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6 Apr 1998

Volume 72, Issue 14, pp. 1667-1789

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Chemical ordering in wurtzite InxGa1−xN layers grown on (0001) sapphire by metalorganic vapor phase epitaxy

P. Ruterana, G. Nouet, W. Van der Stricht, I. Moerman, and L. Considine

Appl. Phys. Lett. 72, 1742 (1998); http://dx.doi.org/10.1063/1.121170 (3 pages) | Cited 56 times

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A diffraction analysis in the transmission electron microscope was carried out on InxGa1−xN layers grown on (0001) sapphire by metalorganic vapor phase epitaxy on top of thick GaN buffer layers. It is found that the ternary InxGa1−xN layers can be chemically ordered. The In and Ga atoms occupy, respectively, the two simple hexagonal sublattice sites related by the glide mirrors and helicoidal axes of the P63 mc symmetry group of the wurtzite GaN. The symmetry of the ordered ternary is subsequently lowered by the disappearance of these operations, and it is shown to agree with the P3ml space group. © 1998 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling

Two-dimensional electron gas formed in a back-gated undoped heterostructure

Y. Hirayama, K. Muraki, and T. Saku

Appl. Phys. Lett. 72, 1745 (1998); http://dx.doi.org/10.1063/1.121171 (3 pages) | Cited 14 times

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By using a back-gate operation, a high-quality two-dimensional electron gas (2DEG) is formed in an undoped GaAs/AlGaAs inverted heterostructure. A high mobility of around 3×106 cm2/V s at 1.6 K is obtained for the structure without any compensating surface doping. The electron density is controllable down to 7×109 cm−2. The relation between electron density and mobility is studied for samples both with and without a surface gate. The obtained results indicate that background impurities and an inhomogeneity of the electric field coming from the surface govern the mobility in a low-electron-density region and that the interface inhomogeneity becomes important at a high electron density. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

p-type conduction in as-grown Mg-doped GaN grown by metalorganic chemical vapor deposition

Lisa Sugiura, Mariko Suzuki, and Johji Nishio

Appl. Phys. Lett. 72, 1748 (1998); http://dx.doi.org/10.1063/1.121172 (3 pages) | Cited 23 times

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We have clarified the effect of H2 and NH3 on the passivation of Mg acceptor in p-type GaN films grown by metalorganic chemical vapor deposition. It has been found that the small amount of H2 carrier gas strongly influences the electrical property of the Mg-doped GaN films. Low-resistivity p-type GaN has been obtained by H2-free growth without any post-treatments. Its acceptor concentration is as high as that obtained by conventional H2-rich growth with subsequent thermal annealing. It has also been clarified that hydrogen produced by NH3 dissociation does not prevent Mg from electrically activating in H2-free growth. © 1998 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Ea III-V semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Rv Passivation

Enhancement of acoustic- and optic-phonon generation by terahertz radiations in a two-dimensional electron system

X. L. Lei and B. Dong

Appl. Phys. Lett. 72, 1751 (1998); http://dx.doi.org/10.1063/1.121173 (3 pages) | Cited 2 times

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We present a theoretical study on the angular and frequency distributions of the acoustic and optic-phonon generation by hot electrons during the terahertz-driven transport in a GaAs-based quantum well. Based on the detailed solution of the nonlinear balance equations in the presence of an oscillating electric field of arbitrary strength, we find that, when the system is exposed to an intense terahertz radiation, emissions of acoustic and optic phonons are significantly enhanced, especially along the polarized direction of the electric field. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
72.30.+q High-frequency effects; plasma effects
71.38.-k Polarons and electron-phonon interactions
68.35.Ja Surface and interface dynamics and vibrations
72.20.Ht High-field and nonlinear effects
73.61.Ey III-V semiconductors
63.20.K- Phonon interactions
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Spectral shifts associated with dark line defects in degraded II-VI laser diodes

L.-L. Chao, G. S. Cargill, T. Marshall, E. Snoeks, J. Petruzzello, and M. Pashley

Appl. Phys. Lett. 72, 1754 (1998); http://dx.doi.org/10.1063/1.121174 (3 pages) | Cited 14 times

