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22 Jul 2002

Volume 81, Issue 4, pp. 571-782

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Real-time optoacoustic imaging using a Schlieren transducer

J. J. Niederhauser, D. Frauchiger, H. P. Weber, and M. Frenz

Appl. Phys. Lett. 81, 571 (2002); http://dx.doi.org/10.1063/1.1495539 (3 pages) | Cited 22 times

Online Publication Date: 16 July 2002

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Optoacoustics, which combines the merits and most compelling features of light and sound, is a technique for diagnosing optical tissue properties and for performing noninvasive medical imaging. We present a detection method based on Schlieren optical imaging used to record optoacoustic waves generated with 6 ns long laser pulses. These waves result from irradiation of optically absorbing targets hidden deep inside highly scattering media. Since they are generated from one single shot, Schlieren images contain all the information necessary for the reconstruction of the absorbing structures. The detection method allows on-line imaging with a spatial resolution of about 30 μm with high contrast. The proposed real-time imaging system not only enhances the level of visible detail but it is ideally suited for monitoring dynamic tissue changes. © 2002 American Institute of Physics.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
43.38.Zp Acoustooptic and photoacoustic transducers
42.79.Mt Schlieren devices
43.80.Qf Medical diagnosis with acoustics
87.63.L- Visual imaging

Highly efficient organic light-emitting diodes with a silole-based compound

H. Y. Chen, W. Y. Lam, J. D. Luo, Y. L. Ho, B. Z. Tang, D. B. Zhu, M. Wong, and H. S. Kwok

Appl. Phys. Lett. 81, 574 (2002); http://dx.doi.org/10.1063/1.1495542 (3 pages) | Cited 93 times

Online Publication Date: 16 July 2002

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Efficient light emission was obtained in a silole-based organic light-emitting diode. A high luminous current efficiency of 20 cd/A, corresponding to an external quantum efficiency of 8%, was achieved. The apparent violation of the upper theoretical limit of 5.5% for the external quantum efficiency of a singlet emitter is discussed. With a suitably designed cathode, a high power efficiency of ∼14 lm/W was obtained. A strong dependence of the power efficiency on the thickness of Alq3 layer is also observed and explained. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.30.De Semiconductor-device characterization, design, and modeling
78.66.Qn Polymers; organic compounds

Highly bright blue organic light-emitting devices using spirobifluorene-cored conjugated compounds

C. C. Wu, Y. T. Lin, H. H. Chiang, T. Y. Cho, C. W. Chen, K. T. Wong, Y. L. Liao, G. H. Lee, and S. M. Peng

Appl. Phys. Lett. 81, 577 (2002); http://dx.doi.org/10.1063/1.1493669 (3 pages) | Cited 55 times

Online Publication Date: 16 July 2002

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An efficient and morphologically stable pyrimidine-containing spirobifluorene-cored oligoaryl, 2,7-bis[2-(4-tert-butylphenyl)pyrimidine-5-yl]-9,9′-spirobifluorene (TBPSF), as an emitter or a host for blue organic light-emitting devices (OLEDs), is reported. The steric hindrance inherent with the molecular structure renders the material a record-high neat-film photoluminescence (PL) quantum yield of 80% as a pure blue emitter (PL peak at 430 nm) of low molecular weight, and a very high glass-transition temperature (Tg) of 195 °C. Blue OLEDs employing this compound as the emitter or the emitting host exhibit unusual endurance for high currents over 5000 mA/cm2. When TBPSF is used as a host for perylene in a blue OLED, maximal brightness of ∼80 000 cd/m2 had been achieved, representing the highest values reported for blue OLEDs under dc driving. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
78.55.Kz Solid organic materials
78.55.Bq Liquids

Chiral wave propagation manifold of the photonic quantum-ring laser

B. H. Park, J. Bae, M. J. Kim, and O’Dae Kwon

Appl. Phys. Lett. 81, 580 (2002); http://dx.doi.org/10.1063/1.1495545 (3 pages) | Cited 10 times

