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12 Oct 1998

Volume 73, Issue 15, pp. 2069-2222

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Green emission from Er-doped GaN grown by molecular beam epitaxy on Si substrates

R. Birkhahn and A. J. Steckl

Appl. Phys. Lett. 73, 2143 (1998); http://dx.doi.org/10.1063/1.122404 (3 pages) | Cited 30 times

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Visible light emission has been obtained from Er-doped α-GaN thin films grown on Si(111). The GaN was grown by molecular beam epitaxy using solid sources (for Ga and Er) and a plasma gas source for N2. Photoexcitation with a He–Cd laser resulted in strong green emission from two narrow green lines at 537 and 558 nm identified as Er transitions from the 2H11/2 and 4S3/2 levels to the 4I15/2 ground state. X-ray diffraction shows the GaN:Er to be a wurtzitic single crystal film. The growth temperature is seen to have a strong effect on the GaN:Er surface morphology. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)

AlxGa1−xN:Si Schottky barrier photodiodes with fast response and high detectivity

E. Monroy, F. Calle, E. Muñoz, F. Omnès, P. Gibart, and J. A. Muñoz

Appl. Phys. Lett. 73, 2146 (1998); http://dx.doi.org/10.1063/1.122405 (3 pages) | Cited 33 times

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Gold and nickel Schottky barrier photovoltaic detectors have been fabricated on Si-doped AlxGa1−xN layers (0 ⩽ x ⩽ 0.22) grown on sapphire by metalorganic vapor phase epitaxy. Responsivity is independent of the Schottky metal or diode size, and also of the incident power in the range measured (10 mW/m2–2 kW/m2). A higher visible rejection has been observed in the spectral response of Au photodiodes (>103). Time response is resistance-capacitance limited, with time constants as short as 14 ns in Al0.22Ga0.78N diodes. Low frequency noise studies are also presented, and detectivities of 6.1×107 and 1.2×107 mHz1/2 W−1 are determined in GaN/Au and Al0.22Ga0.78N/Au detectors, at −2 V bias. © 1998 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
73.50.Pz Photoconduction and photovoltaic effects

Coherent acoustic phonons in PbTe quantum dots

E. R. Thoen, G. Steinmeyer, P. Langlois, E. P. Ippen, G. E. Tudury, C. H. Brito Cruz, L. C. Barbosa, and C. L. Cesar

Appl. Phys. Lett. 73, 2149 (1998); http://dx.doi.org/10.1063/1.122406 (3 pages) | Cited 23 times

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Femtosecond pump-probe studies at 1.5 μm of PbTe quantum dots in a glass matrix have revealed oscillations due to a spheroidal acoustic mode. The wavelength dependence of the observed frequencies indicates size selectivity. The frequency and damping of the mode as a function of wavelength agree with the predictions of an acoustic continuum model that suggests that the dominant damping mechanism is radiative loss from the dots to the surrounding glass. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Le Other inorganic semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.47.-p Spectroscopy of solid state dynamics
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
71.38.-k Polarons and electron-phonon interactions

Evidence of electron confinement in the single-domain (4×1)-In superstructure on vicinal Si(111)

F. Pedreschi, J. D. O’Mahony, P. Weightman, and J. R. Power

Appl. Phys. Lett. 73, 2152 (1998); http://dx.doi.org/10.1063/1.122407 (3 pages) | Cited 20 times

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Reflectance anisotropy spectroscopy is applied to submonolayer growth of In on the vicinal silicon (111) surface. Deposition in the region of 1 monolayer onto a clean stepped Si(111) surface at elevated temperature produces a single-domain In-induced (4×1) superstructure consisting of quasi-one-dimensional chains aligned parallel to the vicinal surface step edges. A significant optical anisotropy (1.65%), uncharacteristic of semiconductor systems, develops in the region of 1.9 eV which saturates upon completion of the (4×1) superstructure. We relate this feature to an optical transition involving a flat, highly populated filled surface state observed previously. We argue that the intensity and direction of this peak are indicative of electronic confinement within this system perpendicular to the In-induced chain length. © 1998 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
78.66.Bz Metals and metallic alloys
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Two-dimensional carrier profiling of InP structures using scanning spreading resistance microscopy

P. De Wolf, M. Geva, T. Hantschel, W. Vandervorst, and R. B. Bylsma

Appl. Phys. Lett. 73, 2155 (1998); http://dx.doi.org/10.1063/1.122408 (3 pages) | Cited 36 times

