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10 Jan 2005

Volume 86, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 021101 (2005); http://dx.doi.org/10.1063/1.1849439 (3 pages)

H. W. Choi, C. W. Jeon, C. Liu, I. M. Watson, M. D. Dawson, P. R. Edwards, R. W. Martin, S. Tripathy, and S. J. Chua
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Luminescence from stacking faults in gallium nitride

R. Liu, A. Bell, F. A. Ponce, C. Q. Chen, J. W. Yang, and M. A. Khan

Appl. Phys. Lett. 86, 021908 (2005); http://dx.doi.org/10.1063/1.1852085 (3 pages) | Cited 124 times

Online Publication Date: 4 January 2005

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A direct correlation has been established between stacking faults in a-plane GaN epilayers and luminescence peaks in the 3.29–3.41 eV range. The structural features of the stacking faults were determined by diffraction-contrast transmission electron microscopy, while the optical emission characteristics were observed by highly spatially resolved monochromatic cathodoluminescence. The studies were performed in the exact same regions of thinned foils. We find that stacking faults on the basal plane are responsible for the strong emission at ∼ 3.14 eV. Luminescence peaks at ∼ 3.33 and ∼ 3.29 eV are associated with the presence of stacking faults on prismatic a planes and partial dislocations at the stacking fault boundaries, respectively.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.Nn Stacking faults and other planar or extended defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)

Femtosecond transient fluorescence spectrometer based on parametric amplification

Piotr Fita, Yuriy Stepanenko, and Czeslaw Radzewicz

Appl. Phys. Lett. 86, 021909 (2005); http://dx.doi.org/10.1063/1.1850591 (3 pages) | Cited 15 times

Online Publication Date: 4 January 2005

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We report an experimental proof-of-principle of a method for recording femtosecond, time-resolved fluorescence spectra in the visible range. The method is based on a noncollinear parametric amplification in a beta barium borate crystal and provides time resolution of the order of 100 fs. We demonstrate that with this method, transient fluorescence spectra as wide as 6000 cm−1 can be recorded in a single time-delay scan. Fluorescence decay dynamics and transient spectra of Coumarin 6 dye dissolved in aniline were measured to test the usefulness of the method.
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07.60.Rd Visible and ultraviolet spectrometers
78.47.-p Spectroscopy of solid state dynamics
78.55.Hx Other solid inorganic materials
78.45.+h Stimulated emission

Einstein oscillator in highly-random-packed bulk metallic glass

M. B. Tang, H. Y. Bai, M. X. Pan, D. Q. Zhao, and W. H. Wang

Appl. Phys. Lett. 86, 021910 (2005); http://dx.doi.org/10.1063/1.1849420 (3 pages) | Cited 10 times

Online Publication Date: 5 January 2005

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Metallic glasses have often been regarded as ideal model systems of dense random packing with strong interaction among their components. Here we report direct evidence for the presence of the Einstein oscillator with an Einstein temperature θE of 74 K, which induces the boson peak at 4.9 meV in bulk metallic glass Zr46.75Ti8.25Cu7.5Ni10Be27.5. The presence of an Einstein oscillator suggests the existence of the vibrations of loose atoms in an independent localized harmonic mode in the highly random packed metallic glasses.
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63.50.-x Vibrational states in disordered systems
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

Direct evidence of nanocluster-induced luminescence in InGaN epifilms

H. J. Chang, C. H. Chen, Y. F. Chen, T. Y. Lin, L. C. Chen, K. H. Chen, and Z. H. Lan

Appl. Phys. Lett. 86, 021911 (2005); http://dx.doi.org/10.1063/1.1843279 (3 pages) | Cited 11 times

Online Publication Date: 5 January 2005

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x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectrometry, and cathodoluminescence measurements have been employed to study the correlation between optical and structural properties in InGaN epitaxial films. In-rich quantum dots were found to be dispersed throughout the film. By the combination of these measurements, we clearly identify that brighter luminescence arises from In-rich regions while dimmer luminescence corresponds to the Ga-rich matrix regions.
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68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Reduction of the threading dislocation density in GaN films grown on vicinal sapphire (0001) substrates

