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3 Dec 2001

Volume 79, Issue 23, pp. 3749-3889

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Electro-optic and electromechanical properties of poled polymer thin films

Wei Shi, Yujie J. Ding, Xiaodong Mu, Xin Yin, and Changshui Fang

Appl. Phys. Lett. 79, 3749 (2001); http://dx.doi.org/10.1063/1.1418448 (3 pages) | Cited 8 times

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A simple interferometric technique has been developed to sequentially measure the piezoelectric and electro-optic (EO) coefficient of the poled polymer films. This technique, similar to the Michelson interferometer, is based on compensating the change of the optical path due to the piezoelectric and electric-optic effect of the poled polymer films by opposite piezoelectric effect of a quartz crystal. Our technique has advantages of simplicity, high sensitivity, and improved accuracies over the previous ones. The experimental values of the EO coefficients agree with the values predicted by the two-level model. © 2001 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
78.66.Qn Polymers; organic compounds
77.55.-g Dielectric thin films
77.84.Jd Polymers; organic compounds
77.22.Ej Polarization and depolarization
77.65.Bn Piezoelectric and electrostrictive constants
78.20.Jq Electro-optical effects

1.5 kW high-peak-power vacuum ultraviolet flash lamp using a pulsed silent discharge of krypton gas

J. Kawanaka, T. Shirai, S. Kubodera, and W. Sasaki

Appl. Phys. Lett. 79, 3752 (2001); http://dx.doi.org/10.1063/1.1421419 (3 pages) | Cited 2 times

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A 1.5 kW high-peak-power discharge lamp with short emission duration of 140 ns has been developed in the vacuum ultraviolet spectral region. Our numerical calculation ensured that the peak emission at 147 nm was due to singlet excimers (1Σ), which were mainly produced via electron-collisional mixing of triplet excimers (3Σ). © 2001 American Institute of Physics.
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42.72.Bj Visible and ultraviolet sources

Recording of transmission phase gratings in glass by ion implantation

I. Bányász, M. Fried, Cs. Dücsö, and Z. Vértesy

Appl. Phys. Lett. 79, 3755 (2001); http://dx.doi.org/10.1063/1.1424468 (3 pages) | Cited 7 times

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Transmission phase gratings of grating constants of 4–12 μm have been designed and fabricated in glass via implantation of helium and nitrogen ions of energies in the 500 keV–1.6 MeV range, through photoresist masks of thickness of 3.3 μm. Multienergy implantations were applied, too. Phase profiles of the gratings were measured via interference and phase contrast microscopy and scanning electron microscopy. Quasisinusoidal profiles were obtained for the finest gratings. The highest first order diffraction efficiencies were around 20%. Dependence of the efficiencies of the gratings on the energy and dose of the implantation have been determined. © 2001 American Institute of Physics.
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42.79.Dj Gratings
42.70.Ce Glasses, quartz
61.43.Fs Glasses
42.86.+b Optical workshop techniques
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Parametric fluorescence in oxidized aluminum gallium arsenide waveguides

A. De Rossi, V. Berger, M. Calligaro, G. Leo, V. Ortiz, and X. Marcadet

Appl. Phys. Lett. 79, 3758 (2001); http://dx.doi.org/10.1063/1.1424063 (3 pages) | Cited 19 times

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Parametric fluorescence in low-loss oxidized aluminum gallium arsenide heterostructure waveguides is quantitatively analyzed. A parametric fluorescence efficiency as high as 6×10−7 W/W has been measured in a 3.2-mm-long waveguide. This corresponds to a normalized conversion efficiency, scaled with the waveguide length, of about 1000% cm−2 W−1, eight times higher than with LiNbO3 waveguides. This opens the perspective of a microoptical parametric oscillation threshold below 100 mW. © 2001 American Institute of Physics.
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42.65.Wi Nonlinear waveguides
42.65.Yj Optical parametric oscillators and amplifiers
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.55.Cr III-V semiconductors
42.82.Et Waveguides, couplers, and arrays

Role of femtosecond pulses in distinguishing third- and fifth-order nonlinearity for semiconductor-doped glasses

K. S. Bindra and A. K. Kar

Appl. Phys. Lett. 79, 3761 (2001); http://dx.doi.org/10.1063/1.1424462 (3 pages) | Cited 19 times

