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1 Mar 1999

Volume 74, Issue 9, pp. 1191-1347

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High voltage (450 V) GaN Schottky rectifiers

Z. Z. Bandić, P. M. Bridger, E. C. Piquette, T. C. McGill, R. P. Vaudo, V. M. Phanse, and J. M. Redwing

Appl. Phys. Lett. 74, 1266 (1999); http://dx.doi.org/10.1063/1.123520 (3 pages) | Cited 56 times

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We fabricated high standoff voltage (450 V) Schottky rectifiers on hydride vapor phase epitaxy grown GaN on sapphire substrate. Several Schottky device geometries were investigated, including lateral geometry with rectangular and circular contacts, mesa devices, and Schottky metal field plate overlapping a SiO2 layer. The best devices were characterized by an ON-state voltage of 4.2 V at a current density of 100 A/cm2 and a saturation current density of 10−5 A/cm2 at a reverse bias of 100 V. From the measured breakdown voltage we estimated the critical field for electric breakdown in GaN to be (2.2±0.7)×106 V/cm. This value for the critical field is a lower limit since most of the devices exhibited abrupt and premature breakdown associated with corner and edge effects. © 1999 American Institute of Physics.
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85.30.Kk Junction diodes
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Femtosecond response times and high optical nonlinearity in beryllium-doped low-temperature grown GaAs

M. Haiml, U. Siegner, F. Morier-Genoud, U. Keller, M. Luysberg, P. Specht, and E. R. Weber

Appl. Phys. Lett. 74, 1269 (1999); http://dx.doi.org/10.1063/1.123521 (3 pages) | Cited 28 times

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We have investigated the effect of beryllium doping on the optical nonlinearity and on the carrier dynamics in low-temperature (LT) grown GaAs for various growth temperatures and doping levels. Pump–probe experiments with 20 fs pulses and quantitative measurements of the nonlinear absorption show that in undoped LT GaAs, ultrafast response times are only obtained at the expense of low absorption modulation. In contrast, in Be-doped LT GaAs, high absorption modulation is maintained for response times as short as 100 fs. These results are qualitatively explained accounting for the point-defect-related optical transitions in LT-GaAs. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
73.50.Dn Low-field transport and mobility; piezoresistance

Modified Stranski–Krastanov growth in stacked layers of self-assembled islands

O. G. Schmidt, O. Kienzle, Y. Hao, K. Eberl, and F. Ernst

Appl. Phys. Lett. 74, 1272 (1999); http://dx.doi.org/10.1063/1.123522 (3 pages) | Cited 87 times

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In a stack of vertically aligned Stranski–Krastanov grown islands, the critical thickness for planar growth for all but the initial dot layer is reduced, if the thickness of the spacer layer ts is smaller than a certain value t0. We present structural and photoluminescence results on the basis of the extensively studied lattice-mismatched material system Si/Ge. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Aa Theory and models of film growth
81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators

Low-resistance ohmic contacts to p-type GaN

Jin-Kuo Ho, Charng-Shyang Jong, Chien C. Chiu, Chao-Nien Huang, Chin-Yuen Chen, and Kwang-Kuo Shih

Appl. Phys. Lett. 74, 1275 (1999); http://dx.doi.org/10.1063/1.123546 (3 pages) | Cited 140 times

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Low-resistance ohmic contacts with high transparency to p-type GaN have been developed by oxidizing Ni/Au thin films. Compared to the metallic Ni/Au contacts, the oxidized Ni/Au contacts exhibited lower specific contact resistance and much improved transparency. The transparency was from 65% to 80% in the wavelength of 450–550 nm. A specific contact resistance below 1.0×10−4 Ω cm2 was obtained by oxidizing Ni(10 nm)/Au(5 nm) on p-type GaN. The mechanism of low-resistance ohmic contact could be related to the formation of NiO. © 1999 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
78.66.Bz Metals and metallic alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.65.Mq Oxidation

Controlled spontaneous emissions from current-driven semiconductor microcavity triodes

