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25 Nov 2002

Volume 81, Issue 22, pp. 4103-4293

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Substrate-free crystallization of distorted hexagonal barium titanate thin films

N. Stavitski, V. Lyahovitskaya, J. Nair, I. Zon, R. Popovitz-Biro, E. Wachtel, Y. Feldman, and I. Lubomirsky

Appl. Phys. Lett. 81, 4177 (2002); http://dx.doi.org/10.1063/1.1524691 (3 pages) | Cited 7 times

Online Publication Date: 19 November 2002

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We show that substrate-free crystallized barium titanate (BaTiO3) films adopt a hexagonal structure, whereas substrate-supported films assume the commonly observed tetragonal phase. However, in contrast to the known hexagonal BaTiO3, the substrate-free crystallized films demonstrate a small but measurable pyroelectric effect, and do not exhibit phase transitions in the 25–423 K temperature range. Thus the substrate-free crystallized BaTiO3 represents a heretofore unreported crystallographic modification of BaTiO3. © 2002 American Institute of Physics.
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77.70.+a Pyroelectric and electrocaloric effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
77.55.-g Dielectric thin films

Porosity effect on the dielectric constant and thermomechanical properties of organosilicate films

Junjun Liu, Dongwen Gan, Chuan Hu, Michael Kiene, Paul S. Ho, Willi Volksen, and Robert D. Miller

Appl. Phys. Lett. 81, 4180 (2002); http://dx.doi.org/10.1063/1.1525054 (3 pages) | Cited 20 times

Online Publication Date: 19 November 2002

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This letter reports a study of the porosity effect on material properties of methylsilsesquioxane films, including the dielectric constant, thermal conductivity, and thermal stress behavior. In a porosity range from 0% to 50%, both the dielectric constant and thermal conductivity decreased with increasing porosity and no significant change was observed at the percolation point where pores became interconnected. In comparison, the stress–temperature slope also decreased with porosity, but as the porosity approached the percolation point, the slope showed a large drop of 40%, indicating a significant degradation of the thermomechanical properties due to percolation of pores. Assuming the coefficients of thermal expansion remain at 17 ppm/°C within the porosity range, the change in the stress–temperature slope corresponds to a decrease of the biaxial modulus from 7 to 5 GPa around the percolation point. © 2002 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Jd Polymers; organic compounds
68.60.-p Physical properties of thin films, nonelectronic
68.55.-a Thin film structure and morphology
77.22.Ch Permittivity (dielectric function)
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
65.40.De Thermal expansion; thermomechanical effects
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Interfacial oxide formation and oxygen diffusion in rare earth oxide–silicon epitaxial heterostructures

V. Narayanan, S. Guha, M. Copel, N. A. Bojarczuk, P. L. Flaitz, and M. Gribelyuk

Appl. Phys. Lett. 81, 4183 (2002); http://dx.doi.org/10.1063/1.1524692 (3 pages) | Cited 19 times

Online Publication Date: 19 November 2002

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We report on controlled interfacial oxide formation within epitaxial (LaxY1−x)2O3/Si(111) heterostructures under UHV environments. Results indicate that exposure of these epitaxial films to molecular oxygen right after deposition results in the formation of an amorphous interfacial layer thicker than that expected when a bare silicon surface is exposed to molecular oxygen under the same conditions. The results imply significant oxygen diffusion through the epitaxial dielectric and reaction at the silicon–oxide interface. Arguments have been developed to explain these observations. © 2002 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Probing the AlxGa1−xN spatial alloy fluctuation via UV-photoluminescence and Raman at submicron scale

Leah Bergman, Xiang-Bai Chen, David McIlroy, and Robert F. Davis

Appl. Phys. Lett. 81, 4186 (2002); http://dx.doi.org/10.1063/1.1526918 (3 pages) | Cited 6 times