Online Publication Date: 16 July 2002

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A torus knot model is presented to analyze the chiral wave propagation of photonic quantum-ring lasers in a three-dimensional Rayleigh–Fabry–Perot toroidal cavity. The Rayleigh–Fabry–Perot cavity gives rise to peculiar multichromatic spectra with nonequal intermode spacings. In particular, the knot model analysis suggests a strange three-dimensional effective index ellipsoid for the cavity with a large birefringence of neff3D(z)−neff2D(x,y) ≈ 0.4–0.5. © 2002 American Institute of Physics.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Ah General laser theory

Current-spreading-induced bistability in bipolar cascade vertical-cavity surface-emitting lasers

T. Knödl, R. Michalzik, M. Golling, and K. J. Ebeling

Appl. Phys. Lett. 81, 583 (2002); http://dx.doi.org/10.1063/1.1494861 (3 pages) | Cited 4 times

Online Publication Date: 16 July 2002

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We present experimental evidence that current spreading in the cavity of two-stage bipolar cascade vertical-cavity surface-emitting lasers is responsible for the formation of bistability loops in the light versus current characteristics. The bistable behavior strongly varies with the detuning between cavity resonance and gain maximum and is attributed to the wavelength and carrier density dependent absorption coefficient. In order to explain the measured dependencies, an analytical model is presented that very well matches the light output characteristics. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Pc Optical bistability, multistability, and switching, including local field effects
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Fc Modulation, tuning, and mode locking

High performance germanium-on-silicon detectors for optical communications

Silvia Famà, Lorenzo Colace, Gianlorenzo Masini, Gaetano Assanto, and Hsin-Chiao Luan

Appl. Phys. Lett. 81, 586 (2002); http://dx.doi.org/10.1063/1.1496492 (3 pages) | Cited 47 times

Online Publication Date: 16 July 2002

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We demonstrate fast and efficient germanium-on-silicon p-i-n photodetectors for optical communications, with responsivities as high as 0.89 and 0.75 A/W at 1.3 and 1.55 μm, respectively, time response <200 ps and dark currents as low as 1.2 μA. Ge was epitaxially grown on Si by chemical vapor deposition, employing a low temperature buffer and cyclic thermal annealing to reduce the dislocation density. The overall performance is well suited for >2.5 Gb/s integrated receivers for the second and third fiber spectral windows. © 2002 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.05.Cy Elemental semiconductors
85.60.Dw Photodiodes; phototransistors; photoresistors
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Fluorescence quantum efficiency measurements of excitation and nonradiative deexcitation processes of rare earth 4f-states in chalcogenide glasses

S. M. Lima, A. S. S. de Camargo, L. A. O. Nunes, T. Catunda, and D. W. Hewak

Appl. Phys. Lett. 81, 589 (2002); http://dx.doi.org/10.1063/1.1495879 (3 pages) | Cited 7 times

Online Publication Date: 16 July 2002

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Thermal lens spectroscopic measurements were performed to quantitatively determine the fluorescence quantum efficiency (η) of different luminescence mechanisms in Nd3+ chalcogenide glasses. Low energy (<1.7 eV) direct resonant pumping at Nd3+ infrared lines resulted in η ∼ 1. High energy ( ∼ 2.4 eV) indirect excitation via energy transfer (ET) from glass conduction band to Nd3+ 4f states, resulted in η = ∼ 0.4 (ET probability ∼ 40%). A minimum η ∼ 0.2 was obtained for intermediate excitation energies ( ∼ 2.2 eV) and attributed to back ET from the Nd3+ 4f state to the glass host. © 2002 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
71.55.Jv Disordered structures; amorphous and glassy solids

Fabrication of large periodic arrays of AlGaAs microdisks by laser-interference lithography and selective etching

K. Petter, T. Kipp, Ch. Heyn, D. Heitmann, and C. Schüller

Appl. Phys. Lett. 81, 592 (2002); http://dx.doi.org/10.1063/1.1495082 (3 pages) | Cited 10 times

