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6 May 1996

Volume 68, Issue 19, pp. 2603-2761

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Growth defects in GaN films on 6H–SiC substrates

F. R. Chien, X. J. Ning, S. Stemmer, P. Pirouz, M. D. Bremser, and R. F. Davis

Appl. Phys. Lett. 68, 2678 (1996); http://dx.doi.org/10.1063/1.116279 (3 pages) | Cited 26 times

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Lattice defects in GaN epilayers grown on 6H–SiC(0001) by metalorganic vapor phase epitaxy (MOVPE) have been characterized by transmission electron microscopy (TEM). The predominant defects in the film were threading dislocations and half‐loops with Burgers vectors 1/3〈1120〉, [0001], and 1/3〈1123〉. Planar faults were also observed in the film that are thought to be inversion domain boundaries (IDBs). © 1996 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Selective deposition of polycrystalline silicon thin films at low temperature by hot‐wire chemical vapor deposition

S. Yu, E. Gulari, and J. Kanicki

Appl. Phys. Lett. 68, 2681 (1996); http://dx.doi.org/10.1063/1.116280 (3 pages) | Cited 6 times

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Polycrystalline silicon thin films have been selectively deposited at a substrate temperature of 300 °C on molybdenum or silicon over silicon dioxide, silicon nitride or Corning 7059 glass substrates in a continuous hot‐wire chemical vapor deposition (HWCVD) process involving hydrogen and disilane. Excellent selectivity is achieved on features as small as 1 μm spaced molybdenum lines. The deposition rate on molybdenum is 60–100 Å/min which is higher than that obtained by a pulsed gas plasma‐enhanced chemical vapor deposition (PECVD) or a very high‐frequency PECVD (VHF‐PECVD). The selective deposition rate obtained in our system is attributed to the high concentration of atomic hydrogen generated when molecular hydrogen passes over a heated tungsten filament. © 1996 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Diffusion of Sb in relaxed Si1−xGex

Arne Nylandsted Larsen and Per Kringhøj

Appl. Phys. Lett. 68, 2684 (1996); http://dx.doi.org/10.1063/1.116281 (3 pages) | Cited 33 times

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Diffusion of antimony in relaxed Si1−xGex alloy layers grown by molecular beam epitaxy has been studied as a function of the composition for 0≤x≤0.5. The diffusivity of antimony was found to increase with the Ge alloy content, and the extracted activation energies for diffusion were found to decrease with increasing germanium content in the investigated composition range. The activation energies, however, are significantly higher than the corresponding activation energies obtained by an extrapolation between the activation energy in pure silicon and germanium. © 1996 American Institute of Physics.
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66.30.J- Diffusion of impurities
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Influence of backsurface argon bombardment on SiO2–Si interface characteristics

P. T. Lai, M. Q. Huang, X. Zeng, S. H. Zeng, and G. Q. Li

Appl. Phys. Lett. 68, 2687 (1996); http://dx.doi.org/10.1063/1.116309 (3 pages) | Cited 2 times

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A low‐energy (550 eV) argon‐ion beam was used to directly bombard the backsurface of polysilicon‐gate metal‐oxide‐semiconductor (MOS) capacitors after the completion of all conventional processing steps. The interface characteristics of the MOS capacitors were investigated. The results show that, as the bombardment dose increases, the active dopant concentration near the oxide‐semiconductor interface gets higher; maximum midgap energy increases; and interface‐state density becomes lower. This simple technique is compatible with existing integrated‐circuit processing, and can easily improve the interface characteristics, and therefore the electrical characteristics of MOS devices. © 1996 American Institute of Physics.
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85.40.Ry Impurity doping, diffusion and ion implantation technology
85.30.Tv Field effect devices

Minority‐carrier‐enhanced reactivation of hydrogen‐passivated Mg in GaN

S. J. Pearton, J. W. Lee, and C. Yuan

Appl. Phys. Lett. 68, 2690 (1996); http://dx.doi.org/10.1063/1.116310 (3 pages) | Cited 26 times

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The influence of minority‐carrier injection on the reactivation of hydrogen passivated Mg in GaN at 175 °C has been investigated in p‐n junction diodes. The dissociation of the neutral MgH complexes is greatly enhanced in the presence of minority carrier and the reactivation process follows second‐order kinetics. Conventional annealing under zero‐bias conditions does not produce Mg‐H dissociation until temperatures ≥450 °C. These results provide an explanation for the e‐beam‐induced reactivation of Mg acceptors in hydrogenated GaN. © 1996 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
71.55.Eq III-V semiconductors

