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29 Dec 2003

Volume 83, Issue 26, pp. 5347-5569

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 5527 (2003); http://dx.doi.org/10.1063/1.1637143 (3 pages)

Chad R. Barry, Nyein Z. Lwin, Wei Zheng, and Heiko O. Jacobs
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Optical excitation of Er ions with 1.5 μm luminescence via the luminescent state in Si nanocrystallites embedded in SiO2 matrices

Tetsuya Makimura, Keiichi Kondo, Hiroshi Uematsu, Changqing Li, and Kouichi Murakami

Appl. Phys. Lett. 83, 5422 (2003); http://dx.doi.org/10.1063/1.1636247 (3 pages) | Cited 7 times

Online Publication Date: 22 December 2003

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Optical excitation bands have been investigated for Er-doped SiO2 films, including Si nanocrystallites as sensitizers. The Er-doped films with photoluminescence at 1.5 μm were fabricated using a laser ablation technique. It is found that the major continuous portion of the excitation bands for Er ions completely coincides with that of Si nanocrystallites at room temperature. Thus, it has been demonstrated that the second indirect absorption band of Si nanocrystallites can be used for efficient excitation of Er ions. The photoluminescence spectroscopy revealed that Er ions are possibly excited from the ground state 4I15/2 to the first excited state 4I13/2 by the energy transfer from the singlet excitons in Si nanocrystallites. © 2003 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
71.55.Ht Other nonmetals
71.35.-y Excitons and related phenomena
73.22.Lp Collective excitations
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Magnetoluminescence properties of GaAsSbN/GaAs quantum well structures

R. T. Senger, K. K. Bajaj, E. D. Jones, N. A. Modine, K. E. Waldrip, F. Jalali, J. F. Klem, G. M. Peake, X. Wei, and S. W. Tozer

Appl. Phys. Lett. 83, 5425 (2003); http://dx.doi.org/10.1063/1.1637439 (3 pages) | Cited 11 times

Online Publication Date: 22 December 2003

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We report a measurement of the variation of the diamagnetic shift of a heavy-hole exciton in a single coherently strained GaAs0.685Sb0.3N0.015/GaAs quantum well as a function of magnetic field up to 32 T at 1.3 K using photoluminescence spectroscopy. The excitons are known to be localized in this alloy system. This localization is simulated by assuming that the hole is completely immobilized, i.e., its mass is infinite. Using this model we have calculated the variation of the diamagnetic shift with magnetic field in this quantum well structure following a variational approach. We find that the observed variation of the diamagnetic shift with magnetic field agrees quite well with that calculated when the mass of the conduction electron in the well is assumed to be 0.09 m0, about 50% larger than in GaAs0.7Sb0.3, an increase similar to that found in GaAsN for the same nitrogen composition. © 2003 American Institute of Physics.
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78.67.De Quantum wells
73.21.Fg Quantum wells
71.35.Ji Excitons in magnetic fields; magnetoexcitons
78.55.Cr III-V semiconductors
78.20.Ls Magneto-optical effects
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

S–d exchange interaction in GaN:Mn studied by electron paramagnetic resonance

Agnieszka Wolos, Maria Palczewska, Zbyslaw Wilamowski, Maria Kaminska, Andrzej Twardowski, Michal Bockowski, Izabella Grzegory, and Sylwester Porowski

Appl. Phys. Lett. 83, 5428 (2003); http://dx.doi.org/10.1063/1.1637451 (3 pages) | Cited 5 times

Online Publication Date: 22 December 2003

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We present the electron paramagnetic resonance investigations of GaN:Mn bulk crystals. The performed measurements revealed the Korringa scattering as the dominant spin relaxation mechanism in the investigated highly n-type GaN:Mn samples. The temperature dependence of the spin relaxation time determines the effective s–d exchange constant for such crystals {N0α} = 14 meV. Weak exchange interaction between Mn2+ and GaN band electrons excludes carrier mediation as an origin of high-temperature ferromagnetism in n-type GaMnN. © 2003 American Institute of Physics.
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75.30.Et Exchange and superexchange interactions
76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)
75.50.Pp Magnetic semiconductors
71.55.Eq III-V semiconductors
71.20.Nr Semiconductor compounds
75.50.Dd Nonmetallic ferromagnetic materials

