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29 Nov 1999

Volume 75, Issue 22, pp. 3437-3575

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Type-II InAs/InAsSb strained-layer-superlattice negative luminescence devices

M. J. Pullin, H. R. Hardaway, J. D. Heber, and C. C. Phillips

Appl. Phys. Lett. 75, 3437 (1999); http://dx.doi.org/10.1063/1.125288 (3 pages) | Cited 29 times

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Negative luminescence operation is reported for p–n diode devices with type-II InAs/InAsSb strained-layer-superlattice active regions which have a spectral peak at 4.2 μm and a negative luminescence efficiency of up to 20%. © 1999 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.60.Fi Electroluminescence
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Kk Junction diodes

Direct imaging of the spectral emission characteristic of an InGaN/GaN-ultraviolet light-emitting diode by highly spectrally and spatially resolved electroluminescence and photoluminescence microscopy

Peter Fischer, Jürgen Christen, Margit Zacharias, Veit Schwegler, Christoph Kirchner, and Markus Kamp

Appl. Phys. Lett. 75, 3440 (1999); http://dx.doi.org/10.1063/1.125289 (3 pages) | Cited 6 times

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The microscopic spectral emission characteristic of an InGaN/GaN double-heterostructure light-emitting diode is directly imaged by highly spectrally and spatially resolved scanning electroluminescence microscopy under operation as a function of injection current density. The luminescence intensity maps and especially the peak-wavelength scanning images provide access to the optical quality of the final device and yield direct images of the In fluctuations with 1 μm spatial resolution. Indium concentrations varying from 6% to 9% are found in the active InGaN region of the ultraviolet diode emitting at 400 nm. While for low injection current densities the electroluminescence is dominated by emission from the p GaN originating from the whole accessible area, the emission from the InGaN active layer increases and takes over for higher injection conditions showing a strongly localized spatial emission characteristic. Correlation of the results with low-temperature scanning photoluminescence microscopy enables the identification of the underlying recombination processes. © 1999 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Optical modulation at around 1550 nm in an InGaAlAs optical waveguide containing an InGaAs/AlAs resonant tunneling diode

J. M. L. Figueiredo, A. R. Boyd, C. R. Stanley, C. N. Ironside, S. G. McMeekin, and A. M. P. Leite

Appl. Phys. Lett. 75, 3443 (1999); http://dx.doi.org/10.1063/1.125290 (3 pages) | Cited 8 times

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We report electroabsorption modulation of light at around 1550 nm in a unipolar InGaAlAs optical waveguide containing an InGaAs/AlAs double-barrier resonant tunneling diode (RTD). The RTD peak-to-valley transition increases the electric field across the waveguide, which shifts the core material absorption band edge to longer wavelengths via the Franz–Keldysh effect, thus changing the light-guiding characteristics of the waveguide. Low-frequency characterization of a device shows modulation up to 28 dB at 1565 nm. When dc biased close to the negative differential conductance region, the RTD optical waveguide behaves as an electroabsorption modulator integrated with a wide bandwidth electrical amplifier, offering a potential advantage over conventional pn modulators. © 1999 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
42.82.Et Waveguides, couplers, and arrays
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.60.-q Optoelectronic devices

Noise suppression in Ti:sapphire laser-based electro-optic sampling

J. M. Zhang, R. L. Ruo, and M. K. Jackson

Appl. Phys. Lett. 75, 3446 (1999); http://dx.doi.org/10.1063/1.125291 (3 pages) | Cited 2 times

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We show that intensity and phase noise are highly correlated in a mode-locked Ti:sapphire laser. This allows electro-optic sampling noise, degraded by the combination of −184 dBc/Hz laser phase noise and birefringent system components, to be reduced 12 dB to the shot noise floor. Two multiorder waveplates can be combined to achieve shot-limited noise while preserving maximum detection efficiency. © 1999 American Institute of Physics.
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42.60.Mi Dynamical laser instabilities; noisy laser behavior
42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.50.Lc Quantum fluctuations, quantum noise, and quantum jumps

Optical spectra of nitride quantum dots: Quantum confinement and electron–hole coupling

Ulrich Hohenester, Rosa Di Felice, Elisa Molinari, and Fausto Rossi

Appl. Phys. Lett. 75, 3449 (1999); http://dx.doi.org/10.1063/1.125292 (3 pages) | Cited 9 times

