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1 Aug 1989

Volume 66, Issue 3, pp. 1013-1504

Page 2 of 4 Pages Previous Page Next Page | Jump to Page

High‐temperature interaction studies of C/Cu/SiO2/Si and related structures

Chin‐An Chang

J. Appl. Phys. 66, 1163 (1989); http://dx.doi.org/10.1063/1.344454 (7 pages) | Cited 10 times

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Thermal stability of the C/Cu bilayer structure is studied up to 800 °C. Using electron‐beam‐evaporated Cu and amorphous C (700 Å) films on SiO2‐coated Si substrates, no out‐diffusion or oxidation of Cu is observed up to a heating of 72 h at 700 °C, or 6 h at 750 °C in a N2‐H2 ambient. Reaction between Cu and the SiO2 layer is, however, observed under such conditions. Concerns such as adhesion are addressed by peeling the films at different stages of heat treatment and analyzing the surfaces exposed. Application of the carbon barrier to the reaction between Cu and other materials is studied using the Au/C/Cu structure. An enhanced out‐diffusion of Cu through C is observed due to the presence of Au, which acts as a receiving layer for Cu. The out‐diffused flux of Cu is enhanced by many orders of magnitude. The resulted dilution of the Au layer, however, is much less than that using Ni as a barrier in the Au/Ni/Cu structure. The mechanisms involved are discussed by considering the structural, chemical, and mechanical effects. Both the advantage and concerns using carbon as a barrier are also discussed.
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68.35.Fx Diffusion; interface formation
68.60.Dv Thermal stability; thermal effects
66.30.-h Diffusion in solids

Thermally induced structural change of a‐Ge:H/a‐GeNx multilayer structures

I. Honma, H. Komiyama, and K. Tanaka

J. Appl. Phys. 66, 1170 (1989); http://dx.doi.org/10.1063/1.343458 (10 pages) | Cited 13 times

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Multilayer structures of a‐Ge:H/a‐GeNx and a‐Ge/a‐GeNx were prepared by a reactive‐sputtering technique and their structural stability was studied through thermal anneals. High‐resolution transmission‐electron‐microscope analyses show that crystallization takes place only in a‐Ge:H(a‐Ge) layers without disturbing atomically smooth and uniform a‐Ge:H(a‐Ge)/ a‐GeNx interfaces. The crystallization temperature of a‐Ge:H(a‐Ge) layers increases with either decreasing thickness of those layers or increasing thickness of a‐GeNx layers. The rise in crystallization temperature is most remarkable when the layer thickness becomes smaller than a couple of hundred angstroms. On the basis of the experimental results, the structural stability of multilayer films is discussed in the light of classical nucleation theory using the free‐energy change of the system. It is demonstrated that the crystallization temperature is strongly affected both by layer thickness and by the nature of a heterointerface which phenomenologically explains well the experimental observations.
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73.40.-c Electronic transport in interface structures
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination

Transition from thermal‐ to electron‐impact decomposition of diborane in plasma‐enhanced chemical vapor deposition of boron films from B2H6+He

Shojiro Komatsu and Yusuke Moriyoshi

J. Appl. Phys. 66, 1180 (1989); http://dx.doi.org/10.1063/1.343459 (5 pages) | Cited 7 times

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The apparent reaction orders for the growth of boron films in plasma‐enhanced chemical vapor deposition from B2 H6 + He were measured as a function of the plasma power, which ranged from 0.4 to 1.6 kW. The conditions were as follows: substrate temperature, 890 °C; pressure, 200 Pa; and total flowrate of gases, 200 sccm. It was found that the reaction order (n) makes a transition from 1/2 to 1 at 900 W with an increase of the plasma power, and which accompanied a corresponding morphological transition. On the basis of a simple kinetic model, the observed reaction‐order transition is related with a transition from thermal‐ to electron‐impact decomposition of diborane occurring at 900 W: the n of 1/2 observed at the power range below 900 W is attributed to a pyrolysis‐dominant growth mechanism in which the association of two BH3 into B2 H6 cannot be neglected, whereas the n of 1 observed at the power range above 900 W is related to a growth mechanism in which the electron‐impact dissociation of diborane is dominant.
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68.55.-a Thin film structure and morphology
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
34.80.Gs Molecular excitation and ionization
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Point‐of‐use arsine generation for organometallic vapor‐phase epitaxial growth

