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11 Oct 1999

Volume 75, Issue 15, pp. 2163-2335

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A technique for evaluating optical confinement in GaN-based lasing structures

S. Bidnyk, B. D. Little, J. J. Song, and T. J. Schmidt

Appl. Phys. Lett. 75, 2163 (1999); http://dx.doi.org/10.1063/1.124952 (3 pages) | Cited 4 times

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We present a technique for evaluating optical confinement in GaN-based lasing structures by studying their spectrally resolved near-field pattern under high optical excitation. Emission spectra were found to be strongly dependent on the position of the collection optics relative to the active region when the sample was excited above the lasing threshold. The spatially resolved spectra contain a modulation signature that can be used to deduce the optical confinement characteristics. We show that the observed index-guided modes result from multiple internal reflections at angles very close to the critical angle for total internal reflection between the semiconductor layers with different refractive indices. This technique was used to evaluate the degree of optical confinement in GaN epilayers and GaN/AlGaN separate confinement heterostructures. The implications of this study on the design of GaN-based laser diodes are discussed. © 1999 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes

Double-chirped semiconductor mirror for dispersion compensation in femtosecond lasers

R. Paschotta, G. J. Spühler, D. H. Sutter, N. Matuschek, U. Keller, M. Moser, R. Hövel, V. Scheuer, G. Angelow, and T. Tschudi

Appl. Phys. Lett. 75, 2166 (1999); http://dx.doi.org/10.1063/1.124953 (3 pages) | Cited 7 times

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A double-chirped mirror structure with broadband negative dispersion was realized with semiconductor technology. The necessary high precision of the fabrication was achieved by using special calibration structures. A single reflection on the obtained low-loss mirror produces sufficient negative dispersion for dispersion compensation in a femtosecond laser cavity. In this way we demonstrate 200 fs pulses from a compact Nd:glass laser without any additional dispersion compensation. © 1999 American Institute of Physics.
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42.79.Bh Lenses, prisms and mirrors
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.86.+b Optical workshop techniques
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Rz Doped-insulator lasers and other solid state lasers

Spectral analysis of InGaAs/GaAs quantum-dot lasers

P. M. Smowton, E. J. Johnston, S. V. Dewar, P. J. Hulyer, H. D. Summers, A. Patanè, A. Polimeni, and M. Henini

Appl. Phys. Lett. 75, 2169 (1999); http://dx.doi.org/10.1063/1.124954 (3 pages) | Cited 14 times

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The cause of the unusual spectral distribution, often observed in InGaAs/GaAs quantum-dot lasers, is investigated by analyzing the spectra from devices fabricated with different substrate thickness (100–400 μm). Using a Fourier transform analysis to determine the optical path length, it is found that the measured modulation period correlates with the device thickness. Such a result provides evidence for spectral modulation mediated by the device structure rather than the quantum-dot material itself and is consistent with the idea that the modulation is due to a mode propagating in the transparent substrate. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
02.30.Nw Fourier analysis
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Optical investigation of infrared dyes in hybrid thin films

M. Casalboni, F. De Matteis, P. Prosposito, and R. Pizzoferrato

Appl. Phys. Lett. 75, 2172 (1999); http://dx.doi.org/10.1063/1.124955 (3 pages) | Cited 16 times

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We report on steady-state absorption and emission measurements for two infrared (IR) dye molecules, IR5 and IR1051, incorporated in hybrid organic/inorganic zirconia-based thin films synthesized with a sol-gel technique. For comparison, measurements in liquid solutions have also been carried out, and an estimation of the relative quantum efficiency in solid glassy material with respect to liquid solution is reported. Absorption and emission spectra are discussed in terms of physical and chemical interactions with the host matrix. The present work provides the evidence of successful doping of solid films with dyes for planar waveguides emitting in the infrared region up to 1.3 μm. © 1999 American Institute of Physics.
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78.66.-w Optical properties of specific thin films
42.79.Wc Optical coatings
33.20.Ea Infrared spectra
78.30.-j Infrared and Raman spectra
33.50.-j Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion)
78.55.-m Photoluminescence, properties and materials

Enhanced harmonic generation in aperiodic optical superlattices

Ben-Yuan Gu, Bi-Zhen Dong, Yan Zhang, and Guo-Zhen Yang

Appl. Phys. Lett. 75, 2175 (1999); http://dx.doi.org/10.1063/1.124956 (3 pages) | Cited 31 times