X. Q. Shen, H. Matsuhata, and H. Okumura

Appl. Phys. Lett. 86, 021912 (2005); http://dx.doi.org/10.1063/1.1849836 (3 pages) | Cited 26 times

Online Publication Date: 5 January 2005

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Structural properties of GaN films grown on vicinal sapphire (0001) substrates with various vicinal angles by plasma-assisted molecular beam epitaxy are investigated. High-resolution x-ray diffraction (HRXRD) results reveal the dramatic improvement of both tilting and twisting grain features of the GaN films when the vicinal angle is larger than 0.5° with the formation of multilayer macro-steps on the surface. The threading dislocation density reduces by over an order of magnitude estimated from the HRXRD results. Cross-sectional transmission electron microscopy observations clearly show that the formation and lateral propagation of macro-steps on the GaN surface play an important role in this dislocation reduction. A method for the reduction of threading dislocation density in GaN epilayers is proposed.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)

Optical trapping of colloidal particles and measurement of the defect line tension and colloidal forces in a thermotropic nematic liquid crystal

I. I. Smalyukh, A. N. Kuzmin, A. V. Kachynski, P. N. Prasad, and O. D. Lavrentovich

Appl. Phys. Lett. 86, 021913 (2005); http://dx.doi.org/10.1063/1.1849839 (3 pages)

Online Publication Date: 5 January 2005

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We demonstrate optical trapping and manipulation of transparent microparticles suspended in a thermotropic nematic liquid crystal with low birefringence. We employ the particle manipulation to measure line tension of a topologically stable disclination line and to determine colloidal interaction of particles with perpendicular surface anchoring of the director. The three-dimensional director fields and positions of the particles manipulated by laser tweezers are visualized by fluorescence confocal polarizing microscopy.
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61.30.Jf Defects in liquid crystals
78.20.Fm Birefringence
42.70.Df Liquid crystals
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
78.55.Bq Liquids
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
82.70.Dd Colloids

Limiting factors of room-temperature nonradiative photoluminescence lifetime in polar and nonpolar GaN studied by time-resolved photoluminescence and slow positron annihilation techniques

S. F. Chichibu, A. Uedono, T. Onuma, T. Sota, B. A. Haskell, S. P. DenBaars, J. S. Speck, and S. Nakamura

Appl. Phys. Lett. 86, 021914 (2005); http://dx.doi.org/10.1063/1.1851619 (3 pages) | Cited 29 times

Online Publication Date: 5 January 2005

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Room-temperature nonradiative lifetime (τnr) of the near-band-edge excitonic photoluminescence (PL) peak in {0001} polar, (11math0), (1math00), and (001) nonpolar GaN was shown to increase with the decrease in density or size of Ga vacancies (VGa) and with the decrease in gross density of point defects including complexes, leading to the increase in the PL intensity. As the edge threading dislocation density decreased, density or size of VGa tended to decrease and τnr tended to increase. However, there existed remarkable exceptions. The results indicate that nonradiative recombination process is governed not by single point defects, but by certain defects introduced with the incorporation of VGa, such as VGa-defect complexes.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.70.Bj Positron annihilation
61.72.J- Point defects and defect clusters
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.55.-a Thin film structure and morphology

Atomistic processes during nanoindentation of amorphous silicon carbide

Izabela Szlufarska, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta

Appl. Phys. Lett. 86, 021915 (2005); http://dx.doi.org/10.1063/1.1849843 (3 pages) | Cited 12 times

Online Publication Date: 5 January 2005

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Atomistic mechanisms of nanoindentation of a-SiC have been studied by molecular dynamics simulations. The load displacement curve exhibits a series of load drops, reflecting the short-range topological order similar to crystalline 3C–SiC. In contrast to 3C–SiC, the load drops are irregularly spaced and less pronounced. The damage is spatially more extended than in 3C–SiC, and it exhibits long-range oscillations consistent with the indenter size. Hardness is ∼ 60% lower than in 3C–SiC and is in agreement with experiment. The onset of plastic deformation occurs at depth ∼ 75% lower than in 3C–SiC.
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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.Qp Friction, tribology, and hardness
61.43.Bn Structural modeling: serial-addition models, computer simulation
68.35.Gy Mechanical properties; surface strains
81.40.Lm Deformation, plasticity, and creep
62.20.M- Structural failure of materials
62.20.F- Deformation and plasticity

