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14 Mar 2005

Volume 86, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 86, 113104 (2005); http://dx.doi.org/10.1063/1.1883725 (3 pages)

S. Bhattacharyya, C. Sinturel, J. P. Salvetat, and M.-L. Saboungi
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Compressibility of Nb2AsC to 41 GPa

Ravhi S. Kumar, Sandeep Rekhi, A. L. Cornelius, and Michel W. Barsoum

Appl. Phys. Lett. 86, 111904 (2005); http://dx.doi.org/10.1063/1.1884261 (3 pages) | Cited 35 times

Online Publication Date: 7 March 2005

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Room temperature synchrotron x-ray diffraction experiments were performed on the layered hexagonal ternary carbide Nb2AsC in a diamond anvil cell to a pressure of 41 GPa. The structure is stable with no phase transitions observed in this pressure range. The bulk modulus is 224±2 GPa, with a pressure derivative of 4; the former is the highest bulk modulus for a Mn+1AXn (MAX) phase, including Ti3SiC2, measured to date. Nb2AsC is also the first MAX phase for which the compressibility along the a direction is higher than along the c direction; in other words, the c/a ratio increases strongly with applied pressure.
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81.40.Lm Deformation, plasticity, and creep
81.40.Vw Pressure treatment
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.50.-p High-pressure effects in solids and liquids
62.20.F- Deformation and plasticity
62.20.D- Elasticity

Vertical electronic coupling between InAs/InP quantum-dot layers emitting in the near-infrared range

P. Miska, J. Even, C. Paranthoen, O. Dehaese, A. Jbeli, M. Senès, and X. Marie

Appl. Phys. Lett. 86, 111905 (2005); http://dx.doi.org/10.1063/1.1865332 (3 pages) | Cited 20 times

Online Publication Date: 7 March 2005

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Stacked InAs quantum dots (QDs) grown on InP(113)B are analyzed both experimentally and theoretically in order to study the influence of the electronic vertical coupling between the QD layers. Improved growth conditions enable us to control the optimum QD height of the samples, thus yielding an emission wavelength of our nanostructures at about 1.55 μm at room temperature. Three samples containing three QD layers with different vertical spacing are studied. The QD electronic structure is studied by continuous-wave photoluminescence and time-resolved photoluminescence experiments at low temperature. A simplified theoretical model is developed, yielding results consistent with experimental data. This analysis evidences the electronic coupling between the QD layers.
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73.21.La Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics

Influence of trapping on the exciton dynamics of AlxGa1−xAs films

A. Amo, M. D. Martin, Ł. Kłopotowski, L. Viña, A. I. Toropov, and K. S. Zhuravlev

Appl. Phys. Lett. 86, 111906 (2005); http://dx.doi.org/10.1063/1.1885173 (3 pages) | Cited 4 times

Online Publication Date: 8 March 2005

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We present a systematic study on the exciton relaxation in high-purity AlGaAs epilayers. The time for the excitonic photoluminescence to reach its maximum intensity, defined as tmax, shows a nonmonotonic dependence on excitation density which is attributed to a competition between exciton localization and carrier–carrier scattering. A phenomenological four level model fully describes the influence of exciton localization on tmax. This localization effect is enhanced by the increase of the Al content in the alloy and disappears when localization is hindered by rising the lattice temperature above the exciton trapping energy.
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71.35.Aa Frenkel excitons and self-trapped excitons
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Stability of tris(8-hydroxyquinoline)-aluminum(III) films investigated by vacuum ultraviolet spectroscopic ellipsometry

C. Himcinschi, O. Gordan, G. Salvan, F. Müller, D. R.T. Zahn, C. Cobet, N. Esser, and W. Braun

Appl. Phys. Lett. 86, 111907 (2005); http://dx.doi.org/10.1063/1.1883314 (3 pages) | Cited 4 times

Online Publication Date: 8 March 2005

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The optical constants of tris(8-hydroxyquinoline)-aluminum(III) (Alq3) thin films were determined in the vacuum ultraviolet range up to 9.5 eV by in situ spectroscopic ellipsometry measurements performed using synchrotron radiation. The exposure to atmosphere of the Alq3 films grown by organic molecular-beam deposition induces changes in ellipsometric spectra that are interpreted in terms of surface morphology changes. Alq3 films deposited by organic vapor phase deposition were found to be more stable upon exposure to atmosphere. Employing time-dependent density functional theory calculations, the features of the extinction coefficient were assigned to singlet-singlet transitions.
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81.05.Hd Other semiconductors
78.66.Li Other semiconductors
78.40.Me Organic compounds and polymers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
81.65.Cf Surface cleaning, etching, patterning
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Mechanical strain and defect distributions in GaAs-based diode lasers monitored during operation