Online Publication Date: 16 July 2002

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By laser-interference lithography, reactive-ion etching, and selective wet-chemical etching using a citric acid-based solution, we have fabricated large periodic arrays of AlGaAs microdisks with periods of 4 μm and disk diameters between 1.5 and 2 μm. The arrays are characterized by temperature-dependent photoluminescence spectroscopy. Taking into account the below-threshold absorption of the quantum wells inside the disks, we get disk quality factors close to the theoretical maximum value. We demonstrate that our technique allows one also to produce one-dimensionally or two-dimensionally coupled arrays of microdisks. © 2002 American Institute of Physics.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.70.Qs Photonic bandgap materials
81.65.Cf Surface cleaning, etching, patterning
78.55.Cr III-V semiconductors
78.67.De Quantum wells

Effects of absorption on coherence domain path length resolved dynamic light scattering in the diffuse regime

Anna L. Petoukhova, Wiendelt Steenbergen, Ton G. van Leeuwen, and Frits F. M. de Mul

Appl. Phys. Lett. 81, 595 (2002); http://dx.doi.org/10.1063/1.1493644 (3 pages) | Cited 8 times

Online Publication Date: 16 July 2002

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A low coherence Mach–Zehnder interferometer is developed for path length resolved dynamic light scattering in highly turbid media. The path length distribution of multiply scattered photons in Intralipid is changed by the addition of absorbing dyes. Path length distributions obtained for various absorption levels are shown to be mutually related by Lambert–Beer’s law. Furthermore, the broadening of path length resolved heterodyne light beating spectra of media with identical scattering properties is shown to be independent of the absorption coefficient. © 2002 American Institute of Physics.
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07.60.Ly Interferometers
82.70.Kj Emulsions and suspensions
78.35.+c Brillouin and Rayleigh scattering; other light scattering
87.80.-y Biophysical techniques (research methods)

Heteroepitaxial growth of a wide-gap p-type semiconductor, LaCuOS

Hidenori Hiramatsu, Kazushige Ueda, Hiromichi Ohta, Masahiro Orita, Masahiro Hirano, and Hideo Hosono

Appl. Phys. Lett. 81, 598 (2002); http://dx.doi.org/10.1063/1.1494853 (3 pages) | Cited 38 times

Online Publication Date: 16 July 2002

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High-quality epitaxial films of LaCuOS, a wide-gap p-type semiconductor, are grown on yittria-stabilized-zirconia (001) or MgO (001) single-crystal substrates by a unique method. Postannealing of a bilayer film composed of an extremely thin metallic copper layer and an amorphous LaCuOS layer at 1000 °C results in an epitaxially grown LaCuOS thin film. This thin copper layer with high orientation, which likely acts as an epitaxial initiator, is essential for epitaxial growth. The resulting epitaxial films exhibit relatively intense ultraviolet emission associated with excitons at room temperature, confirming the high crystal quality of the films. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
78.66.Li Other semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.55.Hx Other solid inorganic materials
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
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Photoluminescence stabilization of anodically-oxidized porous silicon layers by chemical functionalization

Rabah Boukherroub, Danial D. M. Wayner, and David J. Lockwood

Appl. Phys. Lett. 81, 601 (2002); http://dx.doi.org/10.1063/1.1492306 (3 pages) | Cited 25 times

Online Publication Date: 16 July 2002

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Electrochemical oxidation of porous silicon (PSi) produces a surface that is covered with native silicon–hydrogen (Si–Hx) bonds and regions with oxidized Si–Si back-bonds (OSi–Hx). Such anodically oxidized PSi layers were chemically modified using 1-decene under thermal conditions. The hydrosilylation reaction consumes mainly the nonoxidized Si–Hx bonds and yields a surface with oxidized and alkylated regions that were characterized using transmission IR and Raman spectroscopies. The brightest photoluminescence (PL) was obtained when the PSi sample was anodized in 1 M sulfuric acid (H2SO4) at 3 mA/cm2 for 5 min. The chemical process preserves the PL and the physical properties of the porous layer. The derivatized PSi surfaces are stable in boiling CCl4 and in water. © 2002 American Institute of Physics.
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81.65.Rv Passivation
81.65.Mq Oxidation
78.55.Ap Elemental semiconductors
82.45.Jn Surface structure, reactivity and catalysis
78.55.Mb Porous materials
78.30.Am Elemental semiconductors and insulators

