylindrical microcavity formed by rhodamine6G-doped quinoline in a capillary. The envelope of lasing spectrum showed a blueshift induced by the decreasing cavity Q of whispering gallery modes as the pump fluence increases. The thermally induced refractive index changes were measured from the shifts of individual lasing modes. The observed cavity-Q-driven spectral shift was well described by a simple dye laser model, which accounts for the dependence of cavity Q on the thermally induced refractive index change. © 2000 American Institute of Physics.
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42.55.Mv Dye lasers
42.55.Sa Microcavity and microdisk lasers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

Erbium-implanted silica colloids with 80% luminescence quantum efficiency

L. H. Slooff, M. J. A. de Dood, A. van Blaaderen, and A. Polman

Appl. Phys. Lett. 76, 3682 (2000); http://dx.doi.org/10.1063/1.126748 (3 pages) | Cited 47 times

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Silica colloids with a diameter of 240–360 nm, grown by wet chemical synthesis using ethanol, ammonia, water, and tetraethoxysilane, were implanted with 350 keV Er ions, to peak concentrations of 0.2–1.1 at. % and put onto a silicon or glass substrate. After annealing at 700–900 °C the colloids show clear room-temperature photoluminescence at 1.53 μm, with lifetimes as high as 17 ms. By comparing data of different Er concentrations, the purely radiative lifetime is estimated to be 20–22 ms, indicating a high quantum efficiency of about 80%. This high quantum efficiency indicates that, after annealing, the silica colloids are almost free of OH impurities. Spinning a layer of polymethylmethacrylate over the silica spheres results in an optically transparent nanocomposite layer, that can be used as a planar optical waveguide amplifier at 1.5 μm that is fully compatible with polymer technology. © 2000 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
82.70.Dd Colloids
78.55.Kz Solid organic materials
81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions
42.70.Jk Polymers and organics
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Influence of the valence-band offset on gain and absorption in GaNAs/GaAs quantum well lasers

J. Hader, S. W. Koch, J. V. Moloney, and E. P. O’Reilly

Appl. Phys. Lett. 76, 3685 (2000); http://dx.doi.org/10.1063/1.126749 (3 pages) | Cited 22 times

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The dependence of the gain and absorption in GaNAs/GaAs quantum well lasers on the valence-band offset is investigated. The calculated absorption strength, gain amplitudes, and gain bandwidth are found to depend crucially on the value of this offset. The shift of the peak gain transition energy with carrier density is shown to depend strongly on the magnitude of the offset, providing what should be a useful means to determine the offset experimentally. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

IV–VI compound midinfrared high-reflectivity mirrors and vertical-cavity surface-emitting lasers grown by molecular-beam epitaxy

Z. Shi, G. Xu, P. J. McCann, X. M. Fang, N. Dai, C. L. Felix, W. W. Bewley, I. Vurgaftman, and J. R. Meyer

Appl. Phys. Lett. 76, 3688 (2000); http://dx.doi.org/10.1063/1.126750 (3 pages) | Cited 30 times

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Midinfrared broadband high-reflectivity Pb1−xSrxSe/BaF2 distributed Bragg reflectors and vertical-cavity surface-emitting lasers (VCSELs) with PbSe as the active material were grown by molecular-beam epitaxy. Because of an extremely high index contrast, mirrors with only three quarter-wave layer pairs had reflectivities exceeding 99%. For pulsed optical pumping, a lead salt VCSEL emitting at the cavity wavelength of 4.5–4.6 μm operated nearly to room temperature (289 K). © 2000 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.79.Bh Lenses, prisms and mirrors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.66.Li Other semiconductors
81.05.Hd Other semiconductors

Plane wave excited vortices in photorefractive materials

L. Solymar and V. Kalinin

Appl. Phys. Lett. 76, 3691 (2000); http://dx.doi.org/10.1063/1.126751 (3 pages) | Cited 1 time