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We find that harmonic generation can be enhanced with aperiodic optical superlattice (AOS) structures realized by inverting poled ferroelectric domains in sample. The optimal design of the AOS can be achieved with use of the simulated annealing method. The constructed AOSs can implement multiple wavelength second-harmonic generation and the coupled third-harmonic generation with an identical effective nonlinear coefficient. The simulations show that the constructed AOSs can enhance harmonic generation compared with the Fibonacci optical superlattice. The physical origin of this enhancement is ascribed to the constructive interference effect. © 1999 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Wc Optical coatings
78.66.-w Optical properties of specific thin films
77.80.Dj Domain structure; hysteresis

Stress-dependent growth kinetics of ultraviolet-induced refractive index change and defect centers in highly Ge-doped SiO2 core fibers

Tsung-Ein Tsai, Thierry Taunay, and E. Joseph Friebele

Appl. Phys. Lett. 75, 2178 (1999); http://dx.doi.org/10.1063/1.124957 (3 pages)

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The evolution of the index change of type-IIa gratings observed in 28 mol % Ge–SiO2 core fibers with 1.8 μm core diameter under various strains was measured from the optical spectra, and the induced defects at high and low strains were studied with electron spin resonance. Data will be presented to show that the index modulation (Δnmod) of type-IIa gratings is likely associated with Ge E′ centers. © 1999 American Institute of Physics.
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42.81.-i Fiber optics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.J- Point defects and defect clusters
76.30.Mi Color centers and other defects
42.79.Dj Gratings
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Dithered-edge sampling of terahertz pulses

Jake Bromage, Ian A. Walmsley, and C. R. Stroud

Appl. Phys. Lett. 75, 2181 (1999); http://dx.doi.org/10.1063/1.125396 (3 pages) | Cited 2 times

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We introduce a technique for ultrawideband measurement of terahertz pulses called dithered-edge sampling (DES). The technique makes use of a photoconductive receiver, but the detection bandwidth is much wider than that of the receiver alone. The key to increasing the bandwidth is the addition of an ultrafast optically triggered attenuator that chops the terahertz pulse before its detection. The bandwidth is limited only by the duration of the optical pulse used to trigger the attenuator. We use a combination of derivative dither and an integrating receiver to recover the terahertz field directly from the measured signal. When used alone, the slow receiver blurs the measured terahertz pulse width to 1.3 ps. However, the increased time resolution of the DES system (triggered attenuator plus receiver) allows one to measure source-limited terahertz pulse widths (400 fs in this case). © 1999 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Blue emission from Tm-doped GaN electroluminescent devices

A. J. Steckl, M. Garter, D. S. Lee, J. Heikenfeld, and R. Birkhahn

Appl. Phys. Lett. 75, 2184 (1999); http://dx.doi.org/10.1063/1.124958 (3 pages) | Cited 71 times

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Blue emission has been obtained at room temperature from Tm-doped GaN electroluminescent devices. The GaN was grown by molecular beam epitaxy on Si(111) substrates using solid sources (for Ga and Tm) and a plasma source for N2. Indium–tin–oxide was deposited on the GaN layer and patterned to provide both the bias (small area) and ground (large area) transparent electrodes. Strong blue light emission under the bias electrode was observable with the naked eye at room temperature. The visible emission spectrum consists of a main contribution in the blue region at 477 nm corresponding to the Tm transition from the 1G4 to the 3H6 ground state. A strong near-infrared peak was also observed at 802 nm. The relative blue emission efficiency was found to increase linearly with bias voltage and current beyond certain turn-on levels. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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Effects of growth temperature on GaN nucleation layers

M. S. Yi, H. H. Lee, D. J. Kim, S. J. Park, D. Y. Noh, C. C. Kim, and J. H. Je

Appl. Phys. Lett. 75, 2187 (1999); http://dx.doi.org/10.1063/1.124959 (3 pages) | Cited 14 times

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The effects of growth temperature on the microscopic structure of GaN nucleation layers were studied in a synchrotron x-ray scattering experiment. As the growth temperature increases from 467 to 655 °C, the stacking of GaN changes from random stacking to a mixture of cubic and hexagonal stacking. With increasing the growth temperature, the order in the atomic layer positions in the out-of-plane direction increases and the mosaic distribution becomes narrow. The optimal photoluminescence spectrum was obtained on the GaN epilayer deposited on the nucleation layer grown at 505 °C. © 1999 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Microscopy of electronic states contributing to lasing in ridge quantum-wire laser structure

