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24 Jun 1996

Volume 68, Issue 26, pp. 3677-3832

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Persistent spectral hole burning at liquid nitrogen temperature in Eu 3+‐doped aluminosilicate glass

Yalan Mao, P. Gavrilovic, S. Singh, A. Bruce, and W. H. Grodkiewicz

Appl. Phys. Lett. 68, 3677 (1996); http://dx.doi.org/10.1063/1.115740 (3 pages) | Cited 21 times

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The observation of persistent spectral hole burning (PSHB) in Eu3+‐doped aluminosilicate glass at 77 K is reported in this letter. The homogeneous linewidth of the 7F0→ 5D0 transition is measured to be ∼0.5 Å by both PSHB and fluorescence line narrowing techniques. The ratio of inhomogeneous‐to‐hole widths at 77 K is 45. The 7F0→ 5D0 transition is visible directly in transmission due to the high concentration of Eu3+. © 1996 American Institute of Physics.
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78.40.Ha Other nonmetallic inorganics
71.55.Ht Other nonmetals

High power mid‐infrared (λ∼5 μm) quantum cascade lasers operating above room temperature

Jérôme Faist, Federico Capasso, Carlo Sirtori, Deborah L. Sivco, James N. Baillargeon, Albert L. Hutchinson, Sung‐Nee G. Chu, and Alfred Y. Cho

Appl. Phys. Lett. 68, 3680 (1996); http://dx.doi.org/10.1063/1.115741 (3 pages) | Cited 191 times

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The high power operation of mid‐infrared quantum cascade lasers at temperatures up to T=320 K is reported. Gain at high temperature is optimized by a design combining low doping, a funnel injector, and a three‐well vertical transition active region. A molecular beam epitaxy grown InP top cladding layer is also used to optimize heat dissipation. A peak pulsed optical power of 200 mW and an average power of 6 mW are obtained at 300 K and at a wavelength λ=5.2 μm. The devices also operate in continuous wave up to 140 K. © 1996 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.66.Fd III-V semiconductors

Quasi‐phase matched surface emitting second harmonic generation in poled polymer waveguides

A. Otomo, G. I. Stegeman, W. H. G. Horsthuis, and G. R. Möhlmann

Appl. Phys. Lett. 68, 3683 (1996); http://dx.doi.org/10.1063/1.115742 (3 pages) | Cited 5 times

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Quasi‐phase matched (QPM) surface emitting second harmonic generation was demonstrated with nonlinear/linear multilayer waveguides in poled polymer based devices. The nonlinear/linear multilayer film was fabricated with a 4‐dimethylamino‐4′‐nitrostilbene (DANS) side chain polymer and a cross‐linkable clear polymer. Large efficiency improvement was observed with a combination of QPM and strong field parallel poling. © 1996 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Jk Polymers and organics
42.79.Gn Optical waveguides and couplers

Nonlinear optical limiting of C60, platinum poly‐yne, and tetrabenzporphyrin in the near infrared

Shekhar Guha, William T. Roberts, and B. H. Ahn

Appl. Phys. Lett. 68, 3686 (1996); http://dx.doi.org/10.1063/1.115743 (3 pages) | Cited 7 times

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Nonlinear optical limiting behavior of carbon 60 (C60), platinum poly‐yne (PPY), and tetrabenzporphyrin (TBP) was evaluated using lasers with μs and ns pulse widths at the wavelength of 750 nm in an f/5 optical setup. PPY had the lowest clamping level for ns pulses, and TBP had the lowest clamping level for μs pulses. Possible explanations for nonlinear optical behavior are provided. © 1996 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.-k Nonlinear optics

Threshold investigation of oxide‐confined vertical‐cavity laser diodes

Kent D. Choquette, W. W. Chow, M. Hagerott Crawford, K. M. Geib, and R. P. Schneider

Appl. Phys. Lett. 68, 3689 (1996); http://dx.doi.org/10.1063/1.115744 (3 pages) | Cited 16 times

