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27 Mar 1995

Volume 66, Issue 13, pp. 1575-1706

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Femtosecond investigations of spectral hole burning in semiconductor lasers

Chi‐Kuang Sun, Boris Golubovic, Hong‐Kyun Choi, Christine A. Wang, and James G. Fujimoto

Appl. Phys. Lett. 66, 1650 (1995); http://dx.doi.org/10.1063/1.113881 (3 pages) | Cited 9 times

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An investigation of spectral hole burning effects is reported in the gain region of InGaAs/AlGaAs strained‐layer single quantum well diode lasers, using a heterodyne nondegenerate pump‐probe technique. This technique permits simultaneous measurement of the femtosecond dynamics and spectral dependence of transient gain in semiconductor lasers. At high bias current, strong spectral hole burning effects were observed. © 1995 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
78.47.-p Spectroscopy of solid state dynamics

Wafer bonding induced degradation of thermal silicon dioxide layers on silicon

V. V. Afanas’ev, P. Ericsson, S. Bengtsson, and M. O. Andersson

Appl. Phys. Lett. 66, 1653 (1995); http://dx.doi.org/10.1063/1.113882 (3 pages) | Cited 1 time

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Structural and electrical properties of thermal SiO2 layers on Si subjected to wafer bonding were studied. Regions with enhanced etching rate in HF‐solutions were found to appear after the bonding and a subsequent etchback of one of the wafers. The bonding procedure also leads to enhancement of interface state generation and accumulation of oxide trapped charge during injection of electrons or holes into the SiO2 layer. The annealing behavior and capture cross section of these defects are close to those of centers generated when hydrogen is incorporated in the oxide network. Enrichment of the oxide by hydrogen during the bonding and postbonding anneal is suggested to be responsible for the degradation of the thermal oxide. © 1995 American Institute of Physics.
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77.55.-g Dielectric thin films
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.65.-b Surface treatments

In situ electric field perturbations of deep trap accumulation in silicon during proton ion implantation

Yu. N. Erokhin, J. Ravi, G. A. Rozgonyi, and C. W. White

Appl. Phys. Lett. 66, 1656 (1995); http://dx.doi.org/10.1063/1.113883 (3 pages) | Cited 4 times

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The influence of in situ perturbations of the silicon target crystal electronic subsystem during H+ ion implantation has been studied in terms of the type, density, and spatial distribution of accumulated deep traps. A perturbation of the electronic subsystem was achieved through application of a reverse bias to diode test structures. A substantial decrease in deep trap concentration is observed when ion implantation is accompanied by a superimposed reverse bias. The effect is especially pronounced for hydrogen related deep traps at Ec−0.3. © 1995 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.72.uf Ge and Si
71.55.Cn Elemental semiconductors

Calculation of resonant absorption and photoresponse measurement in p‐type GaAs/AlGaAs quantum wells

Frank Szmulowicz and Gail J. Brown

Appl. Phys. Lett. 66, 1659 (1995); http://dx.doi.org/10.1063/1.113884 (3 pages) | Cited 15 times

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The bound‐to‐continuum absorption in p‐type GaAs/AlGaAs quantum wells is calculated based on the electronic structure, wave functions, and optical matrix elements obtained from an 8×8 envelope‐function approximation (EFA) calculation without the use of an artificial large box to enclose the entire system; as such, the present work represents the first true continuum calculation. We show that, for an aluminum content of 30%, the well width of 48 Å (and not the 30 or 40 Å wells used previously) optimizes the linear absorption coefficient for bound‐to‐continuum absorption due to the presence of a resonant LH2 (second light‐hole) state at the top of the well. © 1995 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors

Preparation and characterization of ultrathin porous silicon films

J. von Behren, L. Tsybeskov, and P. M. Fauchet

Appl. Phys. Lett. 66, 1662 (1995); http://dx.doi.org/10.1063/1.113885 (3 pages) | Cited 32 times

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Light emitting porous silicon thin films with thicknesses from ∼0.1 to ∼100 μm were produced by electrochemical etching and subsequently lifted off the silicon wafer by an electropolishing step. The structural integrity of the thinner layers was maintained by deposition on sapphire windows where they remain attached by van der Waals or electrostatic forces. The procedure for manufacturing high quality layers and their structural and optical properties is discussed. © 1995 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.55.Hx Other solid inorganic materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Electron beam irradiation of n‐type porous silicon obtained by photoelectrochemical etching

