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27 Dec 1999

Volume 75, Issue 26, pp. 4049-4210

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Bound exciton dynamics in GaN grown by hydride vapor-phase epitaxy

G. Pozina, J. P. Bergman, T. Paskova, and B. Monemar

Appl. Phys. Lett. 75, 4124 (1999); http://dx.doi.org/10.1063/1.125557 (3 pages) | Cited 31 times

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Temperature-dependent time-resolved photoluminescence measurements were performed on thick GaN layers grown by hydride vapor-phase epitaxy on Al2O3 substrates. Radiative lifetimes were determined for the neutral-donor–bound exciton with position at 3.478 eV and for two neutral-acceptor–bound excitons at 3.473 and 3.461 eV. We report a value of 3600 ps for the radiative lifetime of the acceptor–bound exciton transition at 3.461 eV. The dominant mechanism responsible for the nonradiative recombination of the bound excitons is shown to be connected with dissociation of the bound excitons into free excitons. © 1999 American Institute of Physics.
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71.35.Gg Exciton-mediated interactions
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
71.55.Eq III-V semiconductors

First-principles study of stability, band structure, and optical properties of the ordered Ge0.50Sn0.50 alloy

Ravindra Pandey, Michel Rérat, and Mauro Causà

Appl. Phys. Lett. 75, 4127 (1999); http://dx.doi.org/10.1063/1.125558 (3 pages) | Cited 17 times

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All electron density functional theory calculations were performed on the ordered Ge0.50Sn0.50 alloy in the zinc-blende phase to study its structural, electronic, and optical properties along with its stability with respect to the elemental components. We employed a linear combination of atomic orbitals approach for calculations in which the Bloch functions were constructed as linear combinations of atom-centered Gaussian orbitals. The calculated results show a relative stability of the GeSn alloy in the zinc-blende phase for which the lattice constant and bulk modulus are predicted to be 6.20 Å and 53 GPa, respectively. Analysis of band structure and density of states shows the cubic-ordered alloy to be a direct-gap semiconductor with a small band gap. The optical properties, such as dielectric constant and plasmon energy of the cubic alloy, appear to be about the average of the respective values in its elemental components. © 1999 American Institute of Physics.
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71.20.Nr Semiconductor compounds
71.15.Nc Total energy and cohesive energy calculations
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.66.Fn Inorganic compounds
62.20.D- Elasticity
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Effects of interfacial oxides on Schottky barrier contacts to n- and p-type GaN

X. A. Cao, S. J. Pearton, G. Dang, A. P. Zhang, F. Ren, and J. M. Van Hove

Appl. Phys. Lett. 75, 4130 (1999); http://dx.doi.org/10.1063/1.125559 (3 pages) | Cited 44 times

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Schottky contacts were formed on n- and p-type GaN after either a conventional surface cleaning step in solvents, HCl and HF or with an additional treatment in (NH4)2S to prevent reformation of the native oxide. Reductions in barrier height were observed with the latter treatment, but there was little change in diode ideality factor. A simple model suggests that an interfacial insulating oxide of thickness 1–2 nm was present after conventional cleaning. This oxide has a strong influence on the contact characteristics on both n- and p-type GaN and appears to be responsible for some of the wide spread in contact properties reported in the literature. © 1999 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
68.35.Ct Interface structure and roughness
81.65.Mq Oxidation
85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Kk Junction diodes

Extensional piezoelectric coefficients of gallium nitride and aluminum nitride

I. L. Guy, S. Muensit, and E. M. Goldys

Appl. Phys. Lett. 75, 4133 (1999); http://dx.doi.org/10.1063/1.125560 (3 pages) | Cited 51 times