AlN/AlGaN superlattices as dislocation filter for low-threading-dislocation thick AlGaN layers on sapphire

Hong-Mei Wang, Jian-Ping Zhang, Chang-Qing Chen, Q. Fareed, Jin-Wei Yang, and M. Asif Khan

Appl. Phys. Lett. 81, 604 (2002); http://dx.doi.org/10.1063/1.1494858 (3 pages) | Cited 55 times

Online Publication Date: 16 July 2002

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We report on an approach of using AlN/AlGaN superlattices (SLs) for threading-dislocation-density reduction to grow high quality thick AlGaN on sapphire. Using x-ray diffraction (XRD) measurements and etch pits counting by atomic force microscopy, we show that the insertion of AlN/AlGaN SLs suppresses the material mosaicity and decreases the threading dislocation density by two orders of magnitude, and then eliminates cracking. Dislocation densities deduced from the XRD results and those from chemical etching are in a good agreement. © 2002 American Institute of Physics.
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68.65.Cd Superlattices
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Ps Atomic force microscopy (AFM)
81.05.Ea III-V semiconductors
85.60.Jb Light-emitting devices

Structural characterization of a porous low-dielectric-constant thin film with a non-uniform depth profile

Eric K. Lin, Hae-Jeong Lee, Gary W. Lynn, Wen-li Wu, and Mark L. O’Neill

Appl. Phys. Lett. 81, 607 (2002); http://dx.doi.org/10.1063/1.1495079 (3 pages) | Cited 6 times

Online Publication Date: 16 July 2002

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High-resolution x-ray reflectivity (XR) and small-angle neutron scattering (SANS) are applied to characterize both the nonuniform depth profile and pore structure of a low-dielectric-constant (low-k) thin film as prepared on a silicon substrate. The XR data show that the density depth profile has a multilayered structure with a dense, nonporous top layer and a less dense, porous bulk layer. A scattering invariant analysis of the SANS data is used to determine the average chord length of the pores, (14.8±2.0) nm, independent of the depth profile. Given the elemental composition of the film, the XR and SANS data are combined to calculate the mass density of the top layer, (1.13±0.05) g/cm3, the porosity of the less dense layer, (0.28±0.10), and the wall density, (0.92±0.15) g/cm3. © 2002 American Institute of Physics.
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77.84.Jd Polymers; organic compounds
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
77.22.Ch Permittivity (dielectric function)

Direct transformation of cubic diamond to hexagonal diamond

Hongliang He, T. Sekine, and T. Kobayashi

Appl. Phys. Lett. 81, 610 (2002); http://dx.doi.org/10.1063/1.1495078 (3 pages) | Cited 22 times

Online Publication Date: 16 July 2002

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For a long time, hexagonal diamond has been formed only by static and shock wave compression of well-crystallized graphites. Here, we demonstrate that cubic diamond loses its structure stability and transforms to hexagonal diamond in massive. This transformation has been completed in nanoseconds under a shock wave compression of cubic diamond, in which the shock pressure and temperature are only tens of giga pascal and hundreds of kelvin, thermodynamically being within the stability of cubic diamond. The formation of hexagonal diamond is interpreted as a direct transition (solid to solid) of cubic diamond by a kinetic mechanism due to the shear stress and enhanced temperature induced by the rapid shock wave compression. © 2002 American Institute of Physics.
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64.70.K- Solid-solid transitions
62.50.-p High-pressure effects in solids and liquids

Role of the wetting layer in the carrier relaxation in quantum dots

S. Sanguinetti, K. Watanabe, T. Tateno, M. Wakaki, N. Koguchi, T. Kuroda, F. Minami, and M. Gurioli

Appl. Phys. Lett. 81, 613 (2002); http://dx.doi.org/10.1063/1.1495525 (3 pages) | Cited 31 times