K. A. Salzman and G. A. Davis

J. Appl. Phys. 66, 1185 (1989); http://dx.doi.org/10.1063/1.343460 (5 pages)

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A technique for the continuous generation of arsine as required for organometallic vapor‐phase epitaxial growth is described. Arsine is generated through the reduction of arsenic trichloride by lithium tetrahydridoaluminate in a nonvolatile ether. Reaction conditions appropriate for steady‐state operation, necessary for this application, have been established. Arsenide conversion efficiencies in excess of 95% have been consistently demonstrated with arsine flows up to 100 μmol/min. GaAs grown using generated arsine exhibits a 77‐K carrier concentration of 1.29×1015 cm−3 and mobility of 33 000 cm2/V s.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Window size effect on lateral growth of nickel silicide

Awatar Singh, W. S. Khokle, M. Prudenziati, G. Majni, and B. Morten

J. Appl. Phys. 66, 1190 (1989); http://dx.doi.org/10.1063/1.343461 (5 pages) | Cited 10 times

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Window size effect on lateral growth of nickel silicide in contact windows cut into oxide grown on Si (100) is studied. The growth rate is found to be independent of window size and follows the diffusion‐limited process with activation energy of 1.5 eV. The Si erosions are observed to grow due to predominant Si diffusion for vacuum anneal above 600 °C. This phenomenon becomes greatly pronounced with fine windows of 2 μm in diameter. We attribute this to (i) an enhanced stress level in fine windows causing reduction in the growth temperature of epitaxial NiSi2 in the windows and (ii) difference in surface energies of epitaxial NiSi2 formed and the Si substrate resulting in the shrinkage of the epitaxial NiSi2 dimension in the window. No such behavior is observed under identical conditions when Si (111) is used. We believe this is due to the fact that the lateral growth of nickel silicide in this case is about a quarter of that for Ni‐Si (100) lateral samples. Finally the technological importance of this study is pointed out.
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68.55.-a Thin film structure and morphology

Elimination of thermally induced biaxial stress in GaAs on Si layers by post‐growth patterning

J. P. van der Ziel, Naresh Chand, and J. S. Weiner

J. Appl. Phys. 66, 1195 (1989); http://dx.doi.org/10.1063/1.343462 (4 pages) | Cited 16 times

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The biaxial tensile stress of 2.65 kbar in as‐grown GaAs/Si is reduced by post‐growth patterning of the GaAs and the reduction in stress is dependent on the pattern size and shape. For stripe patterns less than 15 μm wide the stress becomes largely uniaxial with stress relief normal to the stripe direction. Rectangular patterns exhibited stress relief in orthogonal directions, and have the lowest stress in the narrow direction of the rectangle. A 9×12 μm2 rectangle exhibited an average stress of 0.5 kbar.
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68.35.Gy Mechanical properties; surface strains
68.55.-a Thin film structure and morphology

An analysis of complex spectra from deep level transient capacitance measurements

Ermanno Di Zitti, Giacomo M. Bisio, Pier Giorgio Fuochi, Bruno V. Passerini, and Mauro Zambelli

J. Appl. Phys. 66, 1199 (1989); http://dx.doi.org/10.1063/1.343463 (7 pages) | Cited 5 times

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The effect of complex sets of single‐ and double‐level traps on deep level transient spectroscopy (DLTS) spectra is critically discussed using a numerical simulator. The simulation takes into account: the partial trap ionization, the effect of base doping, the dynamics of charged traps, and the depletion layer effect. The modeling of the capacitance transient has been extended when many traps are present. The simulator has been used for the analysis of DLTS spectra of platinum‐doped and high‐energy (12 MeV) electron‐irradiated silicon diodes. These examples evidence how the simulation method increases the resolution of the DLTS technique. A detailed analysis of the emission kinetics of two energy level traps is also presented.
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71.55.-i Impurity and defect levels

