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17 Nov 2003

Volume 83, Issue 20, pp. 4083-4258

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 4238 (2003); http://dx.doi.org/10.1063/1.1627935 (3 pages)

H. B. Peng, T. G. Ristroph, G. M. Schurmann, G. M. King, J. Yoon, V. Narayanamurti, and J. A. Golovchenko
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Time-resolved photoluminescence of the size-controlled ZnO nanorods

Sangsu Hong, Taiha Joo, Won Il Park, Yong Ho Jun, and Gyu-Chul Yi

Appl. Phys. Lett. 83, 4157 (2003); http://dx.doi.org/10.1063/1.1627472 (3 pages) | Cited 46 times

Online Publication Date: 12 November 2003

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Size dependence of the time-resolved photoluminescence (TRPL) has been investigated for the ZnO nanorods fabricated by catalyst-free metalorganic chemical vapor deposition. The nanorods have a diameter of 35 nm and lengths in the range of 150 nm to 1.1 μm. The TRPL decay rate decreases monotonically as the length of the nanorods increases in the range of 150 to 600 nm. Decrease of the radiative decay rate of the exciton-polariton has been invoked to account for the results. © 2003 American Institute of Physics.
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78.55.Et II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.47.-p Spectroscopy of solid state dynamics
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Defect-mediated and resonant optical excitation of Er3+ ions in silicon-rich silicon oxide

D. Kuritsyn, A. Kozanecki, H. Przybylińska, and W. Jantsch

Appl. Phys. Lett. 83, 4160 (2003); http://dx.doi.org/10.1063/1.1627483 (3 pages) | Cited 11 times

Online Publication Date: 12 November 2003

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Sensitization of the 4I13/2–4I15/2 Er3+ luminescence at 1.54 μm in silicon-rich silicon oxide (SRSO) is studied in the blue-green range. We show that defects due to excess Si in silica act as luminescence sensitizers. We also suggest that there exist two types of Er centers—isolated ones and others—strongly coupled to defects. In SRSO competition of direct, resonant excitation of Er3+ and indirect processes via defects is observed. Enhancement of the Er emission for off-resonant excitation does not seem to compensate losses in the direct channel of excitation to the 2H11/2 state of Er3+. We suggest that the emission efficiency of Er3+ is limited by distance-dependent transfer rate and little spectral overlap of the interacting states. © 2003 American Institute of Physics.
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78.55.Hx Other solid inorganic materials

Mapping of strain fields about thin film structures using x-ray microdiffraction

C. E. Murray, I. C. Noyan, P. M. Mooney, B. Lai, and Z. Cai

Appl. Phys. Lett. 83, 4163 (2003); http://dx.doi.org/10.1063/1.1628399 (3 pages) | Cited 6 times

Online Publication Date: 12 November 2003

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Substrate distortions were mapped near pseudomorphically grown SiGe thin film etched lines of various widths from 1.5 to 20 μm on Si(001) and 190 μm diameter Ni dots on Si(111) using reflection x-ray microdiffraction topography. The strain field extended 30–120 times the thickness of the film away from the feature edge. The profile of the enhanced diffracted intensity was found to follow a characteristic curve when the distance from the feature edge is normalized by a mean interaction distance that depends on the feature size. This normalization and the observed strain decay profiles cannot be predicted or modeled using existing micromechanical models. © 2003 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
81.65.Cf Surface cleaning, etching, patterning
68.37.Yz X-ray microscopy

Atomistic modeling of deactivation and reactivation mechanisms in high-concentration boron profiles

Maria Aboy, Lourdes Pelaz, Luis A. Marqués, Juan Barbolla, Ali Mokhberi, Yayoi Takamura, Peter B. Griffin, and James D. Plummer

Appl. Phys. Lett. 83, 4166 (2003); http://dx.doi.org/10.1063/1.1628391 (3 pages) | Cited 19 times