Tran Quoc Tien, Jens W. Tomm, Myriam Oudart, and Julien Nagle

Appl. Phys. Lett. 86, 111908 (2005); http://dx.doi.org/10.1063/1.1883716 (3 pages) | Cited 6 times

Online Publication Date: 8 March 2005

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We monitor the mechanical strain and the defect concentration in AlGaAs–GaAs-based high-power diode laser arrays. This allows studying the interplay between these extrinsic parameters in dependence on device operation. There are two parameters, which contribute to the spread of the mechanical strain, the local position at the device, and, the device operation time that substantially enhances the strain. For midgap levels as well as shallower defect levels, which are due to physically different defects, very different creation scenarios are observed. The concentration of shallow defects and band-tail states is strongly correlated with compressive strain in their vicinity, no matter how the strain is created. For midgap levels, there is no direct correlation; however, an increase by a factor of 3 after 1500 h of operation time is observed. The knowledge on defect creation scenarios is extensible to other GaAs-based devices.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
71.55.Eq III-V semiconductors

Macroscopic energy transport in ZnO monitored by spatiotemporally resolved luminescence

Heiko Priller, Manuel Decker, Robert Hauschild, Heinz Kalt, and Claus Klingshirn

Appl. Phys. Lett. 86, 111909 (2005); http://dx.doi.org/10.1063/1.1882746 (3 pages) | Cited 11 times

Online Publication Date: 9 March 2005

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We report on an experimental study of macroscopic energy transfer in ZnO bulk crystals. We observe the ultraviolet photoluminescence (PL) emission from the near band edge (3.4 eV at room temperature), a green emission band from a deep center transition, and an orange emission band. Unusually, the orange PL is not only visible at the excitation spot and at crystal edges, but we also observe a slow spatial expansion of the light emission in the orange band up to a distance of several millimeters. In contrast to that, the green and ultraviolet emission originate only from the excitation spot or are scattered from the crystal edges. We investigate the temporal dynamics of the orange PL as a function of the distance from the laser spot, by turning on and off the laser excitation. We describe the results with a two-dimensional diffusion model and discuss some possible mechanisms that may cause this energy transfer, such as Förster/Dexter transfer or a thermally induced hopping process.
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78.55.Et II-VI semiconductors
61.82.Fk Semiconductors
79.20.Ds Laser-beam impact phenomena
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Surfactant-mediated epitaxy of Ge on Si(111): Beyond the surface

Th. Schmidt, R. Kröger, T. Clausen, J. Falta, A. Janzen, M. Kammler, P. Kury, P. Zahl, and M. Horn-von Hoegen

Appl. Phys. Lett. 86, 111910 (2005); http://dx.doi.org/10.1063/1.1882760 (3 pages) | Cited 11 times

Online Publication Date: 9 March 2005

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For a characterization of interface and “bulk” properties of Ge films grown on Si(111) by Sb surfactant-mediated epitaxy, grazing incidence x-ray diffraction and transmission electron microscopy have been used. The interface roughness, defect structure, and strain state have been investigated in dependence of film thickness and growth temperature. For all growth parameters, atomically smooth interfaces are observed. For thin Ge layers, about 75% of the strain induced by the lattice mismatch is relaxed by misfit dislocations at the Ge/Si interface. Only a slight increase of the degree of relaxation is found for thicker films. At growth temperatures below about 600 °C, the formation of twins is observed, which can be avoided at higher temperatures.
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81.05.Cy Elemental semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.Ct Interface structure and roughness
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
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)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.60.Bs Mechanical and acoustical properties

X-ray absorption near-edge fine structure study of AlInN semiconductors

Qixin Guo, Jian Ding, Tooru Tanaka, Mitsuhiro Nishio, and Hiroshi Ogawa

Appl. Phys. Lett. 86, 111911 (2005); http://dx.doi.org/10.1063/1.1886914 (3 pages) | Cited 8 times