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The flow of spatially periodic current in a photorefractive film is investigated under the conditions when two coherent plane waves are incident and an electric field is applied. It is shown that in contrast to the usually accepted physical picture the major part of the current does not flow in a simple manner from one boundary to the other boundary. Two examples are given: (i) transients in the perpendicular configuration (grating vector perpendicular to the direction of the applied field) with vertical diffusion neglected and (ii) steady state in the parallel configuration (grating vector parallel with the applied electric field) with vertical diffusion included. The flow of current is plotted with the aid of vector diagrams. It is clearly shown that during transients current may flow from one point on the boundary to another point on the same boundary, and that for the parallel configuration circular currents may flow in the steady state. © 2000 American Institute of Physics.
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42.70.Gi Light-sensitive materials
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Pretreatment effects by aqua-regia solution on field emission of diamond film

Sang Youn Han, Jong Kyu Kim, Jong-Lam Lee, and Young-Joon Baik

Appl. Phys. Lett. 76, 3694 (2000); http://dx.doi.org/10.1063/1.126752 (3 pages) | Cited 4 times

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Field emission of diamond film was enhanced after surface treatment using boiling aqua-regia solution. The current generated by the emission of electrons was distinctly increased and the threshold field was reduced from 18.1 to 13.8 V/μm by the treatment. The amount of C–C bonds was decreased, but the O–C one was increased by the treatment. The Fermi level at the treated surface was increased by 2.2 eV. This provides evidence that the enhancement of electron emission originated from the reduction of the work function, caused by the chemisorption of oxygen atoms at the surface of diamond during the aqua regia treatment. Thus, the effective electron affinity changed from positive to negative, leading to the reduction of the potential barrier height and width for electron emission at the surface of diamond. © 2000 American Institute of Physics.
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85.45.Fd Field emission displays (FEDs)
79.70.+q Field emission, ionization, evaporation, and desorption
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
73.30.+y Surface double layers, Schottky barriers, and work functions
81.65.-b Surface treatments
81.05.ub Fullerenes and related materials
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Effect of interfacial silicon on the structural stability of C54–TiSi2 on SiO2

Dongwoo Suh, Hong Seung Kim, and Jin-Yeong Kang

Appl. Phys. Lett. 76, 3697 (2000); http://dx.doi.org/10.1063/1.126753 (3 pages) | Cited 1 time

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The formation of interconnect C54–TiSi2 on SiO2 substrates suffers severe structural instability upon rapid thermal anneal. To understand the structural instability from a mechanistic point of view, we investigated the interfacial features of the C54–TiSi2 on SiO2 using Auger electron spectroscopy and cross-sectional transmission electron microscopy. As a result, we noted that the surplus silicon layer retained at the interface between the C54–TiSi2 thin film and the SiO2 substrates is indispensable for the stabilization of the C54–TiSi2 on SiO2. We explained the affirmative role of the silicon layer retained at the interface in terms of the residual stress of the C54–TiSi2 thin film. © 2000 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
68.35.Ct Interface structure and roughness
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.72.Cc Kinetics of defect formation and annealing
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
79.20.Fv Electron impact: Auger emission
68.35.Gy Mechanical properties; surface strains

High quality Ge on Si by epitaxial necking

T. A. Langdo, C. W. Leitz, M. T. Currie, E. A. Fitzgerald, A. Lochtefeld, and D. A. Antoniadis

Appl. Phys. Lett. 76, 3700 (2000); http://dx.doi.org/10.1063/1.126754 (3 pages) | Cited 53 times

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We show that pure Ge grown selectively on SiO2/Si substrates in 100 nm holes is highly perfect at the top surface compared to conventional Ge lattice-mismatched growth on planar Si substrates. This result is achieved through a combination of interferometric lithography SiO2/Si substrate patterning and ultrahigh vacuum chemical vapor deposition Ge selective epitaxial growth. This “epitaxial necking,” in which threading dislocations are blocked at oxide sidewalls, shows promise for dislocation filtering and the fabrication of low-defect density Ge on Si. Defects at the Ge film surface only arise at the merging of epitaxial lateral overgrowth fronts from neighboring holes. These results confirm that epitaxial necking can be used to reduce threading dislocation density in lattice-mismatched systems. © 2000 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Cy Elemental semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.Ct Interface structure and roughness
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer

Oxidized Ni/Pt and Ni/Au ohmic contacts to p-type GaN

Li-Chien Chen, Jin-Kuo Ho, Charng-Shyang Jong, Chien C. Chiu, Kwang-Kuo Shih, Fu-Rong Chen, Ji-Jung Kai, and Li Chang