Very shallow donors in n‐type GaAs

M. Benzaquen and D. Walsh

J. Appl. Phys. 66, 1206 (1989); http://dx.doi.org/10.1063/1.343464 (3 pages) | Cited 1 time

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The presence of an unusually shallow donor, with 1.5–2 meV binding energy, in high‐mobility GaAs grown by gas‐source molecular‐beam epitaxy, has recently been inferred from electrical transport and photoluminescence measurements by Cunningham and co‐workers [Appl. Phys. Lett. 53, 1285 (1988)]. We show that the data provided in support of the existence of a donor with this binding energy is not sufficient to draw such a conclusion.
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72.20.My Galvanomagnetic and other magnetotransport effects
32.30.Jc Visible and ultraviolet spectra

Calculation of the transverse acoustoelectric voltage in a piezoelectric‐extrinsic semiconductor structure

P. E. Lippens, M. Lannoo, and J. F. Pouliquen

J. Appl. Phys. 66, 1209 (1989); http://dx.doi.org/10.1063/1.343465 (8 pages) | Cited 4 times

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The transverse acoustoelectric voltage (TAV) is calculated for a piezoelectric‐extrinsic semiconductor structure. Using a small‐signal expansion an analytical but rather complicated expression is obtained and computed for the LiNbO3/n‐Si system. New and simple expressions are given, respectively, for high and low conductivities. In the latter case the TAV can reverse sign as a function of the conductivity and the frequency. This effect is explained from the second‐order variations of the majority carrier concentration. The influence of the air gap between the piezoelectric and the semiconductor is also studied.
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72.50.+b Acoustoelectric effects
43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound
73.50.Rb Acoustoelectric and magnetoacoustic effects
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics

Mechanism of electrostatic potential conduction in semi‐insulating substrates

Yasuo Ohno and Norio Goto

J. Appl. Phys. 66, 1217 (1989); http://dx.doi.org/10.1063/1.343466 (5 pages) | Cited 19 times

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According to Shockley–Read–Hall statistics for deep traps, it has been estimated that the electrostatic potential propagates in semi‐insulating substrates. In n‐i‐n structures made on hole‐trap‐rich substrates, a negative electric potential applied on an n region is carried to the vicinity of the other electrode. On the other hand, substrates with electron traps act like usual insulators. This phenomenon may be the primary origin of GaAs metal‐semiconductor field‐effect transistor side‐gating effects.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Ey III-V and II-VI semiconductors
71.55.-i Impurity and defect levels

Filamentary structure and transport in corrugated InGaAs/InP superlattices grown by vapor levitation epitaxy

S. J. Allen, P. Bastos, H. M. Cox, F. DeRosa, D. M. Hwang, and L. Nazar

J. Appl. Phys. 66, 1222 (1989); http://dx.doi.org/10.1063/1.343467 (5 pages) | Cited 5 times

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Periodic stimulation of a growth instability on (001) vicinal surfaces of InP and InGaAs induces a corrugated growth interface. When this interface is incorporated into a superlattice the two‐dimensional quantum well coalesces into a periodic structure comprised of InGaAs filaments buried in an InP matrix. We have measured the transport in this system by contactless submillimeter wave spectroscopy and show that the electron motion is confined to these filaments, and we have determined the electron density and mobility in these submicrometer filaments.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Resonant tunneling time delay and quantum well sheet density