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Scanning spreading resistance microscopy (SSRM) is an analytical technique originally developed for measuring two-dimensional carrier distribution in Si device structures with high spatial resolution. It is in essence an atomic force microscope equipped with a conducting tip that is biased relative to the sample. The spreading resistance value derived from the measured electrical current is a function of the local carrier concentration at the surface region surrounding the probe’s tip. In this letter, we report the successful application of SSRM to the analysis of InP semiconductor device structures. We imaged a multilayer epitest structure, and a cross section of a three-dimensional structure in which we observed lateral Zn-dopant diffusion. Comparison of the SSRM profiles with one-dimensional secondary ion mass spectrometry depth profiles shows good qualitative agreement. SSRM analysis of InP-based device structures was found to be much simpler than that of Si structures: there is no need for surface preparation of the cleaved surface, a lower tip force is required, and metal tips, rather than doped diamond can be used. © 1998 American Institute of Physics.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
68.35.Fx Diffusion; interface formation

Room-temperature pulsed operation of an electrically injected InGaN/GaN multi-quantum well distributed feedback laser

Daniel Hofstetter, Robert L. Thornton, Linda T. Romano, David P. Bour, Michael Kneissl, and Rose M. Donaldson

Appl. Phys. Lett. 73, 2158 (1998); http://dx.doi.org/10.1063/1.122409 (3 pages) | Cited 14 times

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We demonstrate room-temperature pulsed operation of an electrically injected InGaN/GaN-based distributed feedback laser with an emission wavelength of 403 nm. The threshold current of a 1000-μm-long and 20-μm-wide device was 3.2 A; corresponding to a threshold current density of 16 kA/cm2. The 3rd order grating providing feedback was defined holographically and dry etched into the upper waveguiding layer by chemically assisted ion beam etching. We observed single mode operation of the laser with a side mode suppression ratio of 15 dB over a temperature range of about 30 K. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

On the correlation between the carbon content and the electrical quality of thermally grown oxides on p-type 6H–Silicon carbide

Vickram R. Vathulya, Dong Ning Wang, and Marvin H. White

Appl. Phys. Lett. 73, 2161 (1998); http://dx.doi.org/10.1063/1.122562 (3 pages) | Cited 25 times

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Thermal oxides on p-type silicon carbide exhibit high densities of interface states and fixed charge. Understanding the effect of the oxide composition on the electrical properties is imperative to improve the quality of oxides on p-type silicon carbide. In this work, we use angle resolved x-ray photoelectron spectroscopy to profile the oxide composition. The result is a direct correlation between the carbon content in the oxide and the density of interface states and fixed charge as determined by electrical capacitance–voltage measurements. © 1998 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.Hb Impurity and defect levels; energy states of adsorbed species
79.60.Jv Interfaces; heterostructures; nanostructures

Self-organization of (In,Ga)As/GaAs quantum dots on relaxed (In,Ga)As films

Dong Pan, Jian Xu, Elias Towe, Qin Xu, and J. W. Hsu

Appl. Phys. Lett. 73, 2164 (1998); http://dx.doi.org/10.1063/1.122410 (3 pages) | Cited 8 times

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We report the synthesis of (In,Ga)As/GaAs quantum dots on strain-relaxed (In,Ga)As epitaxial films. It is found that the incorporation of a relaxed prelayer provides a systematic and effective method for controlling the dot distribution and emission wavelength. The robustness of the optical properties of quantum dots to dislocations may provide a method for engineering the band structure of quantum dot devices. We demonstrate, for example, that longer band-to-band emission wavelengths can be obtained by simply decreasing the residual strain in the relaxed films. © 1998 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors
68.60.Bs Mechanical and acoustical properties

Injection level dependence of the defect-related carrier lifetime in light-degraded boron-doped Czochralski silicon

Jan Schmidt, Christopher Berge, and Armin G. Aberle

Appl. Phys. Lett. 73, 2167 (1998); http://dx.doi.org/10.1063/1.122411 (3 pages) | Cited 11 times