Appl. Phys. Lett. 76, 3703 (2000); http://dx.doi.org/10.1063/1.126755 (3 pages) | Cited 30 times

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The Ni/Pt and Ni/Au contacts to p-GaN heat treated in air are investigated to study the effect of the metallic phase of high work function on specific contact resistance (ρc). The current–voltage measurement suggests that there is an optimal microstructure for the oxidized Ni/Au contact to obtain a minimum ρc of 4×10−6 Ω cm2. Such low ohmic contact resistance could be related to the formation of the NiO and the specific microstructure. However, high ρc of about 2–5×10−2 Ω cm2 are obtained for the oxidized Ni/Pt contacts, which is attributed to the different microstructure from that of the oxidized Ni/Pt contact. The NiO phase of the oxidized Ni/Pt contact is separated from p-GaN by a continuous face-centered-cubic Pt–Ni–Ga film. Therefore, the oxidized Ni/Pt contact behaves just like a common metal contact, but not a metal/NiO composite contact. Comparison of the two oxidized contacts implies that the previously proposed model based on metal/p-NiO/p-GaN heterojunction is reliable to explain the low ρc to p-GaN. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Cg Contact resistance, contact potential
81.65.Mq Oxidation

Shock-induced transformation of β-Si3N4 to a high-pressure cubic-spinel phase

T. Sekine, Hongliang He, T. Kobayashi, Ming Zhang, and Fangfang Xu

Appl. Phys. Lett. 76, 3706 (2000); http://dx.doi.org/10.1063/1.126756 (3 pages) | Cited 72 times

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β-Si3N4 powders were shock compressed and quenched from 12 to 115 GPa. β-Si3N4 transforms to the spinel-type Si3N4 (c-Si3N4) by a fast reconstructive process at pressures above about 20 GPa. The yield of c-Si3N4 recovered from 50 GPa and about 2400 K reaches about 80% and the grain sizes are about 10–50 nm. It is proposed that the fast transformation to c-Si3N4 occurs by rearrangement of nitrogen stacking layers, which initiates partial breakup of the SiN4 tetrahedra and formation of SiN6 octahedra at high density. Because of the advantages of massive production and the nanometer characteristics of shock-synthesized c-Si3N4, it is possible to investigate the mechanical properties experimentally and to develop new industrial applications. © 2000 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions

Oxygen migration during epitaxial regrowth in Cs+-irradiated α-quartz investigated by means of nuclear reaction analysis

F. Roccaforte, F. Harbsmeier, S. Dhar, and K. P. Lieb

Appl. Phys. Lett. 76, 3709 (2000); http://dx.doi.org/10.1063/1.126757 (3 pages) | Cited 12 times

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The migration of oxygen in ion-beam-amorphized c-SiO2 (α-quartz) was investigated by means of nuclear reaction analysis using the resonant reaction 18O(p,α)15N for oxygen depth profiling. Only very small amounts of oxygen were observed to diffuse in crystalline or in Xe+-ion beam-amorphized α-quartz after high-temperature annealing. However, a dramatic migration of oxygen occurs in Cs+-implanted α-quartz in the same temperature range (600–900 °C), where Cs diffuses out of the amorphized layer and epitaxial recrystallization occurs. These results point out to a strong correlation of all these processes. A mechanism to explain the observed indiffusion of 18O is proposed and is related to the Cs migration and the topological modification to achieve epitaxial regrowth of the SiO2 matrix. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.60.Wm Other nonelectronic physical properties
66.30.H- Self-diffusion and ionic conduction in nonmetals
61.80.Jh Ion radiation effects
82.80.-d Chemical analysis and related physical methods of analysis
61.43.Er Other amorphous solids
61.82.Ms Insulators

Mechanism of luminescence in InGaN/GaN multiple quantum wells

H. C. Yang, P. F. Kuo, T. Y. Lin, Y. F. Chen, K. H. Chen, L. C. Chen, and Jen-Inn Chyi

Appl. Phys. Lett. 76, 3712 (2000); http://dx.doi.org/10.1063/1.126758 (3 pages) | Cited 40 times