Effects of two-dimensional electron gas on the optical properties of InAs/GaAs quantum dots in modulation-doped heterostructures

T. W. Kim, J. H. Kim, H. S. Lee, J. Y. Lee, and M. D. Kim

Appl. Phys. Lett. 86, 021916 (2005); http://dx.doi.org/10.1063/1.1849853 (3 pages) | Cited 2 times

Online Publication Date: 5 January 2005

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The Shubnikov–de Haas data showed that the carrier density of two-dimensional electron gas (2DEG) in the GaAs active region containing InAs quantum dot (QD) arrays embedded between modulation-doped Al0.25Ga0.75As/GaAs heterostructures increased with increasing doping concentration in the modulation layer. The transmission electron microscopy images showed that the sizes of the self-assembled InAs vertically stacked QD arrays inserted in the GaAs did not change significantly with increasing carrier density of the 2DEG. The photoluminescence (PL) spectra showed that the peaks corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole subband of the InAs QDs shifted to the higher energy side with increasing density of the 2DEG and that the full width at half maximum of the PL spectrum increased slightly with increasing density of the 2DEG.
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73.63.Kv Quantum dots
78.67.Hc Quantum dots
73.21.La Quantum dots
78.55.Cr III-V semiconductors
61.72.S- Impurities in crystals
61.72.uj III-V and II-VI semiconductors
68.37.Lp Transmission electron microscopy (TEM)

Orientation-dependent x-ray absorption fine structure of ZnO nanorods

S.-W. Han, H.-J. Yoo, Sung Jin An, Jinkyoung Yoo, and Gyu-Chul Yi

Appl. Phys. Lett. 86, 021917 (2005); http://dx.doi.org/10.1063/1.1851616 (3 pages) | Cited 13 times

Online Publication Date: 6 January 2005

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The local structure of two samples of vertically well-aligned ZnO nanorods with average diameters of 13 and 37 nm were studied using orientation-dependent x-ray absorption fine structure (XAFS) at the Zn K edge. The aligned ZnO nanorod samples were fabricated on sapphire (0001) substrates with a catalyst-free metalorganic vapor-phase epitaxy method. The XAFS measurements showed that both nanorod samples have a well-ordered wurtzite structure and that no vacancy was observed at either site of zinc or oxygen atoms. However, we found that in both samples the lattice constants of a and b were shrunken by ∼ 0.04 Å while c was elongated by ∼ 0.1 Å, compared with those of their bulk counterparts. Furthermore, there was a substantial amount of disorder in the bond length of the only Zn–O pairs located near the ab plane. This may suggest that the terminating atoms at the boundaries of the nanorods are oxygen atoms.
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61.46.-w Structure of nanoscale materials
78.70.Dm X-ray absorption spectra

Nanoindentation and photoreflectance study on polycrystalline ternary Al–C–N thin films

A. L. Ji, L. B. Ma, C. Liu, P. Zheng, C. R. Li, and Z. X. Cao

Appl. Phys. Lett. 86, 021918 (2005); http://dx.doi.org/10.1063/1.1853507 (3 pages)

Online Publication Date: 6 January 2005

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Berkovich hardness and optical gap were determined by nanoindentation and photoreflectance measurement for ternary Al–C–N thin films of various compositions along with structural characterization. The deposits were fabricated by reactive magnetron sputtering of aluminum target onto Si(100) substrates, with the mixture of argon, nitrogen, and methane as precursor. High-resolution transmission electron microscopy and selected-area electron diffraction revealed a polycrystalline structure with rich defects in the film, and x-ray diffraction displays only one reflection at 2θ ≈ 36° from the basal planes. The hardness is over 26 GPa for all the deposits, it measures 53.4 GPa in the sample Al47C20N33. The optical gap, defined as the photon energy where (1/R)(dR/dE) maximizes, R is the photoreflectance, lies within 5.2 to 5.6 eV. These results indicate the wide-gap nature of aluminum carbonitrides, implying diverse potential applications of their thin films as protective coating of an ultraviolet detector, dielectric barrier layer in electronics, etc.
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68.60.Bs Mechanical and acoustical properties
78.66.Li Other semiconductors