Increased photo- and electroluminescence by zone annealing of spin-coated and vacuum-sublimed amorphous films producing crystalline thin films

Chong-Yang Liu and Allen J. Bard

Appl. Phys. Lett. 83, 5431 (2003); http://dx.doi.org/10.1063/1.1636823 (3 pages) | Cited 5 times

Online Publication Date: 22 December 2003

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Spin-coated and vacuum sublimed amorphous thin films ( ∼ 100 nm thick) were converted into single crystalline films with a simple moving-zone-annealing technique, in which a heated metal wire generated a narrow annealed zone in the film as it is moved across the sample. This annealing resulted in both the photoluminescence and electroluminescence to increase dramatically (by 3–4 times), for example with Ru(bpy)3(ClO4)2 and aluminum 8-hydroxyquinoline, (Alq3), as light emitting devices. This technique is of interest in improving the behavior of highly luminescent thin film optoelectronic devices. © 2003 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
81.40.Tv Optical and dielectric properties related to treatment conditions
42.79.Wc Optical coatings
81.40.Gh Other heat and thermomechanical treatments
81.15.Np Solid phase epitaxy; growth from solid phases
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.A- Nucleation and growth

Influence of alloy composition and interlayer thickness on twist and tilt mosaic in AlxGa1−xN/AlN/GaN heterostructures

T. A. Lafford, P. J. Parbrook, and B. K. Tanner 

Appl. Phys. Lett. 83, 5434 (2003); http://dx.doi.org/10.1063/1.1637717 (3 pages) | Cited 10 times

Online Publication Date: 22 December 2003

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High-resolution x-ray diffraction, in surface symmetric, skew symmetric, and grazing incidence in-plane diffraction geometries, has been used to investigate the effect of an AlN interlayer between micron thick GaN and AlxGa1−xN layers grown by metalorganic vapor phase epitaxy on basal plane sapphire. No change is found in the tilt mosaic (threading screw dislocation density) with thickness or Al fraction x of the upper layer. A linear increase in the twist mosaic (threading edge dislocation density) was observed as a function of interlayer thickness and x. For all samples the twist mosaic of the AlGaN was significantly greater, by at least a factor of two, than that of the GaN layer. With increasing interlayer thickness the in-plane lattice parameter of the AlGaN decreased. The results are explained in terms of extra threading edge dislocations resulting from relaxation at the GaN/AlN interface. © 2003 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Mm Grain and twin boundaries
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Influence of nanocrystal growth kinetics on interface roughness in nickel–aluminum multilayers

D. Aurongzeb, M. Holtz, M. Daugherty, J. M. Berg, A. Chandolu, J. Yun, and H. Temkin

Appl. Phys. Lett. 83, 5437 (2003); http://dx.doi.org/10.1063/1.1637155 (3 pages) | Cited 5 times

Online Publication Date: 22 December 2003

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We study the layer morphology of Ni/Al multilayer structures, with 50 nm period, as deposited and following 10 min anneals up through the melting temperature of Al. X-ray reflectivity measurement of the as-deposited film shows interference fringes, characteristic of a well-defined multilayer stack, with ∼1 nm interface roughness. Over a narrow anneal range of 360–500 °C these fringes diminish in amplitude and disappear, indicating elevated interface roughening. However, fringes are observed for anneal temperatures both below and above this range, indicating the presence of well-defined layers with smooth interfaces. A model, in which nanocrystal domains of intermetallic nickel aluminides form at the interfaces, is developed to quantify the annealing induced interface roughness. This model agrees well with the experimental results. © 2003 American Institute of Physics.
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68.65.Ac Multilayers
68.35.Ct Interface structure and roughness
61.46.-w Structure of nanoscale materials
81.05.Bx Metals, semimetals, and alloys
61.05.cm X-ray reflectometry (surfaces, interfaces, films)
61.72.Cc Kinetics of defect formation and annealing