Shinichi Watanabe, Shyun Koshiba, Masahiro Yoshita, Hiroyuki Sakaki, Motoyoshi Baba, and Hidefumi Akiyama

Appl. Phys. Lett. 75, 2190 (1999); http://dx.doi.org/10.1063/1.124960 (3 pages) | Cited 2 times

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Distribution of electronic states inside ridge quantum-wire (QWR) laser cavity was investigated using spatially and spectrally resolved top-view photoluminescence (PL) imaging method. PL inhomogeneity in QWR has shown that the electronic states were perturbed by the fluctuation of vertical thickness in the scale of ∼ nm, while the optical waveguide was not. The PL images of QWR were traced up to the lasing condition to examine the lasing origin. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.45.+h Stimulated emission
73.20.At Surface states, band structure, electron density of states
78.47.-p Spectroscopy of solid state dynamics
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Photoinduced luminescence quenching and insolubilization of star-like branched organosilicon compounds

Tooru Sonoda, Hidayat Rahmat, Masanori Ozaki, Katsumi Yoshino, Wolfgang Schneider, Kyung Koo Lee, Akinobu Naka, and Mitsuo Ishikawa

Appl. Phys. Lett. 75, 2193 (1999); http://dx.doi.org/10.1063/1.124961 (3 pages) | Cited 2 times

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Soluble star-like branched organosilicon compounds having silanylene and oligothienylene in their arms are stable in vacuum upon light irradiation, and remain highly light emissive, but degrade upon light irradiation in air. Though the change of absorption spectrum upon light irradiation is not so large, photoluminescence (PL) intensity is strongly suppressed without notable change in spectrum shape. Remarkable shortening of PL decay time due to degradation upon light irradiation in air has been confirmed by time-resolved PL measurement. These results are discussed in terms of scission of Si–Si bonds and oxidation. Optical recording utilizing photoinduced insolubilization of these materials has also been demonstrated. © 1999 American Institute of Physics.
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78.55.Kz Solid organic materials
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
78.47.-p Spectroscopy of solid state dynamics

Evidence of multiple states of ordered structures and a phase transition in magnetic fluid films under perpendicular magnetic fields

Chin-Yih Hong, Herng-Er Horng, F. C. Kuo, S. Y. Yang, H. C. Yang, and J. M. Wu

Appl. Phys. Lett. 75, 2196 (1999); http://dx.doi.org/10.1063/1.124962 (3 pages) | Cited 21 times

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When a magnetic fluid thin film is subjected to a perpendicular magnetic field H, the particles in the film agglomerate and form particle columns. With the increasing H, the columns evolve from a disordered column phase to the first-level hexagonal structural pattern and finally reach the second-level hexagonal structural pattern through a phase transition. During the transition phase, each column split into two columns. The split of a column may be attributed to the further alignment of the magnetic particles in each column under higher H’s. Hence the dipolar repulsive force in each column becomes dominant and causes the split of a column. The formation of the second-level hexagonal structure reveals that the minimum energy of the equilibrium system of magnetic fluid thin films under perpendicular magnetic fields has multiple local minima when H varies. © 1999 American Institute of Physics.
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75.50.Mm Magnetic liquids
75.50.Tt Fine-particle systems; nanocrystalline materials
75.70.Ak Magnetic properties of monolayers and thin films
68.15.+e Liquid thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
82.70.-y Disperse systems; complex fluids

Room-temperature 1.3 μm emission from InAs quantum dots grown by metal organic chemical vapor deposition

J. Bloch, J. Shah, W. S. Hobson, J. Lopata, and S. N. G. Chu

Appl. Phys. Lett. 75, 2199 (1999); http://dx.doi.org/10.1063/1.124963 (3 pages) | Cited 19 times

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Using metal organic chemical vapor deposition, we have fabricated self-organized quantum dots that emit efficiently at 1.3 μm at room temperature. They are grown on GaAs and consist of InAs covered with an InGaAs cap layer. Their density is 2×1010 cm−2 as determined by transmission electron microscopy. Room-temperature photoluminescence shows a 36 meV broad line at 1.3 μm, corresponding to the quantum-dot ground state, with excellent uniformity across the wafer. The efficiency of this emission is reduced only by a factor of 4 with respect to low temperature showing the high quality of the sample. © 1999 American Institute of Physics.
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78.55.Cr 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
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Phase separation and ordering coexisting in InxGa1−xN grown by metal organic chemical vapor deposition

M. K. Behbehani, E. L. Piner, S. X. Liu, N. A. El-Masry, and S. M. Bedair

Appl. Phys. Lett. 75, 2202 (1999); http://dx.doi.org/10.1063/1.124964 (3 pages) | Cited 56 times