K. M. S. V. Bandara, D. D. Coon, and Hong Zhao

J. Appl. Phys. 66, 1227 (1989); http://dx.doi.org/10.1063/1.343468 (4 pages) | Cited 17 times

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Time delays, dwell times, resonant state lifetimes, and electron sheet densities associated with tunneling through quantum well structures are analyzed from a scattering theory (S‐matrix) viewpoint. Some of the results differ from intuitively motivated expressions which have appeared in the resonant tunneling literature. It is shown that the sheet density is given by a formula similar to the Tsu–Esaki formula [Appl. Phys. Lett. 22, 562 (1973)] for current density. Sheet density and dwell time are related to Hermitian matrices which are expressed in terms of the S‐matrix and in terms of partial widths associated with resonant states.
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79.60.Dp Adsorbed layers and thin films
79.70.+q Field emission, ionization, evaporation, and desorption
72.10.Di Scattering by phonons, magnons, and other nonlocalized excitations
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Interface charge control of directly bonded silicon structures

Stefan Bengtsson and Olof Engström

J. Appl. Phys. 66, 1231 (1989); http://dx.doi.org/10.1063/1.343469 (9 pages) | Cited 37 times

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The influence of interface states and charges on the properties of Si/Si and Si/SiO2 interfaces prepared by wafer bonding, using the direct bonding technique, has been investigated. Surface potentials of Si/Si interfaces with all combinations of doping type (n‐n,p‐p,p‐n) are dependent on surface and heat treatments in the bonding procedure and on wafer dopant concentration. In earlier reported works, hydrophilic wafer surface properties have been reported as necessary for a good mechanical bonding. We find that wafer treatment in HF giving hydrophobic surfaces not only gives good mechanical properties, but also better electronic properties as well. For all combinations of doping type, lower magnitudes in surface potential were measured in samples prepared from wafers pretreated in HF in order to etch off the native oxide layer, normally present on silicon surfaces. If a native oxide is present when the bonded interface is prepared, the current through the interface will be influenced by an energy barrier due to the presence of charged interface states. The amount of charge trapped at the interface has been found to be dependent on the applied bias. A theoretical description is made for the Si/Si interfaces, and predictions are compared to results obtained from electrical measurements. Based on this theory, using data from the current‐voltage characteristic, an interface state density in the region 5×1010–1012 cm−2 eV−1 at the bonded interface has been deduced for different samples. Bonded Si/SiO2 interfaces with interface state densities of about 1011 cm−2 eV−1 and low flat‐band voltages have been achieved. No influence of different chemical pretreatments, used in this paper, on properties of bonded Si/SiO2 interfaces, as seen in flat‐band voltage and interface state density, was found, although the bonding process is critical in the preparation of the Si/SiO2 interfaces.
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73.20.-r Electron states at surfaces and interfaces
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Density of states and linewidths of quantum wells with applied electric field

Walter L. Bloss

J. Appl. Phys. 66, 1240 (1989); http://dx.doi.org/10.1063/1.343470 (4 pages) | Cited 9 times

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We calculate the density of states and corresponding linewidths for the quasi‐bound energy levels of a quantum well including both barriers of finite height and width, and an applied electric field. For a GaAs/AlxGa1−xAs quantum well with a well width of 85 Å, barrier width of 50 Å, and barrier height of 240 meV, we find a field‐induced linewidth for the excited state that increases from 2.9 meV at a field of 25 kV/cm to 9.5 meV at 150 kV/cm. This corresponds to a tunneling lifetime of 228 fs at 25 kV/cm decreasing to 69 fs at 150 kV/cm. The ground eigenstate has a narrow linewidth, less than 1 meV, up to a field of 150 kV/cm. The quasi‐bound approximation is shown to be applicable to the ground state, but not for the excited state.
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71.10.-w Theories and models of many-electron systems
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Gk Tunneling
72.80.Ey III-V and II-VI semiconductors