S. Yamashita, S. Nakamura, S. Kobayashi, T. Ueda, Y. Kadoya, and M. Yamanishi

Appl. Phys. Lett. 74, 1278 (1999); http://dx.doi.org/10.1063/1.123523 (3 pages) | Cited 2 times

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We demonstrate the alteration of spontaneous emissions in semiconductor microcavity triodes, in which the carriers are injected by current into a single quantum well (QW) active region and the emission wavelength was varied by the voltage applied to the QW through the quantum confined Stark effect. The clear changes in the emission spectra and radiation patterns with the change of the voltage manifest that the spontaneous emission is well modified by the microcavity under the control of the applied voltage. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.20.Jq Electro-optical effects
78.66.Fd III-V semiconductors
78.60.Fi Electroluminescence

Ballistic electron focusing by elliptic reflecting barriers

J. J. Heremans, S. von Molnár, D. D. Awschalom, and A. C. Gossard

Appl. Phys. Lett. 74, 1281 (1999); http://dx.doi.org/10.1063/1.123524 (3 pages) | Cited 5 times

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We investigate reflection of ballistic electrons off an elliptic barrier in a high quality AlGaAs/GaAs heterostructure. Electrons injected at one focal point of an ellipse are collected at the second focal point, or at the midpoint. Application of a magnetic field perpendicular to the plane of the ellipse modifies the focusing effects by distorting the electrons’ paths, resulting in a novel four-terminal negative magnetoresistance phenomenon. Several secondary features in the magnetoresistance are observed and are interpreted in the light of numerical path simulations. © 1999 American Institute of Physics.
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73.23.Ad Ballistic transport
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Fq High-field and nonlinear effects

Preparation of amorphous hydrogenated silicon-germanium material and solar cells using the thermocatalytic chemical vapor deposition

M. Lill and B. Schröder

Appl. Phys. Lett. 74, 1284 (1999); http://dx.doi.org/10.1063/1.123525 (3 pages) | Cited 7 times

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Hydrogenated amorphous silicon-germanium (a-SiGe:H) films were produced by the “thermocatalytic chemical vapor deposition” [(TC-CVD) also called “hot-wire” CVD] method. With respect to proposed superstrate solar cell application of the material, the substrate temperature was kept around 200 °C. The band gap Eg of the films could be varied between 1.1 and 1.77 eV by changing the ratio of silane to germane flow. The photoelectronical properties of the alloy films have been found sufficient for solar cell application when Eg ≥ 1.5 eV and deteriorate for further reduction of the band gap. Using the concept of band gap grading, p-i-n solar cells containing a TC-CVD-a-SiGe:H i layer with initial conversion efficiencies up to η = 6.42% (Eg = 1.5 eV) have been fabricated. The influence of moderate hydrogen dilution of the process gas on the conversion efficiency and stability of the solar cells has also been investigated. © 1999 American Institute of Physics.
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84.60.Jt Photoelectric conversion
81.05.Gc Amorphous semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.61.Jc Amorphous semiconductors; glasses
78.66.Jg Amorphous semiconductors; glasses
73.50.Pz Photoconduction and photovoltaic effects

Growth and characterization of small band gap (∼0.6 eV) InGaAsN layers on InP

Milind R. Gokhale, Jian Wei, Hongsheng Wang, and Stephen R. Forrest

Appl. Phys. Lett. 74, 1287 (1999); http://dx.doi.org/10.1063/1.123526 (3 pages) | Cited 43 times

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We demonstrate the growth of small band gap (Eg ∼ 0.6 eV) strained and lattice matched single crystal InGaAsN alloys on InP substrates. InGaAsN layers with N concentrations varying from 0.6% to 3.25% were grown by gas source molecular beam epitaxy using a radio frequency plasma nitrogen source. Lattice-matched, 0.5-μm-thick InGaAsN layers with smooth surface morphologies and abrupt interfaces were achieved. Low temperature photoluminescence measurements reveal a band gap emission wavelength of 1.9 μm (at 20 K) for lattice matched InGaAsN (N∼2%). Tensile strained In0.53Ga0.47As/In0.53Ga0.47As0.994N0.006 multiple quantum wells emitting at 1.75 μm at 20 K are also reported. © 1999 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Arsenic-doped Si(001) gas-source molecular-beam epitaxy: Growth kinetics and transport properties