Online Publication Date: 12 November 2003

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We use kinetic nonlattice Monte Carlo atomistic simulations to investigate the physical mechanisms for boron cluster formation and dissolution at very high B concentrations, and the role of Si interstitials in these processes. For this purpose, high-dose, low-energy B implants and theoretical structures with fully active box shaped B profiles were analyzed. Along with the theoretical B profile, different Si interstitial profiles were included. These structures could be simplifications of the situation resulting from the regrowth of preamorphized or laser annealed B implants. While for B concentrations lower than 1020 cm−3, B clusters are not formed unless a high Si interstitial concentration overlaps the B profile, our simulation results show that for higher B concentrations, B clusters can be formed even in the presence of only the equilibrium Si interstitial concentration. The existence of a residual concentration of Si interstitials along with the B boxes makes the deactivation faster and more severe. © 2003 American Institute of Physics.
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61.72.uf Ge and Si
61.72.S- Impurities in crystals
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing

Influence of substitutional carbon incorporation on implanted-indium-related defects and transient enhanced diffusion

Chung Foong Tan, Eng Fong Chor, Jinping Liu, Hyeokjae Lee, Elgin Quek, and Lap Chan

Appl. Phys. Lett. 83, 4169 (2003); http://dx.doi.org/10.1063/1.1628814 (3 pages) | Cited 5 times

Online Publication Date: 12 November 2003

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It has been demonstrated that, by incorporating a thin ∼20 nm Si1−yCy (with y as low as 0.1%) layer at the deep indium implant end-of-range (EOR) region, the EOR defects and enhanced diffusion behavior associated with indium implant can be eliminated. The Si1−yCy layer was grown epitaxially followed by a silicon epitaxy cap of 60 nm. Indium implantations were performed at 1×1014 cm−2 at 115 keV followed by spike annealing at 1050 °C. The experimentally observed EOR defect and enhanced diffusion elimination are explained based on the undersaturation of implantation-induced silicon interstitials with the presence of substitutional carbon at the Si1−yCy layer. © 2003 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.up Other materials
66.30.Lw Diffusion of other defects
61.72.S- Impurities in crystals

Spatial distribution of yellow luminescence related deep levels in GaN

J. W. P. Hsu, F. F. Schrey, and H. M. Ng

Appl. Phys. Lett. 83, 4172 (2003); http://dx.doi.org/10.1063/1.1628398 (3 pages) | Cited 7 times

Online Publication Date: 12 November 2003

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Using two-photon excitation, we study the excitation power density dependence and spatial variation of photoluminescence (PL) in GaN films grown by molecular beam epitaxy. Under our experimental conditions, the excitation power density dependence is quadratic for near band-gap emission (NBE) and linear for yellow luminescence (YL), consistent with the YL process being saturated. The PL mapping reveals NBE fluctuations at the domain-size scale while YL is uniform. These results provide strong evidence that the spatial distribution of deep levels associated with YL is uniform; hence, YL is unrelated to dislocations. © 2003 American Institute of Physics.
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78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors

Roughness at ZrO2/Si interfaces induced by accelerated oxidation due to the metal oxide overlayer

Heiji Watanabe

Appl. Phys. Lett. 83, 4175 (2003); http://dx.doi.org/10.1063/1.1629146 (3 pages) | Cited 13 times

Online Publication Date: 12 November 2003

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We investigated reactions at ZrO2/Si interfaces by means of interface oxidation and atomic-scale roughness caused by postoxidation annealing. When fabricating ZrO2 by in situ reoxidation of a thin Zr metal layer, the interface oxidation that results in Zr–silicate formation accelerates, when the initial Zr layer becomes thicker. This implies that interface oxidation is not dominated by oxidant diffusion through the high-k film, but is accelerated by catalytic effects that occurs within the metal oxide. We also found that, in contrast with a SiO2/Si interface, roughness at the high-k/Si interface monotonously increases with the growth of the interface silicate layers. These results demonstrate the importance of postannealing conditions on high-k gate dielectrics. © 2003 American Institute of Physics.
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81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing
68.35.Ct Interface structure and roughness
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Effects of surface treatments on isolation currents in AlGaN/GaN high-electron-mobility transistors

N. A. Moser, J. K. Gillespie, G. D. Via, A. Crespo, M. J. Yannuzzi, G. H. Jessen, R. C. Fitch, B. Luo, F. Ren, B. P. Gila, A. H. Onstine, C. R. Abernathy, and S. J. Pearton

