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19 Jan 2004

Volume 84, Issue 3, pp. 311-452

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 311 (2004); http://dx.doi.org/10.1063/1.1640784 (3 pages)

Ken-ichi Kawamura, Masahiro Hirano, Toshio Kurobori, Daizyu Takamizu, Toshio Kamiya, and Hideo Hosono
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Femtosecond-laser-encoded distributed-feedback color center laser in lithium fluoride single crystals

Ken-ichi Kawamura, Masahiro Hirano, Toshio Kurobori, Daizyu Takamizu, Toshio Kamiya, and Hideo Hosono

Appl. Phys. Lett. 84, 311 (2004); http://dx.doi.org/10.1063/1.1640784 (3 pages) | Cited 36 times

Online Publication Date: 14 January 2004

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Laser-active F2 centers were produced in lithium fluoride (LiF) at a concentration of 2×1018 cm−3 by irradiating focused femtosecond (fs) laser pulses from a mode-locked titanium sapphire laser (wavelength ∼ 800 nm, emission pulse duration ∼ 100 fs). This technique was used to write waveguides embedded in LiF crystals. A refractive index change estimated from a guide propagation method was approximately +1% at a wavelength of 633 nm. Refractive index-modulated volume-type gratings were also encoded inside LiF crystals by a single interfered fs laser pulse. The distributed feedback laser structure was fabricated using the gratings thus encoded, which exhibited a room-temperature F2-color center laser oscillation at 707 nm. This demonstrates a DFB color center laser operating at room temperature utilizing photon written, permanent Bragg gratings. © 2004 American Institute of Physics.
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42.60.By Design of specific laser systems
42.40.My Applications
42.70.-a Optical materials

High-temperature, high-power, continuous-wave operation of buried heterostructure quantum-cascade lasers

A. Evans, J. S. Yu, J. David, L. Doris, K. Mi, S. Slivken, and M. Razeghi

Appl. Phys. Lett. 84, 314 (2004); http://dx.doi.org/10.1063/1.1641174 (3 pages) | Cited 71 times

Online Publication Date: 14 January 2004

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We report cw operation of buried heterostructure quantum-cascade lasers (λ=6 μm) using a thick electroplated Au top contact layer and epilayer-up bonding on a copper heat sink up to a temperature of 333 K (60 °C). The high cw optical output powers of 446 mW at 293 K, 372 mW at 298 K, and 30 mW at 333 K are achieved with threshold current densities of 2.19, 2.35, and 4.29 kA/cm2 respectively, for a high-reflectivity-coated, 9-μm-wide and 3-mm-long laser. © 2004 American Institute of Physics.
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42.60.Pk Continuous operation
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Highly efficient continuous-wave operation at 1030 and 1075 nm wavelengths of LD-pumped Yb3+:Y2O3 ceramic lasers

Kazunori Takaichi, Hideki Yagi, Jianren Lu, Jean-Francois Bisson, Akira Shirakawa, Ken-ichi Ueda, Takagimi Yanagitani, and Alexander A. Kaminskii

Appl. Phys. Lett. 84, 317 (2004); http://dx.doi.org/10.1063/1.1641514 (3 pages) | Cited 35 times

Online Publication Date: 14 January 2004

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Room-temperature cw laser oscillations at 1030 and 1075 nm wavelengths were demonstrated for the TEM00 mode with Yb3+:Y2O3 ceramics by LD-pumping. A maximum extraction efficiency of 72% at 1075 nm lasing wavelengths and of 45% at 1030 nm lasing wavelengths were observed. © 2004 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
68.37.Lp Transmission electron microscopy (TEM)
42.60.By Design of specific laser systems

Near-diffraction-limited coherent emission from large aperture antiguided vertical-cavity surface-emitting laser arrays

Ling Bao, Nam-Heon Kim, Luke J. Mawst, N. N. Elkin, V. N. Troshchieva, D. V. Vysotsky, and A. P. Napartovich