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We calculate the optical properties of nitride-based quantum dots by taking into account quantum confinement as well as electron–hole interaction. We analyze model structures simulating InxGa1−xN dots in InyGa1−yN layers with different alloy compositions. We discuss the trends with the dot size and show that quantum confined excitations exist for a broad range of sizes down to the smallest observed dots. Our results allow us to identify the strong role of Coulomb correlations in the optical spectra and to predict a strong influence of photoexcitation power on selection rules in polarized samples. The signature of quantum confinement can be utilized for a critical interpretation of measured optical spectra. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.40.Fy Semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.23.-b Electronic transport in mesoscopic systems

Quantum well heterostructures grown by molecular beam epitaxy on silicon-on-gallium arsenide substrates

Joanna M. London, Pablo A. Postigo, and Clifton G. Fonstad

Appl. Phys. Lett. 75, 3452 (1999); http://dx.doi.org/10.1063/1.125293 (3 pages) | Cited 2 times

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Silicon-on-gallium arsenide (SonG) wafers have recently been proposed as optimal substrates for monolithic integration of GaAs-based optoelectronic devices with silicon electronics. In this letter it is demonstrated that high quality quantum well heterostructures can be grown on SonG substrates under conditions consistent with the survival of pre-existing electronics. Photoluminescence and cathodoluminescence measurements confirm that these layers are sufficiently high quality to allow integration of light emitting and laser diodes on SonG substrates. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Db Elemental semiconductors and insulators
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.55.Ap Elemental semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
85.60.-q Optoelectronic devices
78.60.Hk Cathodoluminescence, ionoluminescence

Quantum-dot vertical-cavity surface-emitting laser based on the Purcell effect

D. G. Deppe and H. Huang

Appl. Phys. Lett. 75, 3455 (1999); http://dx.doi.org/10.1063/1.125294 (3 pages) | Cited 8 times

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A quantum-dot vertical-cavity surface-emitting laser based on a modified Purcell effect is described. It is shown that the quantum-field confinement can greatly improve the modulation response, while arrays of such elements can generate power levels useful for high-speed data communication. The high-speed pulse response allows bias-free operation and makes the microcavity array an attractive replacement for single-aperture vertical-cavity surface-emitting lasers. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Optical switching of nematic liquid crystal by means of photoresponsive polyimides as an alignment layer

Gi Heon Kim, Shintaro Enomoto, Akihiko Kanazawa, Takeshi Shiono, Tomiki Ikeda, and Lee-Soon Park

Appl. Phys. Lett. 75, 3458 (1999); http://dx.doi.org/10.1063/1.125295 (3 pages) | Cited 7 times

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Photosensitive polyimides (PIs) as an alignment layer induced optical switching of nematic liquid crystal (NLC) on photoirradiation at 366 nm. The orientation of NLC molecule was changed from homogeneous to homeotropic alignment on photoirradiation with a dc electric field as a bias. The optical switching behavior of NLC was largely affected by the chemical structures of PIs. © 1999 American Institute of Physics.
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42.70.Df Liquid crystals
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Jq Electro-optical effects
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Near-field scanning optical microscopy as a simultaneous probe of fields and band structure of photonic crystals: A computational study

Shanhui Fan, Ian Appelbaum, and J. D. Joannopoulos

Appl. Phys. Lett. 75, 3461 (1999); http://dx.doi.org/10.1063/1.125296 (3 pages) | Cited 24 times

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We demonstrate the feasibility of employing near-field scanning optical microscopy (NSOM) imaging to simultaneously obtain both the eigenfield distribution and the band-structure information of a photonic crystal. We introduce the NSOM measurement configuration required and simulate the imaging process, with both the tip and the sample included, using three-dimensional finite-difference time-domain calculations. Both the field-pattern and the frequency–wave-vector relations of photonic crystal eigenmodes are revealed by analyzing simulated images. © 1999 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
71.20.-b Electron density of states and band structure of crystalline solids
07.79.Fc Near-field scanning optical microscopes
02.70.Bf Finite-difference methods
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Morphology and microstructure of BaTiO3/SrTiO3 superlattices grown on SrTiO3 by laser molecular-beam epitaxy

N. Wang, H. B. Lu, W. Z. Chen, T. Zhao, F. Chen, H. Y. Peng, S. T. Lee, and G. Z. Yang

Appl. Phys. Lett. 75, 3464 (1999); http://dx.doi.org/10.1063/1.125297 (3 pages) | Cited 13 times