Photoluminescence, depth profile, and lattice instability of hexagonal InN films

O. K. Semchinova, J. Aderhold, J. Graul, A. Filimonov, and H. Neff

Appl. Phys. Lett. 83, 5440 (2003); http://dx.doi.org/10.1063/1.1634691 (3 pages) | Cited 10 times

Online Publication Date: 22 December 2003

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High quality InN films have been grown on (0001) sapphire substrates by metalorganic molecular beam epitaxy, characterized for crystal structure, chemical composition, and optical properties. Depth profiling indicated a high, increasing oxygen concentration profile towards the volume of the film. Photoluminescence revealed two different, coexisting features: a low energy transition around 0.8 eV, and a high energy feature, peaking near 2 eV. The former band originates from the direct transition in the near surface range. The latter, low intensity band results from the bulk region. Oxynitride formation has been accounted for a spatially varying optical band gap EG, determined to 0.61 eV for pure, defect free material. X-ray diffraction analysis supports defect mediated lattice instability, as proposed recently by a molecular dynamic lattice theory. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.66.Fn Inorganic compounds
71.20.Nr Semiconductor compounds

Epitaxial silicon and germanium on buried insulator heterostructures and devices

N. A. Bojarczuk, M. Copel, S. Guha, V. Narayanan, E. J. Preisler, F. M. Ross, and H. Shang

Appl. Phys. Lett. 83, 5443 (2003); http://dx.doi.org/10.1063/1.1637716 (3 pages) | Cited 42 times

Online Publication Date: 22 December 2003

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Future microelectronics will be based upon silicon or germanium-on-insulator technologies and will require an ultrathin (<10 nm), flat silicon or germanium device layer to reside upon an insulating oxide grown on a silicon wafer. The most convenient means of accomplishing this is by epitaxially growing the entire structure on a silicon substrate. This requires a high quality crystalline oxide and the ability to epitaxially grow two dimensional, single crystal films of silicon or germanium on top of this oxide. We describe a method based upon molecular beam epitaxy and solid-phase epitaxy to make such structures and demonstrate working field-effect transistors on germanium-on-insulator layers. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.Np Solid phase epitaxy; growth from solid phases
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
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Effect of nitrogen on the optical and transport properties of Ga0.48In0.52NyP1−y grown on GaAs(001) substrates

Y. G. Hong, A. Nishikawa, and C. W. Tu

Appl. Phys. Lett. 83, 5446 (2003); http://dx.doi.org/10.1063/1.1637148 (3 pages) | Cited 21 times

Online Publication Date: 22 December 2003

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We report gas-source molecular-beam epitaxy of Ga1−xInxNyP1−y grown on GaAs(100) substrates. Nitrogen incorporation dramatically reduces the Ga1−xInxP band gap. With nitrogen incorporation, the photoluminescence (PL) peak energy exhibits an inverted S-shaped dependence with temperature, and the low-temperature PL spectra exhibit an asymmetric line shape with a low-energy tail. Both indicate the presence of N-related localized states, which dominate the radiative recombination processes at low temperature. N incorporation significantly reduces the free-electron concentration and mobility. The free-electron concentration of N-containing Ga0.48In0.52N0.005P0.995 decreases dramatically with high-temperature annealing (800 °C), from 4.4×1018 to 8.0×1016 cm−3. This is believed to be due to passivation of Si by N through the formation of Si–N pairs. © 2003 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species
78.55.Cr III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.20.Fz Weak or Anderson localization

Effect of nitrogen doping into SiO2 studied by photoemission spectroscopy

S. Toyoda, J. Okabayashi, H. Kumigashira, M. Oshima, K. Ono, M. Niwa, K. Usuda, and N. Hirashita

Appl. Phys. Lett. 83, 5449 (2003); http://dx.doi.org/10.1063/1.1633977 (3 pages) | Cited 9 times