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We report a firm evidence of luminescence from InN clusters in InGaN/GaN multiple quantum wells. Photoluminescence, photoluminescence excitation, and Raman scattering measurements have been employed to study the optical properties of InGaN/GaN multiple quantum wells. A careful examination of the low energy shoulders of the main peak luminescence reveals the fact that their separation is in good agreement with the longitudinal optical phonon energy of pure InN film measured by Raman scattering. A large Stokes-like shift between the emission peak energy and the absorption edge is found; it increases with increasing indium content. All these observations can be explained in a consistent way by the effect of localization due to self-organized InN clusters within InGaN layers. Our results thus strongly suggest that the emission mechanism of InGaN/GaN quantum wells originates from radiation recombination within the localized states of self-organized InN clusters. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.30.Fs III-V and II-VI semiconductors
63.20.-e Phonons in crystal lattices

Organic ligand and solvent kinetics during the assembly of CdSe nanocrystal arrays using infrared attenuated total reflection

Bosang S. Kim, Luis Avila, Louis E. Brus, and Irving P. Herman

Appl. Phys. Lett. 76, 3715 (2000); http://dx.doi.org/10.1063/1.126759 (3 pages) | Cited 15 times

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The self-assembly of amorphous three-dimensional arrays of CdSe nanocrystals is probed in real time using multiple-reflection, infrared attenuated total reflection spectroscopy by following the solvent and the organic ligands that passivate the nanocrystal surface. During the self-assembly of a 250 ML array from pyridine-capped CdSe nanocrystals in pyridine solvent, the solvent molecules evaporate in ∼ 30–40 min and the pyridine-capping molecules leave the array very slowly, apparently limited by diffusion, with ∼ 30±8% remaining after three days. © 2000 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
61.46.-w Structure of nanoscale materials

Theoretical investigation of nitrogen-doping effect on vacancy aggregation processes in Si

Hiroyuki Kageshima, Akihito Taguchi, and Kazumi Wada

Appl. Phys. Lett. 76, 3718 (2000); http://dx.doi.org/10.1063/1.126760 (3 pages) | Cited 29 times

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The nitrogen-doping effect on vacancy aggregation in Si is studied by comparing total energies of various complexes of nitrogen atoms and Si vacancies in terms of first-principles calculations. Two nitrogen atoms are found to form a stable complex with two Si vacancies, strongly suggesting that a supersaturation of “isolated” Si vacancies in growth cooling can be suppressed. The delayed void formation observed in N-doped Czochralski Si indeed supports this suggestion. © 2000 American Institute of Physics.
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61.72.uf Ge and Si
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.J- Point defects and defect clusters
61.82.Fk Semiconductors

X-ray induced luminescence of solid argon at high pressures: A pressure probe

Bruce J. Baer, Choong-Shik Yoo, and Hyunchae Cynn

Appl. Phys. Lett. 76, 3721 (2000); http://dx.doi.org/10.1063/1.126761 (2 pages) | Cited 1 time

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Above 7 GPa, visible luminescence is observed when argon in a diamond anvil cell is irradiated by high energy x rays from a synchrotron source. The spectrum consists of two peaks which shift by −43.6±0.7 cm−1/GPa and −47.5±2.4 cm−1/GPa from ambient pressure emission energies of 17 900±40 and 17 300±140 cm−1, respectively. These shifts are linear up to 60 GPa and reversible on decompression. Extrapolation of the shifts to ambient pressure suggests that this is a 4p–5d atomic transition. © 2000 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
62.50.-p High-pressure effects in solids and liquids
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Modification of the growth mode of Ge on Si by buried Ge islands

N. Usami, Y. Araki, Y. Ito, M. Miura, and Y. Shiraki

Appl. Phys. Lett. 76, 3723 (2000); http://dx.doi.org/10.1063/1.126762 (3 pages) | Cited 10 times

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Photoluminescence experiments on double Ge layers were performed to give deep insights on the growth mode of Ge on Si in the presence of buried 4.5 monolayers of Ge islands. The critical coverage of the island formation and the wetting layer thickness were confirmed to be reduced in the second Ge layer. In addition, a drastic increase of the island density as well as a shape transition were observed by atomic force microscopy. These modifications of the growth mode are explained in terms of the surface strain induced by the buried Ge islands and the reduction of the nucleation barrier due to the alloying. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Aa Theory and models of film growth
81.05.Cy Elemental semiconductors
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
68.35.B- Structure of clean surfaces (and surface reconstruction)
64.60.Q- Nucleation