Template-induced crystallization of amorphous SiO2 and its effects on the mechanical properties of TiN/SiO2 nanomultilayers

Lun Wei, Fanghua Mei, Nan Shao, Ming Kong, Geyang Li, and Jianguo Li

Appl. Phys. Lett. 86, 021919 (2005); http://dx.doi.org/10.1063/1.1853512 (3 pages) | Cited 15 times

Online Publication Date: 6 January 2005

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TiN/SiO2 nanomultilayers with various thicknesses of the SiO2 layer have been prepared by multi-target magnetron sputtering. Studies show that amorphous SiO2, which is more favorable under sputtering condition, crystallizes at smaller layer thickness (0.45–0.9 nm) due to the template effect of TiN layers. Correspondingly, multilayers exhibit coherent epitaxial growth with intensive (111) texture, and show significant hardness enhancement with maximum hardness of 44.5 GPa. Further increase in the SiO2 layer thickness (≳1 nm) leads to the formation of amorphous SiO2 which blocks the coherent growth of the films, and thus decreases the multilayer hardness gradually.
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68.65.Ac Multilayers

Interfacial reactions during GaN and AiN epitaxy on 4H– and 6H–SiC(0001)

Maria Losurdo, Pio Capezzuto, Giovanni Bruno, April Brown, Tong-Ho Kim, Changhyun Yi, D. N. Zakharov, and Z. Liliental-Weber

Appl. Phys. Lett. 86, 021920 (2005); http://dx.doi.org/10.1063/1.1852703 (3 pages) | Cited 5 times

Online Publication Date: 6 January 2005

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Thin layers of AlN and GaN have been grown by plasma-assisted molecular beam epitaxy on Si-face 4H– and 6H–SiC(0001)Si substrates. The impact of the SiC surface preparation and oxide removal via a Ga deposition and desorption process on the chemistry and structure of the GaN/SiC and AlN/SiC interfaces, and on the GaN/SiC subsurface reactivity is characterized. We also investigate the impact of this process on growth mode evolution.
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68.35.Fx Diffusion; interface formation
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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Electrical characteristics of Pt Schottky contacts on sulfide-treated n-type ZnO

Sang-Ho Kim, Han-Ki Kim, and Tae-Yeon Seong

Appl. Phys. Lett. 86, 022101 (2005); http://dx.doi.org/10.1063/1.1839285 (3 pages) | Cited 34 times

Online Publication Date: 30 December 2004

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We have investigated the effect of sulfide treatment on the electrical characteristics of Pt contacts on (000-1) n-type ZnO ( ∼ 5×1015cm−3) single crystals. The Pt contact on conventionally cleaned ZnO surface shows an ohmic behavior. However, the contact produces a Schottky behavior, when the ZnO surface is etched in a boiling (NH4)2Sx solution. Measurements show that the Schottky barrier height, ideality factor, and leakage current at −5 V of the Pt contact on the sulfide-treated ZnO are 0.79 eV, 1.51, and 3.75×10−10 A, respectively. Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) examinations indicate the formation of ZnS phase at the Pt/ZnO interface. Based on the capacitance–voltage, AES, and XPS results, a possible mechanism for the formation of good Schottky contacts is given.
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81.05.Bx Metals, semimetals, and alloys
81.05.Dz II-VI semiconductors
73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
81.65.Cf Surface cleaning, etching, patterning
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Jv Interfaces; heterostructures; nanostructures
68.37.Xy Scanning Auger microscopy, photoelectron microscopy

Ballistic transport mode detected by picosecond time-of-flight measurements for nanocrystalline porous silicon layer

Akira Kojima and Nobuyoshi Koshida

Appl. Phys. Lett. 86, 022102 (2005); http://dx.doi.org/10.1063/1.1848181 (3 pages) | Cited 9 times