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We report an experimental and theoretical analysis of the threshold properties of infrared oxide‐confined vertical‐cavity surface emitting lasers. We find good agreement between experiment and theory on the wavelength dependencies of the threshold current density and intrinsic voltage. The threshold voltage is shown to equal the sum of the calculated quasi‐Fermi energy separation and the ohmic drop arising from a record low 17 to 30 Ω series resistance in these vertical‐cavity lasers. Our analysis provides two independent means for determining the material threshold gain. A threshold gain of 500 cm−1 is found for these oxide‐confined lasers, which is half that estimated for ion‐implanted lasers with inferior electrical and optical confinement. © 1996 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Silicon heterointerface photodetector

Aaron R. Hawkins, Thomas E. Reynolds, Derek R. England, Dubravko I. Babic, Mark J. Mondry, Klaus Streubel, and John E. Bowers

Appl. Phys. Lett. 68, 3692 (1996); http://dx.doi.org/10.1063/1.115975 (3 pages) | Cited 30 times

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We report the demonstration of an infrared avalanche photodetector that uses an InGaAs absorption layer and a Si avalanche multiplication layer bonded by wafer fusion. Photocurrent measurements of the silicon heterointerface photodetector showed high response to 1.3 μm light and gains of up to 130. Frequency response measurements for the detectors yielded 3 dB bandwidth products of up to 81 GHz. © 1996 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Second harmonic generation in LiTaO3 thin films by modal dispersion and quasi phase matching

Florence Armani‐Leplingard, John J. Kingston, and David K. Fork

Appl. Phys. Lett. 68, 3695 (1996); http://dx.doi.org/10.1063/1.115976 (3 pages) | Cited 6 times

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Green light was generated by second harmonic generation in LiTaO3 thin films grown on sapphire. We describe the optical properties of the thin films grown by rf magnetron sputtering. We report on the experimental conditions for second harmonic generation by modal dispersion and quasi phase matching. For quasi phase matching, proton exchange was used to periodically deaden the nonlinearity of the crystal. © 1996 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.82.Et Waveguides, couplers, and arrays
78.66.Nk Insulators
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Investigation of nondegenerate four wave mixing in semiconductor optical amplifier through bias current modulation

H. Soto and D. Erasme

Appl. Phys. Lett. 68, 3698 (1996); http://dx.doi.org/10.1063/1.115977 (3 pages) | Cited 1 time

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An experimental study of the combination of four‐wave mixing and current modulation in a semiconductor optical amplifier is presented. The measurement of the small signal chirp parameter for the conjugate signal is performed giving results between 0 and −1 for all detuning below 1.5 THz. Its value is much smaller than that of the directly modulated amplifier and furthermore is negative. A conjugate pulse traveling along a standard fiber exhibits no noticeable broadening. The results are in very good agreement with the theory developed in the literature. © 1996 American Institute of Physics.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Optical and electrochemical properties of dc magnetron sputtered Ti–Ce oxide films

A. Azens, L. Kullman, D. D. Ragan, C. G. Granqvist, B. Hjörvarsson, and G. Vaivars

Appl. Phys. Lett. 68, 3701 (1996); http://dx.doi.org/10.1063/1.115978 (3 pages) | Cited 17 times

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Reactive dc magnetron sputtering was used to make mixed Ti–Ce oxide films with a Ce/Ti ratio γ between 0 and 0.6. Their optical and electrochemical properties were strongly dependent on the composition. Films with 0.3<γ<0.6 were optically passive under charge insertion, which makes them suitable as counterelectrodes in transparent electrochromic devices. © 1996 American Institute of Physics.
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78.66.Sq Composite materials
81.15.Cd Deposition by sputtering
82.45.-h Electrochemistry and electrophoresis

A quantum structure for high‐temperature operation of AlGaAs lasers: Multiple‐quantum barrier and multiple‐quantum well in active region

Rajesh Kumar, Shouichi Onda, Kunihiko Hara, Hironari Kuno, Takeshi Matsui, and Tetsu Kachi

Appl. Phys. Lett. 68, 3704 (1996); http://dx.doi.org/10.1063/1.115979 (3 pages) | Cited 4 times