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We report Z-scan experiments at a frequency below the band gap of semiconductor-doped glasses using 100 fs laser pulses. A large contribution from the positive third-order nonlinearity is observed in complete contrast with the picosecond z-scan experiments. The third- and fifth-order nonlinearity for semiconductor-doped glasses can be estimated from z-scans for ps and fs pulses. © 2001 American Institute of Physics.
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42.70.Ce Glasses, quartz
42.65.An Optical susceptibility, hyperpolarizability
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.47.-p Spectroscopy of solid state dynamics
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Electrical activation of B in the presence of boron-interstitials clusters

Giovanni Mannino, Sandro Solmi, Vittorio Privitera, and Massimo Bersani

Appl. Phys. Lett. 79, 3764 (2001); http://dx.doi.org/10.1063/1.1423775 (3 pages) | Cited 5 times

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Boron marker-layer structures have been used to analyze the evolution of boron-interstitial clusters (BICs) formed during transient enhanced diffusion. Our approach is based on the measure of B activation by spreading resistance profiling after annealing of Si implantation damage. We investigated a wide range of implant conditions in terms of defect densities below and above the amorphization threshold of Si. We found a common behavior of BICs in terms of trapping and release processes of B atoms. The BICs density as a function of time for different concentration ratios of I and B has been determined. © 2001 American Institute of Physics.
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61.72.Yx Interaction between different crystal defects; gettering effect
61.72.uf Ge and Si
71.55.Cn Elemental semiconductors
66.30.J- Diffusion of impurities
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters

Band-gap energies of sol-gel-derived SrTiO3 thin films

Dinghua Bao, Xi Yao, Naoki Wakiya, Kazuo Shinozaki, and Nobuyasu Mizutani

Appl. Phys. Lett. 79, 3767 (2001); http://dx.doi.org/10.1063/1.1423788 (3 pages) | Cited 58 times

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Band-gap energies of sol-gel-derived SrTiO3 thin films were studied in terms of annealing temperature and film thickness. The band-gap energies of highly crystallized films were comparable to those of single crystals reported, whereas for poor-crystallized films, their band-gap energy values were much larger than those of single crystals. The larger band-gap energy shift was believed to be mainly due to both quantum size effect and existence of amorphous phase in thin films. The band-gap energies also showed a strong dependence on film thickness. There was a critical film thickness (∼200 nm), above which the films had band-gap energies close to those of crystals or bulks, but below that, the values shifted largely, which can be attributed to the influence of crystallinity of thin films. Such a thickness effect of band-gap energy should be of high interest in optical device applications. © 2001 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
71.20.Ps Other inorganic compounds
77.55.-g Dielectric thin films
61.72.Cc Kinetics of defect formation and annealing
42.70.-a Optical materials

Near-infrared electroluminescence from conjugated polymer/lanthanide porphyrin blends

Benjamin S. Harrison, Timothy J. Foley, Mohamed Bouguettaya, James M. Boncella, John R. Reynolds, Kirk S. Schanze, Joonbo Shim, Paul H. Holloway, G. Padmanaban, and S. Ramakrishnan

Appl. Phys. Lett. 79, 3770 (2001); http://dx.doi.org/10.1063/1.1421413 (3 pages) | Cited 55 times

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Near-infrared-emitting polymer light-emitting diodes (PLEDs) have been fabricated using blends of conjugated polymers and lanthanide tetraphenylporphyrin complexes. Host polymers include MEH–PPV and a bis-alkoxy-substituted poly(p-phenylene) (PPP–OR11), and the lanthanide complexes include Yb(TPP)acac and Er(TPP)acac (where TPP = 5,10,15,20-tetraphenylporphyrin and acac=acetylacetonate). Electroluminescence (EL) is observed at 977 nm from devices fabricated using MEH–PPV or PPP–OR11 blended with Yb(TPP)acac, and EL is observed at 1560 nm from a device fabricated using a blend of MEH–PPV and Er(TPP)acac. Visible EL from the host polymers is strongly suppressed in all of the devices, however, in the device fabricated using the PPP–OR11 polymer blue emission from the host is completely quenched. Very efficient quenching of the EL from the host in the PPP–OR11 device is believed to occur due to efficient Förster energy transfer, which is facilitated by the excellent spectral overlap between the PPP–OR11 fluorescence and the Soret absorption band of the TPP ligand. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices

Amorphous carbon nanowires investigated by near-edge-x-ray-absorption-fine-structures

Y. H. Tang, P. Zhang, P. S. Kim, T. K. Sham, Y. F. Hu, X. H. Sun, N. B. Wong, M. K. Fung, Y. F. Zheng, C. S. Lee, and S. T. Lee