Low‐voltage varistors based on zinc antimony spinel Zn7Sb2O12

S. Ezhilvalavan and T. R. N. Kutty

Appl. Phys. Lett. 68, 2693 (1996); http://dx.doi.org/10.1063/1.116311 (3 pages) | Cited 22 times

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It is possible to prepare low‐voltage varistors from the zinc antimony spinel Zn7Sb2O12 with breakdown voltages in the range of 3–20 V and nonlinearity coefficient α=7–15. The varistor property is due to the formation of high ohmic potential barriers at the grain boundary regions on low‐ohmic n‐type grain interiors of the polycrystalline samples. The method of preparation of the spinel, synthesized by coprecipitation followed by annealing under restricted partial pressures of oxygen, controls the mixed valence states for antimony, namely, Sb3+ and Sb5+. This is critical in attaining high nonlinearity and lower breakdown voltages. © 1996 American Institute of Physics.
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72.20.Ht High-field and nonlinear effects
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
81.20.-n Methods of materials synthesis and materials processing

Resonant impurity scattering contribution to the mobility of Pb1−xSnxTe

Run‐Di Hong, John D. Dow, Otto F. Sankey, and Robert S. Allgaier

Appl. Phys. Lett. 68, 2696 (1996); http://dx.doi.org/10.1063/1.116312 (3 pages) | Cited 2 times

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An explanation of the anomalously low mobilities of n‐type In‐doped Pb1−xSnxTe alloys, based on resonant central‐cell scattering by antisite In donors, leads to very close agreement with experimental results. © 1996 American Institute of Physics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.55.Gs II-VI semiconductors

Work function of indium tin oxide transparent conductor measured by photoelectron spectroscopy

Y. Park, V. Choong, Y. Gao, B. R. Hsieh, and C. W. Tang

Appl. Phys. Lett. 68, 2699 (1996); http://dx.doi.org/10.1063/1.116313 (3 pages) | Cited 163 times

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We used ultraviolet and x‐ray photoelectron spectroscopy (XPS) and (UPS) techniques to directly measure absolute values of vacuum work function of indium tin oxide (ITO) thin films. We obtained a work function of 4.4–4.5 eV which is lower than the commonly cited value. These values do not change substantially by heating and Ar ion sputtering. The atomic concentrations of each element in ITO, measured with XPS, are also quite stable under heat treatment and ion sputtering. © 1996 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions

Thermal annealing characteristics of Si and Mg‐implanted GaN thin films

J. S. Chan, N. W. Cheung, L. Schloss, E. Jones, W. S. Wong, N. Newman, X. Liu, E. R. Weber, A. Gassman, and M. D. Rubin

Appl. Phys. Lett. 68, 2702 (1996); http://dx.doi.org/10.1063/1.116314 (3 pages) | Cited 21 times

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In this letter, we report the results of ion implantation of GaN using 28Si and 24Mg species. Structural and electrical characterizations of the GaN thin films after thermal annealing show that native defects in the GaN films dominate over implant doping effects. The formation energies of the annealing induced defects are estimated to range from 1.4 to 3.6 eV. A 40 keV 1014 cm−2 Mg implant results in the decrease of the free‐carrier concentration by three orders of magnitude compared to unimplanted GaN up to an annealing temperature of 690 °C. Furthermore, we have observed the correlation between these annealing‐induced defects to both improved optical and electrical properties. © 1996 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
71.55.Eq III-V semiconductors

Residual strain in GaN epilayers grown on sapphire and (6H)SiC substrates

Wei Li and Wei‐Xin Ni

Appl. Phys. Lett. 68, 2705 (1996); http://dx.doi.org/10.1063/1.116315 (3 pages) | Cited 28 times

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A high‐resolution multiple‐crystal reflection diffractometer was used to determine the residual strain in GaN epilayers grown on different substrates. Our results show that the GaN epilayers with thickness of about 1 μm are not fully relaxed. The strain situation in a GaN epilayer grown on SiC substrate is totally different from that in GaN layer on sapphire, which are the main reason for the scatter in the recent data on the optical properties of group III nitrides. © 1996 American Institute of Physics.
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68.60.-p Physical properties of thin films, nonelectronic

