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28 Apr 2003

Volume 82, Issue 17, pp. 2749-2924

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 2957 (2003); http://dx.doi.org/10.1063/1.1571977 (3 pages)

Tadashi Kawazoe, Kiyoshi Kobayashi, Suguru Sangu, and Motoichi Ohtsu
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Bound-exciton-induced current bistability in a silicon light-emitting diode

J. M. Sun, T. Dekorsy, W. Skorupa, B. Schmidt, and M. Helm

Appl. Phys. Lett. 82, 2823 (2003); http://dx.doi.org/10.1063/1.1570920 (3 pages) | Cited 2 times

Online Publication Date: 21 April 2003

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A bound-exciton-induced current bistability is observed under forward bias in an efficient silicon light-emitting diode at low temperatures. Two stable states of the S-type differential conductivity correspond to empty and filled states of bound excitons, respectively. The relationship between the current–voltage characteristic and the bound-exciton population can be accounted for using a rate equation model for bound and free excitons. The consistency between the theoretical and experimental results indicates that bound excitons, despite their neutral-charged states, contribute to the current bistability in silicon p–n junction diodes. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Frequency multiplication of microwave radiation by propagating space-charge domains in a semiconductor superlattice

R. Scheuerer, M. Haeussler, K. F. Renk, E. Schomburg, Yu. I. Koschurinov, D. G. Pavelev, N. Maleev, V. Ustinov, and A. Zhukov

Appl. Phys. Lett. 82, 2826 (2003); http://dx.doi.org/10.1063/1.1569999 (3 pages) | Cited 5 times

Online Publication Date: 21 April 2003

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We report on frequency multiplication of microwave radiation by propagating space-charge domains in a semiconductor superlattice; the domains were due to a negative differential mobility of miniband electrons. We irradiated an arrangement of two GaAs/AlAs superlattices, mounted in a rectangular waveguide system, with microwave radiation (frequency near 70 GHz) and observed the generation of harmonics; the conversion of radiation power to the third harmonic showed a remarkable efficiency (5%). A theoretical study, based on a drift-diffusion model for the miniband electrons, suggests that the microwave radiation has driven the formation and annihilation of space-charge domains and that the resulting anharmonic current was the source of the frequency-multiplied radiation. Our results indicate that frequency multiplication by space-charge domains in a semiconductor superlattice can be exploited for efficient generation of submillimeter-wave radiation. © 2003 American Institute of Physics.
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84.40.Az Waveguides, transmission lines, striplines
73.63.Hs Quantum wells
73.21.Cd Superlattices
77.22.Jp Dielectric breakdown and space-charge effects
72.20.Ht High-field and nonlinear effects
73.50.Fq High-field and nonlinear effects
78.70.Gq Microwave and radio-frequency interactions

Cu depletion at the CuInSe2 surface

Dongxiang Liao and Angus Rockett

Appl. Phys. Lett. 82, 2829 (2003); http://dx.doi.org/10.1063/1.1570516 (3 pages) | Cited 33 times

Online Publication Date: 21 April 2003

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The chemical composition of the (112)B surface of epitaxial CuInSe2 thin films is investigated by angle resolved x-ray photoelectron spectroscopy. Results show that a severe Cu depletion exists in the top 1–2 atomic layers. No bulk second phase is found at the surface. The source of this depletion and its relation to the Cd doping at the CdS/CuInSe2 interface are discussed. © 2003 American Institute of Physics.
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68.35.Dv Composition, segregation; defects and impurities
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.55.-a Thin film structure and morphology

The use of Simmons’ equation to quantify the insulating barrier parameters in Al/AlOx/Al tunnel junctions

L. S. Dorneles, D. M. Schaefer, M. Carara, and L. F. Schelp

Appl. Phys. Lett. 82, 2832 (2003); http://dx.doi.org/10.1063/1.1569986 (3 pages) | Cited 17 times

Online Publication Date: 21 April 2003

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We have analyzed the electron transport processes in Al/AlOx/Al junctions. The samples were produced by glow-discharge-assisted oxidation of the bottom electrode. The nonlinear I–V curves of 17 samples were measured at room temperature, being very well fitted using the Simmons’ equation with the insulating barrier thickness, barrier height, and the junction area as free parameters. An exponential growth of the area normalized electrical resistance with thickness is obtained, using just values from I–V curve simulations. The effective tunneling area corresponding to the “hot spots” can be quantified and is five orders of magnitude smaller than the physical area in the studied samples. © 2003 American Institute of Physics.
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73.40.Rw Metal-insulator-metal structures
73.61.Ng Insulators
73.40.Gk Tunneling
52.77.Dq Plasma-based ion implantation and deposition
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.65.Mq Oxidation