Appl. Phys. Lett. 79, 3773 (2001); http://dx.doi.org/10.1063/1.1425462 (3 pages) | Cited 16 times

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The structure and bonding of amorphous carbon nanowires and amorphous carbon nanowires-converted multiwalled carbon nanotubes have been investigated with carbon K-edge near-edge x-ray absorption fine structure using surface-sensitive total electron yield, and bulk-sensitive fluorescence yield. The results strongly support that amorphous carbon nanowire is a precursor to multiwalled carbon nanotubes. © 2001 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
61.43.Er Other amorphous solids
78.70.Dm X-ray absorption spectra

Intrinsic stress evolution in aluminum nitride thin films and the influence of multistep processing

Ashok Rajamani, Rod Beresford, and Brian W. Sheldon

Appl. Phys. Lett. 79, 3776 (2001); http://dx.doi.org/10.1063/1.1420774 (3 pages) | Cited 13 times

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Curvature measurements were used to investigate intrinsic stresses in AlN thin films grown by molecular beam epitaxy. In situ stress evolution experiments show that tensile stress is generated at the time where individual islands coalesce into a continuous film, and for some time after coalescence. Compressive stress is also generated both before and after coalescence. Introducing an intermediate annealing stage appears to reduce tensile stress evolution after coalescence, ultimately increasing the final intrinsic compressive stress. The maximum reduction in the tensile intrinsic stress is obtained when the sample is annealed at roughly the time where the islands coalesce into a continuous film.© 2001 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.60.Bs Mechanical and acoustical properties
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Photoluminescence of GaN grown by molecular-beam epitaxy on a freestanding GaN template

M. A. Reshchikov, D. Huang, F. Yun, L. He, H. Morkoç, D. C. Reynolds, S. S. Park, and K. Y. Lee

Appl. Phys. Lett. 79, 3779 (2001); http://dx.doi.org/10.1063/1.1421421 (3 pages) | Cited 19 times

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Photoluminescence (PL) studies were performed on a 1.5-μm-thick GaN layer grown by molecular-beam epitaxy on a freestanding GaN template that in turn was grown by hydride vapor-phase epitaxy. PL spectra from both the epilayer and the substrate contain a plethora of sharp peaks related to excitonic transitions. We identified the main peaks in the PL spectrum. Taking advantage of the observation of donor bound exciton peaks and their associated two-electron satellites, we have determined the binding energies of two distinct shallow donors (28.8 and 32.6 meV), which are attributed to Si and O, respectively. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
68.55.-a Thin film structure and morphology

Microstructure and optical properties of scandium oxide thin films prepared by metalorganic chemical-vapor deposition

Z. Xu, A. Daga, and Haydn Chen

Appl. Phys. Lett. 79, 3782 (2001); http://dx.doi.org/10.1063/1.1424072 (3 pages) | Cited 9 times

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Dense, high-index, and reproducible scandium oxide (Sc2O3) thin films with high mechanical strength were grown on glass substrates by metalorganic chemical-vapor deposition. The influence of deposition temperature on the microstructure evolution and optical properties of Sc2O3 thin films was investigated by x-ray diffraction, scanning electron microscopy, atomic-force microscopy, transmission electron microscopy, and spectrophotometry. A close relationship between microstructure and optical properties was found for Sc2O3 thin films prepared at different deposition temperatures. © 2001 American Institute of Physics.
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78.66.Nk Insulators
42.79.Wc Optical coatings
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.60.Bs Mechanical and acoustical properties
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Ha Other nonmetallic inorganics

Reversible photoinduced spectral change in Eu2O3 at room temperature

Shosuke Mochizuki, Tauto Nakanishi, Yuya Suzuki, and Kimihiro Ishi

Appl. Phys. Lett. 79, 3785 (2001); http://dx.doi.org/10.1063/1.1425064 (3 pages) | Cited 20 times

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When Eu2O3 powder compact and film are irradiated with ultraviolet (UV) laser light in a vacuum, their photoluminescence (PL) spectra change from a red sharp-line structure to a white broad band, which can be clearly seen with the naked eye. After removing the UV laser light, the white PL continues for more than several months at room temperature under room light, in spite of any changes of atmosphere. By irradiating with the same UV laser light at room temperature under O2 gas atmosphere, the original red PL state reappears. Such a reversible phenomenon may well yield materials for white-light-emitting devices and erasable optical storage. © 2001 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
42.70.Ln Holographic recording materials; optical storage media
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.66.Nk Insulators
61.82.Ms Insulators