Online Publication Date: 22 December 2003

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Photoemission spectroscopy using synchrotron radiation has been performed on ultrathin Si oxynitride films on Si(001) to investigate a change of the energy-band structure by nitrogen doping. The valence-band spectra obtained by subtracting the contribution of the Si substrate clearly show the difference in nitrogen doping and two valence-band maxima, assigned as SiO2 and Si3N4, are deduced. The chemical analysis in N 1s spectra suggests a possibility that two phases, SiO2 and Si3N4, are separated in the SiOxNy films, since the sample with high nitrogen concentration (1.7×1022 cm−3) shows a valence-band maximum similar to Si3N4. A change of the valence-band maximum by nitrogen doping can be explained by an increase of the Si3N4 domain size in the SiOxNy film. © 2003 American Institute of Physics.
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71.20.Ps Other inorganic compounds
79.60.Dp Adsorbed layers and thin films

Molecular-beam epitaxy growth of arsenic film and its semimetal-to-semiconductor transition

M. He, X.-C. Yuan, N. Q. Ngo, J. Bu, and X. J. Yi

Appl. Phys. Lett. 83, 5452 (2003); http://dx.doi.org/10.1063/1.1637449 (3 pages) | Cited 1 time

Online Publication Date: 22 December 2003

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Arsenic thin film was grown on a CdTe substrate by molecular-beam epitaxy. The growth process of the film was characterized in situ by reflection high-energy electron diffraction pattern and the film structure was investigated by a transmission electron microscope. The conductivity as a function of temperature was measured by the van de Pauw method. A semimetal-to-semiconductor transition in an arsenic thin film with a thickness equal to or thinner than a critical thickness of 40 nm has been observed. © 2003 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
73.61.At Metal and metallic alloys
73.61.Cw Elemental semiconductors
71.30.+h Metal-insulator transitions and other electronic transitions

Conductivity and Hall effect measurements on intentionally undoped and doped AlGaN/GaN heterostructures before and after passivation

J. Bernát, P. Javorka, M. Marso, and P. Kordoš

Appl. Phys. Lett. 83, 5455 (2003); http://dx.doi.org/10.1063/1.1637154 (3 pages) | Cited 14 times

Online Publication Date: 22 December 2003

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Conductivity and Hall effect measurements were performed before and after Si3N4 passivation of intentionally undoped and doped AlGaN/GaN heterostructures on Si and SiC substrates. An increase of the sheet carrier density (up to ∼30%) and a slight decrease of the electron mobility (less than 10%) are found in all samples after passivation. The passivation induced sheet carrier density is 1.5–2×1012 cm−2 in undoped samples and only 0.7×1012 cm−2 in 5–10×1018 cm−3 doped samples. The decrease of the electron mobility after passivation is slightly lower in highly doped samples. The channel conductivity in both types of unpassivated samples on Si and SiC substrates increases with an increase in doping density. After passivation, a well-resolved increase of channel conductivity is observed in the undoped or lightly doped samples and nearly the same channel conductivity results in the highly doped samples. © 2003 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.65.Rv Passivation

Effects of hydrogen incorporation in GaMnN

K. H. Baik, R. M. Frazier, G. T. Thaler, C. R. Abernathy, S. J. Pearton, J. Kelly, R. Rairigh, A. F. Hebard, W. Tang, M. Stavola, and J. M. Zavada

Appl. Phys. Lett. 83, 5458 (2003); http://dx.doi.org/10.1063/1.1637151 (3 pages) | Cited 9 times