J. A. N. T. Soares, H. Kim, G. Glass, P. Desjardins, and J. E. Greene

Appl. Phys. Lett. 74, 1290 (1999); http://dx.doi.org/10.1063/1.123527 (3 pages) | Cited 5 times

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Arsenic-doped Si(001) layers with concentrations CAs up to 5×1018 cm−3 were grown on Si(001)2×1 at temperatures Ts = 575–900 °C by gas-source molecular-beam epitaxy (GS-MBE) using Si2H6 and AsH3. This is almost an order of magnitude higher than the initially reported “maximum attainable” saturated CAs value for GS-MBE from hydride precursors. At constant JAsH3/JSi2H6, CAs decreases, while the film growth rate RSi increases, with Ts. Temperature programmed desorption measurements show that As segregates strongly to the growth surface and that the observed decrease in CAs at high film growth temperatures is primarily due to increasingly rapid arsenic desorption from the segregated layer. Decreasing Ts enhances As incorporation. However, it also results in lower film growth rates due to higher steady-state As surface coverages which, because of the lone-pair electrons associated with each As adatom, decrease the total dangling bond coverage and, hence, the Si2H6 adsorption rate. At constant Ts, CAs increases, while RSi decreases, with increasing JAsH3/JSi2H6. All incorporated As resides at substitutional electrically active sites for concentrations up to 3.8×1018 cm−3, the highest value yet reported for Si(001):As growth from hydride source gases, and temperature-dependent electron mobilities are equal to those of the best bulk Si:As. © 1999 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uf Ge and Si
73.61.Cw Elemental semiconductors
85.40.Sz Deposition technology
85.40.Ry Impurity doping, diffusion and ion implantation technology
68.55.-a Thin film structure and morphology
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
73.50.Dn Low-field transport and mobility; piezoresistance
73.20.Hb Impurity and defect levels; energy states of adsorbed species

A memory cell with single-electron and metal-oxide-semiconductor transistor integration

Zahid A. K. Durrani, Andrew C. Irvine, Haroon Ahmed, and Kazuo Nakazato

Appl. Phys. Lett. 74, 1293 (1999); http://dx.doi.org/10.1063/1.123528 (3 pages) | Cited 21 times

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A single-electron transistor memory cell with metal-oxide-semiconductor field-effect transistor sensing has been fabricated in silicon-on-insulator material. The single-electron transistor, coupled to a memory node, is defined in the upper silicon layer. The memory node forms the gate of a metal-oxide-semiconductor field-effect transistor with its channel in the substrate silicon. At 4.2 K, there are two different states of the memory-node voltage, separated by the single-electron transistor Coulomb gap. These states are sensed at high-current output levels by the metal-oxide-semiconductor transistor. The metal-oxide-semiconductor transistor current also shows evidence of gate-dependent conductance oscillations in the coupled single-electron transistor. © 1999 American Institute of Physics.
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85.35.Gv Single electron devices
85.30.Tv Field effect devices
73.23.Hk Coulomb blockade; single-electron tunneling
85.35.Ds Quantum interference devices

The effect of disorder on excited state dynamics in organic molecular films

A. J. Mäkinen, S. Xu, Z. Zhang, S. J. Diol, Yongli Gao, M. G. Mason, A. A. Muenter, D. A. Mantell, and A. R. Melnyk

Appl. Phys. Lett. 74, 1296 (1999); http://dx.doi.org/10.1063/1.123529 (3 pages) | Cited 3 times