Influence of Mg doping on structural defects in AlGaN layers grown by metalorganic chemical vapor deposition

Hyung Koun Cho, Jeong Yong Lee, Seong Ran Jeon, and Gye Mo Yang

Appl. Phys. Lett. 79, 3788 (2001); http://dx.doi.org/10.1063/1.1424471 (3 pages) | Cited 8 times

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Influence of Mg doping on structural defects in Al0.13Ga0.87N layers grown on sapphire substrates by metalorganic chemical vapor deposition were studied using transmission electron microscopy. By increasing the Mg source flow rate, the reduction of dislocation density occurred up to the Mg source flow rate of 0.103 μmol/min. While the vertical type inversion domain boundaries (IDBs) were observed in the Al0.13Ga0.87N layers grown with the low Mg source flow rate, the IDBs in the Al0.13Ga0.87N layers grown with the high Mg source flow rate have horizontally multifaceted shapes. The change of polarity by the IDBs of horizontal type also resulted in the 180° rotation of pyramidal defects within the same AlGaN layer. © 2001 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.uj III-V and II-VI semiconductors
61.72.Yx Interaction between different crystal defects; gettering effect

Thermoelectric figure of merit for parallel transport in superlattices

V. B. Antonyuk, A. G. Mal’shukov, Zhongshui Ma, and K. A. Chao

Appl. Phys. Lett. 79, 3791 (2001); http://dx.doi.org/10.1063/1.1421083 (3 pages)

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We have calculated the thermoelectric figure of merit of a superlattice with the temperature gradient and the electric field applied parallel to the interfaces. Including the heat flow between the barriers and the wells, we have derived the temperature distribution in the sample, from which the expressions of the resultant thermal conductivity and hence the figure of merit are obtained. Our numerical result provides relevant information for achieving a high figure of merit. © 2001 American Institute of Physics.
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73.50.Lw Thermoelectric effects
73.63.-b Electronic transport in nanoscale materials and structures

Polariton and free-exciton-like photoluminescence in ZnO

D. C. Reynolds, D. C. Look, B. Jogai, and T. C. Collins

Appl. Phys. Lett. 79, 3794 (2001); http://dx.doi.org/10.1063/1.1412435 (3 pages) | Cited 35 times

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An unusual photoluminescence line X has been observed in ZnO at an energy between that of the common donor-bound excitons (DBEs) and the free excitons (FEs). In the presence of a high carrier concentration, induced by a second below-band gap laser, the DBEs decrease in intensity, due to screening, and both the FEs and X increase. Thus, X has free-exciton, rather than bound-exciton, character. However, its electric-field vector lies in the plane perpendicular to the c axis, as is also found for the DBEs. The appearance of X is discussed in terms of the polariton picture. © 2001 American Institute of Physics.
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78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
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Degradation in metal-oxide-semiconductor structure with ultrathin gate oxide due to external compressive stress

Chao-Chi Hong and Jenn-Gwo Hwu

Appl. Phys. Lett. 79, 3797 (2001); http://dx.doi.org/10.1063/1.1420491 (3 pages) | Cited 9 times

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The effect of external stress on metal-oxide-semiconductor (MOS) structure with ultrathin gate oxide (∼1.5 nm) was studied. J–V characteristics of fresh and stressed samples revealed that the tensile stress had little effect on J–V curves, whereas the compressive stress obviously increased the leakage current by about several hundred in percentages with respect to the fresh sample, in both positive and negative gate biases. This increase in leakage current was suggested to be attributed to the increase of interface states and silicon bulk traps under external compressive stress in the MOS device with an inherent tensile stressed silicon. In addition, we also found that once the device was damaged by the previously applied compressive stress, the second applied compressive stress of the same magnitude would not create more damage unless the device was breakdown. © 2001 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.At Surface states, band structure, electron density of states

Light-induced increase in the open-circuit voltage of thin-film heterogeneous silicon solar cells

K. Lord, B. Yan, J. Yang, and S. Guha

Appl. Phys. Lett. 79, 3800 (2001); http://dx.doi.org/10.1063/1.1420778 (3 pages) | Cited 17 times