Voltage controlled two color light‐emitting electrochemical cells

Yang Yang and Qibing Pei

Appl. Phys. Lett. 68, 2708 (1996); http://dx.doi.org/10.1063/1.116316 (3 pages) | Cited 53 times

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A polymer light‐emitting electrochemical cell (LEC) is a bipolar p‐n junction device; when biased, a dynamic light‐emitting p‐n junction is created. In this letter, we report a two color LEC in which the color can be switched by simply reversing the bias voltage. The two color LEC consists of a polymer bilayer structure sandwiched between two electrodes. In this study, the polymer bilayer consists of a poly(1,4‐phenylene vinylene) (PPV) layer and a poly[2‐methoxy‐5‐ (2′‐ethylhexyloxy)‐1,4‐phenylene vinylene] (MEH‐PPV) layer. When biased at one polarity, the voltage induced p‐n junction is completely inside the PPV layer, and the LEC emits the green light of PPV. When biased at the opposite polarity, the p‐n junction is completely inside the MEH‐PPV layer, and the LEC emits the orange light characteristic of MEH‐PPV. © 1996 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds

Cubic boron nitride synthesis in low‐density supersonic plasma flows

D. H. Berns and M. A. Cappelli

Appl. Phys. Lett. 68, 2711 (1996); http://dx.doi.org/10.1063/1.115573 (3 pages) | Cited 20 times

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We report on the growth of cubic boron nitride films on {100} silicon using a low density, supersonic plasma jet generated by a direct‐current arc discharge expanded to low pressures. The arc discharge was operated on source gas mixtures of nitrogen and argon, with boron trichloride injected downstream of the expansion nozzle. The films were analyzed by infrared absorption and x‐ray photoelectron spectroscopy. Phase selectivity was obtained by the application of a negative bias to the substrate so as to bombard the surface with energetic ions during deposition. The deposition process was found to be highly sensitive to substrate temperature and substrate bias voltage. © 1996 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Electronic density of state at metal/polyimide Langmuir‐Blodgett film interface

Eiji Itoh and Mitsumasa Iwamoto

Appl. Phys. Lett. 68, 2714 (1996); http://dx.doi.org/10.1063/1.115574 (3 pages) | Cited 13 times

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Surface potentials of heat‐treated polyimide Langmuir‐Blodgett (PI LB) films deposited on Au, Cr and Al electrodes were measured in a dark vacuum vessel at room temperature as a function of the number of deposited layers. The potential depended on the thickness of PI LB films and the work function of base electrode. The spatial charge distribution in PI LB films on various electrodes was determined from the relationship between the surface potential and the number of deposited layers. Based on this result, distribution of the density of electronic state in PI LB films was determined. It was experimentally shown that the electrostatic phenomena in PI LB films at the metal/film interface were explained with taking into consideration of surface states which exist within the range of ∼1 nm from the interface and molecular‐ion states which exist in the entire range. © 1996 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions

High optical quality of strained (111)B In0.12Ga0.88As/GaAs and In0.12Ga0.88As/Al0.2Ga0.8As multiple quantum wells

Albert Chin and B. C. Lin

Appl. Phys. Lett. 68, 2717 (1996); http://dx.doi.org/10.1063/1.115575 (3 pages) | Cited 2 times

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We have investigated the growth of high quality In0.12Ga0.88As/GaAs and In0.12Ga0.88As/Al0.25Ga0.75As multiple quantum wells (MQWs) on 1° misoriented (111)B and (100)GaAs substrates. Very narrow photoluminescence (PL) linewidths of 6.6 and 5.6 meV were measured in (100) and (111)B In0.12Ga0.88As/GaAs MQWs, respectively, which indicates the good optical quality of materials. In addition, more than an order of magnitude enhancement of PL intensity was measured from the (111)B sample relative to that from (100), which is consistent with the previously reported strongly enhanced optical property in (111)B AlGaAs/GaAs QW to (100). In contrast, under our normal growth conditions, narrow PL linewidth and large PL intensity were difficult to achieve in (111)B In0.12Ga0.88As/Al0.25Ga0.75 As MQWs. Two‐step growth with a high AlGaAs growth temperature was used to improve the optical quality of (111)B In0.12Ga0.88As/Al0.25Ga0.75 As MQWs. A narrow PL linewidth of 5.1 meV and four times enhanced PL intensity can be obtained by such two‐step growth. Cross‐sectional transmission electron microscopy indicates defects generated in the 550 °C grown (111)B In0.12Ga0.88As/Al0.25Ga0.75 As MQWs, while such defects were reduced or disappeared at a high AlGaAs growth temperature of 620 °C. © 1996 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Control of quasi‐bound states by electron Bragg mirrors in GaAs/Al0.3Ga0.7As quantum wells