J.‐L. Maurice, A. Rivière, A. Alapini, and C. Lévy‐Clément

Appl. Phys. Lett. 66, 1665 (1995); http://dx.doi.org/10.1063/1.113886 (3 pages) | Cited 14 times

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The effects of electron beam irradiation on luminescence and microstructure of n‐type porous silicon (PS) have been investigated, using cathodoluminescence (CL) in the scanning electron microscope (SEM), and electron energy loss spectroscopy in the transmission electron microscope (TEM). In the SEM, the CL rapidly decreased with irradiation. It could be fully restored by boiling the samples in de‐ionized water. In the TEM, freshly restored PS emerged as Si nano‐crystallites embedded in an unstable silicon oxide. The effect of irradiation was to suppress the oxide, and also, in the case of proximity of carbon from the foil holding the sample, to change the crystallite composition to β‐SiC. © 1995 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
61.80.Fe Electron and positron radiation effects
78.55.Hx Other solid inorganic materials

Time domain all‐optical demultiplexing with a semiconductor directional coupler

A. Villeneuve, P. Mamyshev, J. U. Kang, G. I. Stegeman, J. S. Aitchison, and C. N. Ironside

Appl. Phys. Lett. 66, 1668 (1995); http://dx.doi.org/10.1063/1.113887 (3 pages) | Cited 1 time

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We report the demonstration of demultiplexing of 150 fs pulses, without pulse breakup, in an AlGaAs nonlinear directional coupler operated at photon energies below half the band gap energy of AlGaAs. © 1995 American Institute of Physics.  
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.79.Gn Optical waveguides and couplers

Pd induced lateral crystallization of amorphous Si thin films

Seok‐Woon Lee, Yoo‐Chan Jeon, and Seung‐Ki Joo

Appl. Phys. Lett. 66, 1671 (1995); http://dx.doi.org/10.1063/1.113888 (3 pages) | Cited 88 times

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A thin palladium layer (∼40 Å) was selectively formed on top of amorphous silicon films before annealing and the effects of palladium layer on the crystallization behavior of the amorphous silicon films were investigated. It was observed that the amorphous silicon right under the Pd layer could be crystallized to grain sizes of several hundred angstroms by annealing at 500 °C. In addition, the area between the Pd thin pads, patterned by lithography, was found to be crystallized to grain sizes of a few tens of microns in length by the same annealing. Such lateral crystallization was found to reach more than 100 μm in some cases. The lateral crystallization phenomenon might be useful for the fabrication of low temperature polycrystalline‐Si thin film transistors, providing large‐grained Si films. © 1995 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.35.Fx Diffusion; interface formation
61.72.Mm Grain and twin boundaries

Dopant incorporation during epitaxial growth of a multicomponent oxide thin film from vapor phase: A case study of Fe/YBa2Cu3O7−δ system

S. B. Ogale, I. Takeuchi, M. Rajeswari, R. L. Greene, T. Venkatesan, and D. D. Choughule

Appl. Phys. Lett. 66, 1674 (1995); http://dx.doi.org/10.1063/1.113889 (3 pages) | Cited 2 times

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Incorporation of Fe in YBa2Cu3O7−δ matrix during its epitaxial growth on (001) LaAlO3 by pulsed excimer laser ablation is examined. It is shown that oxygen pressure during deposition plays a critical role in the incorporation process and that a low‐temperature postsynthesis annealing is essential for complete substitution. Clustering of iron atoms and its control via the anion controlled reactions are identified as the key features in this context. It is also shown by using atomic force microscopy that Fe incorporation influences the surface morphology. These issues are of importance in the formation of cationic defects in multicomponent thin films. © 1995 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Fg Pulsed laser ablation deposition
74.78.-w Superconducting films and low-dimensional structures

Junction parameters of mtsp;YBa2Cu3O7 step edge junctions on mtsp;LaAlO3 substrates from Fiske resonances

H. R. Yi, D. Winkler, and T. Claeson

Appl. Phys. Lett. 66, 1677 (1995); http://dx.doi.org/10.1063/1.113890 (3 pages) | Cited 14 times

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Strong Fiske type resonance peaks have been observed in current–voltage curves of mtsp;YBa2Cu3O7 step edge junctions on mtsp;LaAlO3 substrates. We determined effective shunting capacitances from the voltages of the resonances. These data compare well with those obtained from the McCumber constant mtsp;βc. Typical values of the shunting capacitance per unit area for these junctions were estimated to be in the range of 20–30 mtsp;fF/μm2. The surface resistance normalized to 1 GHz at the conjugating junction interfaces was estimated to be in the range of 1–3 μΩ. © 1995 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
74.72.-h Cuprate superconductors