Appl. Phys. Lett. 83, 4178 (2003); http://dx.doi.org/10.1063/1.1628394 (3 pages) | Cited 8 times

Online Publication Date: 12 November 2003

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Interdevice isolation currents in mesa-isolated AlGaN/GaN high-electron-mobility transistors are found to exhibit thermally activated behavior, with an activation energy of ∼ 1.5 eV. This value is largely independent of surface cleaning processes or the type of passivation film (SiNX, Sc2O3, MgO) used to reduce the current collapse phenomena in the devices. However, the magnitude of the isolation current is a strong function of the surface treatment employed. The lowest isolation currents for conditions under which current collapse is mitigated are obtained using Sc2O3 passivation layers. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
68.47.Fg Semiconductor surfaces
81.65.Rv Passivation
81.65.Cf Surface cleaning, etching, patterning
73.20.At Surface states, band structure, electron density of states

Temperature dependence of the c-axis mobility in 6H-SiC Schottky diodes

F. Roccaforte, F. La Via, V. Raineri, F. Mangano, and L. Calcagno

Appl. Phys. Lett. 83, 4181 (2003); http://dx.doi.org/10.1063/1.1628390 (3 pages) | Cited 10 times

Online Publication Date: 12 November 2003

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In this work, the temperature dependence of the mobility along the c axis in silicon carbide (6H-SiC) was determined from the I–V characteristics of Schottky diodes. This procedure used series resistance measurements with Norde’s method in Schottky diodes for extracting the mobility values in the epitaxial layer. For a dopant concentration of 3×1015 cm−3, at room temperature a value of 61 cm2 V−1 s−1 was found, which decreased to 24 cm2 V−1 s−1 at 448 K. In the temperature range 298–448 K, a dependence of the mobility as T−2.1 was determined. This result suggests that the lattice scattering, together with other mechanisms such as scattering with defects in the material, rule the carrier transport in this temperature range. © 2003 American Institute of Physics.
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85.30.Hi Surface barrier, boundary, and point contact devices
73.30.+y Surface double layers, Schottky barriers, and work functions
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Le Other inorganic semiconductors
85.30.Kk Junction diodes

Thermal conductivity in strain symmetrized Si/Ge superlattices on Si(111)

S. Chakraborty, C. A. Kleint, A. Heinrich, C. M. Schneider, J. Schumann, M. Falke, and S. Teichert

Appl. Phys. Lett. 83, 4184 (2003); http://dx.doi.org/10.1063/1.1628819 (3 pages) | Cited 16 times

Online Publication Date: 12 November 2003

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We have presented systematic cross-plane thermal conductivity (λ) data for the undoped strain-symmetrized Si/Ge superlattices grown on Si(111) with superlattice (SL) period thickness varying from 3.6 to 16 nm. In thin SL period (L ⩽ 7 nm) samples, the data have shown considerable reductions of λ, by more than 50% and 30% compared to the SiGe alloy and to the earlier reported values in (100)-oriented Si/Ge superlattice structures (SLS), respectively. For the thick SL period samples (L>10 nm), λ has shown a tendency to saturate at the SiGe alloy value. This is understood as, with increasing L, the SLS breaks and the SiGe alloying starts to grow. This structural behavior is clearly observed in the cross-plane transmission electron microscope images as well. In addition to these, for the thin SL period (L ⩽ 7 nm) samples, the data have shown a shallow minimum which is attributed to the competing behavior of the wave nature and the classical particle nature of the localized phonons. Nevertheless, the present study of thermal conductivity on undoped strain-symmetrized Si/Ge SLs in (111) orientation suggests that an enhancement of thermoelectric figure-of-merit Z is possible. © 2003 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
73.50.Lw Thermoelectric effects
72.20.Pa Thermoelectric and thermomagnetic effects
68.65.Cd Superlattices
68.60.Dv Thermal stability; thermal effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Low and anisotropic barrier energy for adatom migration on a GaAs (110) surface studied by first-principles calculations

Akira Ishii, Tsuyoshi Aisaka, Ji-Won Oh, Masahiro Yoshita, and Hidefumi Akiyama

Appl. Phys. Lett. 83, 4187 (2003); http://dx.doi.org/10.1063/1.1627945 (3 pages) | Cited 14 times

