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18 Sep 1995

Volume 67, Issue 12, pp. 1639-1787

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Electron quantum wires in type II single heterostructures on nonplanar substrates

V. Türck, O. Stier, F. Heinrichsdorff, M. Grundmann, and D. Bimberg

Appl. Phys. Lett. 67, 1712 (1995); http://dx.doi.org/10.1063/1.115025 (3 pages) | Cited 7 times

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The existence of electronic quantum wires in the center of homogeneously doped single type II heterojunctions in V grooves is predicted. No additional structural confinement is needed. The valence and conduction band edges in such structures are calculated by solving the 2D‐Poisson and 2D‐Schrödinger equations self‐consistently. As a prototype system we consider a realistic n‐InP/n‐InAlAs heterostructure in a V groove along [011] with a finite curvature. The band bending is found to depend on the position along the heterojunction, inducing two‐dimensionally confined bound states for electrons which can serve as 1D conducting channels. Using proper doping conditions a ground state below the Fermi energy can be achieved. The subband separation is strongly dependent on the radius of curvature of the groove center and amounts to about 15 meV. © 1995 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

High‐performance InP/Ga0.47In0.53As/InP metal‐semiconductor‐metal photodetectors with a strained Al0.1In0.9P barrier enhancement layer

P. T. Chan, H. S. Choy, C. Shu, and C. C. Hsu

Appl. Phys. Lett. 67, 1715 (1995); http://dx.doi.org/10.1063/1.115026 (3 pages) | Cited 4 times

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A reduction in the dark current and an enhancement of the breakdown voltage have been observed in interdigitated InP/Ga0.47In0.53As/InP metal‐semiconductor‐metal photodetectors when a cap layer of Al0.1In0.9P was grown on the epitaxial structure to increase the Schottky barrier. The devices had a dc responsivity of 0.32 A/W and an intrinsic response faster than 74 ps. © 1995 American Institute of Physics.
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73.40.Sx Metal-semiconductor-metal structures
85.60.Gz Photodetectors (including infrared and CCD detectors)

Determination of Al mole fraction for null conduction band offset in In0.5Ga0.5P/AlxGa1−xAs heterojunction by photoluminescence measurement

Kwan‐Shik Kim, Yong‐Hoon Cho, Byung‐Doo Choe, Weon Guk Jeong, and H. Lim

Appl. Phys. Lett. 67, 1718 (1995); http://dx.doi.org/10.1063/1.115027 (3 pages) | Cited 20 times

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Photoluminescence properties of In0.5Ga0.5P/AlxGa1−xAs heterojunctions in both staggered and straddling band alignment regimes have been investigated. From the relation between the energies of below‐band gap luminescence and Al compositions in the staggered band alignment regime, we determined the Al composition for null conduction band offset of the heterojunction as well as the conduction band offset value of In0.5Ga0.5P/GaAs heterojunction. Assuming the transitivity between the conduction band offset values, we also obtained the fraction of the band gap energy difference that is associated with the conduction band offset of an AlGaAs/GaAs heterojunction. © 1995 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.55.Cr III-V semiconductors

Effects of column III alkyl sources on deep levels in GaN grown by organometallic vapor phase epitaxy

W. I. Lee, T. C. Huang, J. D. Guo, and M. S. Feng

Appl. Phys. Lett. 67, 1721 (1995); http://dx.doi.org/10.1063/1.115028 (3 pages) | Cited 46 times

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Two different kinds of n‐type GaN films were prepared by organometallic vapor phase epitaxy, one by using trimethylgallium (TMGa) and another by using triethylgallium (TEGa) as the alkyl source. Schottky diodes with well‐behaved current–voltage and capacitance–voltage characteristics were fabricated. Deep‐level transient spectroscopy studies were performed on these samples. Three distinct deep levels, labeled E1, E2, and E3, were measured in the film grown with TMGa, with an activation energy of 0.14, 0.49, and 1.63±0.3 eV, respectively. Only one level, E3, was observed in the film prepared with TEGa. © 1995 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.
71.55.Eq III-V semiconductors

High resistivity and picosecond carrier lifetime of GaAs implanted with MeV Ga ions at high fluences

C. Jagadish, H. H. Tan, J. Jasinski, M. Kaminska, M. Palczewska, A. Krotkus, and S. Marcinkevicius

Appl. Phys. Lett. 67, 1724 (1995); http://dx.doi.org/10.1063/1.115029 (3 pages) | Cited 17 times