Appl. Phys. Lett. 84, 320 (2004); http://dx.doi.org/10.1063/1.1640799 (3 pages) | Cited 20 times

Online Publication Date: 14 January 2004

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We demonstrate that in-phase mode operation with a near-diffraction-limited beam can be realized in large aperture (up to 100 elements) antiguided vertical-cavity surface-emitting laser (VCSEL) arrays. A selective etching process with two-step metalorganic chemical vapor deposition is used for fabrication of the antiguided VCSEL array structures. Modal discrimination is enhanced by intentionally choosing a GaAs cap thickness so as to introduce suitable loss to array interelement regions. Far field patterns indicate in-phase mode operation from both triangular and rectangular geometry antiguided VCSEL arrays, which is in good agreement with theory. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.60.-q Optoelectronic devices
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Dynamic array of dark optical traps

Vincent Ricardo Daria, Peter John Rodrigo, and Jesper Glückstad

Appl. Phys. Lett. 84, 323 (2004); http://dx.doi.org/10.1063/1.1642752 (3 pages) | Cited 18 times

Online Publication Date: 14 January 2004

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A dynamic array of dark optical traps is generated for simultaneous trapping and arbitrary manipulation of multiple low-index microstructures. The dynamic intensity patterns forming the dark optical trap arrays are generated using a nearly loss-less phase-to-intensity conversion of a phase-encoded coherent light source. Two-dimensional input phase distributions corresponding to the trapping patterns are encoded using a computer-programmable spatial light modulator, enabling each trap to be shaped and moved arbitrarily within the plane of observation. We demonstrate the generation of multiple dark optical traps for simultaneous manipulation of hollow “air-filled” glass microspheres suspended in an aqueous medium. © 2004 American Institute of Physics.
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37.10.Vz Mechanical effects of light on atoms, molecules, and ions
42.79.Hp Optical processors, correlators, and modulators

Electra: Repetitively pulsed, 500 J, 100 ns, KrF oscillator

M. F. Wolford, F. Hegeler, M. C. Myers, J. L. Giuliani, and J. D. Sethian

Appl. Phys. Lett. 84, 326 (2004); http://dx.doi.org/10.1063/1.1641513 (3 pages) | Cited 8 times

Online Publication Date: 14 January 2004

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Electra is a repetitively pulsed, double-sided, electron-beam pumped krypton fluoride laser. Electra has recently operated as an oscillator with an output pulse of 510 J, with 100 ns pulse duration for single shots. At a 1 Hz repetition rate for a ten-shot burst, the laser output averaged 500 J per shot. The dependence of the laser energy on the partial pressures of Kr, Ar, and F2 were examined. Over a 10 to 30 psi total pressure range, the laser output energy decreases with decreasing argon concentration. Specifically, the laser output drops slightly as the argon concentration reduces from 60% to 40%, and then drops more noticeably as it is reduced to 0%. For the 60% Ar case, the optimal fluorine concentration is 0.25%, with a significant falloff in the laser energy from 0.25% to 0.1% and a gradual falloff from 0.25% to 0.7% fluorine. The present burst results indicate that the KrF kinetics is not very sensitive to the gas temperature at a total pressure of 20 psi. © 2004 American Institute of Physics.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems

Discrete wavelength tunable laser using microelectromechanical systems technology

X. M. Zhang, A. Q. Liu, D. Y. Tang, and C. Lu

Appl. Phys. Lett. 84, 329 (2004); http://dx.doi.org/10.1063/1.1639130 (3 pages) | Cited 20 times