Online Publication Date: 12 November 2003

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We determined potential-energy surfaces for Ga and As adatoms on a GaAs (110) surface by first-principles calculations in order to understand the epitaxial growth mechanism. We found small migration barrier energies for Ga and As, which explain the long atom-migration length suggested by experiments. We also found that Ga migration is one dimensional and As migration is two dimensional, and that, for both Ga and As adatoms, the sites near As of the topmost layer are stable while those near Ga are unstable. © 2003 American Institute of Physics.
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68.43.Bc Ab initio calculations of adsorbate structure and reactions
68.47.Fg Semiconductor surfaces
68.55.A- Nucleation and growth

Long coherence times at 300 K for nitrogen-vacancy center spins in diamond grown by chemical vapor deposition

T. A. Kennedy, J. S. Colton, J. E. Butler, R. C. Linares, and P. J. Doering

Appl. Phys. Lett. 83, 4190 (2003); http://dx.doi.org/10.1063/1.1626791 (3 pages) | Cited 60 times

Online Publication Date: 12 November 2003

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Electron-spin-echo experiments reveal phase-memory times as long as 58 μs at 300 K for nitrogen-vacancy centers in chemical vapor deposition (CVD) single crystals. The spins were optically polarized and optically detected. Two high-quality CVD samples were studied. From the current results, it is not clear whether these phase-memory times represent a fundamental limit or are limited by an external source of decoherence. © 2003 American Institute of Physics.
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76.30.Lh Other ions and impurities
61.72.Yx Interaction between different crystal defects; gettering effect
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.J- Point defects and defect clusters

Intrinsic compensation of silicon-doped AlGaN

M. C. Wagener, G. R. James, and F. Omnès

Appl. Phys. Lett. 83, 4193 (2003); http://dx.doi.org/10.1063/1.1628396 (3 pages) | Cited 8 times

Online Publication Date: 12 November 2003

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The silicon doping characteristics of AlxGa1−xN were investigated over the x = 0.2–0.5 composition range. A combination of Hall and capacitance–voltage measurements indicated a significant deepening of the Si level, as well as a systematic increase in carrier compensation with increasing compositions. Optical isothermal capacitance transient spectroscopy also revealed the presence of two midgap states with concentrations in the low 1017 cm−3 range. The two levels, which are thought to be responsible for the observed compensation, have been assigned to the third and second ionization states of the aluminum vacancy. © 2003 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
71.55.Eq III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Improved coherent terahertz emission by modification of the dielectric environment

M. Zedler, C. Janke, P. Haring Bolivar, H. Kurz, and H. Künzel

Appl. Phys. Lett. 83, 4196 (2003); http://dx.doi.org/10.1063/1.1628400 (3 pages) | Cited 5 times

Online Publication Date: 12 November 2003

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We present a generally applicable approach to enhance the conversion efficiency from optical input to usable coherent output power for THz emitters based on optically excited charge carriers. Guided by numerical simulations, the dielectric environment of the emitter is modified to improve radiation rate and spatial emission characteristics. The modifications comprise a sapphire layer applied on the semiconductor surface and a gold backside metallization. Comparison between a standard InGaAs semiconductor surface field emitter and an optimized version yields an increase of one order of magnitude in coherently emitted THz power. This result is in close agreement with the numerical simulations. © 2003 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption

High resistivity annealed low-temperature GaAs with 100 fs lifetimes

I. S. Gregory, C. Baker, W. R. Tribe, M. J. Evans, H. E. Beere, E. H. Linfield, A. G. Davies, and M. Missous

Appl. Phys. Lett. 83, 4199 (2003); http://dx.doi.org/10.1063/1.1628389 (3 pages) | Cited 40 times

Online Publication Date: 12 November 2003

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We demonstrate the critical effect of postgrowth annealing temperature on the properties of low-temperature-grown GaAs. By using annealing temperatures substantially below the 500–600 °C commonly reported, GaAs with high resistivity and with carrier lifetimes as short as 100 fs can be routinely obtained. We discuss the optimum, but different, anneal conditions required for terahertz photoconductive emitters and detectors, and illustrate their use in a continuous-wave system. © 2003 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
61.72.Cc Kinetics of defect formation and annealing
84.40.Ba Antennas: theory, components and accessories
85.60.-q Optoelectronic devices
72.40.+w Photoconduction and photovoltaic effects