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The morphology and microstructure of BaTiO3/SrTiO3 (BTO/STO) superlattices grown epitaxially on STO (001) substrates by a computer-controlled laser molecular-beam epitaxy deposition system have been characterized by means of atomic force microscopy and high-resolution transmission electron microscopy (HRTEM). It is found that the HRTEM images taken along the [120] direction of BTO and STO show the maximal contrast difference. It is, therefore, observed that the superlattices consist of a highly oriented and single-crystalline multilayered structure. As identified by HRTEM, the number of unit cells in each BTO or STO layer matches very well with that obtained from reflection high-energy electron diffraction oscillations. The surfaces and interfaces of the superlattices are atomically smooth. In the superlattices, the ratio between the c axis of BTO and STO is about 4% larger than that measured from BTO or STO bulk crystals. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Fg Pulsed laser ablation deposition
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness
77.55.-g Dielectric thin films

Impurity gettering by high-energy ion implantation in silicon beyond the projected range

Y. M. Gueorguiev, R. Kögler, A. Peeva, D. Panknin, A. Mücklich, R. A. Yankov, and W. Skorupa

Appl. Phys. Lett. 75, 3467 (1999); http://dx.doi.org/10.1063/1.125298 (3 pages) | Cited 8 times

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Deep gettering layers have been formed in Si wafers by MeV implantation of Si+ and P+ ions, followed by annealing. Samples have been subsequently contaminated with Cu. Secondary ion mass spectrometry analysis reveals for P implants gettering of Cu atoms in regions significantly deeper than the projected ion range RP and formation of a separate Cu gettering band there. We call this phenomenon the “trans-RP effect.” The results obtained indicate the presence of an appreciable amount of defects in the region beyond RP. Their gettering ability is much higher than that of the implanted gettering layer at RP. The size of these deep defects is below the resolution limit of transmission electron microscopy. We suggest that they are interstitials and/or small interstitial clusters. An explanation of the mechanism responsible for their migration from RP into the trans-RP region and their clustering is proposed. © 1999 American Institute of Physics.
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81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
61.72.J- Point defects and defect clusters
64.75.-g Phase equilibria
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Photoluminescence in erbium-doped Pb(Mg1/3Nb2/3)O3–PbTiO3 thin films

Jianjun Zheng, Yalin Lu, Xuesheng Chen, Mark Cronin-Golomb, and Jing Zhao

Appl. Phys. Lett. 75, 3470 (1999); http://dx.doi.org/10.1063/1.125299 (3 pages) | Cited 10 times

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Erbium-doped Pb(Mg1/3Nb2/3)O3–PbTiO3(PMN–PT) thin films were grown on (10 math2) sapphire substrate with a purpose of developing an active optical material combining both the large electro-optic (EO) effect and lasing or amplification functions. Strong characteristic Er3+ intra-4f shell emission around 1.54 μm is observed at room temperature and a compositional quenching occurred at where the Er content is larger than 0.5 mol %. The introduction of Er in PMN–PT decreased the EO effect, but the EO coefficient still maintain a reasonable value, which is about 0.4×10−16 (m/V)2 at Er content of 0.5 mol %. These results indicate that Er3+-doped PMN–PT can be a potential candidate for integrated optic active devices. © 1999 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
78.55.Hx Other solid inorganic materials
78.66.Nk Insulators
78.20.Jq Electro-optical effects
77.80.-e Ferroelectricity and antiferroelectricity
77.55.-g Dielectric thin films

The self-assembly of uniform heteroepitaxial islands

Cheng-hsin Chiu

Appl. Phys. Lett. 75, 3473 (1999); http://dx.doi.org/10.1063/1.125300 (3 pages) | Cited 27 times

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We present simulation for the morphological evolution of a Stranski–Krastanow system during the annealing process. By considering the strain energy, the surface-energy anisotropy, and the film–substrate interaction, the simulation demonstrates that the morphological evolution of the system can lead to an array of nearly uniform islands that is stable against coarsening. The stability results from the suppression of strain energy relaxation by strong surface-energy anisotropy and strong film–substrate interaction. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology

On the effect of hydrogen incorporation in strontium titanate layers grown by high vacuum magnetron sputtering

Jochen M. Schneider, Björgvin Hjörvarsson, Xin Wang, and Lars Hultman

Appl. Phys. Lett. 75, 3476 (1999); http://dx.doi.org/10.1063/1.125301 (3 pages) | Cited 20 times