B. Sung, H. C. Chui, E. L. Martinet, and J. S. Harris

Appl. Phys. Lett. 68, 2720 (1996); http://dx.doi.org/10.1063/1.115576 (3 pages) | Cited 9 times

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Electron Bragg mirrors grown on both sides of identical quantum wells were used for confining above‐barrier states at different energies. By varying the thickness of the electron mirrors, a confined above‐barrier state (a quasi‐bound state) changed by over 110 meV in a 40 Å wide GaAs/Al0.3Ga0.7As quantum well. Formation of quasi‐bound states due to the electron Bragg mirrors was theoretically investigated using the envelope function approximation and semi‐infinite superlattice limit of the electron mirror layers. Theoretical calculations for absorption spectra involving quasi‐bound states are compared with experimental results. © 1996 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Revision of H2 passivation of Pb interface defects in standard (111)Si/SiO2

A. Stesmans

Appl. Phys. Lett. 68, 2723 (1996); http://dx.doi.org/10.1063/1.115577 (3 pages) | Cited 32 times

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Passivation with molecular H2 of Pb interface defects in thermal (111)Si/SiO2 (dry; 870 °C) over extended temperature (TH) and time (tH) ranges unveil nonexponential decay of [Pb] vs tH. This contrasts with previously reported exponential behavior, shown to have resulted from inadvertent incorrect monitoring of [Pb] and limited TH and tH ranges. The previous defect‐H2 reaction limited model may still consistently account for the data if expanded by the revealed spread of 0.06 eV around the inferred mean activation energy Ef=1.51 eV vis‐math‐vis the previous single‐valued Ef=1.66 eV; The inferred pre‐exponential factor is now found in compliance with the model. However, results may encourage re‐evaluation of other models previously discarded on the basis of their nonexponential passivation prediction. © 1996 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
61.72.J- Point defects and defect clusters
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Gas phase ultraviolet spectroscopy of high‐temperature superconductor precursors for chemical vapor deposition processing

Brian J. Rappoli and William J. DeSisto

Appl. Phys. Lett. 68, 2726 (1996); http://dx.doi.org/10.1063/1.115578 (3 pages) | Cited 8 times

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UV spectroscopy has been used as an in situ diagnostic to measure the gas phase concentration of 2,2,6,6‐tetramethyl‐3,5‐heptanedionate (thd) complexes of Cu and Y in metalorganic chemical vapor deposition (MOCVD) bubbler effluent. These Cu and Y precursors for MOCVD synthesis of YBa2Cu3O7−δ (YBCO) show marked instability in gas phase concentration as a function of time during the initial bubbler purge. The precursors show ideal behavior as predicted by the Clausius–Clapeyron relation. The UV diagonstic technique has the potential of controlling precursor concentration for MOCVD fabrication of high‐temperature superconducting thin films.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

High resolution characterization of structural inhomogeneities in YBa2Cu3O7−δ crystals with sharp superconducting transitions

S. B. Qadri, M. S. Osofsky, V. M. Browning, and E. F. Skelton

Appl. Phys. Lett. 68, 2729 (1996); http://dx.doi.org/10.1063/1.115579 (3 pages) | Cited 10 times

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Structural inhomogeneities in two single crystals of YBa2Cu3O7−δ are characterized using high resolution x‐ray diffraction. Results of these analyses show a distribution in the c‐axis lattice parameters. These are interpreted as evidence of a distribution in oxygen content. Values of 7−δ range from 6.71 to 7.00 in one crystal and from 6.80 to 6.99 in the other. Nevertheless, the measured superconducting transition widths for both crystals are less than 0.5 K, as determined by ac susceptibility. When examined with conventional x‐ray diffraction techniques, both crystals also appeared to be free of gross defects, but high resolution rocking curves reveal variations in defect density. These results suggest that crystals presumed to be homogeneous based on narrow superconducting transition widths or conventional x‐ray diffractometry, may not be. Therefore, crystals found to exhibit exotic physical properties should be carefully examined for the presence of structural anomalies. If such defects are present, the experimental results may be attributed to sample imperfections, rather than intrinsic phenomena.
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74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.72.-h Cuprate superconductors