Online Publication Date: 16 July 2002

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We present picosecond time resolved photoluminescence measurements of GaAs/AlGaAs quantum dot structures—grown by modified droplet epitaxy—where no wetting layer is connecting the dots. We find a fast carrier relaxation time (30 ps) to the dot ground state, which becomes even faster for increasing the photogenerated carrier injection. This shows that the two–dimensional character of the wetting layer is not relevant in determining the quantum dot capture, in contrast with the conclusions of several models so far presented in literature. We discuss the role of the barrier states as well as the possibility of Auger processes involving the zero-dimensional levels of the quantum dots. © 2002 American Institute of Physics.
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73.21.La Quantum dots
78.67.Hc Quantum dots
73.63.Kv Quantum dots
81.07.Ta Quantum dots
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.47.-p Spectroscopy of solid state dynamics

Large-scale ordered macroporous SiO2 thin films by a template-directed method

Yong-Hong Ye, Simona Badilescu, and Vo-Van Truong

Appl. Phys. Lett. 81, 616 (2002); http://dx.doi.org/10.1063/1.1495902 (3 pages) | Cited 16 times

Online Publication Date: 16 July 2002

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Ordered three-dimensional macroporous SiO2 films were fabricated by colloidal crystal templating. Scanning electron microscope measurements showed that the size of the air sphere replicates that of the initial polystyrene spheres, and that the porous sample exhibits long-range order. Optical measurements show that the macroporous sample exhibits the behavior of a photonic band gap, indicating crystalline order in the sample. Fourier-transform infrared measurements revealed that a strong network of Si–O–Si bonds have been formed throughout the voids of the template before the solidification of the gel. It is proposed that this network hinders the large volume shrinkage during the subsequent heat treatment, and thus high-quality large-scale ordered macroporous films can be obtained. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Rm Porous materials; granular materials
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
78.66.Nk Insulators
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
61.43.Gt Powders, porous materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
42.70.Qs Photonic bandgap materials
81.40.Gh Other heat and thermomechanical treatments
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.50.Lt Crystal binding; cohesive energy
78.30.Hv Other nonmetallic inorganics

Metal–insulator transition at room temperature and infrared properties of Nd0.7Eu0.3NiO3 thin films

F. Capon, P. Laffez, J.-F. Bardeau, P. Simon, P. Lacorre, and M. Zaghrioui

Appl. Phys. Lett. 81, 619 (2002); http://dx.doi.org/10.1063/1.1493645 (3 pages) | Cited 15 times

Online Publication Date: 16 July 2002

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Nd0.7Eu0.3NiO3 thin films are deposited by rf sputtering and subsequent oxygen pressure annealing on (100) oriented silicon substrate. We characterize the thermochromic properties of films by measuring electrical transition, infrared transmittance, and reflectance. The thermochromic effect at room temperature is observed. Resistivity measurements exhibit a sharper hysteresis loop than is usually observed in NdNiO3 thin films. Infrared properties in the 8–14 μm wavelength range spectra reveal a contrast of 30% in reflectance and 55% in transmittance. © 2002 American Institute of Physics.
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71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions
78.66.Nk Insulators
81.40.Rs Electrical and magnetic properties related to treatment conditions
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Ng Insulators
78.30.Hv Other nonmetallic inorganics
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Role of copper in the green luminescence from ZnO crystals

N. Y. Garces, L. Wang, L. Bai, N. C. Giles, L. E. Halliburton, and G. Cantwell

Appl. Phys. Lett. 81, 622 (2002); http://dx.doi.org/10.1063/1.1494125 (3 pages) | Cited 216 times