Online Publication Date: 9 March 2005

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We have carried out the x-ray absorption near-edge fine structure (XANES) measurements of AlInN at Al K edge and the self-consistent-field real-space multiple-scattering theory calculations. It was demonstrated that the Al K-edge XANES spectra of AlInN are the fingerprints of their composition. The theoretical results could give a reasonable reproduction of the experimental spectral structures. This type of combined use of the experimental XANES and the theoretical calculations must be a powerful tool for systematic and qualitative analysis of the structural and electronic structures of nitride semiconductors.
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78.70.Dm X-ray absorption spectra
68.55.Nq Composition and phase identification

Scanning transmission electron microscopy of ErAs nanoparticles embedded in epitaxial In0.53Ga0.47As layers

Dmitri O. Klenov, Daniel C. Driscoll, Arthur C. Gossard, and Susanne Stemmer

Appl. Phys. Lett. 86, 111912 (2005); http://dx.doi.org/10.1063/1.1885172 (3 pages) | Cited 17 times

Online Publication Date: 10 March 2005

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We use high-angle annular dark-field imaging in scanning transmission electron microscopy to investigate the crystal structure and particle morphology of semimetallic ErAs nanoparticles embedded in epitaxial In0.53Ga0.47As layers. Deposition of increasing amounts of Er results in a higher density of particles and particles coalescence for high amounts. Despite overlap with the matrix through the thickness of the sample used for transmission electron microscopy, the crystal structure of ErAs particles is unambiguously identified as rock salt. The As sublattice is continuous across the interface between the particle and the zinc-blende semiconductor.
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68.35.Ct Interface structure and roughness
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials
68.37.Lp Transmission electron microscopy (TEM)

Single-crystal Ti2AlN thin films

T. Joelsson, A. Hörling, J. Birch, and L. Hultman

Appl. Phys. Lett. 86, 111913 (2005); http://dx.doi.org/10.1063/1.1882752 (3 pages) | Cited 28 times

Online Publication Date: 10 March 2005

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We have produced pure thin-film single-crystal Ti2AlN(0001), a member of the Mn+1AXn class of materials. The method used was UHV dc reactive magnetron sputtering from a 2Ti:Al compound target in a mixed Ar–N2 discharge onto (111) oriented MgO substrates. X-ray diffraction and transmission electron microscopy were used to establish the hexagonal crystal structure with c and a lattice parameters of 13.6 and 3.07 Å, respectively. The hardness H, and elastic modulus E, as determined by nanoindentation measurements, were found to be 16.1±1 GPa and 270±20 GPa, respectively. A room-temperature resistivity for the films of 39 μΩ cm was obtained.
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68.60.Bs Mechanical and acoustical properties
68.55.A- Nucleation and growth
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
73.61.Ey III-V semiconductors
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
62.20.Qp Friction, tribology, and hardness
62.20.D- Elasticity
68.35.Gy Mechanical properties; surface strains
68.37.Lp Transmission electron microscopy (TEM)

Enhanced Raman scattering for temperature measurement of a laser-heated atomic force microscope tip

Brendan McCarthy, Yanming Zhao, Ranjan Grover, and Dror Sarid

Appl. Phys. Lett. 86, 111914 (2005); http://dx.doi.org/10.1063/1.1885178 (3 pages) | Cited 13 times

Online Publication Date: 10 March 2005

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Illuminating a silicon cantilever of an atomic force microscope with a focused laser beam creates heat that can be funneled into a nanoscale area at the apex of its tip. To characterize the heating dynamics and measure the temperature of the tip, a Raman scattering pump-and-probe method is used. It is found that at the apex of the tip the intensity of the Raman Stokes and anti-Stokes components are significantly enhanced relative to those obtained on a bulk silicon sample. Modeling the temperature rise at the tip of the cantilever by a closed-form analytical expression gives good agreement with the Raman measurements. This model can be used to design the structure of the cantilever so that the heat delivery to its tip is optimized. Such an optimized cantilever can potentially be used in high-density, heat-assisted magnetic recording, optical data storage using phase-change media and thermomechanical recording systems, for example, where nanoscale heated regions are of importance.
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07.20.Dt Thermometers
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
61.82.Fk Semiconductors
07.79.Lh Atomic force microscopes
81.40.Gh Other heat and thermomechanical treatments
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.30.Am Elemental semiconductors and insulators