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We propose a quantum structure of AlGaAs lasers designed for high‐temperature operation. In this design, the superlattice structure multiple‐quantum barrier (MQB) is located in the middle of active region which improves the injection efficiency of holes from the cladding into the active region, compared to MQB in cladding structure. Simulation results showed that low energy electrons can tunnel through the MQB barriers, while high energy electrons were reflected back by effective potential barrier to suppress the electron overflow from active to the cladding region. Multiple‐quantum wells (MQWs) are integrated at each side of MQB to minimize the overflow of tunneled electrons. A differential quantum efficiency change as small as 5% was achieved in the temperature range of 20–100 °C from MQB+MQW in active lasers. © 1996 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
78.66.Fd III-V semiconductors

Improved materials characterization by pressure‐dependent ultrasonic attenuation in air‐filled permeable solids

Peter B. Nagy and David Linton Johnson

Appl. Phys. Lett. 68, 3707 (1996); http://dx.doi.org/10.1063/1.115980 (3 pages) | Cited 1 time

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Recently developed airborne ultrasonic inspection techniques can supplement other methods routinely used for materials characterization of permeable solids. In particular, the velocity and attenuation of the slow compressional wave transmitted through thin plates of a few millimeter thickness can be used to assess the tortuosity and dynamic permeability of the specimen. The main advantage of the ultrasonic method over conventional flow resistivity, electrical conductivity, and other measurements is that it can be used to study the heterogeneity of the pore structure at scales comparable to the grain size. In the 100–500 kHz frequency range slow wave images can be obtained with resolution on the order of 1 mm or better. However, due to substantial viscous and scattering losses, the sensitivity of the method is relatively low therefore, the technique is limited to materials of at least 10% connected porosity and permeability higher than 200 mD. It is demonstrated in this letter that varying the air pressure significantly enhances the capabilities of slow wave inspection. Using high‐pressure air saturation significantly reduces the absorption losses so that better resolution can be achieved by increasing the frequency. Alternatively, materials of lower permeability or specimens of higher thickness can be inspected at the same frequency. In addition, scattering losses can be eliminated by subtracting images taken at the same frequency but at different pressures. © 1996 American Institute of Physics.
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43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.35.Ae Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in gases
43.35.Yb Ultrasonic instrumentation and measurement techniques

Mass spectroscopic investigations of a hydrocarbon arcjet plasma operating under diamond deposition conditions

K. R. Stalder and W. Homsi

Appl. Phys. Lett. 68, 3710 (1996); http://dx.doi.org/10.1063/1.115981 (3 pages) | Cited 4 times

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We report on mass spectroscopic measurements of species originating near the stagnation point of an arcjet plasma impinging on a tantalum surface. The plasma is produced in a 1‐kW arc through which flows a gas mixture of ∼1% methane in hydrogen. This plasma is near thermal equilibrium, except that a few species such as C2 are slow to equilibrate internally due to the large exothermicity of the reactions that form them. A polycrystalline diamond film grows on the substrate as the measurements are taken. A small gas sampling hole in the deposition substrate samples molecules as they diffuse to the surface. Two stages of differential pumping are used to form a molecular beam which is detected by a quadrupole mass spectrometer. Significant conversion of methane to acetylene (C2H2) and ethylene (C2H4) is observed, as are radicals such as CH3 and C 2H5. © 1996 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Synchrotron radiation excited etching of diamond

Haruhiko Ohashi, Eiji Ishiguro, Tomohiko Sasano, and Kosuke Shobatake

Appl. Phys. Lett. 68, 3713 (1996); http://dx.doi.org/10.1063/1.115982 (3 pages)

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We have succeeded in synchrotron radiation (SR) excited etching of crystalline diamond. It proceeds even at low temperatures at which diamond is thermally not oxidized in the gaseous environment. It has been demonstrated that any of the three types of crystalline diamond, i.e., industrial diamond made at high pressures, thin films grown by chemical vapor deposition, and natural diamond, can be etched by irradiating SR in the O2 atmosphere. From the etched pattern obtained by placing a Ni mesh made of 40 μm wires above the sample, it has been concluded that only the irradiated area is etched and thus surface excitation by SR is essential along with the supply of reactive radical species formed by photodissociation. © 1996 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
81.05.ub Fullerenes and related materials
07.85.Qe Synchrotron radiation instrumentation