Invasive nature of corona charging on thermal Si/SiO2 structures with nanometer-thick oxides revealed by electron spin resonance

A. Stesmans and V. V. Afanas’ev

Appl. Phys. Lett. 82, 2835 (2003); http://dx.doi.org/10.1063/1.1540245 (3 pages) | Cited 10 times

Online Publication Date: 21 April 2003

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Electron spin resonance (ESR) analysis reveals that the versatile noncontacting corona biasing method frequently applied in the electrical analysis of Si/SiO2-based structures is not a noninvasive tool, as usually assumed. In the absence of carrier impact damage, at least five types of ESR-active defects are generated, indicating the drastic impact and jeopardizing inference of intrinsic device properties. © 2003 American Institute of Physics.
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76.30.Mi Color centers and other defects
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Extended wavelength InGaAs on GaAs using InAlAs buffer for back-side-illuminated short-wave infrared detectors

Lars Zimmermann, Joachim John, Stefan Degroote, Gustaaf Borghs, Chris Van Hoof, and Stefan Nemeth

Appl. Phys. Lett. 82, 2838 (2003); http://dx.doi.org/10.1063/1.1569042 (3 pages) | Cited 2 times

Online Publication Date: 21 April 2003

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We conducted an experimental study of back-side-illuminated InGaAs photodiodes grown on GaAs and sensitive in the short-wave infrared up to 2.4 μm. Standard metamorphic InGaAs or IR-transparent InAlAs buffers were grown by molecular-beam epitaxy. We studied dark current and photocurrent as a function of buffer thickness, buffer material, and temperature. A saturation of the dark current with buffer thickness was not observed. The maximum resistance area product was ∼10 Ω cm2 at 295 K. The dark current above 200 K was dominated by generation–recombination current. A pronounced dependence of the photocurrent on the buffer thickness was observed. The peak external quantum efficiency was 46% (at 1.6 μm) without antireflective coating. © 2003 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Dw Photodiodes; phototransistors; photoresistors
73.61.Ey III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
73.50.Pz Photoconduction and photovoltaic effects

Terahertz studies of carrier dynamics and dielectric response of n-type, freestanding epitaxial GaN

W. Zhang, Abul K. Azad, and D. Grischkowsky

Appl. Phys. Lett. 82, 2841 (2003); http://dx.doi.org/10.1063/1.1569988 (3 pages) | Cited 29 times

Online Publication Date: 21 April 2003

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We report the characterization of the complex conductivity and dielectric function of GaN by terahertz time-domain spectroscopy. Transmission measurements are performed on an n-type, 180-μm-thick, freestanding GaN crystal. Frequency dependent electron dynamics, power absorption and optical dispersion are observed over the frequency range from 0.1 to 4.0 THz. The measured conductivity is well fit by Drude theory. © 2003 American Institute of Physics.
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73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
73.50.Mx High-frequency effects; plasma effects
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.-a Thin film structure and morphology

Varistor action in zinc oxide suspension

K. Negita, T. Yamaguchi, T. Tsuchie, and N. Shigematsu

Appl. Phys. Lett. 82, 2844 (2003); http://dx.doi.org/10.1063/1.1569659 (3 pages) | Cited 1 time

Online Publication Date: 21 April 2003

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In a suspension composed of zinc oxide (ZnO) particles and silicone oil, it is found that the current density dramatically increases above a specific electric field (break down field Eb). In ac measurement, the nonlinear coefficient (α), which characterizes the relationship between current density J and the electric field E as J∝Eα, changes from ∼1 to ∼30 when increasing the electric field through Eb. On the basis of the α value, temperature dependence of Eb, etc., the mechanism of the fluid varistor is briefly discussed. © 2003 American Institute of Physics.
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47.85.Np Fluidics
83.80.Gv Electro- and magnetorheological fluids
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
77.22.Jp Dielectric breakdown and space-charge effects
82.70.Kj Emulsions and suspensions
85.30.-z Semiconductor devices
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
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Hot isostatic pressing of powder in tube MgB2 wires