Using local band structure to image strain in semiconductor microstructures

T. H. Stievater, W. S. Rabinovich, D. Park, Peter G. Goetz, J. B. Boos, D. S. Katzer, and M. L. Biermann

Appl. Phys. Lett. 86, 111915 (2005); http://dx.doi.org/10.1063/1.1885181 (3 pages)

Online Publication Date: 10 March 2005

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We demonstrate that polarization-specific nonlinear optical spectroscopy combined with an accurate band structure model can be used to provide a noncontact image of the strain fields within a micromachined quantum well. Optical measurements of the heavy hole excitonic transition strength and anisotropy are converted into measurements of the in-plane strain components with an 8-band k∙p model that includes deformation potentials. The resulting two-dimensional strain image is in excellent agreement with a finite-element structural model of the microstructure, demonstrating the validity of this technique.
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73.21.Fg Quantum wells
81.07.St Quantum wells
68.65.Fg Quantum wells
81.40.Jj Elasticity and anelasticity, stress-strain relations
73.20.At Surface states, band structure, electron density of states
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Triplet exciton interactions in solid films of an electrophosphorescent Pt (II) porphyrin

J. Mężyk, J. Kalinowski, F. Meinardi, and R. Tubino

Appl. Phys. Lett. 86, 111916 (2005); http://dx.doi.org/10.1063/1.1885179 (3 pages) | Cited 14 times

Online Publication Date: 11 March 2005

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We demonstrate the phosphorescence (PH) from neat Pt (II) porphyrin (PtOEP) films to be quenched by bimolecular reactions of monomeric (M) and dimeric (D) triplet (T) excitons. Their respective rate constants, γTT(M) ≅ 8×10−12 cm3/s and γTT(D) ≅ 8×10−15 cm3/s, were found from the kinetics fits to the excitation intensity dependence of the relative PH yield. The exciton decay becomes dominated by mutual annihilation above a critical concentrations of TMcrit ≅ 6.3×1017 cm−3 for M, and TDcrit ≅ 1.2×1019 cm−3 for D triplet excited states. These data allow us to exclude T–T annihilation as the nonradiative pathway quenching the emission from guest aggregates in PtOEP-doped emitters, and predict the onset of the current roll-off in electrophosphorescence efficiency at a current that exceeds four orders of magnitude the values observed experimentally with light-emitting-diodes based on thin PtOEP-doped emitting layers.
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78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
78.60.Fi Electroluminescence
71.35.-y Excitons and related phenomena

Defect reduction in (1math00) m-plane gallium nitride via lateral epitaxial overgrowth by hydride vapor phase epitaxy

B. A. Haskell, T. J. Baker, M. B. McLaurin, F. Wu, P. T. Fini, S. P. DenBaars, J. S. Speck, and Shuji Nakamura

Appl. Phys. Lett. 86, 111917 (2005); http://dx.doi.org/10.1063/1.1866225 (3 pages) | Cited 51 times

Online Publication Date: 11 March 2005

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This letter reports on extended defect density reduction in m-plane (1math00) GaN films achieved via lateral epitaxial overgrowth (LEO) by hydride vapor phase epitaxy. Several dielectric mask patterns were used to produce 10 to 100 μm-thick, partially and fully coalesced nonpolar GaN films. X-ray rocking curves indicated the films were free of wing tilt. Transmission electron microscopy showed that basal plane stacking fault (SF) and threading dislocation (TD) densities decreased from 105 cm−1 and 109 cm−2, respectively, less than 3×103 cm−1 and ∼ 5×106 cm−2, respectively, in the Ga-face (0001) wing of the LEO films. SFs persisted in 〈0001〉-oriented stripe LEO films, though TD reduction was observed in the windows and wings. Band-edge cathodoluminescence intensity increased 2 to 5 times in the wings compared to the windows depending on the stripe orientation. SFs in the low TD density wings of 〈0001〉-stripe films did not appear to act as nonradiative recombination centers.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
61.72.Nn Stacking faults and other planar or extended defects
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.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.37.Lp Transmission electron microscopy (TEM)

Elastic constants and magnetic anisotropy of Co/Pt superlattice thin films

Nobutomo Nakamura, Hirotsugu Ogi, Masahiko Hirao, and Teruo Ono

Appl. Phys. Lett. 86, 111918 (2005); http://dx.doi.org/10.1063/1.1886900 (3 pages) | Cited 3 times