Regimes of particle trapping in inductively coupled plasma processing reactors

Helen H. Hwang and Mark J. Kushner

Appl. Phys. Lett. 68, 3716 (1996); http://dx.doi.org/10.1063/1.115983 (3 pages) | Cited 15 times

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Contamination of wafers by particles in plasma processing reactors is a continuing problem affecting yields of microelectronic devices. In this letter, we report on a computational study of particle contamination of wafers in a high plasma density inductively coupled plasma (ICP) reactor. When operating with an unbiased substrate, particles readily contaminate the wafer due to high ion fluxes which produce large ion‐drag forces. Biasing the substrate with a radio frequency (rf) voltage counteracts the ion‐drag forces by increasing the opposing electrostatic forces in the sheath, thereby shielding the wafer from incoming particles. We have found three regimes of particle contamination for different ICP powers and rf biases. At high rf biases and low ICP powers, particles trap at the edge of the sheath. At low rf bias and high ICP power, ion drag forces dominate, particles do not trap, and wafer contamination is problematic. At intermediate powers and biases, particles quasitrap, leading to moderate particle contamination. © 1996 American Institute of Physics.
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Pulsed corona and dielectric‐barrier discharge processing of NO in N2

B. M. Penetrante, M. C. Hsiao, B. T. Merritt, G. E. Vogtlin, P. H. Wallman, M. Neiger, O. Wolf, T. Hammer, and S. Broer

Appl. Phys. Lett. 68, 3719 (1996); http://dx.doi.org/10.1063/1.115984 (3 pages) | Cited 55 times

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Experimental results on pulsed corona and dielectric‐barrier discharge processing of very dilute concentrations of NO in N2 are presented. These NO reduction experiments measure the G value for electron‐impact dissociation of N2 and are used to infer the effective electron mean energy in an N2 discharge plasma at atmospheric pressure. The data have been obtained from three different laboratories using widely differing electrode structures, voltage wave forms, power measurements, and chemical analyses. The NO reduction yields from the discharge reactors tested are all similar, corresponding to an electron mean energy of 4.0±0.5 eV. © 1996 American Institute of Physics.
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52.80.Hc Glow; corona
52.20.Fs Electron collisions
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
34.80.Gs Molecular excitation and ionization

Theory of improved resolution in depth profiling with sample rotation

R. Mark Bradley and Eun‐Hee Cirlin

Appl. Phys. Lett. 68, 3722 (1996); http://dx.doi.org/10.1063/1.115985 (3 pages) | Cited 16 times

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We advance a theory that explains why sample rotation during depth profiling leads to a dramatic improvement in depth resolution. When the sample is rotated, the smoothing effects of viscous flow and surface self‐diffusion can prevail over the roughening effect of the curvature‐dependent sputter yield and generate a smooth surface. If the sample is not rotated initially and the depth resolution declines, we predict that subsequent rotation leads to improved resolution. This phenomenon has already been observed experimentally. © 1996 American Institute of Physics.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.80.Az Theory and models of radiation effects

A study of the effects of post‐deposition treatments on CdS/CdTe thin film solar cells using high resolution optical beam induced current

S. A. Galloway, A. W. Brinkman, K. Durose, P. R. Wilshaw, and A. J. Holland

Appl. Phys. Lett. 68, 3725 (1996); http://dx.doi.org/10.1063/1.115986 (3 pages) | Cited 10 times

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The optical beam induced current (OBIC) technique was applied using a scanning optical microscope (SOM) to study n‐Cds/p‐CdTe thin film solar cells which had been subjected to different post‐deposition treatments. High spatial resolution maps were obtained of the current collection with and without an applied reverse bias. The quantum efficiency of the devices was also measured with high spatial resolution. The results both quantify and illustrate vividly the manner in which the well known CdCl2 treatment increases collection efficiency. The high uniformity in the best cells indicates that grain boundaries do not play a substantial role in limiting collection efficiency. © 1996 American Institute of Physics.
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84.60.Jt Photoelectric conversion
73.50.Pz Photoconduction and photovoltaic effects