Online Publication Date: 22 December 2003

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Single-phase (Ga,Mn)N layers grown by molecular beam epitaxy with ∼3 at. % Mn were exposed to 2H or 1H plasmas under conditions designed to permeate layers with hydrogen. No evidence of the formation of Mn–H complexes could be detected from either infrared spectroscopy or the changes in magnetic properties. However, the residual magnetization increased ∼20% after hydrogenation, consistent with passivation of crystal defects in (Ga,Mn)N. Hydrogenation may be an attractive method for improving the magnetic properties of these heteroepitaxial materials. © 2003 American Institute of Physics.
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52.77.Dq Plasma-based ion implantation and deposition
75.50.Pp Magnetic semiconductors
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.30.Fs III-V and II-VI semiconductors

Inelastic electron tunneling spectroscopy study of traps in ultrathin high-k gate dielectrics

Wei He and T. P. Ma

Appl. Phys. Lett. 83, 5461 (2003); http://dx.doi.org/10.1063/1.1636519 (3 pages) | Cited 17 times

Online Publication Date: 22 December 2003

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We report the use of inelastic electron tunneling spectroscopy (IETS) as an effective tool in studying traps in high-k gate dielectrics, particularly the electrical stress-induced traps, in metal–oxide–semiconductor (MOS) structures. Two kinds of traps may be identified by the IETS technique: (1) those that contribute to trap-assisted conduction mechanisms and (2) those that contribute to trapping in the gate dielectric. These two kinds of traps can be distinguished from each other, because each of them exhibits a distinct feature in the IETS spectra. The trap energies are readily obtained from the voltage locations where these features occur. From voltage polarity dependence of the IETS spectra, one can get information about the spatial distribution of the traps. Examples will be shown to demonstrate the capability of the IETS technique for studying traps in MOS structures with high-k gate dielectrics. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Reduced self-heating in Si/SiGe field-effect transistors on thin virtual substrates prepared by low-energy plasma-enhanced chemical vapor deposition

T. Hackbarth, H.-J. Herzog, K.-H. Hieber, U. König, M. Bollani, D. Chrastina, and H. von Känel

Appl. Phys. Lett. 83, 5464 (2003); http://dx.doi.org/10.1063/1.1636820 (3 pages) | Cited 15 times

Online Publication Date: 22 December 2003

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This letter reports on the electrical performance of strained Si-based n-type heterostructure field-effect transistors prepared on 500 nm Si0.56Ge0.44 virtual substrates. The method of low-energy plasma-enhanced chemical vapor deposition at low temperature was used for the growth of the relaxed SiGe buffer. The active layers have been deposited by molecular-beam epitaxy. The thin buffer improves the thermal conductivity by a factor of 3 and shows a much lower surface roughness compared to control structures on conventional virtual substrate with a 5-μm-thick graded buffer. Cutoff frequencies of fT = 55 GHz and fmax(U) = 138 GHz have been achieved which are very close to the results of the control sample. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Response function during oxygen sputter profiling and its application to deconvolution of ultrashallow B depth profiles in Si

Lin Shao, Jiarui Liu, Chong Wang, Ki B. Ma, Jianming Zhang, John Chen, Daniel Tang, Sanjay Patel, and Wei-Kan Chu

Appl. Phys. Lett. 83, 5467 (2003); http://dx.doi.org/10.1063/1.1636269 (3 pages) | Cited 3 times

Online Publication Date: 22 December 2003

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The secondary ion mass spectrometry (SIMS) response function to a B “δ surface layer” has been investigated. Using electron-gun evaporation combined with liquid nitrogen cooling of target, we are able to deposit an ultrathin B layer without detectable island formation. The B spatial distribution obtained from SIMS is exponentially decaying with a decay length approximately a linear function of the incident energy of the oxygen during the SIMS analysis. Deconvolution with the response function has been applied to reconstruct the spatial distribution of ultra-low-energy B implants. A correction to depth and yield scales due to transient sputtering near the Si surface region was also applied. Transient erosion shifts the profile shallower, but beam mixing shifts it deeper. These mutually compensating effects make the adjusted distribution almost the same as original data. The one significant difference is a buried B peak observed near the surface region. © 2003 American Institute of Physics.
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61.72.uf Ge and Si
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.47.Fg Semiconductor surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
68.35.Dv Composition, segregation; defects and impurities
61.72.S- Impurities in crystals