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We observe a significant light-induced increase in open-circuit voltage, Voc, of solar cells whose intrinsic (i) layer consists of an amorphous and microcrystalline mixed phase. The increase depends on the i-layer thickness and light-soaking intensity. An increase of as large as 150 mV or 20% of the original Voc is observed. The original Voc is restored after subsequent thermal annealing. The possible mechanism for the Voc increase is discussed. © 2001 American Institute of Physics.
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84.60.Jt Photoelectric conversion
61.72.Cc Kinetics of defect formation and annealing
72.40.+w Photoconduction and photovoltaic effects

Strain-induced piezoelectric field effects on light emission energy and intensity from AlInGaN/InGaN quantum wells

M. E. Aumer, S. F. LeBoeuf, B. F. Moody, and S. M. Bedair

Appl. Phys. Lett. 79, 3803 (2001); http://dx.doi.org/10.1063/1.1418453 (3 pages) | Cited 15 times

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We report on the effects of the piezoelectric field and well width on the transition energy and intensity for InGaN quantum well structures with GaN or AlInGaN quaternary barriers. It was found that the emission energy of compressively strained GaN/In0.08Ga0.92N quantum wells exhibits a strong well width dependence not accounted for by quantum confinement subband energy shifting alone. However, for unstrained quantum well layers with quaternary barriers, no emission energy dependence on width was observed due to the elimination of the piezoelectric field, which was measured to be at least 0.6 MV/cm for the strained quantum wells. Furthermore, the unstrained quantum wells demonstrated a higher intensity than their strained counterparts for all quantum well widths investigated. The current data will help clarify the origin of emission in InGaN quantum wells. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.67.De Quantum wells
77.65.Ly Strain-induced piezoelectric fields
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Mechanism of photoluminescence in GaN/Al0.2Ga0.8N superlattices

C. H. Chen, H. J. Chang, Y. F. Chen, W. S. Fann, H. X. Jiang, and J. Y. Lin

Appl. Phys. Lett. 79, 3806 (2001); http://dx.doi.org/10.1063/1.1420495 (3 pages) | Cited 2 times

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We present photoluminescence (PL) and time-resolved photoluminescence measurements in GaN/Al0.2Ga0.8N superlattices grown by metalorganic chemical vapor deposition under the optimal GaN-like growth conditions. We found that the carrier confinement of our samples is better than most of the previous reports. The dependence of the PL emission energy and intensity on temperature, in the low temperature regime, is consistent with recombination mechanisms involving localized states attributed to a small degree of interface fluctuations. Picosecond time-resolved photoluminescence spectroscopy has been employed to probe the well-width dependence of the lifetime of these superlattices. We see that the recombination lifetime increases with the decrease of well width. This behavior can be interpreted by the fact that the effect of localization keeping carriers away from nonradiative pathways can be enhanced by a decrease in the well width. This explanation is consistent with the temperature-dependent PL data. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.21.Cd Superlattices
78.47.-p Spectroscopy of solid state dynamics

Fabrication of silicon thin films with defects below detection limit of electron spin resonance for solar cells by high-speed zone-melting crystallization of amorphous silicon

Manabu Ihara, Shuhei Yokoyama, Chiaki Yokoyama, Koichi Izumi, and Hiroshi Komiyama

Appl. Phys. Lett. 79, 3809 (2001); http://dx.doi.org/10.1063/1.1421231 (3 pages) | Cited 5 times

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Silicon (Si) thin films with very-low defect density for solar cells were fabricated by using high-speed (0.7–4.5 mm/s) zone-melting crystallization (ZMC) of amorphous-silicon (a-Si) thin films, resulting in films that had defects below the detection limit of electron spin resonance (ESR). In this letter, poly-crystalline silicon (poly-Si) films for zone-melting recrystallization (ZMR) and a-Si films for ZMC were each sandwiched between two SiO2 films. The Si films were 0.3–2.0 μm thick, the top SiO2 films were 0.35–1.5 μm thick, and the bottom SiO2 films were 0.18–1.2 μm thick. The a-Si ZMC films had higher crystal quality than did the poly-Si ZMR films. Over 90% of the grains in the a-Si ZMC films had preferred (100) orientation when the films were formed at scan speeds 0.7–4.5 mm/s. Transmission electron microscopy (TEM) revealed that neither distinct grain boundaries nor defects were visible in the a-Si ZMC films within the 9-μm-diam observation field. The a-Si ZMC films fabricated from the a-Si films with the thickness smaller than 1 μm had no voids. Such a low defect density indicates that silicon thin-film solar cells with high efficiency can be fabricated by using such very-low defect density silicon thin films. © 2001 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.10.Fq Growth from melts; zone melting and refining
76.30.-v Electron paramagnetic resonance and relaxation
84.60.Jt Photoelectric conversion
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Single-electron transistor based on a silicon-on-insulator quantum wire fabricated by a side-wall patterning method