Topographic measurement of electromigration-induced stress gradients in aluminum conductor lines

P.-C. Wang, I. C. Noyan, S. K. Kaldor, J. L. Jordan-Sweet, E. G. Liniger, and C.-K. Hu

Appl. Phys. Lett. 76, 3726 (2000); http://dx.doi.org/10.1063/1.126763 (3 pages) | Cited 10 times

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We report a set of data on the evolution of stress in thin-film metallization wires during the transient region of electromigration. The excellent strain sensitivity of the x-ray microbeam topography technique allows real-time, spatially resolved measurements at the lowest currents reported to date (1.0×104–1.4×105 A/cm2). While the steady-state results agree qualitatively with the Blech’s stress gradient model [I. A. Blech, J. Appl. Phys. 47, 1203 (1976)], the threshold-length product calculated from our data is about 2–3 times smaller than previously reported values. Stress evolution during the transient state displays local fluctuations which cannot be attributed to experimental errors, indicating possible microstructural effects on local flux divergence even in the case of wide, nonbamboo wires. © 2000 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Qa Electromigration
68.35.B- Structure of clean surfaces (and surface reconstruction)

Effects of heat treatment on diffusion of Cu atoms into CdTe single crystals

Y. L. Soo, S. Huang, S. Kim, G. Kioseoglou, Y. H. Kao, A. D. Compaan, D. Grecu, and D. Albin

Appl. Phys. Lett. 76, 3729 (2000); http://dx.doi.org/10.1063/1.126764 (3 pages) | Cited 3 times

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Angular dependence of x-ray fluorescence and x-ray absorption fine structure techniques have been used to study the diffusion of Cu atoms into the photovoltaic material CdTe. Depth profile, effective valency, and local structure of Cu atoms in a Cu-doped single crystal of CdTe were investigated before and after a second heat treatment. Enhanced Cu diffusion into the CdTe single crystal was observed as a result of heating at a moderate temperature around 200 °C, resulting in a redistribution of the Cu impurities through a broader depth profile. Some of the Cu atoms are believed either to form small complexes with Te or occupy interstitial sites in the host but accompanied by a large local lattice distortion while others substitute for Cd on the cation sites. The results thus demonstrate that these nondestructive x-ray characterization methods are useful for probing microstructural changes in CdTe photovoltaic materials/devices in which some Cu-containing compounds are used as back contacts. © 2000 American Institute of Physics.
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66.30.J- Diffusion of impurities
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
78.70.Dm X-ray absorption spectra
61.72.S- Impurities in crystals

In situ transmission electron microscopy study of electric-field-induced microcracking in single crystal Pb(Mg1/3Nb2/3)O3–PbTiO3

Z. Xu, X. Tan, P. Han, and J. K. Shang

Appl. Phys. Lett. 76, 3732 (2000); http://dx.doi.org/10.1063/1.126765 (3 pages) | Cited 25 times

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In this letter, we report in situ transmission electron microscopy (TEM) study of effect of a cyclic electric field on microcracking in a single crystal piezoelectric 0.66Pb(Mg1/3Nb2/3)O3–0.34PbTiO3. A TEM heating stage was modified to permit the in situ application of an electric field on the TEM sample surface. Microcrack initiation from a fine pore under an applied cyclic electric field was directly observed in the piezoelectric single crystal. Experimental procedures for in situ TEM studies were described. © 2000 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.-j Piezoelectricity and electromechanical effects
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Structure of Zn adsorption on GaAs(001)-(2×4)

R. Miotto, G. P. Srivastava, and A. C. Ferraz

Appl. Phys. Lett. 76, 3735 (2000); http://dx.doi.org/10.1063/1.126766 (3 pages) | Cited 2 times

