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24 Jun 1996

Volume 68, Issue 26, pp. 3677-3832

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Photoconductive switches for time‐resolved transport measurements at low temperatures and high magnetic fields

G. Ernst, R. J. Haug, M. Klingenstein, J. Kuhl, K. von Klitzing, and K. Eberl

Appl. Phys. Lett. 68, 3752 (1996); http://dx.doi.org/10.1063/1.115995 (3 pages) | Cited 5 times

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Metal‐semiconductor‐metal photodiodes were optimized as pulse generators for time‐resolved electrical measurements at low temperatures and high magnetic fields, using a laser diode as the light source. For the photoconductor, a heterostructure consisting of high‐quality GaAs and low‐temperature grown GaAs was used. The dependence of the photocurrent pulses on the applied magnetic field was determined. A two‐dimensional electron gas in a magnetic field served as the device under test for the time‐resolved measurements. We observed a splitting of the incident pulse into two transmitted pulses resulting from modal dispersion in the two‐dimensional electron gas. © 1996 American Institute of Physics.
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73.40.Sx Metal-semiconductor-metal structures
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
85.60.Dw Photodiodes; phototransistors; photoresistors

High etch rates of SiC in magnetron enhanced SF6 plasmas

G. F. McLane and J. R. Flemish

Appl. Phys. Lett. 68, 3755 (1996); http://dx.doi.org/10.1063/1.115996 (3 pages) | Cited 12 times

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Magnetron enhanced reactive ion etching of SiC has been investigated in SF6 plasmas. Etch rate was determined as a function of cathode power density (0.1–0.5 W/cm2), pressure (1–5 mTorr), and flow rate (5–15 sccm). The highest SiC etch rates yet reported (450 nm/min) were achieved, at low cathode bias voltage (100 V). Anisotropic etch profiles were obtained with smooth etch surfaces free of micromasking. Addition of O2 to the SF6 feed gas did not increase the etch rate.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Hd Other semiconductors

The dependence of the electrical characteristics of the GaN epitaxial layer on the thermal treatment of the GaN buffer layer

C. F. Lin, G. C. Chi, M. S. Feng, J. D. Guo, J. S. Tsang, and J. Minghuang Hong

Appl. Phys. Lett. 68, 3758 (1996); http://dx.doi.org/10.1063/1.115997 (3 pages) | Cited 29 times

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The GaN buffer layer was grown on the sapphire substrate by low‐pressure metalorganic chemical vapor deposition (LP‐MOCVD) at 525 °C. The following 1.3 μm epitaxial GaN growth was carried out at 1025 °C. We varied the ramping rate from 12.5 to 100 °C/min to study the quality of the epitaxial GaN. It has been found that the x‐ray peak width, photoluminescence (PL) linewidth, Hall mobilities, and carrier concentrations of GaN epitaxial layer strongly depend on the in situ thermal ramping rate. An optimum thermal ramping rate was found to be of 20 °C/min. The maximum mobility is 435 cm2/V s at carrier concentration of 1.7×1017 cm−3. The minimum full width at half maximum (FWHM) of x ray and PL were 5.5 min and 12 meV occur at a ramping rate of 20 °C/min. The decrease of the mobility at high and low ramping rate can be attributed to the thermal stress and the reevaporation of the GaN buffer layer. © 1996 American Institute of Physics.
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73.61.Ey III-V semiconductors
68.60.Dv Thermal stability; thermal effects
81.40.Rs Electrical and magnetic properties related to treatment conditions

High responsitivity intrinsic photoconductors based on AlxGa1−xN

B. W. Lim, Q. C. Chen, J. Y. Yang, and M. Asif Khan

Appl. Phys. Lett. 68, 3761 (1996); http://dx.doi.org/10.1063/1.115998 (2 pages) | Cited 81 times

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This letter reports on the fabrication and characterization of visible‐blind ultraviolet photoconductors using single‐crystal AlxGa1−xN layers deposited on basal plane sapphire substrates. With aluminum mole fractions ranging from 5% to 61%, the long‐wavelength cutoff can be varied from 350 to 240 nm. Photoresponsitivities as high as several hundred amperes per watt were measured with 10 μm interelectrode spacing. © 1996 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
73.61.Ey III-V semiconductors
85.60.Dw Photodiodes; phototransistors; photoresistors

Strain‐sensing cryogenic field‐effect transistor for integrated strain detection in GaAs/AlGaAs microelectromechanical systems