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The carrier recombination lifetime in light-degraded boron-doped 1 Ω cm Czochralski-grown silicon wafers is measured as a function of the bulk excess carrier concentration Δn. The measurements are performed with the quasi-steady state photoconductance method and cover a large injection level range between 1013 and 1.5×1017 cm−3. We observe a very strong increase of the carrier lifetime in the Δn range between 1014 and 2×1016 cm−3, which is attributed to boron–oxygen (BiOi) defect pairs. The observed strong increase of the defect-related carrier lifetime allows us to determine the previously unknown hole capture cross section σp of the BiOi pair. Our analysis gives a σp value of (0.45–1.2)×10−15 cm2, which is 2–3 orders of magnitude smaller than the corresponding electron capture cross section. © 1998 American Institute of Physics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors
72.40.+w Photoconduction and photovoltaic effects

Transmission electron microscopy and photoluminescence studies of Er implanted low-temperature grown GaAs:Be

R. L. Maltez, Z. Liliental-Weber, J. Washburn, M. Behar, P. B. Klein, P. Specht, and E. R. Weber

Appl. Phys. Lett. 73, 2170 (1998); http://dx.doi.org/10.1063/1.122412 (3 pages) | Cited 2 times

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Characteristic 1.54 μm 4f-4f emission has been observed from Er3+ centers in Er-implanted and annealed, low-temperature grown GaAs:Be samples, while cross-sectional transmission electron microscopy (TEM) studies reveal very little structural damage for elevated temperature implants. No Er emission was observed from any of the as-implanted samples, while the Er emission intensity was significantly more intense after 650 °C anneals than after 750 °C anneals. Significant enhancement of the optically active Er incorporation was achieved when the implantation was carried out at 300 °C. For the two total Er fluences employed (5.5×1013 and 13.6×1013 Er/cm2) the Er emission intensity exhibited a linear dependence upon implantation fluence, while TEM indicated no significant increase in the damage level at the higher fluence 300 °C implant. © 1998 American Institute of Physics.
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68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
61.72.uj III-V and II-VI semiconductors
78.55.Cr III-V semiconductors

Current-induced local oxidation of metal films: Mechanism and quantum-size effects

Thomas Schmidt, Richard Martel, Robert L. Sandstrom, and Phaedon Avouris

Appl. Phys. Lett. 73, 2173 (1998); http://dx.doi.org/10.1063/1.122413 (3 pages) | Cited 28 times

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A novel route is introduced for oxidizing thin metal films with nanometer-scale resolution. By locally subjecting Ti and Nb films to high in-plane current densities, metal-oxide tunneling barriers are formed in a self-limiting fashion. The oxidation is triggered by current-induced atomic rearrangements and local heating. At the final stages of the barrier formation, when only atomic-scale channels remain unoxidized, the oxidation rate decreases drastically while the conductance drops in steps of about 2e2/h. This behavior gives evidence of ballistic transport and a superior stability of such metallic nanowires against current-induced forces compared with the bulk metal. © 1998 American Institute of Physics.
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73.61.At Metal and metallic alloys
81.65.Mq Oxidation
73.50.Fq High-field and nonlinear effects
73.50.Mx High-frequency effects; plasma effects

Exciton transport into a single GaAs quantum wire studied by picosecond near-field optical spectroscopy

A. Richter, M. Süptitz, D. Heinrich, Ch. Lienau, T. Elsaesser, M. Ramsteiner, R. Nötzel, and K. H. Ploog

Appl. Phys. Lett. 73, 2176 (1998); http://dx.doi.org/10.1063/1.122414 (3 pages) | Cited 14 times

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We report a time-resolved near-field luminescence study of excitonic real-space transfer into single GaAs quantum wires. Excitons generated by local optical excitation in a 250 nm spot undergo diffusive transport over a length of several microns and are subsequently trapped into the quantum wire by optical phonon emission. Local energy barriers in the vicinity of the quantum wire, originating from the epitaxial growth mechanism of the nanostructure, directly influence the real-space transfer dynamics and trapping efficiency. © 1998 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
63.20.kk Phonon interactions with other quasiparticles
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Nanometer-scale Si selective epitaxial growth on Si surface windows in ultrathin oxide films fabricated using scanning tunneling microscopy

Motoshi Shibata, Yoshiki Nitta, Ken Fujita, and Masakazu Ichikawa

Appl. Phys. Lett. 73, 2179 (1998); http://dx.doi.org/10.1063/1.122415 (3 pages) | Cited 28 times