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Rutherford backscattering spectrometry‐channeling, double‐crystal x‐ray diffraction, optical absorption studies, and electrical measurements have been carried out on 2 MeV Ga‐implanted GaAs at fluences of 1×1015 and 5×1015 cm−2. Implanted samples exhibited a strain field associated with implantation‐induced damage, low resistivity due to hopping conduction and mobilities of about 1 cm2/V s. Annealing of these samples at 600 °C caused substantial recovery of postimplant damage and an increase of resistivity of more than four orders of magnitude, with mobility up to about 2600 cm2/V s. Photocarrier lifetime of annealed samples is in the few picoseconds range. These properties are strikingly similar to those of arsenic implanted GaAs, suggesting that arsenic precipitates are unlikely to be solely responsible for short carrier lifetime in the latter case. Thus Ga‐implanted GaAs may be an interesting prospect for fast optoelectronic device applications. © 1995 American Institute of Physics.
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61.80.Jh Ion radiation effects
71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors

Kinetic modeling of the atomic layer epitaxy processing window in group IV semiconductor growth

Gyula Eres

Appl. Phys. Lett. 67, 1727 (1995); http://dx.doi.org/10.1063/1.115030 (3 pages) | Cited 5 times

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A kinetic model based on two elementary reaction steps was used for exploring the prospects of atomic layer epitaxy (ALE) on the (100) surface of group IV semiconductors using hydridic source gases. Equating the chemisorption step with depletion of active sites, and the molecular hydrogen desorption step with regeneration of active sites allowed first‐principles kinetic modeling of the trends in thin film growth, unencumbered by the lack of mechanistic details of chemisorption and surface decomposition. The combination of first‐order depletion and first‐order regeneration steps was found to be most favorable for achieving ALE type behavior. The model shows that the ALE window is highly sensitive to the duration of the depletion (chemisorption) cycle suggesting short duration and well defined pulses as the most effective method of source gas delivery. © 1995 American Institute of Physics.
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68.55.-a Thin film structure and morphology

Evidence of carrier number fluctuation as origin of 1/f noise in polycrystalline silicon thin film transistors

A. Corradetti, R. Leoni, R. Carluccio, G. Fortunato, C. Reita, F. Plais, and D. Pribat

Appl. Phys. Lett. 67, 1730 (1995); http://dx.doi.org/10.1063/1.115031 (3 pages) | Cited 22 times

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A systematic study of the noise performances of polycrystalline silicon thin film transistors is presented. The drain current spectral density of these devices shows an evident 1/ f behavior and scales, when operating in the linear regime, with the square of the mean value of the drain current. The origin of the noise can be ascribed to carrier number fluctuations related to the dynamic trapping and detrapping of the oxide traps. © 1995 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Td Noise processes and phenomena
85.30.Tv Field effect devices

Growth of epitaxial Si1−xGex layers on Si(001) surface, by catalytical decomposition of disilane and germane: Photoemission studies

R. Chelly, T. Angot, D. Bolmont, and J. J. Koulmann

Appl. Phys. Lett. 67, 1733 (1995); http://dx.doi.org/10.1063/1.115032 (3 pages) | Cited 4 times

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Si1−xGex alloys grown by catalytical decomposition of a mixture of disilane and germane on Si(001) at 620 K and room temperature (RT) have been prepared and analyzed in situ with surface techniques such as x‐ray and ultraviolet photoelectron spectroscopies (XPS and UPS), low energy electron diffraction (LEED), and x‐ray photoelectron diffraction (XPD). A comparison is made with the case of an undecomposed gas mixture under the same experimental conditions. We show that films prepared at RT are amorphous. Films prepared at 620 K are well ordered and exhibit sharp 2×1 LEED patterns. Films grown at RT and subsequently annealed at as high as 820 K have a poorer crystalline quality. © 1995 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Visible electroluminescence from a novel β‐SiC/p‐Si n‐p heterojunction diode prepared by rapid thermal chemical vapor deposition

J. D. Hwang, Y. K. Fang, K. H. Wu, and D. N. Yaung

Appl. Phys. Lett. 67, 1736 (1995); http://dx.doi.org/10.1063/1.115033 (3 pages) | Cited 5 times