R. G. Beck, M. A. Eriksson, R. M. Westervelt, K. L. Campman, and A. C. Gossard

Appl. Phys. Lett. 68, 3763 (1996); http://dx.doi.org/10.1063/1.115999 (3 pages) | Cited 17 times

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We have fabricated a strain‐sensing cryogenic field‐effect transistor (FET) from a GaAs/AlGaAs heterostructure containing a near‐surface two‐dimensional electron gas. The FET has transconductance 100 μS and a small signal drain‐source resistance 10 MΩ. The charge noise has a flat spectrum at high frequencies with magnitude 0.2e/√Hz and 1/f noise corner less than 300 Hz. The piezoelectric effect couples stress in the substrate to the electron density in the FET channel giving an electrical response to applied strain. Strain sensitivity was measured to be 2×10−9/√Hz, limited by FET noise. Integrated strain‐sensing FETs offer advantages for detecting small forces in GaAs/AlGaAs microelectromechanical systems. © 1996 American Institute of Physics.
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85.30.De Semiconductor-device characterization, design, and modeling
07.10.Cm Micromechanical devices and systems
77.65.Ly Strain-induced piezoelectric fields

Effects of biaxial strain on exciton resonance energies of hexagonal GaN heteroepitaxial layers

S. Chichibu, A. Shikanai, T. Azuhata, T. Sota, A. Kuramata, K. Horino, and S. Nakamura

Appl. Phys. Lett. 68, 3766 (1996); http://dx.doi.org/10.1063/1.116000 (3 pages) | Cited 52 times

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Exciton resonance energies of hexagonal (h‐) GaN(0001) epilayers were determined by a combination of high‐resolution modulated photoreflectance methods. The results were analyzed thoretically using the Luttinger‐Kohn type Hamiltonian for the valence bands under the in‐plain biaxial stress, and we obtained the shear deformation potential constants and energy gap in unstrained crystal. Occurrence of the anticrossing of B and C valence bands in tensile biaxially strained h‐GaN was suggested. © 1996 American Institute of Physics.
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78.66.Fd III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.70.Fk Strain-induced splitting

Deep level defects in n‐type GaN compensated with Mg

Gyu‐Chul Yi and Bruce W. Wessels

Appl. Phys. Lett. 68, 3769 (1996); http://dx.doi.org/10.1063/1.116001 (3 pages) | Cited 43 times

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Deep level defects in n‐type epitaxial GaN compensated with Mg were measured using photocapacitance spectroscopy on Schottky barrier diodes. The doped GaN was prepared by atmospheric pressure metalorganic vapor phase epitaxy using bis(cyclopentadienyl)magnesium as the dopant source. The Mg‐doped GaN films were n type as determined by Hall‐effect measurements. Addition of magnesium resulted in the formation of a series of deep centers with optical threshold energies of 1.0, 1.2, 1.8, and 3.1 eV. Upon annealing the Mg compensated GaN in nitrogen at 850 °C the midgap levels disappeared and only the trapping level at 3.1 eV remained. The midgap levels are ascribed to Mg dopant complexes which may be responsible for low doping efficiency of Mg in the as‐grown, doped GaN as well as its semi‐insulating behavior. © 1996 American Institute of Physics.
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72.80.Ey III-V and II-VI semiconductors
71.55.Eq III-V semiconductors

Conservation of photoluminescence splittings related to one‐monolayer thickness variations in GaAs/AlGaAs quantum wells after SiO2 capping‐induced intermixing

A. Pépin, C. Vieu, M. Schneider, R. Planel, H. Launois, and Y. Nissim

Appl. Phys. Lett. 68, 3772 (1996); http://dx.doi.org/10.1063/1.116612 (3 pages) | Cited 1 time

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Intermixing of GaAs/AlGaAs single quantum well heterostructures by SiO2 capping and subsequent annealing was investigated using low‐temperature photoluminescence. In this letter we report the observation of the conservation of splittings related to one‐monolayer thickness variations in the emission of quantum wells after an intermixing process. High photoluminescence intensities and narrow linewidths were also retained although very strong interdiffusion rates inducing energy blueshifts as large as 180 meV were achieved, thus revealing a very homogeneous and high quality intermixing technique. © 1996 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
66.30.Ny Chemical interdiffusion; diffusion barriers