Strained Si/strained Ge dual-channel heterostructures on relaxed Si0.5Ge0.5 for symmetric mobility p-type and n-type metal-oxide-semiconductor field-effect transistors

Minjoo L. Lee and Eugene A. Fitzgerald

Appl. Phys. Lett. 83, 4202 (2003); http://dx.doi.org/10.1063/1.1627469 (3 pages) | Cited 27 times

Online Publication Date: 12 November 2003

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By growing heterostructures that combine a surface strained Si layer with a buried strained Ge layer on Si0.5Ge0.5, we have fabricated metal-oxide-semiconductor field-effect transistors with mobility enhancement factors over bulk Si of 1.7–1.9 for electrons and 10–12 for holes. While high hole mobility can be attained in strained Si/strained Ge heterostructures grown on Si0.3Ge0.7, we have found the electron mobility in similarly grown heterostructures to be limited by defect scattering in the Si cap. Reducing the Ge content of the virtual substrate to Si0.5Ge0.5 and optimizing the strained Si and strained Ge layer thicknesses allowed the realization of devices where the p-channel mobility as a function of inversion density actually matches or exceeds the n-channel mobility. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Electrical characterization of InGaAs/InP quantum wells by scanning capacitance microscopy

K. Maknys, O. Douhéret, and S. Anand

Appl. Phys. Lett. 83, 4205 (2003); http://dx.doi.org/10.1063/1.1625109 (3 pages) | Cited 15 times

Online Publication Date: 12 November 2003

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In this work, cross-sectional scanning capacitance microscopy (SCM) is used to investigate InGaAs/InP quantum wells. It is demonstrated that SCM is indeed capable of detecting the electrons in the quantum wells and that the SCM signal shows a systematic trend for the different wells. Clear dips in the dC/dV signal are observed at the InGaAs quantum wells and imply carrier densities higher than the surrounding barriers. It is also shown that the depletion regions in the barriers adjacent to the wells can be resolved. The results show that geometric tip-averaging effects significantly influence the imaging of electrons in quantum wells and limit the lateral resolution. © 2003 American Institute of Physics.
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73.63.Hs Quantum wells
68.37.-d Microscopy of surfaces, interfaces, and thin films
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
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Direct observation of magnetic bit transition and physical grain boundary in perpendicular recording media

Jun Yu, Joachim Ahner, and Dieter Weller

Appl. Phys. Lett. 83, 4208 (2003); http://dx.doi.org/10.1063/1.1627940 (3 pages) | Cited 1 time

Online Publication Date: 12 November 2003

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The correlation between magnetic bit transition line and physical grain boundary in a multilayer perpendicular recording medium is examined by combined magnetic force and electrostatic force microscopy. Reducing the scan height results in stronger electrostatic interaction between the tip and the sample disk. This electrostatic interaction causes the topographical information to be superimposed onto the magnetic force image and allows simultaneous imaging of the columnar grains and the magnetic bits. It is found that the magnetic transition follows the physical grain boundaries with high accuracy. The correlation of both is quantified by image processing and a correlation coefficient of 0.92 has been determined. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ss Magnetic recording materials
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Mm Grain and twin boundaries

Modification of ferromagnetism in semiconductors by molecular monolayers

T. C. Kreutz, E. G. Gwinn, R. Artzi, R. Naaman, H. Pizem, and C. N. Sukenik

Appl. Phys. Lett. 83, 4211 (2003); http://dx.doi.org/10.1063/1.1625422 (3 pages) | Cited 12 times

Online Publication Date: 12 November 2003

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We report that adsorption of monolayers of organic molecules onto the surface of ferromagnetic semiconductor heterostructures produces large, robust changes in their magnetic properties. The heterostructures have half a monolayer of MnAs embedded in GaAs, 50 Å beneath the surface. The molecules investigated are alkylphosphonic acids that bind to GaAs via a phosphonate group. The organization of the organic monolayer determines the reduction in the Curie temperature, with ordered monolayers producing nearly complete suppression of ferromagnetism. We attribute this striking chemical modulation of magnetic properties to electronic changes brought about by the binding of the molecules to the semiconductor surface. © 2003 American Institute of Physics.
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75.70.Rf Surface magnetism
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
68.43.Fg Adsorbate structure (binding sites, geometry)