Evidence of ferroelectricity weakening in the polycrystalline PbTiO3 thin films

Li Sun, Yan‐Feng Chen, Wen‐Hui Ma, Lian‐Wei Wang, Tao Yu, Ming‐Sheng Zhang, and Nai‐Ben Ming

Appl. Phys. Lett. 68, 3728 (1996); http://dx.doi.org/10.1063/1.115987 (3 pages) | Cited 7 times

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Studies on the polycrystalline PbTiO3 thin films deposited on (001) redoped n‐Si substrates by metalorganic chemical vapor deposition (MOCVD) under reduced pressure indicated the evidence of ferroelectricity weakening [Appl. Phys. Lett. 65, 1906 (1994)] when the grain size of PbTiO3 was down to the scale of ∼1100 Å. X‐ray diffraction patterns demonstrated that the perovskite unit cells have a contraction along the c‐axis direction. All transverse optical phonon modes in the films were observed shift downward in the Raman spectrum measured at 300 K. And the spontaneous polarization of PbTiO3 is determined to be 52 μC/cm2 by using Si substrates as the bottom electrodes. The three related experimental observations are conjected to be attributable to the finite size effect and the surface conditions in the ferroelectric thin film. © 1996 American Institute of Physics.
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61.05.cp X-ray diffraction
68.55.-a Thin film structure and morphology
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

X‐ray standing wave study of a Si‐adsorbed GaAs(001) surface

Munehiro Sugiyama, Satoshi Maeyama, and Masaharu Oshima

Appl. Phys. Lett. 68, 3731 (1996); http://dx.doi.org/10.1063/1.115988 (3 pages) | Cited 4 times

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The adsorption site of Si atoms deposited on a GaAs(001)‐(2×4) surface at 400 °C was investigated by back‐reflection x‐ray standing wave analysis using asymmetric (111) and (111) reflections. It was concluded that Si atoms occupy both As and Ga sites. The occupancy of Si atoms in the Ga site and the As site was estimated to be about 75% and 25%, respectively. The As coverage on a GaAs(001)‐(2×4) clean surface of 0.75 may be related to the occupancy of Si atoms in the Ga site. © 1996 American Institute of Physics.
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61.05.cm X-ray reflectometry (surfaces, interfaces, films)
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.35.Dv Composition, segregation; defects and impurities

Formation and characterization of ultrasmall dimension GeSi wire structure by using pulsed laser‐induced epitaxy

C. Deng, T. W. Sigmon, J. C. Wu, M. N. Wybourne, and J. Rack

Appl. Phys. Lett. 68, 3734 (1996); http://dx.doi.org/10.1063/1.115989 (3 pages) | Cited 7 times

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(100)Si substrates are patterned with arrays of Ge wires ∼60 nm in width and ∼6 nm in thickness. Ultrasmall dimension GeSi surface wire structures are then formed in Si in a pulsed laser‐induced epitaxy process. The wire structures are analyzed by secondary electron microscopy, atomic force microscopy, Auger electron spectroscopy, and cross‐sectional transmission electron microscopy. No defects are observed in the wires structures. However, significant side diffusion of Ge, much more than the vertical diffusion occurred during the ∼40 ns pulsed laser‐induced epitaxy process, is observed in the Si substrate. Surface evolution is also observed. Possible explanations for the abnormal Ge side diffusion are discussed. © 1996 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Tailoring the dielectric properties of HfO2–Ta2O5 nanolaminates

Kaupo Kukli, Jarkko Ihanus, Mikko Ritala, and Markku Leskela

Appl. Phys. Lett. 68, 3737 (1996); http://dx.doi.org/10.1063/1.115990 (3 pages) | Cited 12 times

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Dielectric thin films applicable, for instance, as insulating layers in electroluminescent display devices have been studied. In order to improve dielectric characteristics HfO2–Ta2O5 nanolaminates were prepared by atomic layer epitaxy at 325 °C. The nanolaminates were evaluated in capacitance and current–voltage measurements. By optimizing the layer thicknesses in the nanolaminate structures the dielectric properties, especially leakage current densities, could be tailored remarkably. The best nanolaminates showed charge storage factors improved up to 8 times when compared with those of the single oxide films. The presence of nanosize crystallites of monoclinic and metastable tetragonal HfO2 was observed by x‐ray diffraction analysis. © 1996 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.61.Ng Insulators
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