Thermally stimulated current trap in GaN

D. C. Look, Z.‐Q. Fang, W. Kim, Ö. Aktas, A. Botchkarev, A. Salvador, and H. Morkoç

Appl. Phys. Lett. 68, 3775 (1996); http://dx.doi.org/10.1063/1.116613 (3 pages) | Cited 29 times

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A thermally stimulated current peak, occurring at 100 K for a heating rate of 0.4 K/s, has been found in semi‐insulating GaN grown by molecular beam epitaxy. This peak has contributions from two traps, with the main trap described by the following parameters: emission thermal activation energy E≂90±2 meV, effective capture cross‐section σ≂3±1×10−22 cm−2, and Nμτ≂3±1 × 1014 cm−1 V −1, where N is the trap concentration, μ the mobility, and τ the free‐carrier lifetime. This trap is much deeper than the typical shallow donors in conducting GaN, but shallower than any of the centers reported in recent deep level transient spectroscopy measurements. © 1996 American Institute of Physics.
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71.55.Eq III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Ey III-V and II-VI semiconductors

Tensile‐strained barrier GaAsP/GaAs single quantum‐well lasers

Farid Agahi, Arvind Baliga, Kei May Lau, and Neal G. Anderson

Appl. Phys. Lett. 68, 3778 (1996); http://dx.doi.org/10.1063/1.116614 (3 pages) | Cited 3 times

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Device characteristics of tensile‐strained barrier AlGaAs/GaAs1−yPy/GaAs separate‐confinement heterostructure single‐quantum well (SCH‐SQW) broad area lasers are reported. Three phosphorous compositions of 9%, 15%, and 22% were used for the tensile‐strained GaAs1−yPy barrier. For a 1000 μm long cavity device with a wellwidth of 113 Å and 15% P in the barrier, the threshold current density was as low as 233 A/cm2. The threshold current densities are slightly higher than those observed on similar device structures with tensile‐strained GaAsP wells and unstrained GaAs wells with AlGaAs barriers. © 1996 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.66.Fd III-V semiconductors

Space‐charge‐limited currents in nonstoichiometric GaAs

J. P. Ibbetson and U. K. Mishra

Appl. Phys. Lett. 68, 3781 (1996); http://dx.doi.org/10.1063/1.116615 (3 pages) | Cited 17 times

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A study of space‐charge‐limited transport in nonstoichiometric (NS) GaAs is presented. The NS‐GaAs was grown at 250 °C by molecular beam epitaxy and subsequently annealed at 700 °C so that the room‐temperature low‐field conductivity is due almost entirely to electrons thermally excited to the conduction band from deep traps. Experimental current–voltage characteristics of an n+ GaAs/NS‐GaAs homojunction structure display an unusual current saturation whose onset occurs at an electric field of ∼5 kV/cm. We argue that this behavior is due to a combination of electron velocity saturation and the high concentration of compensated traps in annealed NS‐GaAs. © 1996 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Reliability of Hall effect measurements on chemical vapor deposited polycrystalline B‐doped diamond films

J. T. Huang, W. H. Guo, J. Hwang, and H. Chang

Appl. Phys. Lett. 68, 3784 (1996); http://dx.doi.org/10.1063/1.116616 (3 pages) | Cited 6 times

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In situ boron doped polycrystalline diamond films of very good quality were grown on both scratched n‐Si(100) and Al2O3 substrates. Carrier concentration and Hall mobility are mainly contributed from the n‐Si(100) substrate, rather than the boron doped polycrystalline diamond film, when n‐Si(100) is chosen as the substrate. This indicates that the p‐diamond/n‐Si junction is unable to isolate current flowing from the boron doped polycrystalline diamond to the n‐Si(100) substrate during Hall effect measurement. In contrast, carrier concentration and Hall mobility are reliable when Al2O3 is used as the insulating substrate for boron doped diamond deposition. The Hall mobility of the boron doped polycrystalline diamond film varies from 120 cm2/V s at a hole concentration of 1010/cm3 to 0.4 cm2/V s at 2×1015/cm3.
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73.61.Cw Elemental semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Fabrication of GaAs coupled quantum wires on V‐grooved substrate

Kazuhiro Komori, Xue‐Lun Wang, Mutsuo Ogura, Hirofumi Matsuhata, and Hideki Imanishi

Appl. Phys. Lett. 68, 3787 (1996); http://dx.doi.org/10.1063/1.116617 (3 pages) | Cited 8 times