Online Publication Date: 11 March 2005

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This study is devoted to a correlation between elastic constants and magnetic anisotropy of Co/Pt superlattice thin films. Co/Pt superlattice thin films with various Co–Pt layer wavelengths were deposited on monocrystal silicon substrates by an ultrahigh-vacuum-evaporation method, keeping the volume fractions of the Co and Pt layers unchanged. Their perpendicular magnetic anisotropy ranged between −0.2 and 5.0 MJ/m3. Resonant-ultrasound spectroscopy coupled with laser-Doppler interferometry determined their hexagonal-symmetry elastic constants, which correlate with the magnetic anisotropy; higher perpendicular magnetic anisotropy causes larger in-plane elastic moduli and smaller out-of-plane moduli. The correlation is explained by internal elastic strain associated with lattice misfit at the Co–Pt interfaces.
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75.50.Cc Other ferromagnetic metals and alloys
81.05.Bx Metals, semimetals, and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.60.Bs Mechanical and acoustical properties
75.30.Gw Magnetic anisotropy
62.20.D- Elasticity
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.35.Gy Mechanical properties; surface strains
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Effect of hydrogen peroxide treatment on the characteristics of Pt Schottky contact on n-type ZnO

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

Appl. Phys. Lett. 86, 112101 (2005); http://dx.doi.org/10.1063/1.1862772 (3 pages) | Cited 60 times

Online Publication Date: 7 March 2005

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We report on the formation of good Pt Schottky contacts on the Zn-terminated n-type ZnO (0001) surfaces ( ∼ 2×1017 cm−3) using surface treatment with a hydrogen peroxide solution. The Pt contacts on organic solvent-cleaned ZnO (0001) show leaky behavior with a high leakage current of ∼ −0.05 A under −5 V reverse bias voltage, whereas the hydrogen peroxide-treated contacts show Schottky behavior with very low leakage current of ∼ −6.5×10−8 A under −5 V reverse bias voltage. Schottky barrier heights estimated from current-voltage and capacitance-voltage characteristics are 0.89 and 0.93 eV, respectively. Room-temperature photoluminescence results show that the hydrogen peroxide treatment is fairly effective in removing deep-level defects near the ZnO surface region. In addition, the preliminary deep-level transient spectroscopy result is also presented.
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81.05.Dz II-VI semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions
81.65.Cf Surface cleaning, etching, patterning
73.40.Ns Metal-nonmetal contacts
71.55.Gs II-VI semiconductors
78.68.+m Optical properties of surfaces
78.55.Et II-VI semiconductors

Ab initio computation of the mean inner Coulomb potential of amorphous carbon structures

M. Schowalter, J. T. Titantah, D. Lamoen, and P. Kruse

Appl. Phys. Lett. 86, 112102 (2005); http://dx.doi.org/10.1063/1.1885171 (3 pages) | Cited 5 times

Online Publication Date: 7 March 2005

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The mean inner Coulomb potential (MIP) of amorphous carbon structures was computed for slabs with mass densities between ρ = 2.0 g/cm3 and ρ = 3.5 g/cm3 by the full potential linearized augmented plane-wave (FLAPW) method. The amorphous carbon structures consisting of 64 carbon atoms were generated by a classical metropolis Monte Carlo procedure using the Tersoff potential for carbon. The MIP shows a linear dependence on the mass density. Values of the MIP of the amorphous carbon structures are compared with experimental values and with computed values for the MIP of graphite and diamond.
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61.43.Bn Structural modeling: serial-addition models, computer simulation
61.43.Er Other amorphous solids
68.35.B- Structure of clean surfaces (and surface reconstruction)

Hydrogen sensing properties of a Pt‐oxide‐Al0.24Ga0.76As high-electron-mobility transistor

Chin-Chuan Cheng, Yan-Ying Tsai, Kun-Wei Lin, Huey-Ing Chen, and Wen-Chau Liu

Appl. Phys. Lett. 86, 112103 (2005); http://dx.doi.org/10.1063/1.1883721 (3 pages) | Cited 6 times