Plasma‐induced fixed oxide charge

Jan Bos and Menso Hendriks

J. Appl. Phys. 66, 1244 (1989); http://dx.doi.org/10.1063/1.344449 (8 pages) | Cited 3 times

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The buildup of a plasma‐induced fixed oxide charge (Qf ) in thermally grown silicon dioxide on silicon was studied. Whereas samples located in the plasma showed a persistent instantaneous saturation behavior [Qf (sat) =1.3×1013 charges/cm2], those that were situated in a field‐free region outside the plasma produced dose and oxide thickness dependent buildup curves. A distinction is made between nonpenetrating electron/ion bombardments and penetrating photon irradiation. In the first case, the Qf creation can be explained by hole transport through the oxide film under the influence of an internally generated electric field and successive hole trapping near the interface. In the second case, we have to deal with direct interaction with the SiO2/Si interface. Furthermore, thermal annealing was used to reduce and/or eliminate plasma‐induced Qf. Activation energies of 0.51 and 0.58 eV were found for the annealing process.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Absorption at radio frequencies in superconducting Y1Ba2Cu3Oy

Stephen Ducharme, R. Durny, J. Hautala, D. J. Zheng, P. C. Taylor, O. G. Symko, and S. Kulkarni

J. Appl. Phys. 66, 1252 (1989); http://dx.doi.org/10.1063/1.344450 (9 pages) | Cited 7 times

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The large magnetic‐field‐dependent ac absorption in superconducting Y1 Ba2 Cu3 Oy ceramics and powders decreases slowly with increasing frequency in the range 2–16 MHz. The magnetic‐field‐dependent ac absorption is observed below Tc in superconducting Y1 Ba2 Cu3 Oy ceramics, powders and twinned crystals and in (La,Sr)2 CuO4 and BaPb0.75 Bi 0.25 CuO3 powders and appears to contain distinct contributions from trapped flux and/or intragrain tunnel junctions and from ordinary superconductor surface impedance. The contribution from trapped flux and/or intragrain tunnel junctions is important in dc magnetic fields of up to approximately 20 G at all temperatures below Tc. There is an identifiable modulated ac absorption which changes slowly over more than 12 kG at low temperatures and which we propose is primarily caused by the ac surface impedance with possible contributions from the critical state. A twinned crystal of Y1 Ba2 Cu3 Oy exhibits the same ac absorption except that it has an anisotropic dependence on the applied dc magnetic field.
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74.70.-b Superconducting materials other than cuprates
74.25.N- Response to electromagnetic fields
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.50.+r Tunneling phenomena; Josephson effects

Microwave absorption of aligned crystalline grains of YBa2Cu3O7−x

M. Poirier, G. Quirion, B. Quirion, F. D’Orazio, J. P. Thiel, W. P. Halperin, and K. R. Poeppelmeier

J. Appl. Phys. 66, 1261 (1989); http://dx.doi.org/10.1063/1.344423 (4 pages) | Cited 7 times

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We investigate here the anisotropic magnetic and electric properties of aligned crystalline grains of YBa2Cu3O7−x. The microwave absorption is indeed consistent with the expected temperature behaviors of the resistivity in the normal state along the c axis and in the a‐b plane. In the superconducting state, both the absorptions in pure rf electric and magnetic fields are high compared to the conventional superconductors; for the magnetic case activation energies are deduced and the dispersion is related to the diamagnetic susceptibility. These results are discussed qualitatively in relation to similar data obtained on single crystals and ceramic samples.
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74.25.N- Response to electromagnetic fields

Microstructure‐property correlations in the Bi(Pb)‐Sr‐Ca‐Cu‐O superconducting system

R. Ramesh, S. M. Green, Yu Mei, A. E. Manzi, and H. L. Luo

J. Appl. Phys. 66, 1265 (1989); http://dx.doi.org/10.1063/1.344424 (8 pages) | Cited 6 times

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The microstructure of solid‐state processed (Bi,Pb)‐Sr‐Ca‐Cu‐O ceramics was characterized using transmission electron microscopy techniques. A strong sensitivity of the transport properties to small deviations in the nominal Bi‐Ca ratio is evidenced. Significant differences in the microstructure are shown to correlate to the changes in the transport properties. It is suggested that the microstructure can be predicted by combining the results of resistivity, Meissner, and shielding experiments.
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74.70.-b Superconducting materials other than cuprates
74.25.-q Properties of superconductors
61.66.Fn Inorganic compounds

Thermomagnetic switching on rare‐earth transition‐metal alloy magneto‐optic disks