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A novel structure of β‐SiC/p‐Si has been reported to emit visible electroluminescence (EL). The β‐SiC is grown directly on a Si substrate by rapid thermal chemical vapor deposition (RTCVD) technology. The mechanism of EL emission is shown as a porous silicon (PS) layer. The PS is formed unintentionally at β‐SiC/p‐Si interface owing to a large lattice mismatch (20%) between β‐SiC and Si substrates. In addition, the heterojunction diode exhibits excellent rectifying behavior. The ideality factor n and rectification ratio at 1.0 V are 1.8 and 340, respectively.
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78.60.Fi Electroluminescence
78.66.Li Other semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Optimization of compositional grading in Zn(Se,Te) graded ohmic contacts to p‐type ZnSe

Y. Fan

Appl. Phys. Lett. 67, 1739 (1995); http://dx.doi.org/10.1063/1.115034 (3 pages) | Cited 2 times

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The energy barrier at heterojunctions can be minimized by introducing a parabolic grading potential. For ternary materials with a strong bowing effect in band gap energy, such as Zn(Se,Te), the composition must vary nonparabolically in order to have the required parabolic grading potential. In this letter, a new compositional grading style for Zn(Se,Te) graded band gap ohmic contacts to p‐type ZnSe has been obtained through a simplified analytical model where both the bowing factor in ternary band gap energy and the change in electron affinity χ with alloy composition are included. To show the effectiveness of the proposed grading style, it is compared with both parabolic and linear grading in numerical calculations. The specific contact resistance of the proposed optimized compositional grading is about two orders of magnitude lower than that of a linear grading over a grading distance of 170 to 310 Å, and about one order of magnitude lower than that of a parabolic grading at a grading distance less than 220 Å. © 1995 American Institute of Physics.  
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73.40.Cg Contact resistance, contact potential
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

An isotopic labeling study of the growth of thin oxide films on Si(100)

H. C. Lu, T. Gustafsson, E. P. Gusev, and E. Garfunkel

Appl. Phys. Lett. 67, 1742 (1995); http://dx.doi.org/10.1063/1.115035 (3 pages) | Cited 20 times

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The mechanism of thin (<8 nm) oxide growth on Si(100) has been studied by high‐resolution medium energy ion scattering in combination with oxygen isotope substitution in the T=800–900 °C and 0.1–1 Torr oxygen pressure regime. Isotopic labeling experiments demonstrate that the Deal–Grove model breaks down for these films. In addition to the traditional oxidation reaction at the Si/SiO2 interface, two other spatially specific reactions take place during thermal oxidation: an exchange reaction at the oxide surface and an oxidation reaction in the near‐interfacial region. © 1995 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.65.-b Surface treatments

Growth of AlxGa1−xN:Ge on sapphire and silicon substrates

X. Zhang, P. Kung, A. Saxler, D. Walker, T. C. Wang, and M. Razeghi

Appl. Phys. Lett. 67, 1745 (1995); http://dx.doi.org/10.1063/1.115036 (3 pages) | Cited 47 times

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AlxGa1−xN were grown on (00.1) sapphire and (111) silicon substrates in the whole composition range (0≤x≤1). The high optical quality of the epilayers was assessed by room‐temperature optical absorption and photoluminescence measurements. Layers with higher Al composition are more resistive. Resistive AlxGa1−xN epilayers were successfully doped with Ge and free‐electron concentration as high as 3×1019 cm−3 was achieved. © 1995 American Institute of Physics.
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68.55.-a Thin film structure and morphology
78.55.Cr III-V semiconductors

Current transport in as‐grown and annealed intermediate temperature molecular beam epitaxy grown GaAs

B. Nabet, A. Youtz, F. Castro, P. Cooke, and A. Paolella

Appl. Phys. Lett. 67, 1748 (1995); http://dx.doi.org/10.1063/1.115037 (3 pages) | Cited 5 times

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Molecular beam epitaxy (MBE) GaAs grown in the intermediate temperature range of about 400 °C may provide combination of low lifetime, high resistivity, and high mobility. We compare current conduction in unannealed and annealed material grown at 400 °C by fabricating photodetectors on substrates grown between temperature ranges of 250–500 °C. The unannealed version of the device grown at 400 °C shows substantial difference of conduction properties in dark and under light. It is shown that while at low biases the unannealed material may be semi‐insulating, at high biases more current is conducted than in annealed material. We attribute this to the effect of intergap states on current conduction and suggest that defect state assisted tunneling is the dominant current transport mechanism in these ranges. Quenching of response by light suggests that occupancy of traps can eliminate their role in current conduction. © 1995 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.61.Ey III-V semiconductors