Online Publication Date: 14 January 2004

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A discrete wavelength tunable laser has been demonstrated using microelectromechanical systems (MEMS) technology. The laser system is formed by integrating a semiconductor laser, a single-mode optical fiber, and a MEMS mirror onto a single chip. It has overall dimensions of 1.5 mm×1 mm×0.6 mm (not including the optical fiber), and can be tuned to sweep a wavelength range of 13.5 nm within 1 ms. Unlike the conventional continuously tunable lasers, the laser system enables discrete wavelength tuning by making use of a short external cavity and weak feedback. © 2004 American Institute of Physics.
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42.60.By Design of specific laser systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.60.Fc Modulation, tuning, and mode locking
42.79.Bh Lenses, prisms and mirrors
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Sa Microcavity and microdisk lasers
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Hydrogen ion beam generated by a current-free double layer in a helicon plasma

C. Charles

Appl. Phys. Lett. 84, 332 (2004); http://dx.doi.org/10.1063/1.1643548 (3 pages) | Cited 35 times

Online Publication Date: 14 January 2004

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A current-free double layer in an expanding hydrogen helicon discharge (13.56 MHz) has been discovered by measuring a beam of hydrogen ions at the low potential side of the double layer. The ion beam is supersonic ( ∼ 2.1cs) and is detected using a retarding field energy analyzer positioned downstream of the double layer for pressures below a few mTorr and for radio frequency powers up to 1800 W. © 2004 American Institute of Physics.
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52.59.-f Intense particle beams and radiation sources
52.80.Pi High-frequency and RF discharges
52.40.Kh Plasma sheaths
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Carrier lifetime in conductive and vanadium-doped 6H-SiC substrates

G. Tamulaitis, I. Yilmaz, M. S. Shur, T. Anderson, and R. Gaska

Appl. Phys. Lett. 84, 335 (2004); http://dx.doi.org/10.1063/1.1641172 (3 pages) | Cited 7 times

Online Publication Date: 14 January 2004

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Conductive undoped and semi-insulating vanadium-doped 6H-SiC substrates were studied using the light-induced transient grating technique and photoluminescence (PL) spectroscopy. Carrier lifetime of 400±10 ps and diffusion coefficient of 2.7±0.2 cm2 s−1 were obtained for the nominally undoped wafer, while the corresponding parameters for the V-doped wafer were estimated to be 130±5 ps and 0.9±0.5 cm2 s−1, respectively. The peak PL intensity in the vanadium-doped wafers is more than three orders of magnitude lower than that in nominally undoped wafers. Low-temperature cw PL spectra revealed a band peaked at 507 nm, which is caused by V doping. © 2004 American Institute of Physics.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
66.30.-h Diffusion in solids
78.55.Kz Solid organic materials

Conformal thin-film silicon nitride deposited by hot-wire chemical vapor deposition

Qi Wang, Scott Ward, Lynn Gedvilas, Brian Keyes, Errol Sanchez, and Shulin Wang

Appl. Phys. Lett. 84, 338 (2004); http://dx.doi.org/10.1063/1.1640803 (3 pages) | Cited 13 times

Online Publication Date: 14 January 2004

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We have studied silicon nitride thin films deposited by hot-wire chemical vapor deposition as a function of the substrate temperature and hydrogen dilution. We found that adding H2 to the process significantly enhances silicon nitride film deposition. High-quality films can be grown at low substrate temperatures (<350 °C). At optimized conditions, a 500-Å-thick silicon nitride film gives a nearly 100% surface coverage on a 100 nm scale object. H dilution dramatically increases the NH2 radicals in the process and leads to conformal films. © 2004 American Institute of Physics.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators

Use of deposition pressure to control residual stress in polycrystalline SiC films

Xiao-An Fu, Ronald Jezeski, Christian A. Zorman, and Mehran Mehregany

Appl. Phys. Lett. 84, 341 (2004); http://dx.doi.org/10.1063/1.1640781 (3 pages) | Cited 21 times