A. Serquis, L. Civale, D. L. Hammon, X. Z. Liao, J. Y. Coulter, Y. T. Zhu, M. Jaime, D. E. Peterson, F. M. Mueller, V. F. Nesterenko, and Y. Gu

Appl. Phys. Lett. 82, 2847 (2003); http://dx.doi.org/10.1063/1.1571231 (3 pages) | Cited 57 times

Online Publication Date: 21 April 2003

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The critical current density (Jc) of hot isostatic pressed (HIPed) MgB2 wires, measured by dc transport and magnetization, is compared with that of similar wires annealed at ambient pressure. The HIPed wires have a higher Jc than the annealed wires, especially at high temperatures and magnetic fields, and higher irreversibility field (Hirr). The HIPed wires are promising for applications, with Jc>106 A/cm2 at 5 K and zero field and >104 A/cm2 at 1.5 T and 26.5 K, and Hirr ∼ 17 T at 4 K. The improvement is attributed to a high density of structural defects, which are the likely source of vortex pinning. These defects, observed by transmission electron microscopy, include small angle twisting, tilting, and bending boundaries, resulting in the formation of subgrains within MgB2 crystallites. © 2003 American Institute of Physics.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
74.25.Ha Magnetic properties including vortex structures and related phenomena
81.40.Gh Other heat and thermomechanical treatments
68.37.Lp Transmission electron microscopy (TEM)
61.72.Mm Grain and twin boundaries

Magnetic confinement of weakly ionized plasma with superconducting bulk magnets

Hidenori Matsuzawa, Kazuya Ohishi, Kazuhito Ishikawa, Tomonori Morita, Masaaki Yoshikawa, Hiroshi Ikuta, and Uichiro Mizutani

Appl. Phys. Lett. 82, 2850 (2003); http://dx.doi.org/10.1063/1.1570520 (3 pages) | Cited 1 time

Online Publication Date: 21 April 2003

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This letter describes the application of single-domain superconducting bulk magnets as a plasma confinement. A through-hole was drilled at the center of a Sm123 bulk superconductor of 39 mm diameter and 17 mm thickness. When the sample was field cooled to 77 K, the resulting bulk magnet trapped a magnetic field of ∼0.65 T called a magnetic mirror, in the bore of the hole. The magnet was applied to a weakly ionized neon plasma column. Both the magnet and discharge glass tube were immersed in liquid nitrogen. The spatial distribution in the tube of red fluorescence of the plasma showed that the magnet certainly confined the plasma. These results would provide a clue to applications of the compact magnet of strong magnetic field. © 2003 American Institute of Physics.
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28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
84.71.Ba Superconducting magnets; magnetic levitation devices
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Sharp ferromagnet/semiconductor interfaces by electrodeposition of Ni thin films onto n-GaAs(001) substrates

C. Scheck, P. Evans, G. Zangari, and R. Schad

Appl. Phys. Lett. 82, 2853 (2003); http://dx.doi.org/10.1063/1.1571229 (3 pages) | Cited 10 times

Online Publication Date: 21 April 2003

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We report on the chemical, electrical, and magnetic properties of Ni/GaAs(001) interfaces prepared using electrodeposition. Electrodeposition is an equilibrium process which thus releases much less energy per absorbed atom than other deposition techniques. This allows preparation of chemically sharp interfaces which otherwise show a high degree of reactivity and interdiffusion. This is demonstrated by the example of Ni grown on GaAs(001). Photoelectron spectroscopy shows the absence of surface segregation of substrate material or diffusion into the Ni layer. This is confirmed by the electrical and magnetic properties of the films. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Cc Other ferromagnetic metals and alloys
68.35.Ct Interface structure and roughness
79.60.Jv Interfaces; heterostructures; nanostructures
81.15.Pq Electrodeposition, electroplating
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Enhanced critical current density in overdoped HgBa2CaCu2O6+δ superconducting thin films

Y. Y. Xie and J. Z. Wu

Appl. Phys. Lett. 82, 2856 (2003); http://dx.doi.org/10.1063/1.1569652 (3 pages) | Cited 2 times