Fabrication of highly efficient polythiophene-sensitized metal oxide photovoltaic cells

G. K. R. Senadeera, K. Nakamura, T. Kitamura, Y. Wada, and S. Yanagida

Appl. Phys. Lett. 83, 5470 (2003); http://dx.doi.org/10.1063/1.1633673 (3 pages) | Cited 33 times

Online Publication Date: 22 December 2003

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Poly(3-thiophenylacetic acid)-polymer-sensitized photoelectrochemical cells comprising of either mesoporous TiO2 or SnO2-ZnO electrodes and the electrolyte consisting with redox complex (I3−/I−) were fabricated and characterized. The addition of ionic liquid, 1-methyl- 3-n-hexylimidazolium iodide, into the electrolyte drastically enhanced the cell performance. The cells consisting of the nanoporous TiO2 electrodes showed the incident photon to current conversion efficiency as high as 60% (at 430 nm), while the highest overall power conversion efficiency was ∼2.4% under the irradiance of 100 mW cm−2 (air mass 1.5). The overall efficiency of the cells with nanoporous SnO2-ZnO electrodes was ∼1.5% under the same illumination. © 2003 American Institute of Physics.
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84.60.Jt Photoelectric conversion
82.45.Fk Electrodes
82.47.Jk Photoelectrochemical cells, photoelectrochromic and other hybrid electrochemical energy storage devices

Integrated pulsed photoconductivity of organic light-emitting diodes

A. Tapponnier, I. Biaggio, M. Koehler, and P. Günter

Appl. Phys. Lett. 83, 5473 (2003); http://dx.doi.org/10.1063/1.1629785 (3 pages) | Cited 2 times

Online Publication Date: 22 December 2003

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We analyze the transient photoconductivity induced by short light pulses in organic light-emitting diodes (OLEDs) to characterize the charge transport dynamics with high time resolution over four time decades. We show how integrated pulsed photoconductivity (IPP) can be used as a diagnostic method for finished, packaged OLEDs to determine and characterize the presence of impurities or other effects that influence the efficiency of charge transport. We demonstrate the usefulness of the method by comparing a simple one-layer Alq3 device on indium tin oxide (ITO) to a device where a nanometer thin NPB film separates the Alq3 from the ITO. In the single-layer device a charge transport dynamics stretching over several decades is observed, probably due to Alq3 contamination by its direct contact with ITO. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
73.50.Pz Photoconduction and photovoltaic effects
78.66.Qn Polymers; organic compounds
06.60.Mr Testing and inspecting procedures

Diffusion and drift in terahertz emission at GaAs surfaces

J. N. Heyman, N. Coates, A. Reinhardt, and G. Strasser

Appl. Phys. Lett. 83, 5476 (2003); http://dx.doi.org/10.1063/1.1636821 (3 pages) | Cited 21 times

Online Publication Date: 22 December 2003

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We study terahertz (THz) emission from GaAs as a function of photon energy and electric field. THz radiation arises from transport of photogenerated charge in an electric field and by hot carrier diffusion (the photo-Dember effect). These mechanisms can be separated by experiments in which either the electric field or the kinetic energy of the carriers is varied. For electric fields E ∼ 4 kV/cm, we find that the electric field controls THz emission for carrier temperatures kBTC ⩽ 0.1 eV, while hot-carrier diffusion dominates for kBTC ≈ 1 eV. Both mechanisms contribute at intermediate fields and carrier temperatures. Our results are consistent with estimates of the relative magnitudes of these two effects. © 2003 American Institute of Physics.
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73.25.+i Surface conductivity and carrier phenomena
72.40.+w Photoconduction and photovoltaic effects
72.20.Ht High-field and nonlinear effects

Stimulated emission in nanocrystalline silicon superlattices

J. Ruan, P. M. Fauchet, L. Dal Negro, M. Cazzanelli, and L. Pavesi

Appl. Phys. Lett. 83, 5479 (2003); http://dx.doi.org/10.1063/1.1637720 (3 pages) | Cited 73 times