Online Publication Date: 14 January 2004

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Polycrystalline silicon carbide (poly-SiC) thin films were grown in a large-volume, low pressure chemical vapor deposition furnace using dichlorosilane and acetylene precursors. The deposition temperature was fixed at 900 °C and the pressure was varied between 0.46 and 5 Torr. The residual stress of as-deposited SiC films ranged from highly tensile to moderately compressive as the deposition pressure was increased from 0.46 to 5 Torr, with tensile stress below 50 MPa in films deposited at around 2.5 Torr. Cantilever beams with no vertical deformation were fabricated from the low tensile stress films, and they indicated that the stress gradient was also very low in these films. X-ray diffraction analysis indicated that all the films were highly textured polycrystalline (111) 3C-SiC regardless of the residual stress. Transmission electron microscopy indicated that both the tensile and compressive films were columnar in microstructure, with slight differences in the axial alignment of the grains with respect to the film/substrate interface as well as in the density of features in the grain boundaries. An explanation for the observed differences in residual stress based on differences in film microstructure is proposed. © 2004 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Vw Pressure treatment
81.40.Jj Elasticity and anelasticity, stress-strain relations
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Stress and structural relaxation in amorphous hydrogenated carbon films

M. Lejeune, M. Benlahsen, and R. Bouzerar

Appl. Phys. Lett. 84, 344 (2004); http://dx.doi.org/10.1063/1.1637447 (3 pages) | Cited 15 times

Online Publication Date: 14 January 2004

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The correlation between the residual stress and the atomic-bond structure has been investigated in detail in hydrogenated amorphous films (a-C:H). The relaxation process was studied in relation with the Raman characteristics evolution and the induced metric distortions during growth. The analysis of the Raman data shows that the metric distortions alone cannot explain the stress relaxation in the deposited films. The creation of some topological defects, such as odd rings, is required to explain both the Raman features behavior and the structural relaxation in the a-C:H samples. © 2004 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
81.05.U- Carbon/carbon-based materials
61.43.Er Other amorphous solids
78.66.Tr Fullerenes and related materials
78.30.Na Fullerenes and related materials

Bulk nanostructure formation directly from the multicomponent alloy melt

Jian-Min Li

Appl. Phys. Lett. 84, 347 (2004); http://dx.doi.org/10.1063/1.1642756 (3 pages) | Cited 6 times

Online Publication Date: 14 January 2004

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The first bulk homogeneous nanocrystalline Zr60Al15Ni10Co15 (at. %) alloy prepared by melt casting without the amorphous matrix is reported. In this work, the complete grain refinement directly by solidification processing, when qualitatively compared to the previously reported nanocrystallization by postdevitrification of amorphous alloy solid precursors, produces nanograins that have a relatively narrower size range (7.4 nm in average) and are randomly oriented. The total inhomogeneous chemical affinity of the multicomponent alloy was proposed to thermodynamically favor the three-dimensional nanoscale nucleation from alloy melts. Clustering of different atoms in the ZrAlNiCo alloy occurs while the material is still in the molten state. © 2004 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
64.70.D- Solid-liquid transitions

Roughness and stability of silicon on insulator surfaces

M. Czubanowski, C. Tegenkamp, W. Ernst, and H. Pfnür

Appl. Phys. Lett. 84, 350 (2004); http://dx.doi.org/10.1063/1.1641181 (3 pages) | Cited 5 times

Online Publication Date: 14 January 2004

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The feasibility of low temperature processes (below 800 °C) to obtain in situ atomically clean and smooth surfaces on (100) oriented silicon on insulator material (SOI) with negligible variation of the top Si film thickness was tested. These steps were characterized using low-energy electron diffraction and atomic force microscopy supplemented by conductivity measurements. The most promising method for obtaining atomically smooth and continuous SOI films is the evaporation of Si at 750 °C at a flux of 0.15 ML/min. For lower rates [113]-oriented pits are formed within the SOI layer. It turned out that mobile and volatile oxide formation at the Si/SiO2 interface in these materials can occur already at temperatures below 1000° C, leading to the destruction of the buried oxide layer. © 2004 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.37.Lp Transmission electron microscopy (TEM)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.37.Ps Atomic force microscopy (AFM)