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We have fabricated coupled quantum wires, consisting of two GaAs quantum wires as small as 5 nm thick and 30 nm in width (15 nm in effective width) separated by a 1–3 nm thick AlGaAs barrier, using flow rate modulation epitaxy (FME) on a V‐grooved substrate and observed its optical characteristics. A clear energy splitting between the fundamental coupled state and the higher‐order coupled state of the coupled quantum wires was observed from the room‐temperature photoluminescence. Furthermore, the splitting energy increases as the thickness of barrier decreases from 3 to 1 nm, which is predicted theoretically for coupled quantum systems. © 1996 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Fd III-V semiconductors

A method for the assessment of oxide charge density and centroid in metal‐oxide‐semiconductor structures after uniform gate stress

R. Kies, T. Egilsson, G. Ghibaudo, and G. Pananakakis

Appl. Phys. Lett. 68, 3790 (1996); http://dx.doi.org/10.1063/1.116618 (3 pages) | Cited 5 times

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A method for the extraction of the oxide charge density and distribution centroid based on the exploitation of the Fowler plot derivative characteristics is proposed. To this end, the modification of the tunnel transparency due to the presence of charge within the tunneling region is accounted for. Simple analytical formulas which enable the oxide charge density and centroid to be extracted from the maximum Fowler derivative and its electric field position are derived. The comparison with the DiMaria method confirms the overall consistency of the new approach. The impact of negative charge within the oxide on the apparent Fowler barrier height, which can be deduced from the slope of the Fowler plots after uniform gate stress is also analyzed. Finally, it is pointed out that this method permits the oxide trapping properties to be studied even though only one bias polarization can be utilized for the test structure. © 1996 American Institute of Physics.
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85.30.De Semiconductor-device characterization, design, and modeling
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

p‐ and n‐type carbon doping of InxGa1−xAsyP1−y alloys lattice matched to InP

G. M. Cohen, J. L. Benchimol, G. Le Roux, P. Legay, and J. Sapriel

Appl. Phys. Lett. 68, 3793 (1996); http://dx.doi.org/10.1063/1.116619 (3 pages) | Cited 1 time

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The carbon doping of InxGa1−xAsyP1−y alloys grown by chemical beam epitaxy was studied in the whole range of compositions lattice matched to InP, using carbon–tetrabromide as a source of carbon. The conductivity changed from p‐ to n‐type when going from In0.53Ga0.47As to InP, with a transition point at a composition corresponding to a wavelength of 1.35 μm. The carbon doped n‐type quaternaries were found to be very compensated even for compositions close to InP. The p‐type quaternaries showed little compensation near the transition point, and almost no compensation for compositions close to In0.53Ga0.47As. Reducing the V/III ratio, while keeping all other growth parameters unchanged, increased the incorporation of the carbon atom, and reduced the compensation for p‐type quaternaries. The inversion point position did not change appreciably when the quaternaries were grown with a halved V/III ratio. © 1996 American Institute of Physics.
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71.55.Eq III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Ey III-V semiconductors

Zinc‐blende MnTe(111) on BaF2(111) substrates for optical measurements

E. Janik, E. Dynowska, J. Bak‐Misiuk, J. Domagała, M. Kutrowski, T. Wojtowicz, and A. Stachow

Appl. Phys. Lett. 68, 3796 (1996); http://dx.doi.org/10.1063/1.116620 (3 pages) | Cited 2 times

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Thin films of MnTe having zinc‐blende structure were grown on BaF2(111) substrates under various growth conditions by molecular beam epitaxy. The structural properties of the deposited films were characterized by x‐ray diffraction which evidenced sometimes the presence of other crystallographic phases apart from a dominating zinc‐blende‐like phase. Detailed measurements of symmetrical and asymmetrical reflections showed that the unit cell of (111) MnTe is not cubic, as is the case of epitaxial (001) MnTe, but it is distorted to an orthorhombic one. The transparent BaF2 substrates enabled optical measurements in transmission, thus, permitting a study of the band structure of the material in the vicinity of its fundamental band gap. © 1996 American Institute of Physics.
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68.55.-a Thin film structure and morphology
73.20.At Surface states, band structure, electron density of states
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

High power generation with distributed Josephson‐junction arrays

P. A. A. Booi and S. P. Benz

Appl. Phys. Lett. 68, 3799 (1996); http://dx.doi.org/10.1063/1.116621 (3 pages) | Cited 35 times