Luminescence properties of nitrogen ion implanted ZnSe after thermal annealing

A. Kamata and T. Moriyama

Appl. Phys. Lett. 67, 1751 (1995); http://dx.doi.org/10.1063/1.115038 (3 pages) | Cited 7 times

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Nitrogen atoms were implanted into ZnSe layers which were grown by metalorganic chemical vapor deposition. The implanted crystals were thermally annealed in a nitrogen atmosphere. Photoluminescence spectra show an acceptor‐bound excitonic emission line (I1) and donor‐to‐acceptor pair (DAP) recombination emission, which reveal the activation of nitrogen atoms as shallow acceptors. An additional DAP emission was observed at 462 nm, which is often seen for ZnSe:N grown by molecular beam epitaxy. The selenium vacancy generation accelerates the occupation of nitrogen atoms at the selenium sites and the excess vacancy generation brings about the formation of deep donor complexes. © 1995 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
61.80.Jh Ion radiation effects
71.55.Gs II-VI semiconductors

Reactive ion etching of GaN using CHF3/Ar and C2ClF5/Ar plasmas

Heon Lee, David B. Oberman, and James S. Harris

Appl. Phys. Lett. 67, 1754 (1995); http://dx.doi.org/10.1063/1.115039 (3 pages) | Cited 53 times

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III–V nitride semiconductors have great potential for optoelectronic and electronic devices due to their wide direct band gaps. Because GaN is chemically very stable, dry etching techniques must be established in order to fabricate devices. In this work, we report the reactive ion etching (RIE) of GaN using CHF3/Ar and C2ClF5/Ar plasmas. GaN films on (001) GaAs were grown by electron cyclotron resonance (ECR) plasma associated molecular beam epitaxy (MBE) and the films showed (0001)hex orientation along the surface normal. We used a Drytek DRIE‐184 rf plasma discharge RIE system with no ECR discharge or high energy Ar ion beam. The effects of rf plasma power, pressure, and gas flow rates on the etch rate were investigated and the surface contamination due to RIE was examined by XPS. The etch rate varied between 60 and 470 Å/min. The conditions for etching were 100–500 W of rf plasma power, 60–300 mTorr of pressure, a CHF3 or C2ClF5 flow rate of 5–50 sccm and an Ar flow rate of 0–50 sccm. The highest etch rates were obtained with high rf plasma power and low pressure. © 1995 American Institute of Physics.  
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81.65.-b Surface treatments

Electron–phonon interactions in the wide band‐gap semiconductor GaN

S. J. Sheih, K. T. Tsen, D. K. Ferry, A. Botchkarev, B. Sverdlov, A. Salvador, and H. Morkoç

Appl. Phys. Lett. 67, 1757 (1995); http://dx.doi.org/10.1063/1.115040 (3 pages) | Cited 14 times

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Picosecond Raman spectroscopy has been employed to study electron–phonon interactions in the wide band‐gap semiconductor GaN. By using very intense picosecond laser pulses in the visible spectral range, electron‐hole pairs were generated through the two‐photon absorption in GaN. The relaxation of these high energy electrons and holes were used to interrogate electron–phonon interactions. We have found that electrons thermalize toward the bottom of the conduction band by emitting primarily longitudinal optical phonons. Our work demonstrates that the Fröhlich interaction is much stronger than the deformation potential interaction in wurtzite GaN. © 1995 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics

Electron velocity overshoot in a GaAs‐based p‐i‐n nanostructure semiconductor observed by transient subpicosecond Raman spectroscopy

E. D. Grann, K. T. Tsen, O. F. Sankey, D. K. Ferry, A. Salvador, A. Botcharev, and H. Morkoç

Appl. Phys. Lett. 67, 1760 (1995); http://dx.doi.org/10.1063/1.115041 (3 pages) | Cited 15 times

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We report direct measurements of nonequilibrium electron distributions and electron drift velocities in a GaAs‐based p‐i‐n nanostructure semiconductor by using transient subpicosecond Raman spectroscopy. Experimental conditions are such that the velocity overshoot phenomenon dominates the transport properties of the photoexcited carriers. These experimental results are compared with ensemble Monte Carlo calculations. © 1995 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.30.Fs III-V and II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics

Quantitative high resolution electron microscopy of III‐V compounds: A fuzzy logic approach

R. Hillebrand, H. Hofmeister, P. Werner, and U. Gösele

Appl. Phys. Lett. 67, 1763 (1995); http://dx.doi.org/10.1063/1.114375 (3 pages) | Cited 4 times