Online Publication Date: 19 November 2002

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We present a straightforward method for the study of alloy spatial compositional distribution at the submicron scale via photoluminescence and Raman spectroscopy. The spatial dependence of the band gap light-emission energy of AlxGa1−xN alloys at composition 0 ⩽ x ⩽ 1 was studied via deep UV-photoluminescence and Raman microscopy in order to address the issue of the spatial alloy fluctuation. The data were acquired in a random fashion from an area of ∼1 mm2 on the sample at steps of ∼1–200 μm utilizing the 244 nm laser line of probing spot size ∼300 nm radius. Our study indicates that the photoluminescence emission energy exhibits random type variations depending on locality: the alloys of composition x = 0.12, x = 0.22, x = 50, and x = 0.70 exhibit average variations of ∼10, 30, 45, and 25 meV, respectively. The photoluminescence of the pure GaN exhibits no significant spatial fluctuation. The stress contribution to the observed photoluminescence fluctuations was investigated via Raman analysis and was taken into account in order to estimate the local compositional fluctuation Δx. Our results indicate that for the higher Al composition alloys x = 0.50 and 0.70 the stress and the compositional fluctuation can be resolved, resulting in average spatial fluctuations of Δx = 0.004 and 0.002, respectively. © 2002 American Institute of Physics.
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61.66.Fn Inorganic compounds
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors

Electronic structure of the carbon nanotube tips studied by x-ray-absorption spectroscopy and scanning photoelectron microscopy

J. W. Chiou, C. L. Yueh, J. C. Jan, H. M. Tsai, W. F. Pong, I.-H. Hong, R. Klauser, M.-H. Tsai, Y. K. Chang, Y. Y. Chen, C. T. Wu, K. H. Chen, S. L. Wei, C. Y. Wen, L. C. Chen, et al.

Appl. Phys. Lett. 81, 4189 (2002); http://dx.doi.org/10.1063/1.1523152 (3 pages) | Cited 20 times

Online Publication Date: 19 November 2002

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Angle-dependent x-ray absorption near edge structure (XANES) and scanning photoelectron microscopy (SPEM) measurements have been performed to differentiate local electronic structures of the tips and sidewalls of highly aligned carbon nanotubes. The intensities of both π∗- and σ∗-band C K-edge XANES features are found to be significantly enhanced at the tip. SPEM results also show that the tips have a larger density of states and a higher C 1s binding energy than those of sidewalls. The increase of the tip XANES and SPEM intensities are quite uniform over an energy range wider than 10 eV in contrast to earlier finding that the enhancement is only near the Fermi level. © 2002 American Institute of Physics.
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73.22.Dj Single particle states
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
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Work function and thermal stability of Ti1−xAlxNy for dual metal gate electrodes

Tae-Ho Cha, Dae-Gyu Park, Tae-Kyun Kim, Se-Aug Jang, In-Seok Yeo, Jae-Sung Roh, and Jin Won Park

Appl. Phys. Lett. 81, 4192 (2002); http://dx.doi.org/10.1063/1.1523651 (3 pages) | Cited 16 times

Online Publication Date: 19 November 2002

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Work function and thermal stability of reactive sputtered Ti1−xAlxNy films were investigated for a metal gate electrode using a metal–oxide–semiconductor (MOS) structure. It is found that the work function (ΦM) values of Ti1−xAlxNy are ranged from 4.36 to 5.13 eV with a nitrogen partial flow rate (fN2). The ΦM values of Ti1−xAlxNy films, 4.36 eV for nMOS (n-Ti1−xAlxNy) and 5.10–5.13 eV for pMOS (p-Ti1−xAlxNy), may be applicable to dual metal gate electrodes. Excellent thermal stability up to 1000 °C was obtained on SiO2 as observed by the negligible change of capacitance equivalent thickness and Al 2p core level spectra for p-Ti1−xAlxNy (y ∼ 1.0,fN2 = 50%), whereas a limited stability was attained in case of n-Ti1−xAlxNy (fN2 ⩽ 40%). The p-Ti1−xAlxNy can be a good candidate for pMOS device feasibility because of good thermal stability, while the n-Ti1−xAlxNy may be applicable for nMOS gate electrode in low thermal devices using damascene gate process. © 2002 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.30.+y Surface double layers, Schottky barriers, and work functions
68.60.Dv Thermal stability; thermal effects
73.61.At Metal and metallic alloys
84.32.Tt Capacitors
85.30.Tv Field effect devices

Investigation of localized states in cadmium zinc telluride crystals by scanning photodielectric spectroscopy

V. K. Komar, V. P. Migal, O. N. Chugai, V. M. Puzikov, D. P. Nalivaiko, and N. N. Grebenyuk

Appl. Phys. Lett. 81, 4195 (2002); http://dx.doi.org/10.1063/1.1525883 (3 pages) | Cited 4 times