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Using scanning tunneling microscopy (STM), nanometer-scale Si(111) and Si(001) windows in ultrathin SiO2 films are fabricated by electron-beam-induced thermal decomposition. At 450–630 °C, the oxidized Si surfaces are irradiated with a field emission electron beam from a STM tip with an energy of 70–150 eV and a current of 10–50 nA. The smallest window size is about 40 nm. The shape of the Si crystals selectively grown on the Si(001) windows is that of a frustum of a quadrangular pyramid, while that on the Si(111) windows is an (111) oriented two-dimensional island. We discuss the influence of the field emission electrons on the fabrication and the selective growth. © 1998 American Institute of Physics.
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81.05.Cy Elemental semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
61.80.Fe Electron and positron radiation effects
81.65.Mq Oxidation
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Temperature dependence of noise in a GaAs metal-semiconductor field effect transistor at microwave frequencies

J. A. Fendrich and M. Feng

Appl. Phys. Lett. 73, 2182 (1998); http://dx.doi.org/10.1063/1.122416 (3 pages) | Cited 1 time

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Measurements of the noise parameters of a GaAs metal-semiconductor field effect transistor (MESFET) show the minimum noise figure decreases exponentially into the noise floor with decreasing temperature for most frequencies from 2 to 18 GHz and for most currents. The MESFET noise has a thermal activation energy of ∼ 55 meV which is almost half the value seen in a pseudomorphic high electron mobility field effect transistor (pHEMT). Unlike in the pHEMT, the high-temperature coefficient to the activated behavior for the MESFET is independent of current and frequency. © 1998 American Institute of Physics.
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85.30.Tv Field effect devices
84.40.-x Radiowave and microwave (including millimeter wave) technology

Electrical and optical properties of CdGeAs2 single crystals irradiated with fast electrons

I. Zwieback, D. Perlov, J. P. Maffetone, and W. Ruderman

Appl. Phys. Lett. 73, 2185 (1998); http://dx.doi.org/10.1063/1.122417 (3 pages) | Cited 14 times

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The effects of 10 MeV fast electron irradiation on conductivity type, resistivity, and optical absorption of CdGeAs2 single crystals were studied. Irradiation of as-grown p-type crystals with a fluence of 1×1017 cm−2 caused compensation of the semiconductor and a marked improvement in the optical transmission. A level of absorption below 0.1 cm−1 at 5 ⩽ λ ⩽ 11 μm was registered. Increase in the fluence to 2×1017 cm−2 led to conversion to n-type, a drop in the resistivity and deterioration of the transmission. Analysis of the absorption in p-type crystals showed that transitions from the V2 and V3 split-off bands to the V1 valence band represent the major absorption mechanism. Splitting energies ΔE2−1 = 0.15 eV and ΔE3−1 = 0.35 eV have been calculated. Absorption in n-type crystals increased as λ2.4 indicating absorption by free electrons and their scattering by optical phonons. The effect of irradiation on the optical absorption of CdGeAs2 is assigned to the radiation-induced changes in the compensation level. © 1998 American Institute of Physics.
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72.80.Jc Other crystalline inorganic semiconductors
61.80.Fe Electron and positron radiation effects
78.40.Fy Semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
63.20.K- Phonon interactions

Preliminary investigation of the kinetics of postoxidation rapid thermal anneal induced hole-trap-precursor formation in microelectronic SiO2 films

J. F. Conley, P. M. Lenahan, and W. F. McArthur

Appl. Phys. Lett. 73, 2188 (1998); http://dx.doi.org/10.1063/1.122418 (3 pages) | Cited 6 times

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Measurements of the growth of E′ center precursor and hole trap precursor densities versus postoxidation anneal time show that both approach saturation values and that the approach to these values is more rapid at higher temperatures. Our results, at least qualitatively, show that a kinetic component can be added to a predictive thermodynamics-based model of oxide hole trapping. The results also indicate quite strongly that a thermodynamics approach to oxide hole trap precursor modeling is appropriate, i.e., the relevant defect densities approach thermodynamic equilibrium or quasiequilibrium in reasonable times. © 1998 American Institute of Physics.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ng Insulators
61.72.Cc Kinetics of defect formation and annealing

Room temperature operation of epitaxially grown Si/Si0.5Ge0.5/Si resonant interband tunneling diodes

Sean L. Rommel, Thomas E. Dillon, M. W. Dashiell, H. Feng, J. Kolodzey, Paul R. Berger, Phillip E. Thompson, Karl D. Hobart, Roger Lake, Alan C. Seabaugh, Gerhard Klimeck, and Daniel K. Blanks