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Measurements of piezoelectric coefficients d33 and d31 in wurtzite GaN and AlN using an interferometric technique are presented. We report on the clamped values, d33c of these coefficients found in GaN and AlN thin films, and we derive the respective bulk values, d33b. The clamped value of d33c in GaN single crystal films is 2.8±0.1 pm V−1 which is 30% higher than in polycrystalline films grown by laser assisted chemical vapor deposition. The value of d33b in bulk single crystal GaN is found to be 3.7±0.1 pm V−1. The value of d33c in plasma assisted and laser assisted chemical vapor deposited AlN films was 3.2±0.3 and 4.0±0.1 pm V−1, respectively. The bulk value estimate of d33b in AlN of 5.6±0.2 pm V−1 was deduced. The values of d31, both clamped and bulk, were calculated for wurtzite GaN and AlN. We have also calculated the values of d14 in cubic phase film and bulk GaN and AlN. Interferometric measurements of the inverse piezoelectric effect provide a simple method of identifying the positive direction of the c axis, which was found to be pointing away from the substrate for all films. © 1999 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
77.65.Bn Piezoelectric and electrostrictive constants

Dielectric constant and light emission in Si/SiO2 superlattices

Muoi Tran, Nacir Tit, and M. W. C. Dharma-wardana

Appl. Phys. Lett. 75, 4136 (1999); http://dx.doi.org/10.1063/1.125561 (3 pages) | Cited 7 times

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The real part of the frequency-dependent dielectric function ϵ1(ω) and the light-absorption coefficient α(ω), of Si slabs confined within SiO2 barriers have been calculated as a function of Si-slab thickness dsi. The calculation uses the imaginary part ϵ2(ω) of the dielectric function obtained from tight-binding calculations. The resulting static dielectric constants are found to increase with the decreasing Si-slab width, contrary to some reported theoretical results for H-terminated Si or pure-Si clusters. The calculated integrated light absorption in the range 1.0–2.6 eV is a maximum for for slabs with dsi ∼ 20 Å, in agreement with experimental work on light emission from Si/SiO2 superlattices and other oxidized Si nanostructures. © 1999 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Cw Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
77.22.Ch Permittivity (dielectric function)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Imaging of acoustic charge transport in semiconductor heterostructures by surface acoustic waves

M. Streibl, A. Wixforth, J. P. Kotthaus, A. O. Govorov, C. Kadow, and A. C. Gossard

Appl. Phys. Lett. 75, 4139 (1999); http://dx.doi.org/10.1063/1.125562 (3 pages) | Cited 12 times

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We demonstrate room-temperature acoustic charge transport of electrons and holes in an InGaAs/GaAs heterostructure. The carriers are optically generated by interband absorption and then separated, stored, and transported in the piezoelectric potential superlattice of a surface acoustic wave. The charge distribution is detected with a spatial resolution of a few acoustic wavelengths by a second orthogonal probe beam, genererated by so-called tapered transducers. The image information is given as a phase shift signal in frequency space and allows for the direct comparison of the number of generated and transported carriers. Regions of mere carrier drag and full carrier capture and transport are observed simultaneously. © 1999 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
63.20.K- Phonon interactions
71.38.-k Polarons and electron-phonon interactions
68.35.Gy Mechanical properties; surface strains
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Quantum dots induced by strain from buried and surface stressors

John H. Davies

Appl. Phys. Lett. 75, 4142 (1999); http://dx.doi.org/10.1063/1.125563 (3 pages) | Cited 28 times

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Quantum dots can be induced in a quantum well by strain from a buried, self-assembled dot or from a stressor on the surface. The elastic fields are shown to be significantly different in their ability to trap carriers. There is no dilation around a buried dot, which therefore has no effect on electrons, and the axial strain repels both holes and excitons. A stressor on the surface, in contrast, produces dilation that can confine all carriers. In both cases, the piezoelectric potential may trap electrons and holes separately in space, storing long-lived spatially indirect excitons. © 1999 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.61.-r Electrical properties of specific thin films
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.35.Aa Frenkel excitons and self-trapped excitons
68.35.Gy Mechanical properties; surface strains

Effects of NiO on electrical properties of NiAu-based ohmic contacts for p-type GaN

T. Maeda, Yasuo Koide, and Masanori Murakami

Appl. Phys. Lett. 75, 4145 (1999); http://dx.doi.org/10.1063/1.125564 (3 pages) | Cited 47 times