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In the study of interdiffusion phenomena in layered structures of III‐V compounds by high resolution electron microscopy, contrast features in the micrographs can be correlated with the variation of the chemical composition of the crystals. For quantitative interpretation of the micrographs a fuzzy logic approach is adapted to extract chemical information. The linguistic variable ‘‘similarity of images’’ is derived from the standard deviation (SD) of their difference patterns, which proved to be an appropriate measure. The approach developed is used to analyze simulated contrast tableaus of GaAs/P (As/P variation) and experimental micrographs of Al/GaAs (Al/Ga variation). © 1995 American Institute of Physics.
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68.37.-d Microscopy of surfaces, interfaces, and thin films
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.B- Structure of clean surfaces (and surface reconstruction)

Observation of a nanocrystalline‐to‐amorphous phase transition in luminescent porous silicon

R. R. Kunz, P. M. Nitishin, H. R. Clark, M. Rothschild, and B. Ahern

Appl. Phys. Lett. 67, 1766 (1995); http://dx.doi.org/10.1063/1.114376 (3 pages) | Cited 11 times

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Nanocrystalline silicon aggregates imbedded in a predominantly amorphous silicon layer have been observed in anodically etched p‐Si(100) by using valence band x‐ray photoelectron spectroscopy and lattice imaged high‐resolution transmission electron microscopy (XTEM). XTEM has identified the as‐prepared porous silicon to be a mixed phase of amorphous and nanocrystalline silicon, with the nanocrystalline aggregates being randomly dispersed throughout the full thickness of a 1 μm thick amorphous layer and exhibiting a size distribution from 2 to 5 nm in diameter. The abundance of the nanocrystalline aggregates seems to decrease as the anodic etching proceeds and as the sample is irradiated by x rays at room temperature in ultrahigh vacuum. Valence band photoelectron measurements show evidence for a crystalline‐to‐amorphous phase transition induced by x radiation which may, in part, be activated by photoelectron stimulated hydrogen desorption. The x‐ray irradiated samples also exhibit a significant reduction in photoluminescence yield, possibly caused by a reduction in the density of nanocrystallites. The observed mixed phase porous silicon and the metastability of the nanocrystallites help to explain apparent contradictory descriptions of the nature of porous silicon. © 1995 American Institute of Physics.
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68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
78.55.Hx Other solid inorganic materials
81.65.-b Surface treatments

Magnetic imaging of moat‐guarded superconducting electronic circuits

Mark Jeffery, T. Van Duzer, J. R. Kirtley, and M. B. Ketchen

Appl. Phys. Lett. 67, 1769 (1995); http://dx.doi.org/10.1063/1.114377 (3 pages) | Cited 27 times

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Superconducting electronic circuits surrounded by various configurations of holes in the superconducting ground plane have been imaged using a high resolution scanning superconducting quantum interference device (SQUID) microscope. These data demonstrate that in the weak field limit continuous moats trap flux more effectively to protect the circuits than small holes in the same configuration. © 1995 American Institute of Physics.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Alternating current losses in Bi2Sr2Ca1Cu2O8+δ/Ag tapes at power frequencies

M. N. Pitsakis, T. Haugan, F. C. H. Wong, S. Patel, and D. T. Shaw

Appl. Phys. Lett. 67, 1772 (1995); http://dx.doi.org/10.1063/1.114378 (3 pages)

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Measurements of transport alternating‐current (ac) losses in Bi2Sr2CaCu2O8+x powder‐in‐tube Ag‐sheathed tapes at 4.2 and 65 K and at 20, 60, 200, and 400 Hz were carried out and comparisons to the theoretically predicted hysteretic loss plus ohmic loss were made. The measured loss, albeit larger than predicted, was found to agree with Bean’s critical state model. The loss, having a linear dependence on the frequency of the alternating transport current and increasing with decreasing critical current density, confirms hysteresis as the dominant source of power dissipation at both 4.2 and 65 K. However, at 4.2 K, the loss varies as the square of the amplitude of the transport current, which is not consistent with the model. © 1995 American Institute of Physics.
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74.25.Sv Critical currents
74.72.-h Cuprate superconductors
84.71.Mn Superconducting wires, fibers, and tapes

Resonant tunneling transport across YBa2Cu3O7–SrRuO3 interfaces

Regina Dömel, C. Horstmann, M. Siegel, A. I. Braginski, and M. Yu. Kupriyanov

Appl. Phys. Lett. 67, 1775 (1995); http://dx.doi.org/10.1063/1.114379 (3 pages) | Cited 18 times