J. H. Crasemann, P. Hansen, M. Rosenkranz, and K. Witter

J. Appl. Phys. 66, 1273 (1989); http://dx.doi.org/10.1063/1.344425 (6 pages) | Cited 7 times

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The thermomagnetic switching behavior of magneto‐optic disks with amorphous TbFeCo and GdTbFe films was investigated on a test recorder. Domain length, write and erase fields, and erase laser power required for total domain erasure was studied for various film compositions, which differ in compensation temperature Tcomp and Curie temperature TC. With increasing TC the domain length at fixed writing laser pulse energy is reduced and the power required to erase domains with a certain size is increased. The optimum external field, for minimal write noise, decreases with increasing TC−Tcomp. The experimental dependencies agree with calculated results obtained from the force balance controlling the domain formation.
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72.15.Jf Thermoelectric and thermomagnetic effects
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Gg Ferrimagnetics

Effects of parallel compressions on ring‐shaped polycrystalline ferrimagnetic samples

M. Le Floc’H

J. Appl. Phys. 66, 1279 (1989); http://dx.doi.org/10.1063/1.344426 (6 pages) | Cited 1 time

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This work deals with the behavior of the macroscopic magnetic properties of ring‐shaped polycrystalline yttrium‐iron garnets (YIG) under the action of compressive stresses applied parallel to the measurement direction along the director circles. For this purpose, a high‐pressure cell has been designed consisting of a hydrostatic pressure application on the outer side of the ring. The results are separated in two parts according to the sample used: The first one is concerned with YIG samples called ‘‘type D’’ and so defined because of the dispersed nature of their natural domain‐wall configuration. The second one is concerned with YIG samples called ‘‘type T’’ and so defined because of the toroidal character of their natural domain‐wall configuration. It is shown that the first category (type‐D samples) gives results in good agreement with the classical theory of the magnetoelasticity, while the second (type‐T samples) gives results altogether inconsistent. The difference of behavior between the two types of samples is explained by the difference between their domain‐wall configuration in the spontaneous state. A well‐tried theoretical model is used for the general interpretation.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
75.80.+q Magnetomechanical effects, magnetostriction
75.50.Gg Ferrimagnetics

Analysis of domain structure by calculating magnetostatic energy for magnetic thin film

Chiaki Saka, Kazuo Shiiki, and Kiminari Shinagawa

J. Appl. Phys. 66, 1285 (1989); http://dx.doi.org/10.1063/1.344427 (6 pages) | Cited 6 times

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A method of calculating magnetostatic energy is studied by a two‐dimensional approximation. This is required in order to analyze the domain structure of a magnetic thin film. The energy Es is calculated as the product of demagnetization field Hd and magnetization M. Since Hd varies widely within a domain, Es must be calculated in a number of subdivided regions in which Hd is assumed to be uniform, and their summation is calculated. Good precision can be achieved by subdividing a domain along possible charged surfaces. The closure domain structure of a rectangular film whose triangular domain has an extra wall is thus analyzed. Although the total energy of the film is increased by the addition of an extra wall, the local energy of the triangular domain has a negative minimum value when the magnetization direction is inclined. The calculated magnetization direction corresponding to the minimum energy agrees with the observation by scanning electron microscopy. Thus, it becomes clear that this domain structure can be determined in a quasi‐stable condition by precisely calculating the magnetostatic energy.
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75.60.-d Domain effects, magnetization curves, and hysteresis
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Magnetization reversal in CoCr perpendicular thin films