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Effects of a NiO layer on the electrical properties of NiAu-based ohmic contacts for p-GaN were studied by depositing a p-type NiO layer on the p-GaN using a sputter-deposition technique. NiO layers doped with Li[NiO(Li)] had a p-type conduction with sheet resistivity of around 1 Ω cm after annealing at temperatures lower than 500 °C. A variety of the NiAu-based contacts with the NiO layers such as NiO/Au, NiO(Li)/Au, Ni/NiO(Li)/Au, Ni/Li2O/NiO/Au, and Ni/Li2O/Ni/NiO/Au contacts were prepared by depositing on the p-GaN, where a slash “/” indicates the deposition sequence. However, these contacts did not provide specific contact resistances (ρc) lower than that (ρc ∼ 10−2 Ω cm2) of the conventional Ni/Au contacts prepared by annealing in N2 ambient. From the present results, it was believed that the p-NiO layer did not act as an intermediate semiconductor layer to reduce the Schottky barrier height at the p-GaN/Au interface. © 1999 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.Cc Kinetics of defect formation and annealing

Optical characterization of the self-limiting effect in flow-rate modulation epitaxy of V-shaped GaAs quantum wire

Xue-Lun Wang and Ogura Mutsuo

Appl. Phys. Lett. 75, 4148 (1999); http://dx.doi.org/10.1063/1.125565 (3 pages) | Cited 5 times

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Photoluminescence is used to characterize the self-limiting effect observed during flow-rate modulation epitaxy (FME) of GaAs quantum wires (QWRs) on V-grooved substrate. Our study found that not only the central thickness but also the overall cross-sectional wire shape is maintained to an atomic level in the self-limited growth regions. This result suggests that the self-limited FME technique is a very promising method for an atomically controlled fabrication of high-quality QWRs. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Thermal conductivity of lateral epitaxial overgrown GaN films

C.-Y. Luo, H. Marchand, D. R. Clarke, and S. P. DenBaars

Appl. Phys. Lett. 75, 4151 (1999); http://dx.doi.org/10.1063/1.125566 (3 pages) | Cited 29 times

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The room-temperature thermal conductivity of lateral epitaxial overgrown metalorganic chemical vapor deposition GaN films is reported to be in excess of 155 W/m K. This compares with the reported value of 130 W/m K for bulk single crystals and a similar value (135 W/m K) for a thick (∼50 μm) GaN film grown, without a nucleation layer, on sapphire by hydride vapor phase epitaxy. The measurements were made by a third-harmonic electrical measurement. © 1999 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.60.Dv Thermal stability; thermal effects

Electron effective mass in hexagonal GaN

A. M. Witowski, K. Pakuła, J. M. Baranowski, M. L. Sadowski, and P. Wyder

Appl. Phys. Lett. 75, 4154 (1999); http://dx.doi.org/10.1063/1.125567 (2 pages) | Cited 38 times

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Far-infrared magneto-optical investigations of shallow donors in epitaxial GaN layers on sapphire were carried out by means of Fourier transform spectrometry up to 23 T. From the splitting of the donor p states in a magnetic field, the cyclotron effective mass for conduction electrons was found to be m∗ = 0.222 m0. A precise determination of the mass was made possible by the high quality of the spectra and by taking into account high magnetic field data above 12 T. © 1999 American Institute of Physics.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.55.Eq III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.20.Ls Magneto-optical effects
78.66.Fd III-V semiconductors

Subpicosecond spin relaxation in GaAsSb multiple quantum wells

K. C. Hall, S. W. Leonard, H. M. van Driel, A. R. Kost, E. Selvig, and D. H. Chow

Appl. Phys. Lett. 75, 4156 (1999); http://dx.doi.org/10.1063/1.125586 (3 pages) | Cited 18 times