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We have recently reported the occurrence of phase separation in InxGa1−xN samples with x>0.25. Theoretical studies have suggested that InxGa1−xN can phase-separate asymmetrically into a low InN% phase and an ordered high InN% phase. In this letter, we report on the existence of simultaneous phase separation and ordering of InxGa1−xN samples with x>0.25. In these samples, phase separation was detected by both transmission electron microscopy selected area diffraction (TEM-SAD) and x-ray diffraction. Ordering was detected by both imaging and TEM-SAD. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
64.75.-g Phase equilibria

Model for crystallization kinetics: Deviations from Kolmogorov–Johnson–Mehl–Avrami kinetics

Mario Castro, Francisco Domínguez-Adame, Angel Sánchez, and Tomás Rodríguez

Appl. Phys. Lett. 75, 2205 (1999); http://dx.doi.org/10.1063/1.124965 (3 pages) | Cited 19 times

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We propose a simple and versatile model to understand the deviations from the well-known Kolmogorov–Johnson–Mehl–Avrami kinetics theory found in metal recrystallization and amorphous semiconductor crystallization. We analyze the kinetics of the transformation and the grain-size distribution of the product material, finding a good overall agreement between our model and available experimental data. The information so obtained could help to relate the mentioned experimental deviations due to preexisting anisotropy along some regions, to a certain degree of crystallinity of the amorphous phases during deposition, or more generally, to impurities or roughness of the substrate. © 1999 American Institute of Physics.
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81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
81.15.Aa Theory and models of film growth
64.60.Q- Nucleation
61.43.-j Disordered solids
64.70.D- Solid-liquid transitions
81.10.Jt Growth from solid phases (including multiphase diffusion and recrystallization)
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
61.72.-y Defects and impurities in crystals; microstructure
68.35.Dv Composition, segregation; defects and impurities
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology

GaAs nanostructures and films deposited by a Cu-vapor laser

L. N. Dinh, S. Hayes, C. K. Saw, W. McLean, M. Balooch, and J. A. Reimer

Appl. Phys. Lett. 75, 2208 (1999); http://dx.doi.org/10.1063/1.124966 (3 pages) | Cited 2 times

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The properties of GaAs nanoclusters and films deposited on substrates by a Cu-vapor laser were investigated. Nanoclusters of GaAs were produced by laser ablating a GaAs target in an Ar background gas. X-ray diffraction and transmission electron microscopy revealed that these GaAs nanoclusters had randomly oriented crystalline cores and As-rich amorphous oxide outer shells. These clusters assembled, upon vacuum annealing, along step edges and at defects on substrates to form wire-like structures. Our results also showed that GaAs films, when deposited in vacuum, did not have crystalline cores and were rich in As. Postdeposition annealing in vacuum to between 400 and 500 °C drove off the excess As. The stoichiometry of the films was confirmed by both Auger electron spectroscopy and x-ray photoelectron spectroscopy. © 1999 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials
81.15.Fg Pulsed laser ablation deposition
61.66.Bi Elemental solids
61.66.Dk Alloys

Oxygen-induced amorphous structure of tungsten thin films

Y. G. Shen, Y. W. Mai, W. E. McBride, D. R. McKenzie, and Q. C. Zhang

Appl. Phys. Lett. 75, 2211 (1999); http://dx.doi.org/10.1063/1.124967 (3 pages) | Cited 10 times

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A combination of energy-filtered electron diffraction, electron energy-loss spectroscopy, transmission electron microscopy, and x-ray diffraction are used to establish that oxygen impurities incorporated in tungsten films prepared by magnetron sputtering in the early stage of the deposition play a dominant role in the formation of an amorphous phase. Energy-filtered electron diffraction data collected from a range of amorphous films were Fourier transformed to a reduced density function (RDF) and matched with an amorphous model. The results show that better agreement with the experimental RDF is achieved if the amorphous model consists of a random continuous matrix of clusters with W3O-like symmetry. © 1999 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
79.20.Kz Other electron-impact emission phenomena
61.43.Dq Amorphous semiconductors, metals, and alloys
68.55.-a Thin film structure and morphology

Coexistence of hexagonal and orthorhombic structures in NiSi films containing Pt

J. Y. Dai, D. Mangelinck, and S. K. Lahiri

Appl. Phys. Lett. 75, 2214 (1999); http://dx.doi.org/10.1063/1.124968 (3 pages) | Cited 7 times