Very low chemical disorder in epitaxial NiMnSb films on GaAs(111)B

W. Van Roy, M. Wójcik, E. Jędryka, S. Nadolski, D. Jalabert, B. Brijs, G. Borghs, and J. De Boeck

Appl. Phys. Lett. 83, 4214 (2003); http://dx.doi.org/10.1063/1.1627938 (3 pages) | Cited 20 times

Online Publication Date: 12 November 2003

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Single-crystalline NiMnSb(111) films with negligibly low defect levels have been grown epitaxially on GaAs(111)B using molecular beam epitaxy and characterized by nuclear magnetic resonance. In a film with only 1% deviation from stoichiometry, 1.1% of all Mn atoms is involved in planar defects, ∼ 0.5% of all Sb sites is occupied by AsSb substitutional atoms, and ∼ 0.2% of all Sb atoms has a modified environment. Both the average concentration of defects and the interface orientation are compatible with maintaining a half-metallic band structure at the ferromagnet/semiconductor interface, making these films a good candidate for spin injection into a semiconductor. © 2003 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.40.Ns Metal-nonmetal contacts
75.50.Cc Other ferromagnetic metals and alloys
73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
76.60.-k Nuclear magnetic resonance and relaxation
61.66.Dk Alloys

Narrow commensurate states induced by a periodic array of nanoscale antidots in Nb superconductor

A. A. Zhukov, P. A. J. de Groot, V. V. Metlushko, and B. Ilic

Appl. Phys. Lett. 83, 4217 (2003); http://dx.doi.org/10.1063/1.1627478 (3 pages) | Cited 10 times

Online Publication Date: 12 November 2003

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We examine the interactions of the vortex lattice with a periodic square array of holes in a superconducting Nb film. Using high-resolution magnetic-field measurements of electrical losses, extremely narrow states with a magnetic field width reaching 1% of the matching field value are found at the commensurate points. They are accompanied by pronounced harmonic generation in response to ac modulation of the magnetic field or current. We relate these sharp anomalies to a locked commensurate state with characteristics of a Mott insulator. This offers opportunities for applications of superconducting films with periodic hole arrays as sensitive magnetic field detectors. © 2003 American Institute of Physics.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.78.-w Superconducting films and low-dimensional structures
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
74.25.Jb Electronic structure (photoemission, etc.)
74.25.Ha Magnetic properties including vortex structures and related phenomena
07.55.Ge Magnetometers for magnetic field measurements
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Enhancement of Curie temperature in Ga1−xMnxAs/Ga1−yAlyAs ferromagnetic heterostructures by Be modulation doping

T. Wojtowicz, W. L. Lim, X. Liu, M. Dobrowolska, J. K. Furdyna, K. M. Yu, W. Walukiewicz, I. Vurgaftman, and J. R. Meyer

Appl. Phys. Lett. 83, 4220 (2003); http://dx.doi.org/10.1063/1.1628815 (3 pages) | Cited 39 times

Online Publication Date: 12 November 2003

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The effect of modulation doping by Be on the ferromagnetic properties of Ga1−xMnxAs is investigated in Ga1−xMnxAs/Ga1−yAlyAs heterojunctions and quantum wells. Introducing Be acceptors into the Ga1−yAlyAs barriers leads to an increase of the Curie temperature TC of Ga1−xMnxAs, from 70 K in undoped structures to over 100 K with the modulation doping. This increase is qualitatively consistent with a multiband mean field theory simulation of carrier-mediated ferromagnetism. An important feature is that the increase of TC occurs only in those structures where the modulation doping is introduced after the deposition of the magnetic layer, but not when the Be-doped layer is grown first. This behavior is expected from the strong sensitivity of Mn interstitial formation to the value of the Fermi energy during growth. © 2003 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.J- Point defects and defect clusters
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.55.Eq III-V semiconductors
75.50.Dd Nonmetallic ferromagnetic materials