Appl. Phys. Lett. 73, 2191 (1998); http://dx.doi.org/10.1063/1.122419 (3 pages) | Cited 55 times

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Resonant interband tunneling diodes on silicon substrates are demonstrated using a Si/Si0.5Ge0.5/Si heterostructure grown by low temperature molecular beam epitaxy which utilized both a central intrinsic spacer and δ-doped injectors. A low substrate temperature of 370 °C was used during growth to ensure a high level of dopant incorporation. A B δ-doping spike lowered the barrier for holes to populate the quantum well at the valence band discontinuity, and an Sb δ-doping reduces the doping requirement of the n-type bulk Si by producing a deep n+ well. Samples studied from the as-grown wafers showed no evidence of negative differential resistance (NDR). The effect of postgrowth rapid thermal annealing temperature was studied on tunnel diode properties. Samples which underwent heat treatment at 700 and 800 °C for 1 min, in contrast, exhibited NDR behavior. The peak-to-valley current ratio (PVCR) and peak current density of the tunnel diodes were found to depend strongly on δ-doping placement and on the annealing conditions. PVCRs ranging up to 1.54 were measured at a peak current density of 3.2 kA/cm2. © 1998 American Institute of Physics.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.40.Gk Tunneling

Observation of coherent hybrid reflection with synchrotron radiation

S. L. Morelhão, L. H. Avanci, M. A. Hayashi, L. P. Cardoso, and S. P. Collins

Appl. Phys. Lett. 73, 2194 (1998); http://dx.doi.org/10.1063/1.122420 (3 pages) | Cited 7 times

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High resolution synchrotron radiation has been used to investigate the occurrence of coherent hybrid reflections (CHR) in the In0.49Ga0.51P/GaAs(001) structure. Several ϕ scans at the 002 layer reflection were carried out. The scanned ϕ intervals are correlated by the [001] axis symmetry and should present the same pattern. A break in the symmetry is observed due to constructive/destructive interference of the hybrid amplitudes with the amplitude from the 002 layer reflection. The effects of substrate miscut and interface distance are taken into account to explain the observed patterns. The application of CHR as a high sensitive tool to analyze epitaxial growth is discussed. © 1998 American Institute of Physics.
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68.55.-a Thin film structure and morphology
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High Tc superconducting second-order gradiometer

A. Kittel, K. A. Kouznetsov, R. McDermott, B. Oh, and John Clarke

Appl. Phys. Lett. 73, 2197 (1998); http://dx.doi.org/10.1063/1.122421 (3 pages) | Cited 17 times

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A planar, second-order gradiometer was fabricated from single-layer YBa2Cu3O7−x films. The gradiometer consists of a symmetric flux transformer with an overall length of 80 mm inductively coupled to a directly coupled magnetometer, and has a baseline of 31 mm. The mutual inductance between the flux transformer and the magnetometer is adjusted mechanically to reduce the response to a uniform magnetic field applied perpendicularly to the plane of the gradiometer to typically 50 ppm. From an independent measurement, the residual first-order gradient response was determined to be at most 1.4% relative to the second-order gradient response. © 1998 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Microwave power handling in engineered YBa2Cu3O7−δ grain boundaries

Y. M. Habib, D. E. Oates, G. Dresselhaus, M. S. Dresselhaus, L. R. Vale, and R. H. Ono

Appl. Phys. Lett. 73, 2200 (1998); http://dx.doi.org/10.1063/1.122422 (3 pages) | Cited 11 times

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Microwave-frequency (rf) power-dependence measurements performed on thin-film YBa2Cu3O7−δ grain boundaries engineered on sapphire bicrystal substrates with misorientation angles of θ = 2°, 5°, 10°, and 24° are presented. The data are compared to measurements on films grown on single-crystal substrates. A stripline-resonator measurement technique is employed. The rf results are compared to dc measurements performed on a four-point test structure on the same substrate as the resonator. The measurements demonstrate that low-angle grain boundaries (θ ⩽ 10°) have little effect on the rf power handling, while the high-angle grain boundaries (θ = 24°) cause large nonlinear losses due to Josephson vortices created by rf currents. © 1998 American Institute of Physics.
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74.72.-h Cuprate superconductors
61.72.Mm Grain and twin boundaries
74.78.-w Superconducting films and low-dimensional structures
74.50.+r Tunneling phenomena; Josephson effects
74.25.F- Transport properties
74.25.N- Response to electromagnetic fields
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Spin-dependent conductance quantization in nickel point contacts