Online Publication Date: 19 November 2002

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A method of scanning photodielectric spectroscopy of crystals has been suggested. It is based on the measurements of small increments of the real Δϵ′ and imaginary Δϵ″ parts of effective dielectric permittivity at a smooth variation of the photoexcitation wavelength λ. The spectral functions Δϵ′(λ) and Δϵ″(λ) are presented in a complex plane, that is, in parametric view, and their characteristic points are determined. Application of this method on Cd1−xZnxTe crystals showed a possibility of determining the energy position of the localized states generated in the forbidden zone by the intrinsic structure defects. © 2002 American Institute of Physics.
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71.55.Gs II-VI semiconductors
72.40.+w Photoconduction and photovoltaic effects
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)
71.20.Nr Semiconductor compounds
77.22.Ch Permittivity (dielectric function)
72.80.Ey III-V and II-VI semiconductors

Resonant interband tunneling spin filter

David Z.-Y. Ting and Xavier Cartoixà

Appl. Phys. Lett. 81, 4198 (2002); http://dx.doi.org/10.1063/1.1524700 (3 pages) | Cited 28 times

Online Publication Date: 19 November 2002

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We propose an InAs/GaSb/AlSb-based asymmetric resonant interband tunneling diode as a spin filter. The interband design exploits large valence band spin–orbit interaction to provide strong spin selectivity, without suffering from fast hole spin relaxation. Spin filtering efficiency is also enhanced by the reduction of tunneling through quasibound states near the zone center, where spin spitting vanishes and spin selectivity is difficult. Our calculations show that, when coupled with an emitter or collector capable of lateral momentum selectivity, the asymmetric resonant interband tunneling diode can achieve significant spin filtering in conventional nonmagnetic semiconductor heterostructures under zero magnetic field. © 2002 American Institute of Physics.
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85.75.Mm Spin polarized resonant tunnel junctions
85.30.Kk Junction diodes
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.25.Mk Spin transport through interfaces

On the effects of implantation temperature in helium implanted silicon

E. Oliviero, M. L. David, M. F. Beaufort, J. F. Barbot, and A. van Veen

Appl. Phys. Lett. 81, 4201 (2002); http://dx.doi.org/10.1063/1.1525059 (3 pages) | Cited 5 times

Online Publication Date: 19 November 2002

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He+ ions were implanted into silicon with a fluence of 5×1016 cm−2 at different temperatures ranging from 473 to 1073 K. Samples were analyzed by thermal helium desorption spectroscopy and by transmission electron microscopy. As far as cavity formation is concerned, the behavior can be divided into three stages depending on the implantation temperature. However, it is found that helium release from cavities is governed by a single mechanism regardless of the implantation temperature. © 2002 American Institute of Physics.
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61.72.uf Ge and Si
81.05.Cy Elemental semiconductors
61.80.Jh Ion radiation effects
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.82.Fk Semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
68.43.Vx Thermal desorption
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Synthesis and atomic-level characterization of Ni nanoparticles in Al2O3 matrix

D. Kumar, S. J. Pennycook, A. Lupini, G. Duscher, A. Tiwari, and J. Narayan

Appl. Phys. Lett. 81, 4204 (2002); http://dx.doi.org/10.1063/1.1525052 (3 pages) | Cited 15 times

Online Publication Date: 19 November 2002

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Single domain magnetic nickel nanocrystals were embedded in alumina matrix using a pulsed-laser deposition technique. Structural characterization carried out at the atomic level using scanning transmission electron microscopy with atomic number contrast (STEM-Z) in conjunction with electron energy loss spectroscopy have revealed that the Ni particles are well separated and have interfaces with the host matrix that are atomically sharp and free of any oxide layer. An excellent correlation was found between particle sizes determined theoretically from magnetization versus field data and experimentally using STEM-Z which indicates the absence of any magnetically dead layers on the Ni nanoparticles within an experimental error of 0.1 monolayer. © 2002 American Institute of Physics.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ch Domain walls and domain structure
79.20.Uv Electron energy loss spectroscopy
75.50.Tt Fine-particle systems; nanocrystalline materials
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Procedure to induce a persistent current in superconducting cylinders or rings