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We have investigated the dynamics of highly excited electron states in thin films of N,N′-diphenethyl-3,4,9,10-perylenetetracarboxylic-diimide (DPEP), a well-known organic photoconductor, with time-resolved photoemission spectroscopy. We observe an extremely fast relaxation process of photoexcitations with a typical lifetime of 30 fs in DPEP films and attribute it to a rapid internal conversion process from S2 and S1 levels to the vibrational manifolds of S1 and S0 states. Interestingly, the relaxation rate is almost twice as fast at low excitation energies in polycrystalline DPEP films as it is in less-ordered DPEP films. We explain this difference by fast transitions within the manifold of extended states that are shown to form in ordered DPEP films. © 1999 American Institute of Physics.
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73.61.Ph Polymers; organic compounds
73.50.Pz Photoconduction and photovoltaic effects
78.66.-w Optical properties of specific thin films
79.60.Fr Polymers; organic compounds
78.47.-p Spectroscopy of solid state dynamics

Mechanism for the reduction of interstitial supersaturations in MeV-implanted silicon

V. C. Venezia, T. E. Haynes, Aditya Agarwal, L. Pelaz, H.-J. Gossmann, D. C. Jacobson, and D. J. Eaglesham

Appl. Phys. Lett. 74, 1299 (1999); http://dx.doi.org/10.1063/1.123530 (3 pages) | Cited 44 times

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We demonstrate that the excess vacancies induced by a 1 MeV Si implant reduce the excess interstitials generated by a 40 keV Si implant during thermal annealing when these two implants are superimposed in silicon. It is shown that this previously observed reduction is dominated by vacancy annihilation and not by gettering to deeper interstitial-type extended defects. Interstitial supersaturations were measured using B doping superlattices (DSL) grown on a silicon-on-insulator (SOI) substrate. Implanting MeV and keV Si ions into the B DSL/SOI structure eliminated the B transient enhanced diffusion normally associated with the keV implant. The buried SiO2 layer in the SOI substrate isolates the deep interstitials-type extended defects of the MeV implant, thereby eliminating the possibility that these defects getter the interstitial excess induced by the keV Si implant. © 1999 American Institute of Physics.
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61.72.uf Ge and Si
61.72.J- Point defects and defect clusters
61.72.Yx Interaction between different crystal defects; gettering effect
71.55.Cn Elemental semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.40.Ry Impurity doping, diffusion and ion implantation technology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
66.30.J- Diffusion of impurities
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High-Tc directly coupled direct current SQUID gradiometer with flip-chip flux transformer

Y. J. Tian, S. Linzen, F. Schmidl, L. Dörrer, R. Weidl, and P. Seidel

Appl. Phys. Lett. 74, 1302 (1999); http://dx.doi.org/10.1063/1.123531 (3 pages) | Cited 17 times

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We have designed and fabricated a flip-chip-type gradiometer as a sensor for measurement of weak magnetic signals. The gradiometer consists of a directly coupled direct current superconducting quantum interference device (SQUID) gradiometer coupled to a flux transformer made from a YBa2Cu3O7∗/YBa2Cu3O7/CeO2/YSZ multilayer on 2 in. Si wafer, where YBa2Cu3O7∗(YBCO∗) is a nonsuperconducting crystalline film. The coupling coefficient of 0.18 is obtained for the flip-chip gradiometer. The transformer increases effectively the resolutions of the gradiometer. We obtain a magnetic field gradient resolution of 73 fT cm−1 Hz−1/2 in the white region, and 596 fT cm−1 Hz−1/2 at 1 Hz. The magnetocardiograms were successfully measured at a distance of nearly 100 mm from the gradiometer center to the human heart in a shielded room. © 1999 American Institute of Physics.
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74.72.-h Cuprate superconductors
85.25.Dq Superconducting quantum interference devices (SQUIDs)
07.55.Ge Magnetometers for magnetic field measurements

Exchange biasing in ferromagnetic amorphous wires: A controllable micromagnetic configuration

J. J. Freijo, A. Hernando, M. Vázquez, A. Méndez, and V. R. Ramanan

Appl. Phys. Lett. 74, 1305 (1999); http://dx.doi.org/10.1063/1.123532 (3 pages) | Cited 5 times