Online Publication Date: 22 December 2003

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We studied the conditions under which optical gain is measured in nanocrystalline silicon (nc-Si) using the variable stripe length method. Waveguide samples have been produced by magnetron sputtering of alternating layers of Si and SiO2, followed by high temperature annealing. No optical gain was observed under continuous wave pumping conditions. Under high intensity pulsed excitation, a superlinear fast (10 ns) recombination component yielding an optical gain up to 50 cm−1 has been independently measured in two different laboratories. A control experiment confirmed that the presence of nc-Si is necessary to achieve gain in our structures. © 2003 American Institute of Physics.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.45.+h Stimulated emission
42.82.Et Waveguides, couplers, and arrays
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
61.46.-w Structure of nanoscale materials
81.15.Cd Deposition by sputtering
42.79.Gn Optical waveguides and couplers
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Observation of the barrier structure in magnetic tunnel junctions using high-resolution electron microscopy and electron holography

F. Shen, T. Zhu, X. H. Xiang, John Q. Xiao, E. Voelkl, and Z. Zhang

Appl. Phys. Lett. 83, 5482 (2003); http://dx.doi.org/10.1063/1.1637129 (3 pages) | Cited 8 times

Online Publication Date: 22 December 2003

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Microstructures of the NiFe/AlOx/NiFe magnetic tunnel junctions and the barrier shape profile have been studied with atomic resolution using high-resolution electron microscopy and electron holography. A clear relationship between the growth morphologies of the electrodes and the quality of the barrier has been obtained. Although the bottom interface between electrode and barrier is very sensitive to the oxidation condition, a sharp interface can be achieved in optimumally oxidized junctions. The top interface, on the other hand, is always slightly oxidized due to the three-dimensional growth of top electrode above the barrier, independent of the oxidation condition of the barrier. Furthermore, charge accumulation seems to exist at the sharp interfaces. It is also interesting, yet surprising, that both interfaces are actually sharp in underoxidized junctions. Furthermore, charge accumulation seems to exist at the sharp interfaces. © 2003 American Institute of Physics.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Electronic and magnetic properties of MnAs nanoclusters studied by x-ray absorption spectroscopy and x-ray magnetic circular dichroism

J. Okabayashi, M. Mizuguchi, M. Oshima, H. Shimizu, M. Tanaka, M. Yuri, and C. T. Chen

Appl. Phys. Lett. 83, 5485 (2003); http://dx.doi.org/10.1063/1.1637430 (3 pages) | Cited 2 times

Online Publication Date: 22 December 2003

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We have investigated the electronic and magnetic properties of a MnAs:GaAs granular film with MnAs clusters embedded in the GaAs matrix fabricated by high-temperature annealing of Ga1−xMnxAs using x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). The XAS line shapes in the Mn 2p core level changed from a localized structure to an itinerant NiAs-type one. Magnetic-field dependence of the XMCD revealed no hysteresis curves at the fixed photon energy where the large XMCD signals were observed, suggesting the superparamagnetic behavior at 100 K. © 2003 American Institute of Physics.
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73.22.-f Electronic structure of nanoscale materials and related systems
75.50.Tt Fine-particle systems; nanocrystalline materials
78.70.Dm X-ray absorption spectra
75.20.Ck Nonmetals
81.07.Bc Nanocrystalline materials
81.40.Gh Other heat and thermomechanical treatments

Ferromagnetism in cobalt-implanted ZnO

D. P. Norton, M. E. Overberg, S. J. Pearton, K. Pruessner, J. D. Budai, L. A. Boatner, M. F. Chisholm, J. S. Lee, Z. G. Khim, Y. D. Park, and R. G. Wilson

Appl. Phys. Lett. 83, 5488 (2003); http://dx.doi.org/10.1063/1.1637719 (3 pages) | Cited 83 times