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The structure of Ni(Pt)Si films was investigated using high-resolution electron microscopy (HREM), electron microdiffraction and image simulation techniques. Such films with 5 at. % Pt were sputter deposited onto (111) Si and annealed for 1 min at 500 °C by rapid thermal annealing. Analysis of the HREM pictures, diffraction patterns, and simulation results has revealed that NiSi films containing Pt can assume both hexagonal and orthorhombic structures that can coexist in the same film. The presence of film stresses and Pt seems to play a role in the formation of hexagonal NiSi. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.60.Bs Mechanical and acoustical properties
81.40.Gh Other heat and thermomechanical treatments

Diameter grouping in bulk samples of single-walled carbon nanotubes from optical absorption spectroscopy

O. Jost, A. A. Gorbunov, W. Pompe, T. Pichler, R. Friedlein, M. Knupfer, M. Reibold, H.-D. Bauer, L. Dunsch, M. S. Golden, and J. Fink

Appl. Phys. Lett. 75, 2217 (1999); http://dx.doi.org/10.1063/1.124969 (3 pages) | Cited 79 times

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The influence of the synthesis parameters on the mean characteristics of single-wall carbon nanotubes in soot produced by the laser vaporization of graphite has been analyzed using optical absorption spectroscopy. The abundance and mean diameter of the nanotubes were found to be most influenced by the furnace temperature and the cobalt/nickel catalyst mixing ratio. Via an analysis of the fine structure in the optical spectra, the existence of preferred nanotube diameters has been established and their related fractional abundance could be determined. The results are consistent with nanotubes located mainly around the armchair axis. © 1999 American Institute of Physics.
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78.66.Tr Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
78.30.Na Fullerenes and related materials
78.40.Ri Fullerenes and related materials
81.05.ub Fullerenes and related materials
82.30.Vy Homogeneous catalysis in solution, polymers and zeolites

Thermal expansion measurements of glass-forming alloys in the melt and the undercooled state under microgravity conditions

B. Damaschke and K. Samwer

Appl. Phys. Lett. 75, 2220 (1999); http://dx.doi.org/10.1063/1.124970 (3 pages) | Cited 17 times

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We present measurements of the thermal expansion of the glass forming alloys Zr57Cu15.4Ni12.6Nb5Al10, Zr65Cu17.5Al7.5Ni10, Zr11Cu47Ti34Ni8, Zr60Cu18Al10Ni9Co3, Pd78Cu6Si16, and Pd82Si18 in the melt and the undercooled state in the TEMPUS facility under microgravity conditions. The samples were imaged with a high-resolution charge-coupled device-camera with on-board recording. After the mission, the video tapes were analyzed by digital image processing. The volume was found to be a linear function of temperature in the temperature range investigated. The thermal expansion coefficients in the melt and the undercooled state are between 5.5×10−5 and 7.9×10−5 K−1. The volume increment at the melting point was between 1% and 2.1%. Phase separations could be observed by a change of the slope of the volume versus temperature curve. The thermal expansion data can be interpreted qualitatively in terms of the free volume model. © 1999 American Institute of Physics.
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65.40.De Thermal expansion; thermomechanical effects
81.70.Ha Testing in microgravity environments
64.70.D- Solid-liquid transitions

Epitaxial growth of Y2O3:Eu thin films on LaAlO3

H-J. Gao, D. Kumar, K. G. Cho, P. H. Holloway, R. K. Singh, X. D. Fan, Y. Yan, and S. J. Pennycook

Appl. Phys. Lett. 75, 2223 (1999); http://dx.doi.org/10.1063/1.124971 (3 pages) | Cited 15 times

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We report the epitaxial growth of europium-activated yttrium oxide (Y2O3:Eu) (001) thin films on LaAlO3 (001) using laser ablation deposition at a substrate temperature of 775 °C and 10 Hz pulse repetition rate. The orientation relationship between the films and the substrates is [110]Y2O3∥[100]LaAlO3 and [−110]Y2O3∥[010]LaAlO3 which results in a lattice mismatch of only 0.8%. Transmission electron microscopy (TEM) of the films reveals the single crystalline Y2O3:Eu thin film to contain small pores. Scanning transmission electron microscopy (STEM) imaging of the films shows the substrate always terminates with the Al sublattice. Moreover, the STEM reveals that no precipitates of Eu had formed in the films. © 1999 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
68.55.-a Thin film structure and morphology
81.05.Rm Porous materials; granular materials