Jian‐Gang Zhu and H. Neal Bertram

J. Appl. Phys. 66, 1291 (1989); http://dx.doi.org/10.1063/1.344428 (17 pages) | Cited 49 times

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Computer simulation has been utilized to study magnetization reversal processes in CoCr perpendicular films. The model is based on the columnar structure of the film. Each column is considered to be a single crystal with perpendicular uniaxial crystalline anisotropy. The model assumes that each column is always uniformly magnetized even during its magnetization reversal. The gyromagnetic equation of motion with phenomenological Landau–Lifshitz damping is utilized to describe the magnetization rotation of this coupled system. The study focuses on the collective magnetization reversal modes of the particles due to magnetostatic interactions and intergranular exchange coupling. Low nucleation fields occur which are characterized by a planar chain nucleation mode. This yields coercivities equal to or less than the crystalline anisotropy field 2K/M. It is argued that, due to this collective process, the uniform rotation reversal mechanism for the individual particles in the film is energetically more favorable than nonuniform reversal, such as curling. Intercolumn exchange coupling significantly reduces the coercivity and an increase of the exchange coupling strength changes the magnetization behavior from ‘‘particulate’’ to ‘‘continuous.’’
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure

A new analysis of the results of thermally stimulated measurements in polymers

Jean‐Pierre Crine

J. Appl. Phys. 66, 1308 (1989); http://dx.doi.org/10.1063/1.344429 (6 pages) | Cited 21 times

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It is shown that the compensation law observed in thermally stimulated measurements (TSC and TSDC) between the activation energy E and the preexponential term τ0 in the Arrhenius equation for various polymers can be explained by a linear relation between the activation enthalpy ΔH‡ and entropy ΔS‡ of the process. When this relation is combined with the well‐known rate theory, TSC or TSDC results with polymers indicate that both techniques yield very similar results. It is also deduced that they are especially sensitive to entropy changes in the polymers studied. This points out the non‐negligible value of ΔS‡ in polymer relaxations, and this implies that the proper energy term describing a polymer relaxation is not E but a free‐energy term ΔG. The relation between the Vogel–Tammann–Fulcher and rate theory equations is also made. The correlations between the ΔG, ΔH‡, and ΔS‡ values, and the polymer thermodynamic and morphological properties are also briefly discussed.
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77.22.Ej Polarization and depolarization
82.20.Pm Rate constants, reaction cross sections, and activation energies
77.22.Gm Dielectric loss and relaxation

Charge transfer in ZnS‐type electroluminescence

E. Bringuier

J. Appl. Phys. 66, 1314 (1989); http://dx.doi.org/10.1063/1.344430 (12 pages) | Cited 61 times

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In this paper, a simple model for the charge transfer in thin‐film, ac‐driven electroluminescent structures of doped ZnS type is proposed. We first review the minimal assumptions needed to account for the carrier emission under high‐field conditions and its subsequent feedback on the field strength; it opens the way to a quantitative description of the field variation with time and the conduction current under arbitrary low‐frequency drive conditions and without using any adjustable parameter. The charge‐voltage relationships are also examined in detail. Conduction in the phosphor layer is assumed to originate from deep levels (traps) in the phosphor forbidden band gap, located at the insulator‐phosphor interface. These levels act for charge storage, too. When a discrete trap level is considered, field clamping in the active layer is obtained; when a smooth interface‐state energy density is assumed, deviations from the field clamping are possible and simply related to the interface parameters. Most of the work is analytical and the model is shown to exhibit the main qualitative features of nonmemory devices.
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78.60.Fi Electroluminescence

Ellipsometric measurement of the optical constants of solid and molten aluminum and copper at λ=10.6 μm

M. Brückner, J. H. Schäfer, and J. Uhlenbusch

J. Appl. Phys. 66, 1326 (1989); http://dx.doi.org/10.1063/1.344431 (7 pages) | Cited 12 times

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The index of refraction, the extinction coefficient, and the absorptance were measured under ultrahigh vacuum conditions in a temperature range from 295 to 1000 K for aluminum and from 295 to 1400 K for copper for the CO2 laser wavelength at λ=10.6 μm. A photometric infrared ellipsometer was applied. The absorptance of the clean metallic surfaces jumps discontinuously from 3% to 7% in the case of aluminum and from 2% to 6% in the case of copper at the melting point. Calculations of the optical constants basing on the model of free electrons taking account of the effective mass and the anomalous skin effect describe the measurements for the solid state very well, but are less accurate for the molten state.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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