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Hydrogen incorporation in strontium titanate thin films grown in a high vacuum environment by rf magnetron sputtering on MgO(001) substrates was investigated by nuclear resonance analysis. The amount of hydrogen in the films is strongly affected by the growth temperature. Films deposited at or below 200 °C have a close-to-amorphous microstructure, are oxygen rich and exhibit hydrogen incorporation up to 0.08 (atomic ratio). As the growth temperature is increased to ⩾250 °C, crystalline growth of stoichiometric SrTiO3 is obtained, with a hydrogen content of 0.006. The results provide evidence that hydrogen incorporation is decisive for the composition as well as the microstructure evolution of the layers. © 1999 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Cd Deposition by sputtering
61.72.S- Impurities in crystals
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
82.80.Jp Activation analysis and other radiochemical methods
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Hydrogen stability in diamond-like carbon films during wear tests

B. Racine, M. Benlahsen, K. Zellama, M. Zarrabian, J. P. Villain, G. Turban, and A. Grosman

Appl. Phys. Lett. 75, 3479 (1999); http://dx.doi.org/10.1063/1.125361 (3 pages) | Cited 9 times

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Hydrogen stability has been investigated during wear tests in particular diamond-like carbon films deposited in a dual electron cyclotron resonance radio frequency glow discharge plasma system, at two different substrate bias voltages equal to −30 and −600 V, for series I and series II, respectively. Combined infrared absorption and elastic recoil detection analysis experiments are used to fully characterize the films in their as-deposited state and after wear tests. The results indicate clearly that the total bonded hydrogen content as well as the total hydrogen concentration decrease during wear tests for the two series. Two mechanisms are discussed to explain these results, e.g., the surface contact graphitization due to heating effect and the hydrogen diffusion to the free surface as a result of plastic deformation process. © 1999 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
62.20.Qp Friction, tribology, and hardness
61.72.S- Impurities in crystals
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.35.+c Brillouin and Rayleigh scattering; other light scattering
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Db Elemental semiconductors and insulators
66.30.J- Diffusion of impurities
81.70.-q Methods of materials testing and analysis
62.20.F- Deformation and plasticity

Effects of Mo-free C40 Ti(Si1−xGex)2 precursors and the thickness of an interposed Mo layer on the enhanced formation of C54 Ti(Si1−xGex)2

Jian-Shing Luo, Jun-Chieh Huang, Wen-Tai Lin, C. Y. Chang, and P. S. Shih

Appl. Phys. Lett. 75, 3482 (1999); http://dx.doi.org/10.1063/1.125362 (3 pages) | Cited 3 times

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The effects of Mo-free C40 Ti(Si1−xGex)2 precursors and the thickness of an interposed Mo layer between Ti films and Si0.76Ge0.24 substrates on the lowering of formation temperature of C54 Ti(Si1−xGex)2 were studied. Metastable C40 Ti(Si1−xGex)2 precursors were grown by pulsed KrF laser annealing. Upon rapid thermal annealing, the Mo-free C40 phase could not be directly transformed to the C54 phase without going through the C49 phase. When the thickness of the interposed Mo layer increased, up to 2.5 nm, the temperature at which the C54 phase was initially formed changed from 750 to 600 and then to 650 °C. The present result showed that with increasing Mo concentration in the reacted layer, the phase stability shifted from C54 to C40 and no C49 was observed. It seems that apart from the C40 template mechanism, the electron/atom ratio also plays an important role in the enhanced formation of the C54 phase. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
64.70.K- Solid-solid transitions
81.05.Bx Metals, semimetals, and alloys

GaN avalanche photodiodes grown by hydride vapor-phase epitaxy

K. A. McIntosh, R. J. Molnar, L. J. Mahoney, A. Lightfoot, M. W. Geis, K. M. Molvar, I. Melngailis, R. L. Aggarwal, W. D. Goodhue, S. S. Choi, D. L. Spears, and S. Verghese

Appl. Phys. Lett. 75, 3485 (1999); http://dx.doi.org/10.1063/1.125363 (3 pages) | Cited 33 times

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Avalanche photodiodes have been demonstrated utilizing GaN grown by hydride vapor-phase epitaxy. Spatially uniform gain regions were achieved in devices fabricated on low-defect-density GaN layers that exhibit no microplasma behavior. A uniform multiplication gain up to 10 has been measured in the 320–360 nm wavelength range. The external quantum efficiency at unity gain is measured to be 35%. The electric field in the avalanche region has been determined from high-voltage C–V measurements to be ∼1.6 MV/cm at the onset of the multiplication gain. Electric fields as high as 4 MV/cm have been measured in these devices. Response times are found to be less than 5 μs, limited by the measurement system. © 1999 American Institute of Physics.
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81.05.Ea III-V semiconductors
85.60.Dw Photodiodes; phototransistors; photoresistors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.61.Ey III-V semiconductors