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Spectral shifts associated with 〈100〉 dark line defects of degraded II-VI laser diodes based on ZnCdSe/ZnSSe/MgZnSSe separate confinement heterostructures have been studied by spatially resolved cathodoluminescence at room temperature. Dark line defects were induced by electron-beam bombardment. Peak shifts as large as 2 nm were observed towards the blue or the red depending on the local circumstances. Peak widths usually became narrower after degradation. Redshifts and blueshifts are explained in terms of strain relaxation and Cd out-diffusion associated locally with degradation, as well as the kinetic energy dependence of the degradation-related carrier capture cross section. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.Lk Linear defects: dislocations, disclinations
78.66.Fd III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.80.Fe Electron and positron radiation effects
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
66.30.H- Self-diffusion and ionic conduction in nonmetals
68.35.Fx Diffusion; interface formation
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Mixing effect of chelate complex and metal in organic light-emitting diodes

Jae-Gyoung Lee, Youngkyoo Kim, Sei-Hum Jang, Soon-Nam Kwon, and Kwangho Jeong

Appl. Phys. Lett. 72, 1757 (1998); http://dx.doi.org/10.1063/1.121175 (3 pages) | Cited 5 times

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Organic light-emitting diodes using thin film dispersing a hole transport material into a soluble polyimide as a hole transport layer and the sublimed molecular film of a chelate complex as an emissive layer were fabricated. In order to improve the injection of electrons into the emissive layer as well as the durability of devices, we have attempted mixing the chelate complex and metal between the emissive layer and the cathodic electrode. The charge injection of the device with the mixed layer was initialized at an applied voltage of 4.19 V. It was observed from the electroluminescent spectra that the oscillator strength was dramatically enhanced with the applied voltage. © 1998 American Institute of Physics.
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85.60.Jb Light-emitting devices
64.75.-g Phase equilibria
68.35.Ct Interface structure and roughness
73.40.Ns Metal-nonmetal contacts
73.20.At Surface states, band structure, electron density of states
78.60.Fi Electroluminescence
79.60.Jv Interfaces; heterostructures; nanostructures
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.66.-w Optical properties of specific thin films
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A probe for the investigation of the superconducting metastable state in YBa2Cu3O7−x step-edge junctions

S. Barbanera, M. G. Castellano, G. Torrioli, and M. Cirillo

Appl. Phys. Lett. 72, 1760 (1998); http://dx.doi.org/10.1063/1.121176 (3 pages) | Cited 3 times

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We have investigated the pair tunneling process in YBa2Cu3O7−x step-edge Josephson junctions by studying the lifetime of the metastable zero-voltage state determined by the thermal activation out of the potential well. The junctions have a hysteretic current–voltage characteristic at 4.2 K, which allows the recording of transitions and switching distribution from the Josephson current to the resistive state. By applying an external magnetic field, we have found a strong dependence of the activation energy on the field intensity. Striking similarities with analogous measurements performed on low Tc conventional tunnel junctions suggest that the high Tc counterparts can be described by a standard model for long junctions. © 1998 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.50.+r Tunneling phenomena; Josephson effects
74.40.-n Fluctuation phenomena
74.78.Fk Multilayers, superlattices, heterostructures
74.20.Fg BCS theory and its development

Superconducting YBa2Cu3O7−x thin films on polycrystalline ferrite for magnetically tunable microwave components

Q. X. Jia, A. T. Findikoglu, P. Arendt, S. R. Foltyn, J. M. Roper, J. R. Groves, J. Y. Coulter, Y. Q. Li, and G. F. Dionne

Appl. Phys. Lett. 72, 1763 (1998); http://dx.doi.org/10.1063/1.121177 (3 pages) | Cited 11 times

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Superconducting YBa2Cu3O7−x (YBCO) thin films with a surface resistance of 0.86 mΩ at 10 GHz and 76 K have been grown on polycrystalline ferrite yttrium iron garnet (YIG) substrates. The chemical and structural mismatches between YBCO and YIG are solved by using a double buffer layer of biaxially oriented yttria-stabilized zirconia (YSZ) and CeO2, where YSZ is deposited by an ion-beam-assisted-deposition technique. The YBCO films are c axis oriented with an in-plane mosaic spread [full width at half maximum of an x-ray ϕ-scan on (103) reflection] of less than 8°. The films have a superconductive transition temperature above 88 K with a transition width less than 0.3 K, giving a critical current density above 106 A/cm2 in self field at 75 K. At 75 K in an external magnetic field of 1 T perpendicular to the film surface, the films maintain a critical current density over 2×105 A/cm2. © 1998 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
85.25.-j Superconducting devices