H. González-Jorge, J. Peleteiro, E. Carballo, L. Romaní, and G. Domarco

Appl. Phys. Lett. 81, 4207 (2002); http://dx.doi.org/10.1063/1.1525057 (2 pages) | Cited 5 times

Online Publication Date: 19 November 2002

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A procedure to induce a persistent current in superconducting cylinders or rings was developed using a coil and a ferromagnetic core. Using the field cooling method, the current is induced from the combined effect of the coil magnetic field and the core magnetization. The proposed method was checked using four Bi-2223 samples. The main usefulness seems to be that a high persistent current can be induced using small both probe currents and coils. © 2002 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.72.-h Cuprate superconductors

Effects of Co-doping level on the microstructural and ferromagnetic properties of liquid-delivery metalorganic-chemical-vapor-deposited Ti1−xCoxO2 thin films

Nak-Jin Seong, Soon-Gil Yoon, and Chae-Ryong Cho

Appl. Phys. Lett. 81, 4209 (2002); http://dx.doi.org/10.1063/1.1525397 (3 pages) | Cited 35 times

Online Publication Date: 19 November 2002

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Polycrystalline Ti1−xCoxO2 thin films on SiO2 (200 nm)/Si (100) substrates were prepared using liquid-delivery metalorganic chemical vapor deposition, and the microstructure and ferromagnetic properties were investigated as a function of doped Co concentration. Ferromagnetic behaviors of polycrystalline films were observed at room temperature, and the magnetic and structural properties strongly depended on the Co distribution, which varied widely with doped Co concentration. The annealed Ti1−xCoxO2 thin films with x ⩽ 0.05 showed a homogeneous structure without any clusters, and pure ferromagnetic properties of thin films are only attributed to the Ti1−xCoxO2 (TCO) phases. On the other hand, in case of thin films above x = 0.05, Co1−xTix clusters having a soft magnetic (SM) property formed in a homogeneous Ti1−xCoxO2 phase, and the overall ferromagnetic (FM) properties depended on both FMTCO and SMCo–Ti. Co1−xTix clusters with about 150 nm size decreased the value of Hc (coercive field) and increased the saturation magnetic field. © 2002 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
75.50.Pp Magnetic semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
75.30.Hx Magnetic impurity interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Dd Nonmetallic ferromagnetic materials
68.55.A- Nucleation and growth

A key to room-temperature ferromagnetism in Fe-doped ZnO: Cu

S-J. Han, J. W. Song, C.-H. Yang, S. H. Park, J.-H. Park, Y. H. Jeong, and K. W. Rhie

Appl. Phys. Lett. 81, 4212 (2002); http://dx.doi.org/10.1063/1.1525885 (3 pages) | Cited 144 times

Online Publication Date: 19 November 2002

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Successful synthesis of room-temperature ferromagnetic semiconductors, Zn1−xFexO, is reported. The essential ingredient in achieving room-temperature ferromagnetism in bulk Zn1−xFexO was found to be additional Cu doping. A transition temperature as high as 550 K was obtained in Zn0.94Fe0.05Cu0.01O; the saturation magnetization at room temperature reached a value of 0.75μB per Fe. A large magnetoresistance was also observed below 100 K. © 2002 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
72.80.Ey III-V and II-VI semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
72.20.My Galvanomagnetic and other magnetotransport effects
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Realizing intrinsic piezoresponse in epitaxial submicron lead zirconate titanate capacitors on Si

V. Nagarajan, A. Stanishevsky, L. Chen, T. Zhao, B.-T. Liu, J. Melngailis, A. L. Roytburd, R. Ramesh, J. Finder, Z. Yu, R. Droopad, and K. Eisenbeiser

Appl. Phys. Lett. 81, 4215 (2002); http://dx.doi.org/10.1063/1.1516857 (3 pages) | Cited 51 times