Online Publication Date: 30 December 2004

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The electron transport mechanism in nanocrystalline porous silicon (nc-PS) with a controlled structure has been studied for a self-supporting sample by time-of-flight (TOF) measurements at room and low temperatures using a picosecond-width UV laser pulse. In contrast to both single-crystalline silicon (c‐Si) and hydrogenated amorphous silicon (a‐Si:H), the TOF signals of nc-PS show characteristic behavior that involves a ballistic component. The drift velocity vd determined from observed TOF signals shows no signs of saturation with increasing field strength F. At F ∼ 3×104 V/cm, the vd value in nc-PS at room temperature reaches 2.2×108 cm/s. The corresponding electron mean free path is 1.6 μm. These values are considerably larger than those in c‐Si. The ballistic transport mode becomes clear at low temperatures. The results support the model that electrons can travel ballistically with little scattering losses in a nanocrystalline silicon dot chain interconnected via thin silicon dioxide films.
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73.63.Bd Nanocrystalline materials
73.23.Ad Ballistic transport
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Jv Interfaces; heterostructures; nanostructures

Single-crystal field-effect transistors based on copper phthalocyanine

R. Zeis, T. Siegrist, and Ch. Kloc

Appl. Phys. Lett. 86, 022103 (2005); http://dx.doi.org/10.1063/1.1849438 (3 pages) | Cited 79 times

Online Publication Date: 3 January 2005

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Copper phthalocyanine (Cu–Pc) single crystals were grown by physical vapor transport and field-effect transistors (FETs) on the surface of these crystals were prepared. These FETs function as p-channel accumulation-mode devices. Charge carrier mobilities of up to 1 cm2/V s combined with a low field-effect threshold were obtained. These remarkable FET characteristics, along with the highly stable chemical nature of Cu–Pc, make it an attractive candidate for device applications.
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85.30.Tv Field effect devices
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Le Polymers; organic compounds (including organic semiconductors)
81.10.Bk Growth from vapor

Direct comparison of field-effect and electrochemical doping in regioregular poly(3-hexylthiophene)

Hidekazu Shimotani, Gildas Diguet, and Yoshihiro Iwasa

Appl. Phys. Lett. 86, 022104 (2005); http://dx.doi.org/10.1063/1.1850614 (3 pages) | Cited 55 times

Online Publication Date: 3 January 2005

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We have measured carrier mobility of regioregular poly(3-hexylthiophene) films by both field-effect and electrochemical doping on identical devices, which allowed us a direct comparison between the two doping processes. The carrier mobility of electrochemical doping at low doping levels was lower than that of field-effect doping by two orders of magnitudes, while that of electrochemical doping steeply increased with doping levels, reaching comparable or higher values than that of field-effect doping. These results are attributable to carrier trapping by the Coulomb potentials of dopant anions at low doping levels, demonstrating a significant difference between field-effect and chemical doping.
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85.30.Tv Field effect devices
61.72.up Other materials
73.61.Ph Polymers; organic compounds
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Dn Low-field transport and mobility; piezoresistance
61.72.S- Impurities in crystals
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Evaluation of nickel and molybdenum silicides for dual gate complementary metal-oxide semiconductor application

Nivedita Biswas, Jason Gurganus, Veena Misra, Yan Yang, and Susanne Stemmer

Appl. Phys. Lett. 86, 022105 (2005); http://dx.doi.org/10.1063/1.1849850 (3 pages) | Cited 6 times

Online Publication Date: 4 January 2005

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Characteristics of NiSi and MoSi via full consumption of undoped silicon layers have been studied. Interaction of nickel (Ni) and molybdenum (Mo) silicides with SiO2 was evaluated in terms of work function and thermal stability. For nickel silicide, the work function values were low for samples annealed at 400 °C even after full consumption of silicon. The work function increased with the anneal temperature and stabilized at 600 °C to close to midgap values. Dielectric interaction as a result of silicide formation was studied using current–voltage characteristics. Low leakage currents in these stacks indicated minimum dielectric damage due to silicided gates. Silicidation of Mo was found to be incomplete as the capacitance–voltage curves were marked with larger EOT values and negative shifts in the flatband voltages even at 700 °C. Auger depth profiling, high resolution transmission electron microscopy (HRTEM) and x-ray diffraction (XRD) were used for material analysis of the silicided gate stacks.
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73.61.Ng Insulators
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.Cc Kinetics of defect formation and annealing
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
68.37.Lp Transmission electron microscopy (TEM)