Site-controlled self-organization of individual InAs quantum dots by scanning tunneling probe-assisted nanolithography

Shigeru Kohmoto, Hitoshi Nakamura, Tomonori Ishikawa, and Kiyoshi Asakawa

Appl. Phys. Lett. 75, 3488 (1999); http://dx.doi.org/10.1063/1.125364 (3 pages) | Cited 65 times

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A nanometer-scale site-control technique for individual InAs quantum dots (QDs) has been developed by using scanning tunneling microscope (STM) -assisted nanolithography and self-organizing molecular-beam epitaxy. We find that nanometer-scale deposits can be created on a GaAs surface by applying voltage and current pulses between the surface and a tungsten probe of the STM, and that they act as “nanomasks” on which GaAs does not grow directly. Accordingly, subsequent thin GaAs growth produces GaAs nanoholes above the deposits. By supplying 1.1 ML InAs on this surface, QDs are self-organized at the hole sites, while hardly any undesirable Stranski–Krastanov QDs are formed in the flat surface region. Using this technique with nanometer precision, a QD pair with 45 nm pitch is fabricated. © 1999 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
85.40.Hp Lithography, masks and pattern transfer
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Flow effect in the chiral-homeotropic liquid-crystal cell

Shu-Hsia Chen and Li-Yi Chen

Appl. Phys. Lett. 75, 3491 (1999); http://dx.doi.org/10.1063/1.125365 (3 pages) | Cited 4 times

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We investigated the dynamics of the chiral-homeotropic liquid-crystal cell and found that the flow of liquid crystal causes an optical bounce after switching on a high applied voltage. We analyzed the behavior of the directors by computer simulation and found that the field-induced backflow effect results in the abnormal twist of the directors near the substrates. The abnormal twist slows down the rising speed of the chiral-homeotropic cell and produces an optical bounce during the rising period. Our results indicate that the backflow effect should be considered on the design of fast chiral-homeotropic liquid-crystal cells. The significant distinctions between this field-induced optical bounce and the well-known optical bounce of the twisted nematic liquid-crystal cell are also described in this letter. © 1999 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
78.20.Jq Electro-optical effects
47.65.-d Magnetohydrodynamics and electrohydrodynamics

Asymmetric luminescence line shape and exciton energy relaxation in Zn1−x−yMgxCdySe epilayers

J. X. Shen, R. Pittini, Y. Oka, S. P. Guo, and M. C. Tamargo

Appl. Phys. Lett. 75, 3494 (1999); http://dx.doi.org/10.1063/1.125366 (3 pages) | Cited 6 times

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The asymmetric line shape of the transient photoluminescence (PL) spectra of high-quality Zn1−x−yMgxCdySe epilayers is deconvoluted to a narrow and a broad Gaussian peak at each time delay. The fitted energy difference between the two peaks corresponds to one longitudinal optical (LO) phonon energy. We assign the narrow peak to the recombination of free excitons (FXs) and the broad peak to the recombination of excitons localized in the broad band tail characteristic for this quaternary compound. The broad PL peak is found to arise from the energy relaxation of the FX at the exciton mobility edge to the localized states by LO phonon emission. Therefore, the population peak of the localized excitons is formed at one LO phonon energy below the FX for all times after the laser excitation. © 1999 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
63.20.kk Phonon interactions with other quasiparticles
71.35.-y Excitons and related phenomena

Precipitation of icosahedral phase from a supercooled liquid region in Zr65Cu7.5Al7.5Ni10Ag10 metallic glass

J. Saida, M. Matsushita, T. Zhang, A. Inoue, M. W. Chen, and T. Sakurai

Appl. Phys. Lett. 75, 3497 (1999); http://dx.doi.org/10.1063/1.125367 (3 pages) | Cited 47 times