Online Publication Date: 19 November 2002

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We report on the out-of-plane piezoelectric response (d33), measured via piezoresponse scanning force microscopy, of submicron capacitors fabricated from epitaxial PbZrxTi1−xO3 thin films. Investigations on 1 μm2 and smaller capacitors show that the substrate-induced constraint is dramatically reduced by nanostructuring. At zero field, the experimentally measured values of d33 for clamped as well as submicron capacitors are in good agreement with the predictions from thermodynamic theory. The theory also describes very well the field dependence of the piezoresponse of clamped capacitors of key compositions on the tetragonal side of the PbZrxTi1−xO3 phase diagram as well as the behavior of submicron PbZr0.2Ti0.8O3 (hard ferroelectric) capacitors. However, the field-dependent piezoresponse of submicron capacitors in compositions closer to the morphotropic phase boundary (soft ferroelectrics) is different from the behavior predicted by the theoretical calculations. © 2002 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
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors

Suppressed crystallization of Hf-based gate dielectrics by controlled addition of Al2O3 using atomic layer deposition

M.-Y. Ho, H. Gong, G. D. Wilk, B. W. Busch, M. L. Green, W. H. Lin, A. See, S. K. Lahiri, M. E. Loomans, Petri I. Räisänen, and T. Gustafsson

Appl. Phys. Lett. 81, 4218 (2002); http://dx.doi.org/10.1063/1.1522826 (3 pages) | Cited 57 times

Online Publication Date: 19 November 2002

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We demonstrate significantly improved thermal stability of the amorphous phase for hafnium-based gate dielectrics through the controlled addition of Al2O3. The (HfO2)x(Al2O3)1−x films, deposited using atomic layer deposition, exhibit excellent control over a wide range of composition by a suitable choice of the ratio between the Al and Hf precursor pulses. By this method, extremely predictable hafnium aluminate compositions are obtained, with Hf cation fractions ranging from 20% up to 100%, as measured by medium energy ion scattering. Using x-ray diffraction, we show that (HfO2)x(Al2O3)1−x films with Hf:Al ∼ 3:1 (25% Al) remain amorphous up to 900 °C, while films with Hf:Al ∼ 1:3 (75% Al) remain amorphous after a 1050 °C spike anneal. © 2002 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
77.55.-g Dielectric thin films
61.43.Er Other amorphous solids
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
68.55.Nq Composition and phase identification
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Ultrathin zirconium silicate gate dielectrics with compositional gradation formed by self-organized reactions

Heiji Watanabe

Appl. Phys. Lett. 81, 4221 (2002); http://dx.doi.org/10.1063/1.1525392 (3 pages)

Online Publication Date: 19 November 2002

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Zirconium silicate gate dielectrics with compositional gradation in depth were fabricated by in situ reoxidation of thin metal layers on oxidized Si surfaces. The silicate is composed of a trilayer structure, in which Si-rich layers are formed both at the top and the bottom of the film. The zirconium element is localized at the center of the silicate and, thus, the advantages of the silicate material can be obtained, while keeping sufficient permittivity. The compositionally graded silicates show promising electrical properties, such as a leakage current of less than 0.11 A/cm2 for an equivalent oxide thickness of 1.1 nm and an improved flatband voltage shift that is a result of postdeposition annealing and oxidation. © 2002 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
81.65.Mq Oxidation
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.22.Ch Permittivity (dielectric function)
61.72.Cc Kinetics of defect formation and annealing
68.55.Nq Composition and phase identification

Grain-boundary and crack effects on the dielectric response of high-permittivity films and ceramics

I. Rychetský, J. Petzelt, and T. Ostapchuk

Appl. Phys. Lett. 81, 4224 (2002); http://dx.doi.org/10.1063/1.1525394 (3 pages) | Cited 28 times

Online Publication Date: 19 November 2002

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Grain-boundary and crack effects on the dielectric response of high-permittivity films and ceramics were analyzed using the generalized effective-medium approximation. It was demonstrated that the brick-wall and coated spheres models, which become equivalent for a small porosity, best describe the strong reduction of the dielectric response and hardening of the soft-mode frequency recently revealed in SrTiO3 films and PbZrO3 ceramics. © 2002 American Institute of Physics.
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77.22.Ch Permittivity (dielectric function)
61.72.Mm Grain and twin boundaries
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

Characterization of silicate/Si(001) interfaces

M. Copel, E. Cartier, V. Narayanan, M. C. Reuter, S. Guha, and N. Bojarczuk

Appl. Phys. Lett. 81, 4227 (2002); http://dx.doi.org/10.1063/1.1524296 (3 pages) | Cited 27 times