Enhanced luminescence of Gd2O3:Eu3+ thin-film phosphors by Li doping

Soung-soo Yi, Jong Seong Bae, Kyoo Sung Shim, Jung Hyun Jeong, Jung-Chul Park, and P. H. Holloway

Appl. Phys. Lett. 84, 353 (2004); http://dx.doi.org/10.1063/1.1641526 (3 pages) | Cited 45 times

Online Publication Date: 14 January 2004

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Gd2O3:Eu3+ and Li-doped Gd2O3:Eu3+ luminescent thin films have been grown on Al2O3 (0001) substrates using pulsed-laser deposition. The films grown under different deposition conditions show different microstructural and luminescent characteristics. Both cubic and monoclinic crystalline structures were observed in Gd2O3:Eu3+ films, but only the cubic crystalline structure was observed for Li-doped Gd2O3:Eu3+ films grown under certain condition. The photoluminescence (PL) brightness data obtained from Li-doped Gd2O3:Eu3+ films indicate that sapphire is a promising substrate for growth of high-quality Li-doped Gd2O3:Eu3+ thin-film red phosphor. In particular, incorporation of Li+ ions into the Gd2O3 lattice can induce a remarkable increase of PL. The highest emission intensity was observed with LiF-doped Gd1.84Li0.08Eu0.08O3, whose brightness was a factor of 2.3 larger than that from Gd2O3:Eu3+ films. This phosphor is promising for applications in flat-panel displays. © 2004 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
78.66.Nk Insulators
61.72.up Other materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Deep ultraviolet scanning near-field optical microscopy for the structural analysis of organic and biological materials

Hiroyuki Aoki, Toyohiro Hamamatsu, and Shinzaburo Ito

Appl. Phys. Lett. 84, 356 (2004); http://dx.doi.org/10.1063/1.1642757 (3 pages) | Cited 7 times

Online Publication Date: 14 January 2004

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Scanning near-field optical microscopy (SNOM) using a deep ultraviolet (DUV) light source was developed for in situ imaging of a variety of chemical species without staining. Numerous kinds of chemical species have a carbon–carbon double bond or aromatic group in their chemical structure, which can be excited at the wavelength below 300 nm. In this study, the wavelength range available for SNOM imaging was extended to the DUV region. DUV–SNOM allowed the direct imaging of polymer thin films with high detection sensitivity and spatial resolution of several tens of nanometers. In addition to the polymer materials, we demonstrated the near-field imaging of a cell without using a fluorescence label. © 2004 American Institute of Physics.
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78.55.Qr Amorphous materials; glasses and other disordered solids
78.55.Kz Solid organic materials
68.55.-a Thin film structure and morphology
68.37.Uv Near-field scanning microscopy and spectroscopy
61.66.Hq Organic compounds

High fluorescence quantum efficiency of 1.8 μm emission in Tm-doped low silica calcium aluminate glass determined by thermal lens spectrometry

S. L. Oliveira, S. M. Lima, T. Catunda, L. A. O. Nunes, J. H. Rohling, A. C. Bento, and M. L. Baesso

Appl. Phys. Lett. 84, 359 (2004); http://dx.doi.org/10.1063/1.1640782 (3 pages) | Cited 10 times

Online Publication Date: 14 January 2004

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In this work, thermal lens spectrometry is performed to determine the fluorescence quantum efficiency (η) of the 3F4 level (1.8 μm emission) of 4 and 5 wt % Tm-doped water free low silica calcium aluminate glass. The η value obtained for both high Tm contents was approximately 30%, which is in agreement with the Judd–Ofelt calculation. It is also verified that heat generation under 0.79 μm pumping, which presents a high quantum defect, is minimized by a cross-relaxation mechanism. The high η values, and the excellent chemical and thermomechanical properties indicate this system is a potential host material for diode-pumped laser sources operating in the midinfrared spectral range. © 2004 American Institute of Physics.
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78.55.Qr Amorphous materials; glasses and other disordered solids
42.55.Xi Diode-pumped lasers
42.72.Ai Infrared sources