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We have experimentally coupled emission from a distributed series array of 1968 wide Josephson junctions to an on‐chip 10.8 Ω load and detected 0.16 mW at 240 GHz. This result is achieved by reducing the parasitic inductance associated with shunt resistors so that junctions with critical currents of 23 mA are effectively shunted at the operating frequency. This power is less than the 1.3 mW expected from theory due to the presence of a large impedance mismatch. Optimization of the load design will allow the detection of mW power. © 1996 American Institute of Physics.
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74.25.Sv Critical currents
85.25.Cp Josephson devices
84.40.Dc Microwave circuits

London moment for heavy‐fermion superconductors

Martin A. Sanzari, H. L. Cui, and Francis Karwacki

Appl. Phys. Lett. 68, 3802 (1996); http://dx.doi.org/10.1063/1.116622 (3 pages) | Cited 9 times

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Measurements of the London magnetic moment generated in rotating heavy‐fermion supercon‐ ductors are presented. The magnitude of the London moment is found to be identical to that of conventional superconductor, as well as that of high‐Tc superconductors, within the experimental resolution of 5%–10%. © 1996 American Institute of Physics.
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74.70.Tx Heavy-fermion superconductors
74.25.Ha Magnetic properties including vortex structures and related phenomena

High‐Tc superconductor/normal‐metal/superconductor edge junctions and SQUIDs with integrated groundplanes

B. D. Hunt, M. G. Forrester, J. Talvacchio, J. D. McCambridge, and R. M. Young

Appl. Phys. Lett. 68, 3805 (1996); http://dx.doi.org/10.1063/1.116623 (3 pages) | Cited 47 times

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Epitaxial, high‐Tc superconductor/normal‐metal/superconductor (SNS) edge‐geometry weak links and superconducting quantum interference devices (SQUIDs) have been fabricated with integrated YBa2Cu3O7 (YBCO) groundplanes and SrTiO3 insulators, using a process which incorporates six epitaxial layers. The SNS edge junctions were produced using off‐axis sputtered films and Co‐doped‐YBCO normal metal interlayers. These devices show excellent performance with typical critical current‐resistance (IcRn) products of 500–800 μV for 100–150 Å thick normal metal layers at 65 K, and 1‐σ critical current density ( Jc) spreads as small as 12%. SNS SQUIDs incorporating groundplanes exhibit voltage modulation of up to 130 μV at 65 K and 40 μV at 77 K. SQUID inductance measurements indicate microstrip inductance values of 1 pH per square at 65 K. © 1996 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions

A multilayer YBa2Cu3Ox Josephson junction process for digital circuit applications

W. H. Mallison, S. J. Berkowitz, A. S. Hirahara, M. J. Neal, and K. Char

Appl. Phys. Lett. 68, 3808 (1996); http://dx.doi.org/10.1063/1.116624 (3 pages) | Cited 43 times

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We have demonstrated a multilayer high‐Tc junction process capable of fabricating small‐scale digital circuits. The process uses superconductor/normal–metal/superconductor YBa2Cu3Ox (YBCO) edge junctions with a cobalt‐doped YBCO barrier and an integrated YBCO ground plane. We have measured spreads in the junctions’ critical currents as low as 12% (1σ) both on and off the ground plane. The proper functioning of the ground plane was verified by measuring the reduced inductance of superconducting quantum interference devices (SQUIDs) on the ground plane compared to identical SQUIDs off the ground plane. At a temperature of 70 K, the inductance on the ground plane is as low as 1.2 pH/☒. The inferred YBCO penetration depth is 250 nm at 70 K and 280 nm at 77 K. © 1996 American Institute of Physics.
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85.25.Cp Josephson devices
85.25.Hv Superconducting logic elements and memory devices; microelectronic circuits
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.72.-h Cuprate superconductors

Superconductor‐normal‐superconductor behavior of Josephson junctions scribed in Y1Ba2Cu3O7−δ by a high‐brightness electron source

B. A. Davidson, J. E. Nordman, B. M. Hinaus, M. S. Rzchowski, K. Siangchaew, and M. Libera

Appl. Phys. Lett. 68, 3811 (1996); http://dx.doi.org/10.1063/1.116625 (3 pages) | Cited 22 times