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Spin relaxation times in GaAsxSb1−x quantum wells are measured at 295 K using time-resolved circular dichroism induced by 1.5 μm, 100 fs pulses. Values of 1.03 and 0.84 ps are obtained for samples with x = 0 and 0.188, respectively. These times are >5 times shorter than those in InGaAs and InGaAsP wells with similar band gaps. The shorter relaxation times are attributed to the larger spin-orbit conduction-band splitting in the Ga(As)Sb system, consistent with the D’yakonov–Perel theory of spin relaxation [M. I. D’yakonov and V. I. Perel, Sov. Phys. JETP 38, 177 (1974)]. Our results indicate the feasibility of engineering an all-optical, polarization switch at 1.5 μm with response time <250 fs. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.20.Fm Birefringence
78.47.-p Spectroscopy of solid state dynamics
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Mg-doped GaN: Similar defects in bulk crystals and layers grown on Al2O3 by metal–organic chemical-vapor deposition

Z. Liliental-Weber, M. Benamara, W. Swider, J. Washburn, I. Grzegory, S. Porowski, D. J. H. Lambert, C. J. Eiting, and R. D. Dupuis

Appl. Phys. Lett. 75, 4159 (1999); http://dx.doi.org/10.1063/1.125568 (3 pages) | Cited 43 times

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Defects were observed in GaN:Mg grown on sapphire substrates using metal–organic chemical-vapor deposition (MOCVD) with Mg-delta doping similar to those previously observed in bulk GaN:Mg grown from Ga solution under high hydrostatic pressure of nitrogen. Pyramidal defects (pinholes) with (1100) hexagonal facets on the (0001) base plane and six {11math2} side facets, and defects with a rectangular shape also delineated by planar facets on the basal (0001) planes, were observed for growth with Ga polarity for both of these very different growth methods. The Mg dopant is apparently responsible for their formation since the oxygen concentration in the MOCVD-grown samples was orders of magnitude lower than in the bulk samples. Mg segregation on these planes apparently does not allow uniform continuous growth on these planes leading to these hollow defects. Some defects in the heterolayers also develop into longer nanotubes elongated along the c axis. Change of polarity from Ga to N followed by a change back to Ga polarity also resulted in formation of planar defects previously observed in bulk samples for growth with N polarity. © 1999 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Nn Stacking faults and other planar or extended defects
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.uj III-V and II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
64.75.-g Phase equilibria
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The generation and detection of high flux atomic oxygen for physical vapor deposition thin film growth

N. J. C. Ingle, R. H. Hammond, M. R. Beasley, and D. H. A. Blank

Appl. Phys. Lett. 75, 4162 (1999); http://dx.doi.org/10.1063/1.125569 (3 pages) | Cited 15 times

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The growth of many epitaxial thin-film oxides is significantly enhanced with the use of an oxidizing agent such as atomic oxygen, ozone, or NO2. We developed a flow-through microwave plasma source to generate large atomic oxygen fluxes while maintaining vacuum pressures of less that 1×10−4 Torr. Continuous and real-time detection of the atomic oxygen was achieved by atomic absorption of the 130 nm atomic oxygen lines. Atomic oxygen fluxes of at least 1.4×1018 atoms/cm2 s and dissociation efficiencies of around 100% were obtained. © 1999 American Institute of Physics.
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52.50.Dg Plasma sources
81.15.Kk Vapor phase epitaxy; growth from vapor phase
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Effective microwave surface resistance of gold-contacted YBa2Cu3O7−x thin films

A. G. Zaitsev, R. Schneider, J. Geerk, G. Linker, F. Ratzel, and R. Smithey

Appl. Phys. Lett. 75, 4165 (1999); http://dx.doi.org/10.1063/1.125570 (3 pages) | Cited 9 times