Ultrahigh temperature vibration sensors using aluminum nitride thin films and W/Ru multilayer electrodes

Morito Akiyama, Toshihiro Kamohara, Keiko Nishikubo, Naohiro Ueno, Hideaki Nagai, and Takeshi Okutani

Appl. Phys. Lett. 86, 022106 (2005); http://dx.doi.org/10.1063/1.1850193 (3 pages) | Cited 1 time

Online Publication Date: 4 January 2005

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Ultrahigh temperature vibration sensors have been fabricated from highly c-axis-oriented aluminum nitride (AlN) thin films and tungsten/ruthenium (W/Ru) multilayer bottom electrodes. These films and electrodes were prepared by radio-frequency magnetron sputtering on zirconium oxide (ZrO2) substrates, such as AlN/W/Ru/ZrO2. The vibration sensors resisted the heat treatment of 1450 °C for 1 h in argon, and after that, peeling and cracks were not observed in the sensor surface. The “tough” behavior of the vibration sensors in the high temperature is probably attributed to the chemical composition change of the W/Ru multilayer bottom electrodes to Ru60W40 and Ru15W85 solid solutions that prevent chemical reactions and relax thermal stress.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
07.10.Pz Instruments for strain, force, and torque
68.60.Bs Mechanical and acoustical properties
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
77.55.-g Dielectric thin films
82.33.-z Reactions in various media
68.35.Gy Mechanical properties; surface strains
62.20.M- Structural failure of materials
77.65.-j Piezoelectricity and electromechanical effects
81.40.Gh Other heat and thermomechanical treatments

Hot-electron transport in 4H–SiC

L. Ardaravičius, A. Matulionis, O. Kiprijanovic, J. Liberis, H.-Y. Cha, L. F. Eastman, and M. G. Spencer

Appl. Phys. Lett. 86, 022107 (2005); http://dx.doi.org/10.1063/1.1851001 (3 pages) | Cited 4 times

Online Publication Date: 5 January 2005

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Nanosecond-pulsed technique is used to study hot-electron transport in donor-doped 4H–SiC (n = 2×1017 cm−3) biased parallel to the basal plane. The measurements of current with 1 ns voltage pulses are carried out at average electric fields up to 570 kV/cm. A region with a negative differential conductance is observed for the range of fields exceeding 280 kV/cm, followed by a sharp increase in the current at fields over 345 kV/cm. The dependence of drift velocity on electric field is deduced for the field range below the onset of the negative differential conductance to appear: the value of the saturation velocity is estimated as 1.4×107 cm/s at room temperature.
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72.20.Ht High-field and nonlinear effects
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Jc Other crystalline inorganic semiconductors

Distribution of electrically active defects in chemical vapor deposition diamond: Model and measurement

A. Balducci, Marco Marinelli, E. Milani, M. E. Morgada, G. Pucella, G. Rodriguez, A. Tucciarone, G. Verona-Rinati, M. Angelone, and M. Pillon

Appl. Phys. Lett. 86, 022108 (2005); http://dx.doi.org/10.1063/1.1842856 (3 pages) | Cited 7 times

Online Publication Date: 5 January 2005

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Defects limiting the movement of charge carriers in polycrystalline chemical vapor deposition (CVD) diamond films are located within the grains or in grain boundaries. Their geometrical distribution in the sample is different and is usually unknown. We present here a method to quantitatively evaluate the concentration and distribution of in-grain and grain-boundary located active carrier traps. Since the impact of these two kinds of defects on the performance of CVD diamond based devices is different, it is possible to obtain the defect distribution by measuring the response of diamond alpha particle detectors as a function of film thickness. The Hecht theory, describing the efficiency of a semiconductor particle detector, has been modified to take into account the polycrystalline nature of CVD diamond. This extended Hecht model was then used to fit experimental data and extract quantitative information about the defect distribution.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Mm Grain and twin boundaries
73.61.Cw Elemental semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Dn Low-field transport and mobility; piezoresistance
68.55.-a Thin film structure and morphology

Electronic insulator-conductor conversion in hydride ion-doped 12CaO∙7Al2O3 by electron-beam irradiation