Online Publication Date: 21 April 2003

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Overdoped HgBa2CaCu2O6+δ (Hg-1212) high-temperature superconducting thin films have been synthesized in a fluorine-assisted cation-exchange process followed by postannealing in flowing oxygen. The overdoped Hg-1212 thin films have lowered superconducting transition temperature Tc of about 114–115 K. Critical current density Jc, however, is nearly twice as that for optimally doped Hg-1212 films. The enhancement in magnetic irreversible field Hirr has also been observed in the overdoped Hg-1212 films, while a similar scaling law of Hirr ∼ (1−T/Tc)n with n = 1.2–1.3 in field range below 1 T was observed for both optimally doped and overdoped samples. Such a fluorine-assisted cation-exchange process, hence, provides a simple practical route for achieving high-current carrying Hg-1212 films on oxide and metal substrates. © 2003 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

FeRh/FePt exchange spring films for thermally assisted magnetic recording media

Jan-Ulrich Thiele, Stefan Maat, and Eric E. Fullerton

Appl. Phys. Lett. 82, 2859 (2003); http://dx.doi.org/10.1063/1.1571232 (3 pages) | Cited 99 times

Online Publication Date: 21 April 2003

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The temperature-dependent magnetic response of exchange-coupled FePt/FeRh thin films is described. The FePt forms a high magnetocrystalline anisotropy, high-coercivity ferromagnetic layer. The FeRh layer is antiferromagnetic at room temperature but, upon heating above a transition temperature, becomes ferromagnetic with a large magnetic moment and low magnetocrystalline anisotropy, forming an exchange–spring system and significantly lowering the coercive field of the composite system. This feature opens intriguing possibilities for media applications for thermally assisted magnetic recording where the ferromagnetic phase of FeRh is exploited to help write the media while the antiferromagnetic phase supports the long-time stability. © 2003 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Ee Antiferromagnetics
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Prediction of large polar Kerr rotation in the Heusler-related alloys AuMnSb and AuMnSn

Laila Offernes, P. Ravindran, and A. Kjekshus

Appl. Phys. Lett. 82, 2862 (2003); http://dx.doi.org/10.1063/1.1569425 (3 pages) | Cited 10 times

Online Publication Date: 21 April 2003

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Theoretical spectra for the magneto-optical Kerr effect have been obtained for the Heusler-related alloys AuMnSb and AuMnSn, and repeated calculations are performed for the isostructural PtMnSb phase. Using experimental lattice constants, our calculations predict a Kerr rotation exceeding −1° in the 0.5–0.8 eV region for AuMnSb and a somewhat smaller rotation for AuMnSn. Supercell calculations indicate that half-metallic behavior can be induced on hole/electron doping in the AuMnSn1−xSbx solid-solution phase for 0.50<x<0.75.© 2003 American Institute of Physics.
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78.20.Ls Magneto-optical effects
61.66.Dk Alloys

Evidence of electronic phase separation in Er3+-doped La0.8Sr0.2MnO3

V. Ravindranath, M. S. Ramachandra Rao, R. Suryanarayanan, and G. Rangarajan

Appl. Phys. Lett. 82, 2865 (2003); http://dx.doi.org/10.1063/1.1570001 (3 pages)

Online Publication Date: 21 April 2003

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Er3+ doping at the La site in La0.8Sr0.2MnO3 showed an unusual increase in Curie/peak resistivity temperature (TC/TP) above a certain nominal dopant concentration (x ≥ 0.086). This increase is attributed to the presence of a cation-deficient ErMnO3 phase. Further, with increase in TP the overall resistivity of these compounds also decreases. We explain these results assuming the presence of a nanoscale mixture of charge-ordered antiferromagnetic insulating (CO-AFMI) phase in a ferromagnetic metallic matrix, wherein the increase in TC/TP with increase in Er3+ content is due to the local destruction of the CO-AFMI phase by the presence of the cation-deficient ErMnO3 phase. We thus provide an indirect evidence of electronic phase separation in these compounds. © 2003 American Institute of Physics.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions

Effect of ac susceptibility in superconductors on magnetic shielding

M. Maruyama, M. Hidaka, and T. Satoh

Appl. Phys. Lett. 82, 2868 (2003); http://dx.doi.org/10.1063/1.1569421 (3 pages)