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We have investigated superconductor–normal metal–superconductor junctions with metallic perovskite SrRuO3 barriers. Ramp‐type junctions with ion‐beam‐etched and wet‐chemical‐etched YBa2Cu3O7 (YBCO) ramps have been compared with planar junctions where the interfaces were fabricated completely in situ. Regardless of the fabrication method, the junction properties were determined not by the metallic SrRuO3 barrier, but by an insulating layer at the interface. The shape of the I–V curves, and the temperature dependence of the normal resistance of junctions, could be well explained by quasiparticle resonant tunneling via two localized states in the interface layer. Furthermore, a model for the Cooper pair transport will be discussed that assumes resonant tunneling via one localized state as transport mechanism. © 1995 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions

Microwave compatible YBa2Cu3O7−x films on ferrimagnetic garnet substrates

A. Piqué, K. S. Harshavardhan, J. Moses, M. Mathur, E. Belohoubek, T. Venkatesan, E. J. Denlinger, D. Kalokitis, A. Fathy, V. Pendrick, M. Rajeswari, and Wu Jiang

Appl. Phys. Lett. 67, 1778 (1995); http://dx.doi.org/10.1063/1.114380 (3 pages) | Cited 10 times

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High quality epitaxial YBa2Cu3O7−x (YBCO) thin films have been deposited onto ferrimagnetic yttrium iron garnet (100) substrates using a double buffer layer lattice engineering scheme. The YBCO films are c‐axis oriented and show superconductive transition temperatures of 88–89 K with transition widths ≤0.5 K. The films also exhibited Jc’s of 2.7×106 A/cm2 in zero field and 1.1 ×106 A/cm2 in 2000 G at 77 K. Dielectric resonator measurements indicated unloaded Q values of 29 000 at 77 K and 24 GHz for unpatterned films. These values correspond to a surface resistance (RS) of 500 μΩ at 77 K, 10 GHz, which is the lowest obtained to date for a YBCO film on a ferrimagnetic substrate. Such films could be used for fabricating miniature‐high‐temperature superconducting microwave elements such as nonreciprocal and passive microwave devices, making possible, their integration on a single ferrimagnetic wafer. © 1995 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices

Possibility of depositing magnetic iron oxide films by excimer laser ablation of an organometallic polymer

Meng Ouyang and Hiroyuki Hiraoka

Appl. Phys. Lett. 67, 1781 (1995); http://dx.doi.org/10.1063/1.114381 (2 pages)

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Magnetic iron oxide films were successfully deposited on heated fused‐quartz substrates via the plume generated by the excimer laser ablation of poly(ferric methacrylate), an organometallic polymer, in an oxygen atmosphere. The investigation for the deposited films by means of x‐ray photoelectron spectroscopy, Raman spectroscopy, x‐ray diffraction, and scanning electron microscopy demonstrates that these films consist of iron‐rich Fe3O4 and α‐Fe2O3 phases that are made up of ball‐like grains with nanometer‐size structure. Magnetic hysteresis loop of the deposited film was also measured. The values of saturation magnetization, remanence magnetization, and coercivity are 35.6 emu/cm3, 6.13 emu/cm3, and 200 Oe, respectively. © 1995 American Institute of Physics.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
81.15.Fg Pulsed laser ablation deposition

Colossal magnetoresistance of 1 000 000‐fold magnitude achieved in the antiferromagnetic phase of La1−xCaxMnO3

Guo‐Qiang Gong, Chadwick Canedy, Gang Xiao, Jonathan Z. Sun, Arunava Gupta, and William J. Gallagher

Appl. Phys. Lett. 67, 1783 (1995); http://dx.doi.org/10.1063/1.114382 (3 pages) | Cited 102 times

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Record values of colossal magnetoresistance (CMR) have been achieved in the antiferromagnetic phase of the La1−xCaxMnO3 system. At 125 K, the CMR of the La0.5Ca0.5MnO3 reaches nearly 1 000 000%. It increases exponentially to 100 000 000% at 57 K. While the ground state is primarily an antiferromagnet, application of a magnetic field induces a ferromagnetic alignment of spins that is highly beneficial to the electron conduction. Other ferromagnetic samples exhibit very sharp magnetic phase transitions, with which the magnetotransport is closely correlated. © 1995 American Institute of Physics.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
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