Minimization of detrimental effect of air in HgBa2CaCu2O6+δ thin film processing

B. W. Kang, A. A. Gapud, X. Fei, T. Aytug, and J. Z. Wu

Appl. Phys. Lett. 72, 1766 (1998); http://dx.doi.org/10.1063/1.121178 (3 pages) | Cited 1 time

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We have studied the effects of halogenizing HgBa2CaCu2O6+δ (Hg-1212) thin films and have found that the addition of chlorine/fluorine significantly enhances (1) the reproducibility and stability of Hg-1212 thin films, (2) the phase purity of Hg-1212 to over 90%, and (3) the magnetic critical current density (Jc,mag) both at zero field and in-field. A possible mechanism of preventing contamination of precursor materials by chlorine/fluorine doping is proposed. © 1998 American Institute of Physics.
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81.15.Cd Deposition by sputtering
74.25.Sv Critical currents
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors

Proximity effect in bilayer films of YBa2Cu2.7Fe0.3Oy and YBa2Cu3O7−δ

O. Nesher, G. Koren, E. Polturak, and G. Deutscher

Appl. Phys. Lett. 72, 1769 (1998); http://dx.doi.org/10.1063/1.121179 (3 pages) | Cited 4 times

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We studied the proximity effect in a series of YBa2Cu2.7Fe0.3Oy/YBa2Cu3O7−δ bilayer film with varying YBa2Cu3O7−δ thickness. In a bilayer of isolated YBCO islands, a Tc of 72 K was observed, much higher than Tc of 32 K of the YBa2Cu2.7Fe0.3Oy film. Tc and Jc of thicker bilayers of continuous YBa2Cu3O7−δ films were found to decrease with decreasing YBCO thickness. This behavior of Tc and Jc can be explained by the Deutscher de Gennes theory for the proximity effect, provided one models the film as a series of grains whose lateral dimensions scale with the average film thickness. © 1998 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.50.+r Tunneling phenomena; Josephson effects
74.25.Sv Critical currents
74.72.-h Cuprate superconductors
74.10.+v Occurrence, potential candidates

Nonlinear I–V characteristics and proximity effects for PrBa2Cu3O7−δ/YBa2Cu3O7−δ bilayered structures grown on (001) YBa2Cu3O7−δ single crystal substrates

Toshiyuki Usagawa, Yoshihiro Ishimaru, Jianguo Wen, Tadashi Utagawa, Satoshi Koyama, and Youichi Enomoto

Appl. Phys. Lett. 72, 1772 (1998); http://dx.doi.org/10.1063/1.121180 (3 pages) | Cited 8 times

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We have observed superconductivity induced by proximity effects for 100 nm thick (001) PrBa2Cu3O7−δ films pseudomorphically grown on (001) YBa2Cu3O7−δ single crystal substrates by vertical four-probe measurements. The induced superconductivity disappeared around 28 K and was recovered at around 15 K. The 220 nm thick (001) PrBa2Cu3O7−δ/YBa2Cu3O7−δ bilayers show nonlinear I–V behavior with 0.2 mV built-in potential at low temperature below 50 K. The local maximum of the vertical resistance appears around 25 K. © 1998 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures
74.78.Fk Multilayers, superlattices, heterostructures
74.72.-h Cuprate superconductors
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Magnetoelastic coupling and magnetic anisotropy in La0.67Ca0.33MnO3 films

J. O’Donnell, M. S. Rzchowski, J. N. Eckstein, and I. Bozovic

Appl. Phys. Lett. 72, 1775 (1998); http://dx.doi.org/10.1063/1.121181 (3 pages) | Cited 88 times

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We report the results of magnetization measurements on pseudomorphic (fully strained) c-axis oriented colossal magnetoresistance manganite thin films grown by molecular beam epitaxy. We observe uniaxial magnetic anisotropy (hard axis/easy plane) with the easy plane being the film plane. Within the plane a weaker biaxial anisotropy is observed with [100] (Mn–O bond direction) easy axes. The magnetization dependence of the uniaxial anisotropy constant follows the predicted magnetization dependence of the magnetostriction constants within single-ion models indicating that the anisotropy energy is dominated by strain-induced anisotropy from the lattice constant mismatch with the SrTiO3 substrate. These results indicate a magnetostriction constant λ100 ≈ +7×10−5, and an induced orbital moment of at least 0.02μb/Mn ion. We predict that by appropriate substrate selection an equilibrium out-of-plane magnetization can be produced. © 1998 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.80.+q Magnetomechanical effects, magnetostriction
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
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Quantitative topographic imaging using a near-field scanning microwave microscope