Online Publication Date: 22 December 2003

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The magnetic and structural properties of cobalt-implanted ZnO single crystals are reported. High-quality, (110)-oriented single-crystal Sn-doped ZnO substrates were implanted at ∼ 350 °C with Co to yield transition metal concentrations of 3–5 at. % in the near-surface (∼2000 Å) region. After implantation, the samples were subject to a 5 min rapid thermal annealing at 700 °C. Magnetization measurements indicate ferromagnetic behavior, with hysteresis observed in the M vs H behavior at T = 5 K. Coercive fields were ⩽100 Oe at this measurement temperature. Temperature-dependent magnetization measurements showed evidence for ordering temperatures of >300 K, although hysteresis in the M vs H behavior was not observed at room temperature. Four-circle x-ray diffraction results indicate the presence of (110)-oriented hexagonal phase Co in the ZnO matrix. From the 2θ full width at half maximum (FWHM) of the Co (110) peak, the nanocrystal size is estimated to be ∼3.5 nm, which is below the superparamagnetic limit at room temperature. In-plane x-ray diffraction results show that the nanocrystals are epitaxial with respect to the ZnO host matrix. The magnetic properties are consistent with the presence of Co nanocrystals, but do not preclude the possibility that a component of the magnetism is due to Co substitution on the Zn site in the ZnO matrix. © 2003 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Pp Magnetic semiconductors
81.05.Dz II-VI semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
75.50.Tt Fine-particle systems; nanocrystalline materials

Electronic structures and the estimated Curie temperatures of (Ga1−yIny)1−xMnxAs

K. Miura, M. Iwasawa, S. Imanaga, and T. Ami

Appl. Phys. Lett. 83, 5491 (2003); http://dx.doi.org/10.1063/1.1638632 (3 pages) | Cited 2 times

Online Publication Date: 22 December 2003

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The electronic structures of (Ga1−yIny)1−xMnxAs have been investigated using the Korringa, Kohn and Rostoker (KKR) method with the coherent potential approximation (CPA). The estimated Curie temperature (TC) of Ga1−xMnxAs is higher than that of (Ga0.5In0.5)1−xMnxAs and In1−xMnxAs when x≲0.10. On the other hand, the estimated TC of Ga1−xMnxAs saturates with an increase of x when x≳0.05, but that of (Ga0.5In0.5)1−xMnxAs and In1−xMnxAs does not saturate even when x>0.10. These results are in good agreement with the previous experimental results. Our calculated results predict that the TC of (Ga0.5In0.5)1−xMnxAs and In1−xMnxAs will be higher than that of Ga1−xMnxAs when x≳0.10. © 2003 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.20.Nr Semiconductor compounds
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Lk Spin glasses and other random magnets
75.10.Lp Band and itinerant models
71.15.-m Methods of electronic structure calculations
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Lateral epitaxial growth of (Ba,Sr)TiO3 thin films

Jang-Sik Lee, H. Wang, Sang Yeol Lee, S. R. Foltyn, and Q. X. Jia

Appl. Phys. Lett. 83, 5494 (2003); http://dx.doi.org/10.1063/1.1637445 (3 pages) | Cited 13 times

Online Publication Date: 22 December 2003

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We report a technique for epitaxial thin-film growth by combination of selective heteroepitaxial and lateral homoepitaxial growth. (Ba,Sr)TiO3 (BST) thin films were deposited on LaAlO3 having amorphous SiOx masking layers with stripe patterns at 450 °C by pulsed-laser deposition. Postannealing was carried out thereafter for lateral epitaxial growth. The difference in BST nucleation temperatures from the amorphous masking regions and lattice-matched single-crystalline substrates enables selective nucleation. Heteroepitaxial growth takes place in the regions of single-crystalline substrates, whereas lateral homoepitaxial growth evolves from the crystallized BST towards the SiOx masked region during postannealing process. © 2003 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.37.Lp Transmission electron microscopy (TEM)
61.72.Cc Kinetics of defect formation and annealing
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