Rapid single‐flux‐quantum balanced comparator based on high‐Tc bicrystal Josephson junctions

B. Oelze, B. Ruck, M. Roth, R. Dömel, M. Siegel, A. Yu. Kidiyarova‐Shevchenko, T. V. Filippov, M. Yu. Kupriyanov, G. Hildebrandt, H. Töpfer, F. H. Ihlmann, and W. Prusseit

Appl. Phys. Lett. 68, 2732 (1996); http://dx.doi.org/10.1063/1.115580 (3 pages) | Cited 23 times

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A balanced current comparator based on high‐Tc bicrystal Josephson junctions has been designed, fabricated, and experimentally tested. The operation of the balanced comparator has been demonstrated in the temperature range from 4.2 to 70 K. The correct sequence of switching of the Josephson junctions has been determined by dc measurements for different values of operating frequency and signal current Ix. The threshold uncertainty ΔIx of the balanced comparator, measured at 40 K, was 60 μA at 40 GHz and 300 μA at 240 GHz. © 1996 American Institute of Physics.
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85.25.Hv Superconducting logic elements and memory devices; microelectronic circuits

Influence of thermal cycling on the levitation force of melt‐textured YBaCuO

M. Ullrich, A. Leenders, and H. C. Freyhardt

Appl. Phys. Lett. 68, 2735 (1996); http://dx.doi.org/10.1063/1.115581 (3 pages) | Cited 3 times

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The influence of thermal cycling on the levitation force of VGF melt‐textured YBaCuO is investigated. With an increasing number of thermal cycles from room temperature down to the boiling point of liquid nitrogen the levitation force is decreasing. This decrease could be explained by the generation and propagation of cracks inside the melt‐textured domains which decrease the radii of the screening currents. Furthermore, water condensed at the surface of the superconductor leads to a decomposition of the superconducting Y1Ba2Cu3O7−δ phase and the formation of large nonsuperconducting areas. © 1996 American Institute of Physics.
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84.71.Ba Superconducting magnets; magnetic levitation devices
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
74.72.-h Cuprate superconductors

Secondary ion mass spectroscopy study of Au trapping and migration in the Au‐irradiated YBa2Cu3O7−δ film

Yupu Li, J. A. Kilner, J. R. Liu, W. K. Chu, G. A. Wagner, and R. E. Somekh

Appl. Phys. Lett. 68, 2738 (1996); http://dx.doi.org/10.1063/1.115582 (3 pages) | Cited 3 times

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The range data and migration of Au in YBa2Cu3O7−δ film were studied with implanted 197Au (1.5 MeV 5×1015 Au+/cm2) as a tracer. The film was a c‐axis oriented film, ∼750 nm thick, deposited by high‐pressure planar dc sputtering on 〈100〉 LaAlO3. Analysis by secondary ion mass spectroscopy shows that the as‐implanted Au concentration distribution is essentially Gaussian‐like and the depth (mathp) of maximum Au concentration (∼1.2 wt %) is 201 nm. The projected range (mathp) and (mathp) are found to be in very good agreement with the simulated data by TRIM−95, whereas the measured ‘‘straggle’’ (ΔRp∗) is about 20% larger than that by TRIM−95 simulation. It has also been found that the implanted 197Au starts to migrate within the film at a temperature between 650 and 700 °C, which is much higher than that for the implanted 2H (∼175 °C) and the implanted 18O (between 250 and 300 °C) in c‐oriented YBa2Cu3O7−δ films. © 1996 American Institute of Physics.
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61.72.up Other materials
66.30.J- Diffusion of impurities
74.72.-h Cuprate superconductors

Bolometric detection in a precipitation free Y1Ba2Cu3O7−δ film at 77 K

Hsiung Chou, H. Z. Chen, M. T. Hong, Y. C. Chen, and T. C. Chow

Appl. Phys. Lett. 68, 2741 (1996); http://dx.doi.org/10.1063/1.115583 (3 pages) | Cited 3 times