Oxygen arrangement on Hg0.5Tl0.5Ba2CuOx (100) surface studied by high-resolution electron microscopy

Takeo Oku and Satoru Nakajima

Appl. Phys. Lett. 75, 2226 (1999); http://dx.doi.org/10.1063/1.124972 (3 pages) | Cited 12 times

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Oxygen arrangement on Hg0.5Tl0.5Ba2CuOx (100) surface was studied by high-resolution electron microscopy. The {100} planes were found to be stable and to have preferred atomic surface. A surface structure model of Hg0.5Tl0.5Ba2CuOx was proposed and compared to the image calculations, which indicated the surface consists of Ba layers and oxygen atoms on the (Hg, Tl) layers. The present work indicates that the stable {100} planes of Hg-1201-type superconducting oxides would be suitable for the future device application. © 1999 American Institute of Physics.
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74.72.-h Cuprate superconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

X-ray-absorption studies of boron-doped diamond films

H. H. Hsieh, Y. K. Chang, W. F. Pong, M.-H. Tsai, F. Z. Chien, P. K. Tseng, I. N. Lin, and H. F. Cheng

Appl. Phys. Lett. 75, 2229 (1999); http://dx.doi.org/10.1063/1.124973 (3 pages) | Cited 5 times

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X-ray-absorption near-edge structure (XANES) measurements have been performed for a variety of boron-doped and undoped diamond films at the C K edge using the sample drain current mode. The C K-edge XANES spectra of B-doped diamonds resemble that of the undoped diamond regardless of the B concentration, which suggests that the overall bonding configuration of the C atom is unaltered. B impurities are found to enhance both the sp3- and sp2-bond derived resonance features in the XANES spectra. © 1999 American Institute of Physics.
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78.70.Dm X-ray absorption spectra
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.ub Fullerenes and related materials
61.72.S- Impurities in crystals
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Thermal relaxation processes probed by intersubband and inter-valence-band transitions in Si/Si1−xGex multiple quantum wells

B. Adoram, D. Krapf, J. Shappir, A. Sa’ar, M. Levy, R. Beserman, S. G. Thomas, and K. L. Wang

Appl. Phys. Lett. 75, 2232 (1999); http://dx.doi.org/10.1063/1.124974 (3 pages) | Cited 1 time

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Thermal relaxation processes due to strain relaxation and Si/Ge interdiffusion were investigated in pseudomorphic p-type SiGe/Si quantum wells using infrared-polarization-resolved absorption spectroscopy. The samples were annealed from room temperature up to 1060 °C and intersubband transitions between the lowest heavy-hole states and inter-valence-band transitions between heavy-hole and spin-split-off hole states were utilized to probe thermal activation processes. The strain relaxation process is activated at temperatures above 750 °C and causes a decrease of the intersubband absorption and an increase of the inter-valence-band absorption. At temperatures above 940 °C, we found that a second process of Si/Ge interdiffusion causes a reduction of all absorption lines in the spectrum. We proposed a simple model that provides a qualitative explanation to the above results. © 1999 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Db Elemental semiconductors and insulators
78.66.Li Other semiconductors
78.30.Am Elemental semiconductors and insulators
78.30.Hv Other nonmetallic inorganics

Electrical characteristics of thin-film transistors using field-aided lateral crystallization

Seung-Ik Jun, Yong-Ho Yang, Jae-Bok Lee, and Duck-Kyun Choi

Appl. Phys. Lett. 75, 2235 (1999); http://dx.doi.org/10.1063/1.124975 (3 pages) | Cited 26 times

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A polycrystalline silicon thin-film transistor (TFT) technology, field-aided lateral crystallization (FALC), has been explored. Polycrystalline silicon thin film, as an active layer, was prepared by applying an electric field to amorphous silicon film during Ni metal-induced lateral crystallization (MILC). Compared with the conventional metal-induced lateral crystallization thin-film transistors (MILC TFTs), these field-aided lateral crystallization thin-film transistors (FALC TFTs) show a low off-state leakage current of 1.79×10−11 A at Vg = −10 V and a high on/off current ratio of 8.82×105. Moreover, the threshold voltage is lower and field-effect mobility is higher than those of MILC TFTs. Therefore, the possibility of high-performance and low-temperature (<500 °C) polycrystalline silicon TFTs was demonstrated by using FALC technology. © 1999 American Institute of Physics.
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73.61.Cw Elemental semiconductors
85.30.Tv Field effect devices
73.50.Dn Low-field transport and mobility; piezoresistance
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