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The microwave surface resistance (Rs) of YBa2Cu3O7−x (YBCO) films sputtered simultaneously on both sides of CeO2 coated sapphire wafers of 3 in. diameter was measured using the disk resonator technique at a frequency of 1.92 GHz. By deposition of Au layers of various thicknesses on the unpatterned YBCO side of the disk resonator, we studied the effective Rs of the Au-contacted YBCO films. Although the Au layer was not directly exposed to the microwave power, it dramatically increased the effective Rs of the YBCO film. For example, Rs(77 K) = 16.5 μΩ of a 300-nm-thick YBCO film increased to 85 μΩ by the deposition of a 0.1-μm-thick Au layer. The increase of the Au thickness to 1.2 μm resulted in a further enhancement of the effective Rs up to 560 μΩ. We explain this effect in terms of the impedance transformation model. According to this model the effective Rs of the Au/YBCO bilayer decreases with increasing YBCO film thickness. However, Au layers with thicknesses above 1 μm considerably enhance the effective Rs even for thick YBCO films (700–800 nm). A higher quality of the YBCO films (in terms of shorter London penetration depths) reduces the effect of a Au layer, while a low electrical resistivity of this layer leads to a further increase of the effective Rs. © 1999 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.F- Transport properties
74.25.N- Response to electromagnetic fields
73.25.+i Surface conductivity and carrier phenomena
72.30.+q High-frequency effects; plasma effects
74.25.Ha Magnetic properties including vortex structures and related phenomena

Self-assembly of floating magnetic particles into ordered structures: A promising route for the fabrication of tunable photonic band gap materials

M. Golosovsky, Y. Saado, and D. Davidov

Appl. Phys. Lett. 75, 4168 (1999); http://dx.doi.org/10.1063/1.125571 (3 pages) | Cited 49 times

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We report stable ordered arrays of millimeter-size magnetic particles floating on a liquid surface. Self-assembly into a regular two-dimensional lattice results from lateral magnetic interactions between the particles. The lattice constant may be easily tuned by the application of external magnetic field. The array symmetry is designed by using different particle shapes, magnets, and magnet position inside the particle, so that complex symmetries may be achieved. Three-dimensional ordered arrays are obtained in a stack of troughs containing floating magnets. Computer simulations of electromagnetic wave propagation in such three-dimensional structures suggest an opening of a tunable photonic band gap in the microwave range. © 1999 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
68.18.-g Langmuir-Blodgett films on liquids
42.50.-p Quantum optics
42.70.Qs Photonic bandgap materials
41.20.Jb Electromagnetic wave propagation; radiowave propagation
81.05.Zx New materials: theory, design, and fabrication

Microstructure-dependent coercivity in monodispersed hematite particles

C. Rath, K. K. Sahu, S. D. Kulkarni, S. Anand, S. K. Date, R. P. Das, and N. C. Mishra

Appl. Phys. Lett. 75, 4171 (1999); http://dx.doi.org/10.1063/1.125572 (3 pages) | Cited 24 times

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Microstructure and magnetic properties of monodispersed pseudocubic and trapezoidal particles with varying sizes prepared through the hydrothermal precipitation route are reported. The coercivity for trapezoidal particles was similar to that of reported values. For pseudocubic particles, however, the coercivity is unusually high (∼6 kOe) as compared to the maximum value (3 kOe) reported in the literature. Detailed microstructural analysis revealed that particles with a well-defined shape are, in fact, polycrystalline. The high coercivity and its variation with particle shape and size are correlated to the internal nanostructure of the particles. © 1999 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.-w Structure of nanoscale materials
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
81.40.Rs Electrical and magnetic properties related to treatment conditions

Magnetic configurations in exchange-biased double superlattices

S. G. E. te Velthuis, G. P. Felcher, J. S. Jiang, A. Inomata, C. S. Nelson, A. Berger, and S. D. Bader

Appl. Phys. Lett. 75, 4174 (1999); http://dx.doi.org/10.1063/1.125573 (3 pages) | Cited 21 times

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The layer-by-layer magnetization of a “double-superlattice” Fe/Cr(211) exchange-bias junction was determined by polarized neutron reflectometry. An n-layered [Fe/Cr]n antiferromagnetic (AF) superlattice is coupled with an m-layered [Fe/Cr]m ferromagnetic (F) superlattice, to provide a controlled exchange bias. In low magnetic fields, the magnetizations of the two superlattices are collinear. The two magnetized states (along or opposite to the bias field) differ only in the relative orientation of the F and adjacent AF layer. At higher fields, the AF moments flop to the direction perpendicular to the applied field. The structure, thus determined, explains the magnitude of the bias field. © 1999 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics

Suppression of growth-induced perpendicular magnetic anisotropy in Co–Pt alloys by trace amounts of Si

A. L. Shapiro, O. Vajk, F. Hellman, K. M. Ring, and K. L. Kavanagh

Appl. Phys. Lett. 75, 4177 (1999); http://dx.doi.org/10.1063/1.125574 (3 pages)

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(CoxPt1−x)1−ySiy alloys with Si content from 1 to 20 at. % have been grown over a range of growth conditions. Co-deposition of even trace amounts of Si with Co–Pt alloys causes the growth-induced magnetic anisotropy and chemical clustering found in these vapor-deposited alloy films to decrease or vanish. It also causes significant reduction in grain size. Addition of 5 at. % Si eliminates anisotropy completely. Addition of 1 at. % Si produces a film with magnetic properties identical to pure Co–Pt alloys grown at lower deposition temperatures. We suggest this suppression of anisotropy and related effects are due to a decrease in surface mobility during growth in the presence of even trace amounts of Si. © 1999 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
81.40.Rs Electrical and magnetic properties related to treatment conditions
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
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Sensing characteristics of in-plane polarized lead zirconate titanate thin films

Baomin Xu, Ronald G. Polcawich, Susan Trolier-McKinstry, Yaohong Ye, L. Eric Cross, Jonathan J. Bernstein, and Raanan Miller

Appl. Phys. Lett. 75, 4180 (1999); http://dx.doi.org/10.1063/1.125575 (3 pages) | Cited 19 times

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The sensing characteristics of in-plane polarized lead zirconate titanate (PZT) thin films were studied and compared with the through-thickness polarized PZT films. The in-plane polarized PZT films were deposited on ZrO2-passivated silicon substrates and had interdigitated electrode systems on the top surface; hence, they can be polarized in the film plane. This in-plane polarization configuration separates the electrode spacing and film thickness as independent variables; thus, the voltage sensitivity can be increased by using wider electrode spacing even for fixed film thickness. The results show that for films with a thickness of 1 μm the voltage sensitivity of in-plane polarized PZT films can be more than 20 times higher than that of the conventional, through-thickness polarized PZT films which were deposited on Pt-buffered silicon substrates. © 1999 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
77.22.Ej Polarization and depolarization
07.10.Cm Micromechanical devices and systems
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Effect of mechanical constraint on the dielectric and piezoelectric behavior of epitaxial Pb(Mg1/3Nb2/3)O3(90%)–PbTiO3(10%) relaxor thin films

V. Nagarajan, C. S. Ganpule, B. Nagaraj, S. Aggarwal, S. P. Alpay, A. L. Roytburd, E. D. Williams, and R. Ramesh

Appl. Phys. Lett. 75, 4183 (1999); http://dx.doi.org/10.1063/1.125576 (3 pages) | Cited 47 times

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The effect of heteroepitaxy-induced constraint on the structure and piezoelectric properties of the relaxor ferroelectric lead magnesium niobate–lead titanate (PMN–PT) were investigated. Relaxor PMN–PT epitaxial thin films with oxide electrodes were grown by pulsed-laser deposition on (100) LaAlO3 substrates. We observe a systematic decrease in the phase transition temperature (temperature at which a maximum in dielectric response occurs), from around 250 to around 60 °C as the relaxor thickness is increased from 100 to 400 nm. This is accompanied by an increase in the relative dielectric constant (ϵr), measured at room temperature and 10 kHz, from 300 to 2000. The piezoelectric coefficient d33 measured using a scanned probe microscope, increase by almost an order of magnitude with increasing film thickness. © 1999 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.65.Bn Piezoelectric and electrostrictive constants
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ch Permittivity (dielectric function)

Activation field and fatigue of (Pb, La)(Zr, Ti)O3 thin films

I-Wei Chen and Y. Wang

Appl. Phys. Lett. 75, 4186 (1999); http://dx.doi.org/10.1063/1.125577 (3 pages) | Cited 17 times