Online Publication Date: 21 April 2003

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We have theoretically studied the effect of ac susceptibility in superconductors on magnetic shielding. Our recent study of measured wave form distortion observed in a high-Tc superconductor sampler system suggests that the magnetic field leaks into the sampler circuit through the YBa2Cu3O7−x ground plane when an ac magnetic field is applied. The occurrence of such magnetic leakage can be explained by complex susceptibility in the ground plane because a shielding magnetic field with a phase shifted due to an imaginary part of the susceptibility cannot cancel an applied ac magnetic field completely. A simple calculation shows that the residual magnetic field should have an advanced phase of 45°–90°, which coincides with the results obtained in the sampler system. © 2003 American Institute of Physics.
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74.25.Ha Magnetic properties including vortex structures and related phenomena

Current-induced magnetization switching in magnetic tunnel junctions

Yaowen Liu, Zongzhi Zhang, P. P. Freitas, and J. L. Martins

Appl. Phys. Lett. 82, 2871 (2003); http://dx.doi.org/10.1063/1.1569044 (3 pages) | Cited 49 times

Online Publication Date: 21 April 2003

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Current-induced magnetization switching (CIMS) in low-resistance magnetic tunnel junctions was shown at average critical current densities (Jc = 1.33×106 A/cm2). When large vertical currents pass through the junctions, spin-transfer torque, and vortex fields can rotate the magnetization of the free layer from the initial parallel state to a vortex state, resulting in 10.8% CIMS resistance change at zero-bias current, which is about half of the resistance change (22%) induced when switching is created by an external field. A micromagnetic simulation including the spin-transfer torque and the vortex field correctly predicts the critical negative-current-inducing switching from the parallel state into the vortex state, but fails to explain the reverse switching from the vortex state into the parallel state at an approximately symmetric positive critical current. Lead fields were analyzed and found to be not the cause of the observed switching. The very small dependence of the switching currents on an external magnetic field suggests the existence of hot-spots where local current densities may be much larger. © 2003 American Institute of Physics.
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75.47.Np Metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.25.Mk Spin transport through interfaces
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Atomic layer deposition of ZrO2 on W for metal–insulator–metal capacitor application

Sang-Yun Lee, Hyoungsub Kim, Paul C. McIntyre, Krishna C. Saraswat, and Jeong-Soo Byun

Appl. Phys. Lett. 82, 2874 (2003); http://dx.doi.org/10.1063/1.1569985 (3 pages) | Cited 63 times

Online Publication Date: 21 April 2003

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A metal–insulator–metal (MIM) capacitor using ZrO2 on tungsten (W) metal bottom electrode was demonstrated and characterized in this letter. Both ZrO2 and W metal were synthesized by an atomic layer deposition (ALD) method. High-quality 110 ∼ 115 Å ZrO2 films were grown uniformly on ALD W using ZrCl4 and H2O precursors at 300 °C, and polycrystalline ZrO2 in the ALD regime could be obtained. A 13 ∼ 14-Å-thick interfacial layer between ZrO2 and W was observed after fabrication, and it was identified as WOx through angle-resolved x-ray photoelectron spectroscopy analysis with wet chemical etching. The apparent equivalent oxide thickness was 20 ∼ 21 Å. An effective dielectric constant of 22 ∼ 25 including an interfacial WOx layer was obtained by measuring capacitance and thickness of MIM capacitors with Pt top electrodes. High capacitance per area (16 ∼ 17 fF/μm2) and low leakage current (10−7 A/cm2 at ±1 V) were achieved. © 2003 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
84.32.Tt Capacitors
73.40.Rw Metal-insulator-metal structures
77.55.-g Dielectric thin films
68.55.A- Nucleation and growth
85.40.Sz Deposition technology
85.30.Tv Field effect devices
77.22.Ch Permittivity (dielectric function)
79.60.Dp Adsorbed layers and thin films
79.60.Jv Interfaces; heterostructures; nanostructures

High tunability in compositionally graded epitaxial barium strontium titanate thin films by pulsed-laser deposition

S. G. Lu, X. H. Zhu, C. L. Mak, K. H. Wong, H. L. W. Chan, and C. L. Choy

Appl. Phys. Lett. 82, 2877 (2003); http://dx.doi.org/10.1063/1.1569427 (3 pages) | Cited 76 times