Online Publication Date: 19 November 2002

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Many of the proposed high permittivity gate dielectrics for silicon-based microelectronics rely on a stack configuration, with an SiO2 buffer layer to provide an interface. We describe a means for creating gate dielectrics with a direct yttrium silicate–silicon interface through the solid-state reaction of yttria and silicon oxynitride, avoiding the preparation of an oxide-free silicon surface. Characterization by medium-energy ion scattering indicates complete consumption of the underlying oxide through silicate formation during high-temperature annealing. Furthermore, the silicate dielectric exhibits small flat-band voltage shifts, indicating low quantities of charge, without passivation steps. Creation of a silicate–silicon interfaces by a simple route may enable the study of an alternate class of dielectrics. © 2002 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.35.Ct Interface structure and roughness
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
61.72.Cc Kinetics of defect formation and annealing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Degradation of ferroelectric properties in integrated Pt/SrBi2Ta2O9/Pt capacitor by impurity diffusion from interlevel dielectric layer

Sang-Hyun Oh, Suk-Kyoung Hong, Jin Gu Kim, Jin Yong Seong, Young-Jin Park, and Deok-Won Lee

Appl. Phys. Lett. 81, 4230 (2002); http://dx.doi.org/10.1063/1.1525060 (3 pages) | Cited 4 times

Online Publication Date: 19 November 2002

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The ferroelectric properties of integrated Pt/SrBi2Ta2O9 (SBT)/Pt capacitors with boron (B)- and phosphorus (P)-doped silicate glass (BPSG) as an interlevel dielectric layer were investigated. After annealing at 800 °C to densify the BPSG, a significant reduction in remanent polarization was observed. Both transmission electron microscopy and nanoprobe energy dispersive spectroscopy analysis showed bismuth (Bi) and P interdiffusion across the interface between the SBT and BPSG layers. This strongly suggests that Pt/SBT/Pt capacitor degradation results from Bi loss in the surface region of the SBT layer, which is induced by P diffusion into the SBT. The degradation in ferroelectric properties was prevented by inserting a thin undoped silicate glass (USG) layer between the SBT and the BPSG, which blocked P diffusion. From the USG thickness dependence of the remanent polarization, P-induced degradation was also verified. © 2002 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
84.32.Tt Capacitors
68.35.Fx Diffusion; interface formation
85.50.Gk Non-volatile ferroelectric memories
77.55.-g Dielectric thin films

Modeling of Si 2p core-level shifts at Si–(ZrO2)x(SiO2)1−x interfaces

Feliciano Giustino, Angelo Bongiorno, and Alfredo Pasquarello

Appl. Phys. Lett. 81, 4233 (2002); http://dx.doi.org/10.1063/1.1526172 (3 pages) | Cited 10 times

Online Publication Date: 19 November 2002

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We model Si 2p core-level shifts at Si–(ZrO2)x(SiO2)1−x interfaces for varying Zr content x. Using a first-principles approach, we calculate Si 2p shifts for a model interface and for cluster models, and establish the validity of a linear dependence of these shifts on both the number of second-neighbor Zr atoms and the O coordination of these Zr atoms. Applying this relation to model structures of amorphous Zr silicates generated by classical molecular dynamics, we find that the Si 2p line shifts to lower binding energies with increasing Zr content x, in accord with experimental data. © 2002 American Institute of Physics.
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73.20.-r Electron states at surfaces and interfaces
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
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Exciton–exciton interaction engineering in coupled GaN quantum dots

Sergio De Rinaldis, Irene D’Amico, and Fausto Rossi

Appl. Phys. Lett. 81, 4236 (2002); http://dx.doi.org/10.1063/1.1519353 (3 pages) | Cited 13 times

Online Publication Date: 19 November 2002

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We present a fully three-dimensional study of the multiexciton optical response of vertically coupled GaN-based quantum dots via a direct-diagonalization approach. The proposed analysis is crucial in understanding the fundamental properties of few-particle/exciton interactions and, more important, may play an essential role in the design/optimization of semiconductor-based quantum information processing schemes. In particular, we focus on interdot exciton–exciton coupling, the key ingredient in recently proposed all-optical quantum processors. Our analysis demonstrates that there is a large window of realistic parameters for which both biexcitonic shift and oscillator strength are compatible with such implementation schemes. © 2002 American Institute of Physics.
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73.21.La Quantum dots
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.Gg Exciton-mediated interactions
03.67.Lx Quantum computation architectures and implementations
78.67.Hc Quantum dots