Layer-by-layer diamond-like woodpile structure with a large photonic band gap

Martin Maldovan, Edwin L. Thomas, and Craig W. Carter

Appl. Phys. Lett. 84, 362 (2004); http://dx.doi.org/10.1063/1.1642279 (3 pages) | Cited 14 times

Online Publication Date: 14 January 2004

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A layer-by-layer periodic dielectric structure with a large photonic band gap is presented. It consists of a layer-by-layer approximation to the triply periodic bicontinuous level set D surface structure having diamond (Fd3m) symmetry. The structure retains the ease of fabrication of the standard woodpile while increasing the maximum quality factor of the gap by 28%. Photonic band gap properties of this structure were calculated using the plane-wave method and its band gap optimized at a fixed index contrast of 3.6:1. © 2004 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
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Spin-dependent transport in lateral periodic magnetic modulations: Scheme for spin filters

J. Zhou, Q. W. Shi, and M. W. Wu

Appl. Phys. Lett. 84, 365 (2004); http://dx.doi.org/10.1063/1.1640805 (3 pages) | Cited 18 times

Online Publication Date: 14 January 2004

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A scheme for spin filters is proposed by studying the coherent transport of electrons through quantum wires with lateral magnetic modulation. Unlike other schemes reported in the literature, the modulation in our scheme is much weaker than the Fermi energy. Large spin polarization through the filter is predicted. Further study suggests the robustness of this spin filter. © 2004 American Institute of Physics.
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73.63.Nm Quantum wires
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
73.23.Ad Ballistic transport
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Germanium-concentration dependence of arsenic diffusion in silicon germanium alloys

S. Eguchi, C. N. Chleirigh, O. O. Olubuyide, and J. L. Hoyt

Appl. Phys. Lett. 84, 368 (2004); http://dx.doi.org/10.1063/1.1641169 (3 pages) | Cited 9 times

Online Publication Date: 14 January 2004

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The germanium-concentration dependence of arsenic diffusion in relaxed silicon germanium (Si1−xGex) alloys with Ge content ranging from 0 to 40% has been investigated. Arsenic was implanted into relaxed epitaxial layers at 15 keV to a dose of 3×1015 cm−2, and diffusion during furnace and rapid thermal annealing was studied. Under equilibrium extrinsic conditions, the arsenic diffusivity increases exponentially with increasing Ge content in Si1−xGex. Under transient diffusion conditions, the arsenic diffusivity in Si1−xGex is retarded compared to the diffusivity for longer times, while a slight transient enhancement of As diffusion is observed in Si. The degree of transient retardation depends on the germanium concentration in the alloy. © 2004 American Institute of Physics.
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66.30.J- Diffusion of impurities
85.30.Tv Field effect devices

Comparison of stability of WSiX/SiC and Ni/SiC Schottky rectifiers to high dose gamma-ray irradiation

Jihyun Kim, F. Ren, G. Y. Chung, M. F. MacMillan, A. G. Baca, R. D. Briggs, D. Schoenfeld, and S. J. Pearton

Appl. Phys. Lett. 84, 371 (2004); http://dx.doi.org/10.1063/1.1642271 (3 pages) | Cited 8 times

Online Publication Date: 14 January 2004

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SiC Schottky rectifiers with moderate breakdown voltages of ∼450 V and with either WSiX or Ni rectifying contacts were irradiated with Co-60 γ-rays to doses up to ∼315 Mrad. The Ni/SiC rectifiers show severe reaction of the contact after irradiation at the highest dose, badly degrading the forward current characteristics and increasing the on-state resistance by up to a factor of 6 after irradiation. By sharp contrast, the WSiX/SiC devices show little deterioration of the contact with the same conditions and changes in on-state resistance of <20%. The WSiX contacts appear promising for applications requiring improved contact stability. © 2004 American Institute of Physics.
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85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices
61.80.Ed γ-ray effects