Microwave noise in high‐Tc Josephson junctions

Erich N. Grossman, Leila R. Vale, and D. A. Rudman

Appl. Phys. Lett. 66, 1680 (1995); http://dx.doi.org/10.1063/1.113891 (3 pages) | Cited 2 times

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We have measured the noise of YBa2Cu3O7−δ superconductor‐normal‐superconductor (SNS) junctions whose high normal‐state resistances and characteristic frequencies make them suitable for THz frequency mixers. By directly measuring the 1 GHz power spectral density delivered to a low‐noise 50 Ω radiometer system, the noise could be measured over a wide range of dc voltage and temperature, without complications due to 1/f noise, and without invoking any specific model. At a physical temperature of 4 K, the lowest noise junction had an available noise temperature of 31±2 K, corresponding to an effective noise temperature of the normal resistance of 9 K. The effective noise temperature of the normal resistance is approximately equal to the physical temperature at high temperatures, but approaches a limiting value at low temperatures, implying an excess current noise of unknown origin.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.50.+r Tunneling phenomena; Josephson effects
74.40.-n Fluctuation phenomena
85.25.Cp Josephson devices

Domain structures in magnetoresistive granular metals

A. Gavrin, M. H. Kelley, John Q. Xiao, and C. L. Chien

Appl. Phys. Lett. 66, 1683 (1995); http://dx.doi.org/10.1063/1.113892 (3 pages) | Cited 24 times

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We have imaged the magnetic domain structure of several heterogeneous CoxAg1−x alloys by using scanning electron microscopy with polarization analysis. These images show that extended domain structures exist in both the as‐deposited samples and in samples annealed at moderate temperatures. This suggests that a significant fraction of the cobalt in these materials does not contribute to the giant magnetoresistance. Only those samples annealed at 600 °C and containing less than 40% cobalt by volume show no domain structure. © 1995 American Institute of Physics.
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75.60.Ch Domain walls and domain structure
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Tt Fine-particle systems; nanocrystalline materials

Three‐dimensional atom probe analysis of a sputter‐deposited Co–Cr thin film

K. Hono, K. Yeh, Y. Maeda, and T. Sakurai

Appl. Phys. Lett. 66, 1686 (1995); http://dx.doi.org/10.1063/1.113893 (3 pages) | Cited 15 times

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Three‐dimensional atom probe (3DAP) was employed to study nanoscale compositional heterogeneities in Co‐22 at. %Cr sputter‐deposited thin films. Compositional fluctuations were visualized on a nanometer scale through a 3D reconstruction of collected atoms. Transmission electron microscopy observations of the same specimen area of before and after 3DAP analysis made it possible to scale the analyzed volume precisely. The resulting data show that a Co‐22 at. %Cr thin film sputter deposited at elevated temperature was composed of two phases with a lamellarlike structure, one phase was ferromagnetic containing approximately 90 at. %Co, and the other was paramagnetic, containing approximately 60 at. %Co. © 1995 American Institute of Physics.
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81.15.Cd Deposition by sputtering
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
68.37.Vj Field emission and field-ion microscopy

Influence of preparation on resistivity behavior of epitaxial Nd0.7Sr0.3MnO3−δ and La0.67Ba0.33MnO3−δ thin films

G. C. Xiong, Q. Li, H. L. Ju, R. L. Greene, and T. Venkatesan

Appl. Phys. Lett. 66, 1689 (1995); http://dx.doi.org/10.1063/1.113894 (3 pages) | Cited 98 times

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The influence of sample preparation on the resistivity and magnetoresistance (MR) behavior of doped manganese oxides has been studied. Two systems, Nd0.7Sr0.3MnO3−δ and La0.67Ba0.33MnO3−δ thin films, have been chosen for this study. The former has the largest reported MR ratio at 60 K and the latter has a large MR ratio at room temperature. Two processes, deposition at a high temperature and annealing at a high temperature, have opposite influences on the resistivity behavior of these films. The results suggest that oxygen stoichiometry and diffusion are important factors in causing the behavior observed in doped manganese oxide films. © 1995 American Institute of Physics.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.15.Fg Pulsed laser ablation deposition

Direct formation of ordered CoPt and FePt compound thin films by sputtering

M. R. Visokay and R. Sinclair

Appl. Phys. Lett. 66, 1692 (1995); http://dx.doi.org/10.1063/1.113895 (3 pages) | Cited 141 times