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Nonmagnetostrictive Co-rich amorphous wires, 130 μm in diameter, were stress annealed to induce a transverse anisotropy. The resultant structure consists of a circular-magnetization single domain except in a thin core, 2 μm in diameter, where magnetization is axially oriented. The wall interconnecting the outer shell with the core magnetization induces a local helical anisotropy during the annealing. As a consequence, a strong link between the magnetization directions in both regions appears. It is shown that direct current axial fields produce remarkable shifts of the circular hysteresis loops. © 1999 American Institute of Physics.
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75.50.Cc Other ferromagnetic metals and alloys
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy

Measuring the gigahertz response of recording heads with the magnetic force microscope

Roger Proksch, Peter Neilson, Shane Austvold, and J. J. Schmidt

Appl. Phys. Lett. 74, 1308 (1999); http://dx.doi.org/10.1063/1.123533 (3 pages) | Cited 23 times

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We compare two different techniques for measuring the high frequency response of recording heads using a magnetic force microscope. The first technique is based on driving the recording head with a high frequency current. We separated the high and low frequency response of the recording head by making two measurements, one with the current on, one with the current off. The second technique is based on amplitude modulation of the high frequency current driving the recording head. This technique has the advantage of separating the low and high frequency response in a single measurement. We used both of these techniques to study the spatially dependent response of recording heads operating up to and beyond 1 GHz. © 1999 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Magnetic phase diagram of ultrathin Co/Si(111) film studied by surface magneto-optic Kerr effect

Jyh-Shen Tsay and Yeong-Der Yao

Appl. Phys. Lett. 74, 1311 (1999); http://dx.doi.org/10.1063/1.123534 (3 pages) | Cited 29 times

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A magnetic phase diagram of the ultrathin Co/Si(111) film deposited at 300 K has been established by the surface magneto-optic Kerr effect technique. The temperature, where ferromagnetism vanishes, increases from 375 to 625 K as the coverage of the Co film increases from 3.5 to 16 monolayers. A quantitative calculation of the normalized Auger signal of CoSi2 shows that the calculated values lie between the experimental measured Auger signals before and after ferromagnetism vanishes for films with coverage between 3.5 and 9.1 monolayers. For samples with higher coverage, the experimental data are smaller than that by calculation. This may be qualitatively explained by Co atoms escaping from the CoSi2 phase to diffuse into the Si substrate. The disappearance of ferromagnetism is mainly attributed to silicide formation. © 1999 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Cc Other ferromagnetic metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
78.20.Ls Magneto-optical effects
75.70.Rf Surface magnetism
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.35.Fx Diffusion; interface formation
78.66.Bz Metals and metallic alloys

Increasing the exchange-bias field of Ni0.5Co0.5O films by microstructural control

Dinesh Martien, Kentaro Takano, A. E. Berkowitz, and David J. Smith

Appl. Phys. Lett. 74, 1314 (1999); http://dx.doi.org/10.1063/1.123535 (3 pages) | Cited 10 times

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The exchange-bias field produced by antiferromagnetic monoxide films has been shown to scale with the density of uncompensated interfacial spins. The uncompensated spin density is inversely proportional to the interfacial grain diameter. Accordingly, we have prepared Ni0.5Co0.5O films in which the average interfacial grain diameter is small, but the grains are elongated, thus avoiding thermally activated fluctuations of the spin system associated with small grain volumes. The exchange-bias field remained inversely proportional to the interfacial grain diameter, and was increased to twice its previous maximum value without introducing significant thermal instability. © 1999 American Institute of Physics.
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75.50.Ee Antiferromagnetics
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Et Exchange and superexchange interactions
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Observation of supercurrent distribution in YBa2Cu3O7−δ thin films using THz radiation excited with femtosecond laser pulses

S. Shikii, T. Kondo, M. Yamashita, M. Tonouchi, M. Hangyo, M. Tani, and K. Sakai

Appl. Phys. Lett. 74, 1317 (1999); http://dx.doi.org/10.1063/1.123536 (3 pages) | Cited 17 times