Fabrication of dot matrix, comb, and nanowire structures using laser ablation by interfered femtosecond laser beams

Yoshiki Nakata, Tatsuo Okada, and Mitsuo Maeda

Appl. Phys. Lett. 81, 4239 (2002); http://dx.doi.org/10.1063/1.1522481 (3 pages) | Cited 25 times

Online Publication Date: 19 November 2002

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A line of periodic dot structure with an interval of 6.25 μm on a gold thin film was fabricated with a single shot of interfered femtosecond laser beams split by a diffraction beam splitter. The total length of the structure was 6 mm. In addition, dot matrix and comb structures were fabricated with transportation of samples at an arbitrary speed during the process. The samples worked as transmission and reflection gratings. In addition, nanowires were fabricated by peeling the comb structure, of which the thickness was 200 nm. © 2002 American Institute of Physics.
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81.16.Mk Laser-assisted deposition
42.79.Dj Gratings

Vacuum thermionic refrigeration with a semiconductor heterojunction structure

Yoshikazu Hishinuma, Boris Y. Moyzhes, Theodore H. Geballe, and Thomas W. Kenny

Appl. Phys. Lett. 81, 4242 (2002); http://dx.doi.org/10.1063/1.1523653 (3 pages) | Cited 13 times

Online Publication Date: 19 November 2002

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We consider possibilities for refrigeration by emission of electrons into vacuum using a semiconductor layered heterostructure and applying electric field in the order of 106 V/cm. Under the influence of a strong electric field, the height of the vacuum potential barrier is significantly reduced due to the Schottky effect and penetration of electric field into the semiconductor layer allowing high emission current. Joule heating inside the semiconductor layer can be minimized by creating a heterostructure with decreasing electron affinity from the metal–semiconductor boundary to the semiconductor–vacuum boundary. We find it is possible to obtain large Peltier currents while minimizing joule heating in the semiconductor. We find it is realistic to expect cooling of 10–100 W/cm2 at room temperature and down to 100 K by adjusting the thickness, and electron affinities of the semiconductor within practical ranges. © 2002 American Institute of Physics.
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79.40.+z Thermionic emission
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Breaking and restoring a molecularly bridged metal∣quantum dot junction

Z. Hens, D. V. Tallapin, H. Weller, and D. Vanmaekelbergh

Appl. Phys. Lett. 81, 4245 (2002); http://dx.doi.org/10.1063/1.1525396 (3 pages) | Cited 13 times

Online Publication Date: 19 November 2002

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Nanometer-sized insulating quantum dots (CdSe and ZnO) have been attached to a Au(111) substrate, using molecular bridges with thiol and carboxylate end functions. We demonstrate that the quantum dots can be probed by a scanning tunneling microscope at negative substrate bias. At positive bias, however, the gold–sulfur bond is broken and the quantum dots are transferred to the tip. Individual CdSe quantum dots can be picked up by the tip and displaced on the substrate in a controlled way. © 2002 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.05.Dz II-VI semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.Ct Interface structure and roughness

Si rings, Si clusters, and Si nanocrystals—different states of ultrathin SiOx layers

L. X. Yi, J. Heitmann, R. Scholz, and M. Zacharias

Appl. Phys. Lett. 81, 4248 (2002); http://dx.doi.org/10.1063/1.1525051 (3 pages) | Cited 70 times

Online Publication Date: 19 November 2002

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Amorphous SiO/SiO2 superlattices were prepared by reactive evaporation of SiO powder in an oxygen atmosphere. Infrared absorption and photoluminescence spectra were measured as a function of annealing temperature. Three photoluminescence emission bands were observed. A band centered at 560 nm is present in as-prepared samples and vanishes for annealing above 700 °C. The second band around 760 nm to 890 nm is detected for annealing temperatures above 500 °C. A strong red luminescence is observed for annealing temperatures above 900 °C. The origin of the different photoluminescence bands and different states of the phase separation of ultrathin SiOx layers is discussed. © 2002 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.55.Hx Other solid inorganic materials
68.65.Cd Superlattices
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
61.46.-w Structure of nanoscale materials
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