Online Publication Date: 16 July 2002

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Electron paramagnetic resonance (EPR), photoluminescence, and infrared optical absorption have been used to investigate a ZnO crystal before and after a thermal anneal for 1 h in air at 900 °C. The sample was an undoped high quality crystal grown by the chemical vapor transport method. In addition to shallow donor impurities, the crystal contained trace amounts of copper ions. Prior to the thermal anneal, these ions were all in the Cu+ (3d10) state and the observed luminescence at 5 K, produced by 364 nm light, consisted of a broad structureless band peaking at 500 nm. After the high-temperature anneal, the Cu2+ (3d9) EPR spectrum was observed and the luminescence had changed significantly. The emission then peaked near 510 nm and showed structure identical to that reported by Dingle [Phys. Rev. Lett. 23, 579 (1969)]. Our data reaffirm that the structured green emission in ZnO is associated with Cu2+ ions. We suggest that the unstructured green emission (observed before the high-temperature anneal) is donor–acceptor pair recombination involving the Cu+ acceptors. © 2002 American Institute of Physics.
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78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors
81.05.Dz II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)
61.72.Cc Kinetics of defect formation and annealing
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Local order of Sb and Bi dopants in hydrogenated amorphous germanium thin films studied by extended x-ray absorption fine structure

G. Dalba, P. Fornasini, R. Grisenti, F. Rocca, and I. Chambouleyron

Appl. Phys. Lett. 81, 625 (2002); http://dx.doi.org/10.1063/1.1496137 (3 pages) | Cited 2 times

Online Publication Date: 16 July 2002

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This letter reports on the investigation of the local order and coordination of Sb and Bi impurities in hydrogenated amorphous germanium thin films. The study uses the extended x-ray absorption fine structure technique in fluorescence mode at room temperature. The investigation includes doping concentrations ranging from 1.1×1019 to 5×1020 cm−3. For both impurities, the evidence is that the thermal equilibrium model is not applicable in this case. This result qualitatively follows the behavior of Ga and In impurities in hydrogenated amorphous germanium (a-Ge:H) samples except for Bi. These findings are consistent with data on the transport properties of Sb- and Bi-doped a-Ge:H films. © 2002 American Institute of Physics.
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61.43.Dq Amorphous semiconductors, metals, and alloys
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
78.70.Dm X-ray absorption spectra
71.55.Cn Elemental semiconductors
61.72.uf Ge and Si

Pseudodielectric function of ZnGeP2 from 1.5 to 6 eV

V. Blickle, K. Flock, N. Dietz, and D. E. Aspnes

Appl. Phys. Lett. 81, 628 (2002); http://dx.doi.org/10.1063/1.1492022 (3 pages) | Cited 2 times

Online Publication Date: 16 July 2002

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We report pseudodielectric function data 〈ε〉 = 〈εa1〉+i〈εa2〉 and 〈ε〉 = 〈εc1〉+i〈εc2〉 for the optically uniaxial material ZnGeP2, critical point energies of structures in these data, and dielectric function data for the natural oxide. Annealing reduces the values of the peaks of 〈εa2〉. © 2002 American Institute of Physics.
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77.22.Ch Permittivity (dielectric function)
81.05.Hd Other semiconductors
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Epitaxial growth of dielectric CaCu3Ti4O12 thin films on (001) LaAlO3 by pulsed laser deposition

Y. Lin, Y. B. Chen, T. Garret, S. W. Liu, C. L. Chen, L. Chen, R. P. Bontchev, A. Jacobson, J. C. Jiang, E. I. Meletis, J. Horwitz, and H.-D. Wu

Appl. Phys. Lett. 81, 631 (2002); http://dx.doi.org/10.1063/1.1490624 (3 pages) | Cited 55 times

Online Publication Date: 16 July 2002

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High dielectric CaCu3Ti4O12 (CCTO) thin films were epitaxially grown on (001) LaAlO3 (LAO) substrates by pulsed laser deposition. Microstructural studies by x-ray diffraction, pole figure measurements, and transmission electron microscopy show that the as-grown films are good single crystalline quality with an interface relationship of (001)CCTO//(001)LAO and [100]CCTO//[100]LAO. Dielectric property measurements show that the films have an extremely high dielectric constant with value of 10 000 at 1 MHz at room temperature. It is interesting to note that the twinned substrate results in the formation of twinning or dislocations inside the CCTO film. © 2002 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
77.22.Ch Permittivity (dielectric function)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Thermal annealing below the glass transition temperature: A general way to increase performance of light-emitting diodes based on copolyfluorenes

Yu-Hua Niu, Qiong Hou, and Yong Cao

Appl. Phys. Lett. 81, 634 (2002); http://dx.doi.org/10.1063/1.1495898 (3 pages) | Cited 23 times