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We report a substantial improvement in the behavior of Josephson junctions scribed in Y1Ba2Cu3O7−δ films using a high‐brightness field‐emission electron gun source instead of a lower‐brightness thermionic source. These junctions exhibit resistively shunted junction behavior over the entire temperature range from the coupling temperature to at least 4 K, a temperature window which can be larger than 55 K. Superconductor‐normal‐superconductor character is indicated by the exponential dependence of the critical current on temperature for all temperatures below 90 K. The data demonstrate that electron irradiation under these conditions produces a modified region which is completely normal above 4 K and is narrower in width than previously obtained. © 1996 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
74.72.-h Cuprate superconductors
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions

Viscous drag measurements utilizing microfabricated cantilevers

P. I. Oden, G. Y. Chen, R. A. Steele, R. J. Warmack, and T. Thundat

Appl. Phys. Lett. 68, 3814 (1996); http://dx.doi.org/10.1063/1.116626 (3 pages) | Cited 60 times

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The influence of viscous drag forces on cantilevers is investigated using standard atomic force microscope (AFM) cantilevers. Viscosity effects on several geometrically different cantilevers manifest themselves as variations in resonance frequencies, quality factors, and cantilever response amplitudes. With this novel measurement, a single cantilever can be used to measure viscosities ranging from η=10−2 to 102 g/cm s. © 1996 American Institute of Physics.
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51.20.+d Viscosity, diffusion, and thermal conductivity
07.79.Lh Atomic force microscopes

The chemistry of the light rare‐earth elements as determined by electron energy loss spectroscopy

J. A. Fortner and E. C. Buck

Appl. Phys. Lett. 68, 3817 (1996); http://dx.doi.org/10.1063/1.116627 (3 pages) | Cited 18 times

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The energy loss spectra of the rare earths are characterized by sharp M4,5 edges, the relative intensities of which are characteristic of the 4f‐shell occupancy of the excited ion. For the light rare earths, the dependence of these relative peak heights on 4f‐shell occupancy is quite pronounced. Thus they may be used to determine the oxidation state of the multivalent elements Ce and Pr. The second derivative of the spectrum is shown to be extremely sensitive to the chemical environment. Modern instrumentation and detection techniques allow the oxidation state of Ce and Pr to be determined even when they are present as only minor constituents. © 1996 American Institute of Physics.
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68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
71.20.Eh Rare earth metals and alloys

Formation of copper and silver nanometer dimension clusters in silica by the sol‐gel process

G. De, L. Tapfer, M. Catalano, G. Battaglin, F. Caccavale, F. Gonella, P. Mazzoldi, and R. F. Haglund

Appl. Phys. Lett. 68, 3820 (1996); http://dx.doi.org/10.1063/1.116628 (3 pages) | Cited 62 times

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Ag and Cu (pure and/or mixture) nanoclusters doped silica films were prepared by the sol‐gel process. In the case of Ag and Cu codoped silica films, Cu/Ag molar ratio was 1, 2, and 3 at constant (Ag+Cu)/SiO2 molar ratio of 0.175. Separated Ag and Cu nanoclusters are formed in the silica matrix. The size of the clusters and their distribution are dependent on the film composition. Optical absorption was measured from 185 to 800 nm. Intensity‐dependent nonlinear refractive index was measured for pure Cu and Ag–Cu (1:1 molar ratio) samples using z‐scan technique in the wavelength range from 570 to 596 nm. The measured nonlinear refractive index is of the order of 10−13 m2/W at a pulse repetition rate of 15.2 MHz. © 1996 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.07.-b Nanoscale materials and structures: fabrication and characterization
78.66.Sq Composite materials

Thin‐film growth of the charge‐density‐wave oxide Rb0.30MoO3

H. S. J. van der Zant, O. C. Mantel, C. Dekker, J. E. Mooij, and C. Træholt

Appl. Phys. Lett. 68, 3823 (1996); http://dx.doi.org/10.1063/1.116629 (3 pages) | Cited 10 times

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We report on the thin‐film fabrication of a charge‐density wave (CDW) compound. Single‐phase epitaxial films of the model CDW oxide Rb0.30MoO3 have been grown by pulsed‐laser deposition. Detailed analyses show that the Rb0.30MoO3 films have μm‐size grains with the CDW chains oriented parallel to the substrate. On SrTiO3 (510), the CDW chains align into a single direction within the film plane. The electrical resistance of the films demonstrates a CDW state below about 182 K. Structures patterned in films will permit unprecedented studies of phase‐coherent CDW transport, as well as the exploration of devices based on CDWs. © 1996 American Institute of Physics.
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71.45.Lr Charge-density-wave systems
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
72.15.Nj Collective modes (e.g., in one-dimensional conductors)
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