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A photodetector with high responsivity has been fabricated with a high quality Y1Ba2Cu3O7−δ film on a regular SrTiO3 (100) substrate that has no thinning or etching. The film exhibits a precipitation‐free morphology and has an extremely smooth surface having a rms roughness smaller than 5 nm. The film was patterned into a 25×650 μm2 long microbridge by a conventional photolithography technique. The Tco of the microbridge can be tuned by applying different bias currents, which results in a tunable operation temperature of the photodetector at 77.35±1 K. This makes it operationally more practical and economical. The noise voltage at 10 mA bias current is less than the resolution of our setup, 15 nV  Hz−0.5. A high responsivity of 2.3×103 V/W was obtained when a bias current of 8 mA and a low power density He–Ne laser of 0.08 J/cm2 s chopped at 2 Hz were applied on the microbridge at 77.35 K. Under the same condition, the noise equivalent power (NEP) and detectivity (D∗) have been measured to be 4.34×10−12 W Hz−0.5 and 3×109 cm Hz0.5 W−1, respectively. © 1996 American Institute of Physics.
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85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors

Nanometer‐scale magnetic MnAs particles in GaAs grown by molecular beam epitaxy

J. De Boeck, R. Oesterholt, A. Van Esch, H. Bender, C. Bruynseraede, C. Van Hoof, and G. Borghs

Appl. Phys. Lett. 68, 2744 (1996); http://dx.doi.org/10.1063/1.115584 (3 pages) | Cited 123 times

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Spherical MnAs ferromagnetic particles with controllable diameters (5–30 nm) are embedded in a high quality GaAs matrix. The particles are formed in a two step process consisting of the epitaxy of a homogeneous Ga1−xMnxAs layer at low temperatures using molecular beam epitaxy followed by phase separation upon annealing. During the annealing step, the excess arsenic in the as‐grown film forms magnetic MnAs precipitates with the Mn from the Ga1−xMnxAs lattice. Structural and room‐temperature magnetic properties of the heterogeneous GaAs:MnAs films are described. The magnetic MnAs rich layers can be incorporated into semiconductor heterostructures as demonstrated by growing (GaAs/AlAs) multiple quantum well structures in combination with GaAs:MnAs layers. © 1996 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
81.05.Rm Porous materials; granular materials

Phenomenological model for giant magnetoresistance in lanthanum manganite

J. E. Núñez‐Regueiro and A. M. Kadin

Appl. Phys. Lett. 68, 2747 (1996); http://dx.doi.org/10.1063/1.115585 (3 pages) | Cited 14 times

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The electrical conductivity of doped lanthanum manganite exhibits activated semiconducting behavior at high temperatures, and a transition to metallic behavior at low temperatures in the ferromagnetic state. These two regimes are combined in a new phenomenological equation for the conductivity that uses a mean‐field magnetization and physically reasonable fitting parameters. This allows us to account quantitatively for reports of giant negative magnetoresistance in single crystals and thin films. We present new data on sputtered epitaxial thin films of La1−xCaxMnO3, and analyze other recent reports in the literature. The physical basis for such an expression is discussed. © 1996 American Institute of Physics.
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72.60.+g Mixed conductivity and conductivity transitions
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.47.De Giant magnetoresistance

In situ scanning tunneling microscopy observation of surface evolution in magnetically coupled Co/Cu multilayers

Timothy J. Minvielle, Robert J. Wilson, and Robert L. White

Appl. Phys. Lett. 68, 2750 (1996); http://dx.doi.org/10.1063/1.115586 (3 pages) | Cited 9 times

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A series of bilayers of the form Cu(100)/[Co(21 Å)/Cu(21 Å)]n were grown by both ion beam and DC magnetron sputtering techniques. Scanning tunneling microscopy images of the developing layers demonstrate a marked difference in the way in which roughness evolves through the films. The higher energy ion beam sputtered systems show a nonconformal roughness that is characterized by comparatively large lateral length scales. The less energetic magnetron‐formed systems exhibit an island‐upon‐island growth that is conformal from layer to layer. Kerr effect measurements show that the former is ferromagnetically coupled and the latter is antiferromagnetically coupled. An explanation is presented that attributes the differences in roughness to the potential barriers at step edges. Adatom mobility and incident energy are shown to be the determining factors for this kind of conformal growth. © 1996 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
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