Online Publication Date: 16 July 2002

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Polymer light-emitting diodes based on copolyfluorene with barium/aluminum cathode were thermally annealed at different temperatures through different time periods. It was found that by annealing just below the glass transition temperature (sub-Tg) of these copolymers the device performance was greatly enhanced. Lower turn-on voltage, higher maximum brightness, and more than two times higher external electroluminescent (EL) quantum efficiency could be achieved in this way. We found out that the enhancement in electron injection and the increase in carrier mobility after thermal annealing at a temperature close to Tg of the EL polymers are responsible for the improvement in device performance. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics

Capacitance–voltage studies of Al-Schottky contacts on hydrogen-terminated diamond

J. A. Garrido, C. E. Nebel, M. Stutzmann, E. Snidero, and P. Bergonzo

Appl. Phys. Lett. 81, 637 (2002); http://dx.doi.org/10.1063/1.1496495 (3 pages) | Cited 14 times

Online Publication Date: 16 July 2002

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The electrical properties of Al contacts on hydrogen-terminated diamond have been characterized. Capacitance–voltage experiments were carried out in order to obtain further insight into the origin of the Schottky contact behavior of Al. Schottky diodes with different areas and peripheries were fabricated and analyzed. We have found that the capacitance of these structures is not proportional to the area but to the length of the contact periphery, supporting the two-dimensional nature of the surface charge layer in hydrogen-terminated diamond. A model based on the negative electron affinity of hydrogen-terminated diamond and the work function of Al is used to explain the in-plane capacitance of the Al Schottky contacts. © 2002 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
81.05.U- Carbon/carbon-based materials
81.05.Bx Metals, semimetals, and alloys
73.40.Ns Metal-nonmetal contacts
81.05.Cy Elemental semiconductors
85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Kk Junction diodes

Influence of the growth procedure on the Cd distribution in CdSe/ZnSe heterostructures: Stranski–Krastanov versus two-dimensional islands

D. Litvinov, A. Rosenauer, D. Gerthsen, P. Kratzert, M. Rabe, and F. Henneberger

Appl. Phys. Lett. 81, 640 (2002); http://dx.doi.org/10.1063/1.1496133 (3 pages) | Cited 30 times

Online Publication Date: 16 July 2002

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Molecular beam epitaxy is used to grow different types of ZnSe/CdSe/ZnSe heterostructures. The topography of the bare CdSe surface studied with in situ atomic force microscopy is compared with high-resolution transmission electron microscopy data on overgrown structures. The growth procedure critically influences morphology and Cd distribution. Only use of thermal activation after low-temperature CdSe deposition enables the accomplishment of a distinct Stranski–Krastanov (SK) morphology with three-dimensional islands with a core of pure CdSe. Interdiffusion effects during activation of the SK transition as well as overgrowth are of minor importance. © 2002 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Ct Interface structure and roughness
68.55.-a Thin film structure and morphology
81.05.Dz II-VI semiconductors
68.37.Ps Atomic force microscopy (AFM)
68.37.Lp Transmission electron microscopy (TEM)
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation

Boron suboxide: As hard as cubic boron nitride

Duanwei He, Yusheng Zhao, L. Daemen, J. Qian, T. D. Shen, and T. W. Zerda

Appl. Phys. Lett. 81, 643 (2002); http://dx.doi.org/10.1063/1.1494860 (3 pages) | Cited 63 times

Online Publication Date: 16 July 2002

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The Vickers hardness of boron suboxide single crystals was measured using a diamond indentation method. Under a loading force of 0.98 N, our test gave an average Vickers hardness of 45 GPa. The average fracture toughness was measured as 4.5 MPa m1/2. We also measured the hardness of the cubic boron nitride and sapphire single crystals for comparison. The average measured hardness for boron suboxide was found to be very close to that of cubic boron nitride under the same loading force. Our results suggest that the boron suboxide could be a new superhard material for industrial applications, surpassed in hardness only by diamond and cubic boron nitride. © 2002 American Institute of Physics.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
62.20.M- Structural failure of materials
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