D. H. Kim, S.-K. Sung, J. S. Sim, K. R. Kim, J. D. Lee, B.-G. Park, B. H. Choi, S. W. Hwang, and D. Ahn

Appl. Phys. Lett. 79, 3812 (2001); http://dx.doi.org/10.1063/1.1421081 (3 pages) | Cited 15 times

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We propose and implement a promising fabrication technology for geometrically well-defined single-electron transistors based on a silicon-on-insulator quantum wire and side-wall depletion gates. The 30-nm-wide silicon quantum wire is defined by a combination of conventional photolithography and process technology, called a side-wall patterning method, and depletion gates for two tunnel junctions are formed by the doped polycrystalline silicon sidewall. The good uniformity of the wire suppresses unexpected potential barriers. The fabricated device shows clear single-electron tunneling phenomena by an electrostatically defined single island at liquid nitrogen temperature and insensitivity of the Coulomb oscillation period to gate bias conditions. © 2001 American Institute of Physics.
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85.35.Gv Single electron devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.63.Nm Quantum wires
85.40.Hp Lithography, masks and pattern transfer

Investigation of oxidation mechanism for ohmic formation in Ni/Au contacts to p-type GaN layers

Chi-Sen Lee, Yow-Jon Lin, and Ching-Ting Lee

Appl. Phys. Lett. 79, 3815 (2001); http://dx.doi.org/10.1063/1.1425065 (3 pages) | Cited 24 times

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To investigate the function and mechanisms of oxidation, we present the ohmic performances for Ni/Au contacts to p-type GaN treated with various conditions. When the p-type GaN sample was preoxidized at 750 °C for 30 min in air ambient and then treated with (NH4)2Sx solution, we routinely obtained a specific contact resistance of 4.5×10−6 Ω cm2 for the Ni/Au contacts to samples alloyed at 500 °C for 10 min in air ambient. The fact that, in this configuration, ohmic performance improved one order of magnitude [compared with (NH4)2Sx surface treatment], is attributable to the strengthened formation of GaOx (aided by the preoxidation process), as well as the fact that more holes were induced on the oxidation-free p-type GaN surface. © 2001 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
81.65.Mq Oxidation
73.40.Cg Contact resistance, contact potential
79.60.Jv Interfaces; heterostructures; nanostructures
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Beam model for calculating magnetostriction strains in thin films and multilayers

Robert C. Wetherhold and Harsh Deep Chopra

Appl. Phys. Lett. 79, 3818 (2001); http://dx.doi.org/10.1063/1.1421224 (3 pages) | Cited 12 times

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A standard technique to measure the magnetostriction strain in thin films involves measurement of the end deflection or slope of cantilever beams using optical deflectometry or capacitive methods. This article presents a general beam model for inferring magnetostriction strain from the end deflection or slope data. This model greatly extends the range of applicability over existing shell models, allowing for inference of magnetostriction strains for practical film/substrate thickness ratios that are important in microelectromechanical systems (MEMS) and bio-microelectromechanical systems (bio-MEMS). If the properties of individual layers are known, the beam theory can be used to design multilayer MEMS or bio-MEMs beams over a full range of thickness ratios. © 2001 American Institute of Physics.
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75.80.+q Magnetomechanical effects, magnetostriction
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Temperature dependent switching properties of patterned 200 nm Ni81Fe19 elements

Jian Li, Jing Shi, and Saied Tehrani

Appl. Phys. Lett. 79, 3821 (2001); http://dx.doi.org/10.1063/1.1424470 (3 pages) | Cited 18 times

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Quasistatic magnetization switching of patterned 200 nm wide Ni81Fe19 elements has been systematically studied over a wide range of temperatures. In large aspect-ratio elements, the switching field between two bistable magnetization states decreases linearly as the temperature increases, in good agreement with thermally activated nucleation theory. In small aspect-ratio elements, however, switching occurs through a third stable state: the magnetization vortex state. Although the switching mechanism is drastically different in these small aspect-ratio structures, the switching fields also are linearly dependent on temperature. © 2001 American Institute of Physics.
Show PACS
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
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