Reversible axial-strain effect and extended strain limits in Y-Ba-Cu-O coatings on deformation-textured substrates

N. Cheggour, J. W. Ekin, C. C. Clickner, D. T. Verebelyi, C. L. H. Thieme, R. Feenstra, and A. Goyal

Appl. Phys. Lett. 83, 4223 (2003); http://dx.doi.org/10.1063/1.1628818 (3 pages) | Cited 48 times

Online Publication Date: 12 November 2003

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The dependence of transport critical-current density Jc on axial tensile strain ε was measured at 76 K and self-magnetic field for YBa2Cu3O7−δ (YBCO) coatings on buffered, deformation-textured substrates of pure Ni, Ni–5-at. %-W, and Ni–10-at. %-Cr–2-at. %-W. Expectations have been that the strain tolerance of these composites would be limited by the relatively low yield strains of the deformation-textured substrates, typically less than 0.2%. However, results show that the irreversible degradation of Jc(ε) occurs at a strain equal to about twice the yield strain of the substrate. Therefore, YBCO/Ni-alloy composites may satisfy axial-strain performance requirements for electric devices, including the most demanding applications, motors and generators in which a strain tolerance exceeding 0.25% is needed. Furthermore, the YBCO/Ni–5-at. %-W conductors showed a reversible strain effect, which may be induced by a reversible strain-field broadening around mismatch dislocations at the grain boundaries. This effect may contribute to the unexpectedly large usable strain range of these conductors. © 2003 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Sv Critical currents
61.72.Mm Grain and twin boundaries
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Dielectric characteristics of low-permittivity silicate using electron beam direct patterning for intermetal dielectric applications

Po-Tsun Liu, T. C. Chang, T. M. Tsai, Z. W. Lin, C. W. Chen, B. C. Chen, and S. M. Sze

Appl. Phys. Lett. 83, 4226 (2003); http://dx.doi.org/10.1063/1.1628401 (3 pages) | Cited 4 times

Online Publication Date: 12 November 2003

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A direct patterning technology of low-permittivity silicate-based polymer is investigated with electron-beam lithography for multilevel interconnections. The smallest feature size of 60 nm for damascene lines can be directly patterned in the silicate film. In this direct patterning, dielectric regions exposed by electron beam are crosslinked and form desirable patterns, while the others are dissolvable in an aqueous solution containing 2.38% tetramethylammonium hydroxide. With an optimum condition of electron-beam lithography, the electron-beam-irradiated silicate exhibits superior dielectric properties than that of the furnace-cured silicate film, due to minimizing the break of Si–H bonds and moisture uptake. The explanation is in agreement with the analyses of Fourier transform infrared spectroscopy and thermal desorption spectroscopy. © 2003 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
77.84.Jd Polymers; organic compounds
85.40.Ls Metallization, contacts, interconnects; device isolation
77.22.Ch Permittivity (dielectric function)
77.55.-g Dielectric thin films

Use of the final thermally stimulated discharge current technique to analyze space charge behavior in dielectrics

E. R. Neagu

Appl. Phys. Lett. 83, 4229 (2003); http://dx.doi.org/10.1063/1.1626790 (3 pages) | Cited 2 times

Online Publication Date: 12 November 2003

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The final thermally stimulated discharge current technique is proposed for analyzing space charge (SC) trapping/detrapping. The letter investigates the effects associated with SC behavior in polyamide 11 in an attempt to discriminate between dipolar and SC related effects. An apparent peak, located 5–13 °C above the charging temperature, and a second peak around 96 °C were observed. Both peaks scale linearly with the field revealing a similar behavior of dipolar and interfacial polarization. The peaks position and the apparent activation energy W do not change with the charging field, but are very sensitive to the previous charging/discharging times. A distribution of the apparent activation energies in a range from 0.45 to 2.20 eV is revealed for the apparent peaks. The isothermal decay of SC at 35 °C is proportional to log t, a behavior that may be characteristic for the interfacial polarization. © 2003 American Institute of Physics.
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77.84.Jd Polymers; organic compounds
77.22.Ej Polarization and depolarization
77.22.Jp Dielectric breakdown and space-charge effects
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