Katsuro Hayashi, Yoshitake Toda, Toshio Kamiya, Masahiro Hirano, Minako Yamanaka, Isao Tanaka, Takahisa Yamamoto, and Hideo Hosono

Appl. Phys. Lett. 86, 022109 (2005); http://dx.doi.org/10.1063/1.1852723 (3 pages) | Cited 9 times

Online Publication Date: 6 January 2005

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We report formation of persistent carrier electrons in hydride ion (H−)-incorporated 12CaO∙7Al2O3 (C12A7) by electron-beam irradiation. The electrical conductivity of H−-doped C12A7 single crystals increases with the electron-beam irradiation dose, accompanied with a green coloration attributable to a carrier electron formation. A 25 keV electron beam with a dose of ∼ 500 μC cm−2 fully converts the conductivity in surface layers to the depth of ∼ 4 μm. Carrier electron formation is most likely due to electron-hole pairs generated in the electron excitation volume and subsequent energy transfer to the H− ions. The estimated carrier formation yield per an incident electron is ∼ 30. These findings may enable a fine patterning of the conductive area without photomasks and photoresists.
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73.50.-h Electronic transport phenomena in thin films
74.25.-q Properties of superconductors
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Microscopic simulation of the percolation of manganites

Shuai Dong, Han Zhu, X. Wu, and J.-M. Liu

Appl. Phys. Lett. 86, 022501 (2005); http://dx.doi.org/10.1063/1.1848184 (3 pages) | Cited 8 times

Online Publication Date: 30 December 2004

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The one-orbital double exchange model is studied using the METROPOLIS Monte Carlo method and the microscopic resistor network. The phase competition and percolation are displayed microscopically. As far as the resistivity is concerned, the metal–insulator transition is described by the competition between a fraction p of metallic resistors and a fraction 1−p of insulating resistors. p can be obtained as a function of temperature T, doping percentage x, and external field H. In the present model, systems with different x, T, and H can be unified into a single class of percolation, which is different from the standard picture.
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75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
64.60.A- Specific approaches applied to studies of phase transitions
71.30.+h Metal-insulator transitions and other electronic transitions
72.80.Ga Transition-metal compounds
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

The effect of oxygenation on the superconducting properties of MgB2 thin films

K. A. Yates, Z. Lockman, A. Kursumovic, G. Burnell, N. A. Stelmashenko, J. L. MacManus Driscoll, and M. G. Blamire

Appl. Phys. Lett. 86, 022502 (2005); http://dx.doi.org/10.1063/1.1849837 (3 pages) | Cited 8 times

Online Publication Date: 3 January 2005

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The effects of oxygen on the superconducting properties of thin films of MgB2 have been studied. It is found that after annealing for short times in flowing O2 at 400 °C, complex oxides of Mgx(ByO)z are formed that cause a “two-step” behavior in the resistively determined superconducting transition. These oxides are not stable at room temperature and decay into MgO and B2O3 precipitates. As the complex oxides decay so the original Tc behavior of the films is restored to its preoxygenation level.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.78.-w Superconducting films and low-dimensional structures
74.62.Dh Effects of crystal defects, doping and substitution
74.25.F- Transport properties
81.40.Gh Other heat and thermomechanical treatments

Enhancing domain wall motion in magnetic wires by ion irradiation

F. Cayssol, J. L. Menéndez, D. Ravelosona, C. Chappert, J.-P. Jamet, J. Ferré, and H. Bernas

Appl. Phys. Lett. 86, 022503 (2005); http://dx.doi.org/10.1063/1.1846935 (3 pages) | Cited 6 times

Online Publication Date: 3 January 2005

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The influence of low-energy He ion irradiation on the dynamics of a single Bloch domain wall was studied in magnetic wires based on Pt∕Co∕Pt trilayers exhibiting perpendicular anisotropy. The domain wall velocity is highly enhanced (up to three orders of magnitude) after irradiation at moderate fluence. A study in the thermally activated regime shows that this is consistent with a reduction of the density of pinning centers and of the pinning force. Uniform ion irradiation significantly improves domain wall motion, as required for future magnetic devices.
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78.20.Ls Magneto-optical effects
85.60.-q Optoelectronic devices
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