Online Publication Date: 21 April 2003

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Compositionally graded barium strontium titanate [(BaxSr1−x)TiO3BST, x = 0.75, 0.8, 0.9, and 1.0] thin films are fabricated by pulsed-laser deposition on a LaAlO3 substrate with (La0.7Sr0.3)MnO3 as the bottom electrode. A high dielectric permittivity and temperature characteristic without Curie–Weiss law are obtained. A tunability of over 70% is obtained at frequency of 1 MHz, which is higher than that of single BST layer with the same compositions. All the results indicate that the graded thin films have better electrical properties than a single-layer film. © 2003 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
77.22.Ch Permittivity (dielectric function)
81.15.Fg Pulsed laser ablation deposition

Dielectric properties of Pb(Zr20Ti80)O3/Pb(Zr80Ti20)O3 multilayered thin films prepared by rf magnetron sputtering

Can Wang, Q. F. Fang, Z. G. Zhu, A. Q. Jiang, S. Y. Wang, B. L. Cheng, and Z. H. Chen

Appl. Phys. Lett. 82, 2880 (2003); http://dx.doi.org/10.1063/1.1569658 (3 pages) | Cited 35 times

Online Publication Date: 21 April 2003

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A series of Pb(Zr,Ti)O3 (PZT) films with tetragonal/rhombohedral multilayered structures has been grown on Pt/TiO2/SiO2/Si substrates by rf magnetron sputtering at a relative low temperature. All the films comprise 12 periodicities of Pb(Zr20Ti80)O3/Pb(Zr80Ti20)O3 in constant thickness of 40 nm, but the layer thicknesses of tetragonal phase (dT) and rhombohedral phase (dR) in one periodicity are varied. The electric properties of the films are investigated as a function of dT/dR from 10/30 to 35/5. An enhanced dielectric property is observed in the multilayered films. Especially, a optimal value of dT/dR = 30/10 is obtained, where the dielectric constant reaches maximum value of 469 at 100 kHz with a loss tangent of 0.037, and the dielectric constant is about five times that of the single tetragonal phase PZT film formed under the identical condition. Moreover, the polarization also increases in the multilayered films, and remarkably, the film of 30/10 exhibits larger remanent polarization, lower coercive voltage, and more symmetric hysteresis than the other films. The enhancement of dielectric properties is attributed to the presence of interfaces between the tetragonal and the rhombohedral phase layer. This study suggests that the design of the multilayered PZT film capacitor with tetragonal and rhombohedral phase should be an effective way to enhance the dielectric and ferroelectric performance in devices. © 2003 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
68.65.Ac Multilayers
77.80.Dj Domain structure; hysteresis
84.32.Tt Capacitors
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
77.22.Ej Polarization and depolarization
81.15.Cd Deposition by sputtering
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
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Atomic-layer deposition of wear-resistant coatings for microelectromechanical devices

T. M. Mayer, J. W. Elam, S. M. George, P. G. Kotula, and R. S. Goeke

Appl. Phys. Lett. 82, 2883 (2003); http://dx.doi.org/10.1063/1.1570926 (3 pages) | Cited 55 times

Online Publication Date: 21 April 2003

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Friction and wear are major concerns in the performance and reliability of microelectromechanical systems (MEMS) devices employing sliding contacts. While many tribological coating materials are available, most traditional surface coating processes are unable to apply conformal coatings to the high aspect ratio (height/width) structures typical of MEMS devices. We demonstrate that thin, conformal, wear-resistant coatings can be applied to Si surface-micromachined structures by atomic-layer deposition (ALD). For this demonstration, we apply 10-nm-thick films of Al2O3 using a binary reaction sequence with precursors of trimethyl aluminum and water. Deposition is carried out in a viscous flow reactor at 1 Torr and 168 °C, with N2 as a carrier gas. Cross-section transmission electron microscopy analysis shows that films are uniform to within 5% on MEMS device structures with aspect ratio ranging from 0 to >100. Films are stoichiometric Al2O3, with no evidence of contamination from other species, and are amorphous. Preliminary friction and wear data show that ALD films have promising properties for application to MEMS devices. © 2003 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Nanobelts as nanocantilevers

William L. Hughes and Zhong L. Wang

Appl. Phys. Lett. 82, 2886 (2003); http://dx.doi.org/10.1063/1.1570497 (3 pages) | Cited 94 times