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For a class of (Pb, La)(Zr, Ti)O3 ferroelectric thin films, the Merz equation adequately describes the dynamics of switching resistance. A single parameter, activation field, can be used to relate the coercive field throughout the polarization fatigue process. We suggest that the increased switching resistance causes fatigue, and that it could originate from the dielectric degradation of the film. The constitutive equation for the coercive field and its correlation with the switchable polarization offer a tool for fatigue characterization and life prediction. © 1999 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Fm Switching phenomena
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
62.20.M- Structural failure of materials
68.60.Bs Mechanical and acoustical properties

Comparative study of broadband electrodynamic properties of single-crystal and thin-film strontium titanate

A. T. Findikoglu, Q. X. Jia, C. Kwon, D. W. Reagor, G. Kaduchak, K. Ø. Rasmussen, and A. R. Bishop

Appl. Phys. Lett. 75, 4189 (1999); http://dx.doi.org/10.1063/1.125578 (3 pages) | Cited 1 time

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We have used a coplanar waveguide structure to study broadband electrodynamic properties of single-crystal and thin-film strontium titanate. We have incorporated both time- and frequency-domain measurements to determine small-signal effective refractive index and loss tangent as functions of frequency (up to 4 GHz), dc bias (up to 106 V/m), and cryogenic temperature (17 and 60 K). The large-signal impulse response of the devices and the associated phenomenological nonlinear wave equation illustrate how dissipation and nonlinearity combine to produce the overall response in the large-signal regime. © 1999 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
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Gm Dielectric loss and relaxation
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Enhancement of hot-carrier injection resistance for deep submicron transistor gate dielectric with a powered solenoid

Cher-Liang Cha, Kheng-Chok Tee, Eng-Fong Chor, Hao Gong, Krishnamachar Prasad, Anthony J. Bourdillon, Alex See, Lap Chan, and Mike Myung-Ok Lee

Appl. Phys. Lett. 75, 4192 (1999); http://dx.doi.org/10.1063/1.125579 (3 pages)

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The operational reliability of ultrathin gate dielectrics in forthcoming metal–oxide–semiconductor field-effect transistors (MOSFETs) will be impaired if there is the occurrence of hot-carrier injection (HCI) into the gate across the gate dielectric. In this work, a method is proposed to mellow the undesired effects incurred by HCI in a n-type MOSFET (NMOSFET) via a reduction in its frequency. The method involves the powering of a polycrystalline silicon (polysilicon) solenoid at the same time when the gate and drain of transistors are powered. The localized magnetic field generated from the solenoid can impose a downward force (Hall effect) to counteract or compensate the upward driving force exerted on the energetic electrons reaching the drain by the applied gate voltage. Fewer electrons will be trapped and the quality, reliability, and lifetime of the device will improve as a consequence. © 1999 American Institute of Physics.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
77.55.-g Dielectric thin films
73.50.Fq High-field and nonlinear effects
84.32.Hh Inductors and coils; wiring
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Strain-balanced GaAsP/InGaAs quantum well solar cells

N. J. Ekins-Daukes, K. W. J. Barnham, J. P. Connolly, J. S. Roberts, J. C. Clark, G. Hill, and M. Mazzer

Appl. Phys. Lett. 75, 4195 (1999); http://dx.doi.org/10.1063/1.125580 (3 pages) | Cited 53 times

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A strain-balance multiquantum well (MQW) approach to enhance the GaAs solar cell efficiency is reported. Using a p-i-n diode structure, the strain-balanced GaAsP/InGaAs MQW is grown on a GaAs substrate and equals a good GaAs cell in terms of power conversion efficiency. The cell design is presented together with measurements of the forward bias dark current density, quantum efficiency, and 3000 K light-IV response. Cell efficiencies under standard air mass (AM) 1.5 and AM 0 illumination are projected from experimental data and the suitability of this cell for enhancing GaInP/GaAs tandem cell efficiencies is discussed. © 1999 American Institute of Physics.
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84.60.Jt Photoelectric conversion
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.60.Dw Photodiodes; phototransistors; photoresistors
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