Hirotaka Oshima and Kenjiro Miyano

Appl. Phys. Lett. 73, 2203 (1998); http://dx.doi.org/10.1063/1.122423 (3 pages) | Cited 53 times

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We have observed systematic change of the quantized conductance in point contacts of macroscopic nickel wires under varying external parameters, the temperature (above and below Tc) and the applied magnetic field. The observed quantized conductance can be explained by the number of the channels for electronic transport through the point contact and the spin-dependent transmission coefficient. © 1998 American Institute of Physics.
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73.40.Jn Metal-to-metal contacts
75.50.Cc Other ferromagnetic metals and alloys
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Probing interfacial and bulk magnetic hysteresis in roughened CoFe thin films

J. W. Freeland, K. Bussmann, P. Lubitz, Y. U. Idzerda, and C.-C. Kao

Appl. Phys. Lett. 73, 2206 (1998); http://dx.doi.org/10.1063/1.122424 (3 pages) | Cited 17 times

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The hysteretic behavior of interfacial magnetic moments for CoFe thin films with varying roughness is determined in an element specific manner by monitoring the applied magnetic field dependence of the specular and off-specular (diffuse) contributions to the x-ray resonant magnetic scattering signal. Increasing the interfacial roughness generates a larger variation of the relative coercive field associated with the interfacial moment in comparison to the bulk. © 1998 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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Effect of surface roughness on the secondary ion yield in ion sputtering

Maxim A. Makeev and Albert-László Barabási

Appl. Phys. Lett. 73, 2209 (1998); http://dx.doi.org/10.1063/1.122425 (3 pages)

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There is extensive experimental evidence that, at low temperatures, surface erosion by ion bombardment roughens the sputtered substrate, leading to a self-affine surface. These changes in the surface morphology also modify the secondary ion yield. Here, we calculate analytically the secondary ion yield in terms of parameters characterizing the sputtering process and the interface roughness. © 1998 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Operation of a single column focused ion/electron beam system based on a dual ion/electron source

L. W. Chen and Y. L. Wang

Appl. Phys. Lett. 73, 2212 (1998); http://dx.doi.org/10.1063/1.122426 (3 pages) | Cited 3 times

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A focused ion/electron beam system has been constructed by introducing a dual ion/electron point source into an optical column of electrostatic lenses. Ions are extracted from a W needle covered by liquid In while electrons are from the same source after the In has been in situ solidified. The switching between ion and electron beam is achieved by exchanging the polarity of the potentials applied to the electrodes. In comparison to the ion emission, the electron emission appears to exhibit narrower angular distribution but larger intensity fluctuation and emission point migration. Despite the undesirable features in the electron source, the first operation of the focused ion/electron beam system has demonstrated the potential of a dual-beam single-column system. © 1998 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
41.75.Ak Positive-ion beams
07.77.Ka Charged-particle beam sources and detectors
41.85.Ne Electrostatic lenses, septa

In situ ultrasonic monitoring of photoresist development

Susan L. Morton, F. Levent Degertekin, and B. T. Khuri-Yakub

Appl. Phys. Lett. 73, 2215 (1998); http://dx.doi.org/10.1063/1.122427 (3 pages) | Cited 1 time

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We have developed an in situ method to measure the change in thickness of photoresist during development. The phase of a high frequency ultrasound signal is monitored as it is reflected from the silicon/photoresist interface during resist development. The method was tested using a 1.5 μm film of Shipley 1811 resist. The total phase change during development of 19° was consistent with theoretical calculations at 280 MHz, and this change was used to obtain the resist thickness during development. The method was used to find the development rate of this positive-tone resist as a function of exposure dose in the 20–68 mJ/cm2 range. As expected, there was an increase in development rate as the exposure time increased; this continued up to about 40 s of exposure, beyond which the rates were essentially unchanged. Measurements on a wafer with microelectronic devices ranging in topography from 0.10 to 1.0 μm show that the method is applicable to wafers with typical circuit topography. © 1998 American Institute of Physics.
Show PACS
85.40.Hp Lithography, masks and pattern transfer
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
43.35.Yb Ultrasonic instrumentation and measurement techniques
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