A combined in situ optical reflectance–electron diffraction study of Co/Cu and Co/Au multilayers grown by molecular beam epitaxy

C. M. Emmerson, T‐H. Shen, S. D. Evans, and H. Allinson

Appl. Phys. Lett. 68, 3740 (1996); http://dx.doi.org/10.1063/1.115991 (3 pages) | Cited 1 time

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The variation in optical reflectance during growth was investigated in situ for Co/Cu and Co/Au multilayers prepared in a molecular beam epitaxy (MBE) chamber, while the specular RHEED (reflection high energy electron diffraction) intensity was simultaneously monitored. The experimental reflectance data were found to agree well with the prediction of a numerical simulation. The final reflectance and the effective optical constants of the films are affected by the modulation of the multilayer structures. The RHEED data indicated different growth behaviors for Cu and Au and an unexpected drop in reflectance for the initial deposition of Cu on Co layers was confirmed. A similar effect was observed for the growth of Au on Co. © 1996 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
78.66.Bz Metals and metallic alloys

Reduction of internal stress in sputter‐deposited films by energetic ion bombardment

R. Nowak, Y. Horino, Y. Ando, and S. Maruno

Appl. Phys. Lett. 68, 3743 (1996); http://dx.doi.org/10.1063/1.115992 (3 pages) | Cited 11 times

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Considerable relaxation of the high internal stresses which arise in HfN thin films during their deposition by a sputtering method has been accomplished through bombarding the films with energetic silicon ions. The internal stresses have been estimated from the measurements of the surface curvature. Our results indicate a relaxation of the internal compressive stresses in the films, which occurs via a transport of the interstitial defects within the thermal spikes created by a post‐deposition energetic ion bombardment. The mechanical properties of HfN films before and after the treatment have been studied by depth‐sensing indentation technique while the structural analysis has been made using x‐ray diffraction, Rutherford backscattering, and Auger electron spectroscopy. Ion bombardment did not affect resistivity of the thin films while improving their plastic properties. © 1996 American Institute of Physics.
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61.80.Jh Ion radiation effects
68.35.Gy Mechanical properties; surface strains

Optical gain in GaInN/GaN heterostructures

G. Frankowsky, F. Steuber, V. Härle, F. Scholz, and A. Hangleiter

Appl. Phys. Lett. 68, 3746 (1996); http://dx.doi.org/10.1063/1.115993 (3 pages) | Cited 52 times

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By optical gain spectroscopy we have studied the fundamental laser properties of GaInN/GaN heterostructures grown on sapphire. Utilizing the stripe excitation method we have measured optical gain spectra at room temperature. Due to the low symmetry of the wurtzite structure and the resulting splitting of the uppermost valence bands, we find optical gain only for the TE mode. Our analysis shows that the optical gain is due to direct band‐to‐band transitions in an electron‐hole plasma. For gain amplitudes typically found in lasers, we find carrier densities up to 3×1019 cm−3, which are likely to lead to rather large threshold current densities. © 1996 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.45.+h Stimulated emission
42.55.Px Semiconductor lasers; laser diodes

Hopping conduction in SiO2 films containing C, Si, and Ge clusters

Minoru Fujii, Yoku Inoue, Shinji Hayashi, and Keiichi Yamamoto

Appl. Phys. Lett. 68, 3749 (1996); http://dx.doi.org/10.1063/1.115994 (3 pages) | Cited 18 times

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Temperature dependence of electrical characteristics of SiO2 films doped with C, Si, and Ge were studied. The conductivity σ was found to vary with the temperature as lnσ∝T−1/4 over a wide temperature range, indicative of the conduction by the variable range hopping (VRH) mechanism. Since the previous optical studies for the same films indicate the existence of clusters in the films, it is very likely that the VRH through localized states associated with clusters dominates the conduction process, irrespective of the kind of group IV elements. © 1996 American Institute of Physics.
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73.63.-b Electronic transport in nanoscale materials and structures
61.46.-w Structure of nanoscale materials
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