Online Publication Date: 21 April 2003

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Semiconducting oxide nanobelts of ZnO have been sectioned and manipulated, for microelectromechanical systems, using an atomic force microscopy probe. Structurally modified nanobelts demonstrate potential for nanocantilever based technologies. With dimensions ∼ 35–1800 times smaller than conventional cantilevers, the nanocantilevers are expected to have improved physical, chemical, and biological sensitivity for scanning probe microscopy and sensor applications. © 2003 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
81.16.Ta Atom manipulation

Structural and optical properties of coherent GaN islands grown on 6H-SiC(0001)-(√3×√3)

C.-W. Hu, A. Bell, L. Shi, F. A. Ponce, D. J. Smith, and I. S. T. Tsong

Appl. Phys. Lett. 82, 2889 (2003); http://dx.doi.org/10.1063/1.1570000 (3 pages) | Cited 6 times

Online Publication Date: 21 April 2003

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Coherent islands of GaN with base widths in the range of 100 to 500 nm were grown on 6H-SiC(0001)-(√3×√3) surfaces via the vapor–liquid–solid (VLS) mechanism. The microstructure of GaN islands was studied by high-resolution cross-sectional transmission electron microscopy. The morphological details of the islands were imaged by atomic force microscopy and the same assembly of islands was identified in a scanning electron microscope in which site-specific cathodoluminescence (CL) spectroscopy was conducted on individual islands. The broadening of the CL linewidths together with the shift to lower wave numbers in the E2 Raman mode detected by micro-Raman spectroscopy suggest the existence of tensile strain in the GaN islands. The strain is due to the heavy Si doping of the GaN islands by Si adatoms on the (√3×√3) substrate surface during the VLS growth process. © 2003 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.60.Hk Cathodoluminescence, ionoluminescence
68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Lp Transmission electron microscopy (TEM)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Ps Atomic force microscopy (AFM)
78.30.Fs III-V and II-VI semiconductors
68.60.Bs Mechanical and acoustical properties
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Formation of lateral quantum dot molecules around self-assembled nanoholes

Rudeesun Songmuang, Suwit Kiravittaya, and Oliver G. Schmidt

Appl. Phys. Lett. 82, 2892 (2003); http://dx.doi.org/10.1063/1.1569992 (3 pages) | Cited 85 times

Online Publication Date: 21 April 2003

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We fabricate groups of closely spaced self-assembled InAs quantum dots (QDs)—termed lateral QD molecules—on GaAs (001) by a combination of molecular-beam epitaxy and AsBr3 in situ etching. An initial array of homogeneously sized nanoholes is created by locally strain-enhanced etching of a GaAs cap layer above InAs QDs. Deposition of InAs onto the nanoholes causes a preferential formation of the InAs QD molecules around the holes. The number of QDs per QD molecule ranges from 2 to 6, depending on the InAs growth conditions. By decreasing the substrate temperature, the number of QDs per QD molecule increases, but the statistical distribution is wider due to a reduced In atom diffusion length. Our photoluminescence investigation documents the nanohole and QD molecule formation step by step and confirms the high crystal quality of these structures. An analysis of the nanohole geometry as a function of annealing time and InAs filling allows us to propose a model for the QD molecule formation process. © 2003 American Institute of Physics.
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81.07.Ta Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
68.37.Ps Atomic force microscopy (AFM)
66.30.H- Self-diffusion and ionic conduction in nonmetals

Size-tunable infrared (1000–1600 nm) electroluminescence from PbS quantum-dot nanocrystals in a semiconducting polymer

L. Bakueva, S. Musikhin, M. A. Hines, T.-W. F. Chang, M. Tzolov, G. D. Scholes, and E. H. Sargent

Appl. Phys. Lett. 82, 2895 (2003); http://dx.doi.org/10.1063/1.1570940 (3 pages) | Cited 136 times

Online Publication Date: 21 April 2003

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Nanocomposites consisting of PbS nanocrystals in a conjugated polymer matrix were fabricated. We report results of photo- and electroluminescence across the range of 1000 to 1600 nm with tunability obtained via the quantum-size effect. The intensity of electroluminescence reached values corresponding to an internal quantum efficiency up to 1.2%. We discuss the impact of using different-length capping ligands on the transfer of excitations from polymer matrix to nanocrystals. © 2003 American Institute of Physics.
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78.60.Fi Electroluminescence
78.67.Hc Quantum dots
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
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