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We have demonstrated that the supercurrent distribution in current-biased YBa2Cu3O7−δ thin films can be obtained by measuring the radiation power of THz electromagnetic pulses excited with femtosecond laser pulses. As the radiation power is proportional to the square of the bias current density at the laser spot position, the two-dimensional current distribution can be obtained from the intensity distribution of THz radiation by scanning the laser spot. The characteristic supercurrent distribution is analyzed by using the critical-state model. © 1999 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.25.N- Response to electromagnetic fields

Contributions of individual Fe sites to magnetocrystalline anisotropy of Y2Fe17−xGax compounds

Zhao-hua Cheng, Bao-gen Shen, Fang-wei Wang, and H. Kronmüller

Appl. Phys. Lett. 74, 1320 (1999); http://dx.doi.org/10.1063/1.123537 (3 pages) | Cited 4 times

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At present, individual Fe sites anisotropies of Y2Fe17 compound cannot be directly measured by ordinary magnetization measurement. Alternatively, they are derived from the relationship between occupancy factors of Fe atoms at different sites and anisotropy constants of Y2Fe17−xGax compounds. It is found that only Fe atoms at 9d site have a significantly positive contribution to the uniaxial anisotropy, while those at 6c and 18h sites have strongly negative contributions; the contribution of Fe atoms at 18f site is slightly negative and less important. The planar anisotropy is rapidly weakened and finally a uniaxial anisotropy is induced by the Ga substitution. These results can be explained by the preferential occupancies of Ga atoms at 18h site for low Ga concentration as well as 6c and 18f sites for high Ga concentration. © 1999 American Institute of Physics.
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75.50.Bb Fe and its alloys
61.66.Dk Alloys

Superconducting transport properties of 2.2-GeV Au-ion irradiated c-axis twist Bi2Sr2CaCu2O8+δ bicrystals

Qiang Li, Y. N. Tsay, M. Suenaga, G. Wirth, G. D. Gu, and N. Koshizuka

Appl. Phys. Lett. 74, 1323 (1999); http://dx.doi.org/10.1063/1.123538 (3 pages) | Cited 6 times

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2.2-GeV Au-ions irradiation is used to study the effect of columnar defects on the transport properties of Bi2Sr2CaCu2O8+δ (Bi2212) bicrystals with high quality c-axis twist grain boundary. The studies show a similar increase in the irreversible temperature determined within the single crystals and across the grain boundaries after irradiation. However, the irradiation enhancement on the grain boundary critical current (Ic) at low temperatures is small, compared to the more than an order of magnitude increase of single crystal Ic. © 1999 American Institute of Physics.
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74.72.-h Cuprate superconductors
61.82.Ms Insulators
74.25.Sv Critical currents
61.72.Mm Grain and twin boundaries
61.80.Jh Ion radiation effects
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Injection-controlled size effect on switching of ferroelectric thin films

A. K. Tagantsev and I. A. Stolichnov

Appl. Phys. Lett. 74, 1326 (1999); http://dx.doi.org/10.1063/1.123539 (3 pages) | Cited 105 times

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The effect of near-by-electrode charge injection on switching of a thin film ferroelectric capacitor is theoretically analyzed. We develop a model of switching affected by charge injection through a surface dielectric layer to calculate the coercive field of the capacitor as a function of both film thickness and maximal polarization of the switching cycle. The predictions of the model are verified by electrical measurements on sol–gel derived Pb(Zr, Ti)O3 thin films of thickness ranging from 100 to 1000 nm with Pt electrodes. The model gives a good description of the size effect on switching in the Pt/Pb(Zr, Ti)O3/Pt system and enables an explanation for a much smaller magnitude of this effect in Bi-containing and oxide–electrode thin films. © 1999 American Institute of Physics.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Fm Switching phenomena
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
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Ultrahigh-density atomic force microscopy data storage with erase capability

G. Binnig, M. Despont, U. Drechsler, W. Häberle, M. Lutwyche, P. Vettiger, H. J. Mamin, B. W. Chui, and T. W. Kenny

Appl. Phys. Lett. 74, 1329 (1999); http://dx.doi.org/10.1063/1.123540 (3 pages) | Cited 103 times