Impact of carbon on trap states in n-type GaN grown by metalorganic chemical vapor deposition

A. Armstrong, A. R. Arehart, B. Moran, S. P. DenBaars, U. K. Mishra, J. S. Speck, and S. A. Ringel

Appl. Phys. Lett. 84, 374 (2004); http://dx.doi.org/10.1063/1.1643540 (3 pages) | Cited 30 times

Online Publication Date: 14 January 2004

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The effect of excess C incorporation on the deep level spectrum of n-type GaN grown by metalorganic chemical vapor deposition was investigated. Low-pressure (LP) growth conditions were used to intentionally incorporate excess C compared to atmospheric pressure (AP) growth conditions. GaN samples with high C content are found to be highly resistive, and samples codoped with C and Si are heavily compensated. From a comparison of deep level optical spectroscopy and deep level transient spectroscopy measurements of the LP-grown codoped GaN:C:Si sample with the AP-grown unintentionally doped GaN, two deep levels at Ec−Et = 1.35 and 3.28 eV are observed to have a direct relation to excess C incorporation. Comparing these activation energies to previous theoretical studies strongly suggests that the levels may be associated with a C interstitial and CN defect, respectively. These results suggest that C forms not only a shallow acceptor level but also a deep acceptor level in GaN, and these levels contribute to the compensation of the free carriers in n-type GaN:C. © 2004 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.55.Eq III-V semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.J- Point defects and defect clusters
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
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High critical current density and its field dependence in mixed rare earth (Nd,Eu,Gd)Ba2Cu3O7−δ thin films

C. Cai, B. Holzapfel, J. Hänisch, L. Fernández, and L. Schultz

Appl. Phys. Lett. 84, 377 (2004); http://dx.doi.org/10.1063/1.1640802 (3 pages) | Cited 37 times

Online Publication Date: 14 January 2004

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Compared with mono-rare earth 123 films, ternary rare earth (Nd,Eu,Gd)Ba2Cu3O7−δ (NEG123) films show higher critical current density (Jc) and improved irreversibility field (Hirr), but no increase in the characteristic field corresponding to a crossover from a low-field plateau to a linear region in a log Jc–log H plot. At intermediate fields, Jc vs H scales as H(−0.5±0.05) for NEG123, in contrast to H(−0.73±0.05) for mono-rare earth samples such as Gd123. The slow power decay of Jc vs H together with the improved Jc and Hirr strongly implies that extra flux pinning centers exist in NEG123, which are thought to be noncorrelated stress fields induced by lattice mismatch. © 2004 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents

Switching by point-contact spin injection in a continuous film

T. Y. Chen, Y. Ji, and C. L. Chien

Appl. Phys. Lett. 84, 380 (2004); http://dx.doi.org/10.1063/1.1641170 (3 pages) | Cited 23 times

Online Publication Date: 14 January 2004

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Spin-polarized currents injected through a point-contact into a continuous Co/Cu/Co trilayer film can reversibly switch the magnetization of small magnetic bits in the top Co layer. The magnetic states written depend on the polarity of the injection currents, and remain stable at room temperature. The reversible writing can be achieved for a wide range of contact resistances with a well-defined voltage for the reversal. © 2004 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Interfacial disorder in the L10 FePt particles capped with amorphous Al2O3

Y. K. Takahashi and K. Hono

Appl. Phys. Lett. 84, 383 (2004); http://dx.doi.org/10.1063/1.1641175 (3 pages) | Cited 26 times

Online Publication Date: 14 January 2004

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L10-FePt particles disorder at the interface when an amorphous Al2O3 layer is capped on an ordered FePt particulate film at room temperature. The coercivity decreases drastically as a result. Interfacial disordering does not progress when the capped layer is deposited at elevated temperature, indicating that the disordering is driven by the strain at the interface. The FePt particulate film becomes magnetized more easily by the Al2O3 capping. © 2004 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.70.Ak Magnetic properties of monolayers and thin films
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