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The atomic structures of four possible models for the adsorption of Zn on GaAs(001)–(2×4) are investigated by means of a first-principles pseudopotential technique. Our calculations suggest that Zn atoms adsorb preferentially in trench (third layer) sites. All structures are characterized by the breaking of the arsenic dimer and the formation of two mixed dimers in the vertical plane containing the original As–As dimer. The Zn atom lies 0.16 Å higher than the As atoms, and the mixed dimer has a bond length of 2.31 Å. All other structural features for the four models studied (e.g., minimum interplanar distance, and remaining As dimer bond lengths) retain the characteristics of the free surface. © 2000 American Institute of Physics.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
68.35.B- Structure of clean surfaces (and surface reconstruction)

Photoemission spectroscopic investigation on the interface formation of a ladder-type poly(para-phenylene) with aluminum

N. Koch, R. Pairleitner, Q. Toan Le, E. W. Forsythe, Y. Gao, and G. Leising

Appl. Phys. Lett. 76, 3738 (2000); http://dx.doi.org/10.1063/1.126767 (3 pages) | Cited 3 times

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The formation of the interface between a thin film of a ladder-type poly(para-phenylene) m-LPPP and aluminum was investigated with x-ray and ultraviolet photoemission spectroscopy. The physical properties of this interface are of actual interest as m-LPPP is successfully applied as active material in organic light emitting devices (LED). Almost no changes in the core-level and valence electronic structure of the polymer upon increasing coverage with aluminum (in situ) are found. This gives indication for a weak interaction of Al with m-LPPP, ruling out the formation of chemical bonds between the two materials. The rapid occurrence of metallic aluminum at rather low coverage in the presented experiment is an important finding for the understanding of charge injection and the interfacial electronic structure in organic LEDs. © 2000 American Institute of Physics.
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79.60.Jv Interfaces; heterostructures; nanostructures
68.35.Fx Diffusion; interface formation
71.20.Rv Polymers and organic compounds
73.40.Ns Metal-nonmetal contacts
73.20.-r Electron states at surfaces and interfaces
85.60.Jb Light-emitting devices
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Self-organized type-II In0.55Al0.45As/Al0.50Ga0.50As quantum dots realized on GaAs(311)A

H. Y. Liu, W. Zhou, D. Ding, W. H. Jiang, B. Xu, J. B. Liang, and Z. G. Wang

Appl. Phys. Lett. 76, 3741 (2000); http://dx.doi.org/10.1063/1.126768 (3 pages) | Cited 5 times

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Self-organized In0.55Al0.45As/Al0.50Ga0.50As quantum dots are grown by the Stranski–Krastanow growth mode using molecular beam epitaxy on the GaAs(311)A substrate. The optical properties of type-II InAlAs/AlGaAs quantum dots have been demonstrated by the excitation power and temperature dependence of photoluminescence spectra. A simple model accounting for the size-dependent band gap of quantum dots is given to qualitatively understand the formation of type-II In0.55Al0.45As/Al0.50Ga0.50As quantum dots driven by the quantum-confinement-induced Γ→X transition. The results provide new insights into the band structure of InAlAs/AlGaAs quantum dots. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Effects of nitridation and annealing on interface properties of thermally oxidized SiO2/SiC metal–oxide–semiconductor system

P. T. Lai, Supratic Chakraborty, C. L. Chan, and Y. C. Cheng

Appl. Phys. Lett. 76, 3744 (2000); http://dx.doi.org/10.1063/1.126769 (3 pages) | Cited 15 times

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The effects of N2O nitridation and subsequent annealing in different conditions on thermally oxidized n-type 6H–silicon carbide (SiC) metal–oxide–semiconductor (MOS) interface properties were investigated. Influence of high-field stress on the MOS system was also studied. The nitrided device annealed in dry or wet O2 is found to have lower interface-state density compared to the device annealed in N2 because the reoxidation can reduce nitridation-induced interface damage. Furthermore, significantly less shift of flatband voltage during high-field stress for all nitrided devices indicates much better oxide reliability by replacing strained Si–O bonds with stronger Si–N bonds during nitridation. This is further supported by the fact that annealing of the nitrided device in dry or wet oxygen slightly reduces the robustness of the oxide. In summary, the O2-annealing conditions have to be optimized to deliver a proper tradoff between interface quality and reliability. © 2000 American Institute of Physics.
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81.65.Mq Oxidation
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.40.Gh Other heat and thermomechanical treatments
73.20.At Surface states, band structure, electron density of states
68.35.Ct Interface structure and roughness
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