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We report a simple atomic force microscopy-based concept for a hard disk-like data storage technology. Thermomechanical writing by heating a Si cantilever in contact with a spinning polycarbonate disk has already been reported. Here the medium has been replaced with a thin polymer layer on a Si substrate, resulting in significant improvements in storage density. With this new medium, we achieve bit sizes of 10–50 nm, leading to data densities of 500 Gbit/in.2. We also demonstrate a novel high-speed and high-resolution thermal readback method, which uses the same Si cantilevers that are used in the writing process, and the capability to erase and rewrite data features repeatedly. © 1999 American Institute of Physics.
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07.79.Lh Atomic force microscopes
07.10.Cm Micromechanical devices and systems
68.60.Bs Mechanical and acoustical properties
68.60.Dv Thermal stability; thermal effects

Microscale lithography via channel stamping: Relationships between capillarity, channel filling, and debonding

P. M. Moran and F. F. Lange

Appl. Phys. Lett. 74, 1332 (1999); http://dx.doi.org/10.1063/1.123541 (3 pages) | Cited 27 times

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A polymer or metallo-organic precursor solution may be transferred from the channels of a stamp to a substrate producing a micron or submicron scale pattern. The stamped polymer pattern is used as a mask for device fabrication. The stamped metallo-organic precursor solution is heat treated to produce a metal or ceramic pattern directly. Here we report conditions that optimize the filling of channels, the debonding of the solution from the channels during evaporation, and the transfer of the pattern to a substrate. We show that poor wetting can optimize these conditions. © 1999 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
68.03.Cd Surface tension and related phenomena
81.40.Gh Other heat and thermomechanical treatments
64.70.F- Liquid-vapor transitions
68.08.Bc Wetting

A four-color quantum well infrared photodetector

M. Z. Tidrow, Xudong Jiang, Sheng S. Li, and K. Bacher

Appl. Phys. Lett. 74, 1335 (1999); http://dx.doi.org/10.1063/1.123542 (3 pages) | Cited 14 times

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A four-color quantum well infrared photodetector (QWIP) has been demonstrated in this work. Four stacks of quantum well structures with four different detection wavelengths are sandwiched among three highly doped contact layers. The peak wavelengths of the four colors are centered at 4.7, 8.5, 9, and 12.3 μm. The 4.7 and 8.5 μm stacks are separated from the 9 and 12.3 μm stacks by a middle ohmic contact layer, and the change of peak detection wavelengths within the two-stack QWIPs is achieved by varying the bias voltage. Four different combinations of two-color simultaneous reading can be obtained. The detector could achieve simultaneous reading of four colors by adding two extra contact layers to the design with appropriate readout circuitry. By using a small number of quantum wells, we are able to use all four stacks for voltage-tunable detection with two terminals. In spite of using InGaAs/AlGaAs and GaAs/AlGaAs materials in the four stacks, the device shows excellent material quality and performance characteristics. © 1999 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
07.60.Dq Photometers, radiometers, and colorimeters

High-density three-dimensional optical data storage in a stacked compact disk format with two-photon writing and single photon readout

Haridas E. Pudavar, Mukesh P. Joshi, Paras N. Prasad, and Bruce A. Reinhardt

Appl. Phys. Lett. 74, 1338 (1999); http://dx.doi.org/10.1063/1.123543 (3 pages) | Cited 77 times

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Using a polymer block doped with a highly efficient two-photon dye, we have achieved a high density data storage with gray-scale control in multiple planes as stacked compact disks at a separation of 10 μm. The absorption and fluorescence of the dye at the written spot shift to a longer wavelength, permitting an easy fluorescence mode readout with a linear excitation using an inexpensive laser source. The storage capacity in this case is estimated to be 1012 bits/cm3. © 1999 American Institute of Physics.
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42.79.Vb Optical storage systems, optical disks
42.70.Jk Polymers and organics
78.55.Kz Solid organic materials
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