C. P. Vlahacos, D. E. Steinhauer, S. K. Dutta, B. J. Feenstra, Steven M. Anlage, and F. C. Wellstood

Appl. Phys. Lett. 72, 1778 (1998); http://dx.doi.org/10.1063/1.121182 (3 pages) | Cited 15 times

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We describe a technique for extracting topographic information using a scanning near-field microwave microscope. By monitoring the shift of the system’s resonant frequency, we obtain quantitative topographic images of uniformly conducting metal surfaces. At a frequency of 9.572 GHz, our technique allows a height discrimination of about 55 nm at a separation of 30 μm. We present topographic images of uneven, conducting samples and compare the height response and sensitivity of the system with theoretical expectations. © 1998 American Institute of Physics.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
07.79.Fc Near-field scanning optical microscopes
68.35.B- Structure of clean surfaces (and surface reconstruction)

Alkanethiol self-assembled monolayers as the dielectric of capacitors with nanoscale thickness

Maria A. Rampi, Olivier J. A. Schueller, and George M. Whitesides

Appl. Phys. Lett. 72, 1781 (1998); http://dx.doi.org/10.1063/1.121183 (3 pages) | Cited 82 times

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Alkanethiol self-assembled monolayers (SAMs) on a mercury surface are used to build a junction consisting of two opposing mercury surfaces with interposed SAMs: Hg-SAM/SAM-Hg. The liquid mercury surface provides a support for the SAM that is smooth, compliant, free of defects, and without the incommensurate lattice properties that characterize solid metal surfaces. The thickness of the dielectric ( ∼ 30–90 Å) in this junction can be easily changed by using alkanethiols with different lengths. From capacitance measurements, a dielectric constant of 2.7±0.3 is calculated for the SAMs. The conductivity of SAMs on the Hg surface is σ = 6±2×10−15 Ω−1 cm−1, a value close to that of bulk polyethylene. The junction sustains an electric field of 6 MV/cm. © 1998 American Institute of Physics.
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84.32.Tt Capacitors
73.40.Rw Metal-insulator-metal structures
77.84.Jd Polymers; organic compounds
77.22.Ch Permittivity (dielectric function)

Capacitance–voltage characteristics of Bi4Ti3O12/p-Si interface

Liwei Fu, Kun Liu, Bo Zhang, Junhao Chu, Hong Wang, and Min Wang

Appl. Phys. Lett. 72, 1784 (1998); http://dx.doi.org/10.1063/1.121184 (3 pages) | Cited 9 times

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Electrical properties of the interface between Bi4Ti3O12 ferroelectric film and p-Si substrate have been studied by capacitance–voltage (C–V) characteristics. It is found that the interface barrier can be broken down temporally because of the charge injection from Si substrate into the ferroelectric thin film, and this charge injection behavior induces hump and valley structures in the C–V curves. It is also found that the polarization in the Bi4Ti3O12 film is aligned along a preferential direction from semiconductor to ferroelectric thin film, which is attributed to the ferroelectric/p-Si contact. © 1998 American Institute of Physics.
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77.55.-g Dielectric thin films
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.80.Cw Elemental semiconductors
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Sr0.8Bi2.5Ta1.2Nb0.9O9+x ferroelectric thin films prepared by two-target off-axis radio frequency magnetron sputtering

Huei-Mei Tsai, Pang Lin, and Tseung-Yuen Tseng

Appl. Phys. Lett. 72, 1787 (1998); http://dx.doi.org/10.1063/1.120571 (3 pages) | Cited 31 times

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Ferroelectric Sr0.8Bi2.5Ta1.2Nb0.9O9+x thin films on a Pt/SiO2/Si substrate were prepared by using two-target off-axis radio frequency magnetron sputtering, and their structural and electrical properties were investigated. The films crystallized with high (115) diffraction intensity at a substrate temperature of 600 °C, and showed columnar microstructure. The 600 °C sputtered films with a thickness of 440 nm exhibited remanent polarization (2Pr) of 52 μC/cm2 and coercive field (2Ec) 28 kV/cm at an applied voltage of 1.5 V. The leakage current density was about 6×10−6 A/cm2 at an electric field of 50 kV/cm. The films demonstrated fatigue free characteristics up to 1.0×1010 switching cycles under a 3 V bipolar 1 MHz square wave. © 1998 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
77.22.Ej Polarization and depolarization
61.72.-y Defects and impurities in crystals; microstructure
77.80.Fm Switching phenomena
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