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Equiatomic CoPt and FePt alloy films were deposited by cosputtering at substrate temperatures between 25 and 640 °C. Those deposited at high temperatures (≥400 and ≥520 °C for FePt and CoPt, respectively) contained ordered intermetallic compounds with the L10 crystal structure while those deposited at lower temperatures were chemically disordered. Deposition on single crystal [001] MgO and [0001] Al2O3 resulted in [001] and [111] oriented films, respectively, for all deposition temperatures. Ordered alloys have out‐of‐plane magnetic easy axes and modified magneto‐optic Kerr rotation spectra relative to the disordered case. A difference in the Kerr rotation spectrum is observed between ordered, but not disordered, [001] and [111] films. © 1995 American Institute of Physics.
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81.15.Cd Deposition by sputtering
78.20.Ls Magneto-optical effects
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

Detection of mercury vapor using resonating microcantilevers

T. Thundat, E. A. Wachter, S. L. Sharp, and R. J. Warmack

Appl. Phys. Lett. 66, 1695 (1995); http://dx.doi.org/10.1063/1.113896 (3 pages) | Cited 145 times

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Oscillating silicon nitride microcantilevers coated with a thin gold film have been used to detect mercury vapor in air. Cantilever resonance frequency changes due to surface mass loading as a result of adsorption of mercury vapor. Furthermore, cantilever bending is also altered due to changes in surface stress induced by mercury adsorption on the gold overlayer. Both of these phenomena can be used to quantitatively detect adsorbed vapors with picogram mass resolution. © 1995 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
82.80.-d Chemical analysis and related physical methods of analysis

Two‐photon excitation 4Pi confocal microscope: Enhanced axial resolution microscope for biological research

P. E. Hänninen, S. W. Hell, J. Salo, E. Soini, and C. Cremer

Appl. Phys. Lett. 66, 1698 (1995); http://dx.doi.org/10.1063/1.113897 (3 pages) | Cited 39 times

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The applicability of two photon excitation 4Pi confocal fluorescence microscopy to biological imaging is demonstrated. We show that 4Pi confocal microscopy in combination with a simple deconvolution algorithm allows axial localization and quantification with 0.14 μm resolution in a biological sample. The 4Pi‐confocal microscope extends the applicability of far field fluorescence microscopy to high resolution three‐dimensional imaging and quantification of subcellular structures.
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87.64.K- Spectroscopy

Dependence of the nematic liquid crystal pretilt angle on the thickness of the orientation layer

A. L. Alexe‐Ionescu, R. Barberi, M. Giocondo, G. Cnossen, and T. H. van der Donk

Appl. Phys. Lett. 66, 1701 (1995); http://dx.doi.org/10.1063/1.113898 (3 pages) | Cited 15 times

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The influence of an isotropic substrate on the anchoring properties of a nematic liquid crystal has been investigated by varying the thickness of a polyimide orientation layer. By invoking the screening effect of the polymer film on the anisotropic van der Waals interactions between the nematic and the solid substrate, the dependence of the pretilt angle on the thickness of the film has been theoretically evaluated. The agreement of the proposed theory with the experimental data is fairly good. © 1995 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Preparation of monolithic barium titanate xerogels by sol–gel processing and the dielectric properties of their sintered bodies

M. Kuwabara, K. Miki, S. Takahashi, and H. Shimooka

Appl. Phys. Lett. 66, 1704 (1995); http://dx.doi.org/10.1063/1.113899 (3 pages) | Cited 4 times

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Monolithic xerogels of crystalline barium titanate, with dimensions of ∼3 mm thick and ∼6 mm in diameter, have been produced by sol–gel processing using metal alkoxides. An excess amount of water with the H2O/Ba ratio≳100 (for hydrolysis of the barium titanate precursor alkoxides) and aging time≳8 days were necessary to produce the monolithic crystalline xerogels without breaking during drying (at 90 °C). The barium titanate xerogels as‐dried, with a porosity of about 70%, have been found to consist of crystalline grains in the range of 10–20 nm. Firing the xerogels at 1000 °C in air yielded porous barium titanate ceramics with an average grain size around 50 nm and a decreased porosity around 60%. The dielectric constant (ϵr)–temperature (T) characteristics of these ceramics have been found to be rather flat below 120 °C with a broad peak around this temperature, and those above 120 °C showed a specific behavior of ferroelectric materials described by a Curie–Weiss equation, ϵr=C/(T–T0), with C≊2×104 K and T0≊230 K (−43 °C); although these values are quite different from those of ferroelectric barium titanate. © 1995 American Institute of Physics.
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81.10.Dn Growth from solutions
81.05.Rm Porous materials; granular materials
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
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