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The formation of an icosahedral phase from the rapidly quenched Zr65Cu7.5Al7.5Ni10Ag10 metallic glass was confirmed and the kinetics of the precipitation upon isothermal annealing in the supercooled liquid region were examined by differential scanning calorimetry. Based on the kinetic analysis, it is clarified that the precipitation in the supercooled liquid region takes place by an interfacial controlled growth with a nearly steady-state nucleation rate. The Arrhenius plot between effective time lag, τ, of nucleation and isothermal annealing temperature yields a single linear relation, in which the activation energy for nucleation is evaluated to be 366 kJ/mol. It is concluded that the transformation of amorphous to quasicrystal proceeds by a homogeneous nucleation mode, which is different from those of Pd–U–Si and Al–Cu–V quasicrystals arising from an inhomogeneous distribution of quenched-in nuclei. © 1999 American Institute of Physics.
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61.43.Fs Glasses
64.75.-g Phase equilibria
61.44.Br Quasicrystals

Femtosecond near-field spectroscopy of a single GaAs quantum wire

T. Guenther, V. Emiliani, F. Intonti, C. Lienau, T. Elsaesser, R. Nötzel, and K. H. Ploog

Appl. Phys. Lett. 75, 3500 (1999); http://dx.doi.org/10.1063/1.125368 (3 pages) | Cited 23 times

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Quasi-two-color femtosecond pump and probe spectroscopy and near-field scanning optical microscopy are combined to study the carrier dynamics in single semiconductor nanostructures. In temporally, spectrally, and spatially resolved measurements with a time resolution of 200 fs and a spatial resolution of 200 nm, the nonlinear change in reflectivity of a single quantum wire is mapped in real space and time. The experiments show that carrier relaxation in a single quantum wire occurs on a 100 fs time scale at room temperature. © 1999 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
78.66.Fd III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
78.55.Cr III-V semiconductors
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Evidence for grain-boundary-assisted diffusion of sulfur in polycrystalline CdS/CdTe heterojunctions

M. K. Herndon, A. Gupta, V. Kaydanov, and R. T. Collins

Appl. Phys. Lett. 75, 3503 (1999); http://dx.doi.org/10.1063/1.125369 (3 pages) | Cited 28 times

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We present a near-field scanning optical microscopy (NSOM) study of S interdiffusion in polycrystalline CdS/CdTe heterojunctions. S diffusion from CdS into CdTe leads to the formation of a CdTe1−xSx ternary phase. Because the band gap of CdTe1−xSx varies with S composition, we were able to combine NSOM with a tunable laser source to microscopically identify S-rich regions in the CdTe layer. S composition was found to be very nonuniform and frequently to be greater along grain boundaries than in the grain centers, identifying grain boundaries as locations of enhanced interdiffusion. © 1999 American Institute of Physics.
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81.05.Dz II-VI semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.Mm Grain and twin boundaries
68.35.Fx Diffusion; interface formation
73.61.Ga II-VI semiconductors
66.30.Ny Chemical interdiffusion; diffusion barriers

Detection of gate oxide charge trapping by second-harmonic generation

J. Fang and G. P. Li

Appl. Phys. Lett. 75, 3506 (1999); http://dx.doi.org/10.1063/1.125370 (3 pages) | Cited 12 times

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The high-electric-field-induced trapped oxide charge and neutral oxide traps of a metal–oxide–semiconductor field-effect transistor gate oxide are investigated by surface second-harmonic light generation (SHG). The electric-field dependence of the SHG intensity is sensitive to the charge trapped at the interface between the oxide and the silicon substrate. The time dependence of the SHG intensity probes the characteristics of the neutral trap sites in the oxide. © 1999 American Institute of Physics.
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85.30.Tv Field effect devices
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.20.Jq Electro-optical effects
85.30.De Semiconductor-device characterization, design, and modeling

X-ray reflectivity of ultrathin twist-bonded silicon wafers

J. Eymery, F. Fournel, F. Rieutord, D. Buttard, H. Moriceau, and B. Aspar

Appl. Phys. Lett. 75, 3509 (1999); http://dx.doi.org/10.1063/1.125371 (3 pages) | Cited 12 times

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Ultrathin Si (001) layers (<15 nm) are hydrophobic bonded to a full 4 in. Si (001) wafer. The interface quality and surface roughness, checked by specular x-ray reflectivity, are very good. This technique, well suited to measure the homogeneity thickness, shows that the samples have very small thickness fluctuations, and no extended defects. Quantitative analysis proves that the interfacial layer resulting from the bonding is very thin (about 8 Å). Its atomic density is significantly different from bulk Si only for large bonding twist angles (>5°). © 1999 American Institute of Physics.
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68.35.Ct Interface structure and roughness
81.05.Cy Elemental semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
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