Online Publication Date: 7 March 2005

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The interesting hydrogen sensing performances of a Pt-oxide-AlGaAs (MOS) high electron mobility transistor (HEMT) are studied and demonstrated. The effects of hydrogen adsorption on device performances such as the threshold voltage shift ΔVth, drain saturation current variation ΔIDS, and transient response are presented. ΔVth and ΔIDS decreased with increasing operating temperature. This suggests that, at higher temperature, less hydrogen atoms diffuse through the Pt bulk and reach the interface between the Pt metal and oxide layer resulting from the relatively faster formation rate of hydroxyl on the Pt surface. The response curves of the studied Pt-AlGaAs MOS HEMT show various profiles at different temperatures. The influences of hydrogen concentration and temperature on the interface sites occupied by adsorbed atoms are also studied.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Tv Field effect devices
82.80.-d Chemical analysis and related physical methods of analysis

Charge transport and recombination in bulk heterojunction solar cells studied by the photoinduced charge extraction in linearly increasing voltage technique

A. J. Mozer, N. S. Sariciftci, L. Lutsen, D. Vanderzande, R. Österbacka, M. Westerling, and G. Juška

Appl. Phys. Lett. 86, 112104 (2005); http://dx.doi.org/10.1063/1.1882753 (3 pages) | Cited 51 times

Online Publication Date: 8 March 2005

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Charge carrier mobility and recombination in a bulk heterojunction solar cell based on the mixture of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-phenylene vinylene] (MDMO-PPV) and 1-(3-methoxycarbonyl)propyl-1-phenyl-(6,6)-C61 (PCBM) has been studied using the novel technique of photoinduced charge carrier extraction in a linearly increasing voltage (Photo-CELIV). In this technique, charge carriers are photogenerated by a short laser flash, and extracted under a reverse bias voltage ramp after an adjustable delay time (tdel). The Photo-CELIV mobility at room temperature is found to be μ = 2×10−4 cm2 V−1 s−1, which is almost independent on charge carrier density, but slightly dependent on tdel. Furthermore, determination of charge carrier lifetime and demonstration of an electric field dependent mobility is presented.
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84.60.Jt Photoelectric conversion

pH measurements with single ZnO nanorods integrated with a microchannel

B. S. Kang, F. Ren, Y. W. Heo, L. C. Tien, D. P. Norton, and S. J. Pearton

Appl. Phys. Lett. 86, 112105 (2005); http://dx.doi.org/10.1063/1.1883330 (3 pages) | Cited 60 times

Online Publication Date: 8 March 2005

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Single ZnO nanorods with Ohmic contacts at either end exhibit large changes in current upon exposing the surface region to polar liquids introduced through an integrated microchannel. The polar nature of the electrolyte introduced led to a change of surface charges on the nanorod, producing a change in surface potential at the semiconductor∕liquid interface. The nanorods exhibit a linear change in conductance between pH 2 and 12 of 8.5 nS/pH in the dark and 20 nS/pH when illuminated with ultraviolet (365 nm) light. The nanorods show stable operation with a resolution of ∼ 0.1 pH over the entire pH range. The results indicate that ZnO nanorods may have applications in integrated chemical, gas, and fluid monitoring sensors.
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82.47.Rs Electrochemical sensors
82.45.Gj Electrolytes
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.40.Mr Semiconductor-electrolyte contacts
73.40.Ns Metal-nonmetal contacts
73.25.+i Surface conductivity and carrier phenomena
72.40.+w Photoconduction and photovoltaic effects

Integration of a gate electrode into carbon nanotube devices for scanning tunneling microscopy

J. Kong, B. J. LeRoy, S. G. Lemay, and C. Dekker

Appl. Phys. Lett. 86, 112106 (2005); http://dx.doi.org/10.1063/1.1883301 (3 pages) | Cited 5 times

Online Publication Date: 8 March 2005

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We have developed a fabrication process for incorporating a gate electrode into suspended single-walled carbon nanotube structures for scanning tunneling spectroscopy studies. The nanotubes are synthesized by chemical vapor deposition directly on a metal surface. The high temperature (800 °C) involved in the growth process poses challenging issues such as surface roughness and integrity of the structure which are addressed in this work. We demonstrate the effectiveness of the gate on the freestanding part of the nanotubes by performing tunneling spectroscopy that reveals Coulomb blockade diamonds. Our approach enables combined scanning tunneling microscopy and gated electron transport investigations of carbon nanotubes.
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85.35.Kt Nanotube devices
81.07.De Nanotubes
73.63.Fg Nanotubes
73.23.Hk Coulomb blockade; single-electron tunneling
61.46.-w Structure of nanoscale materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Hydrogenation∕deuteration of the Si–SiO2 interface: Atomic-scale mechanisms and limitations

L. Tsetseris and S. T. Pantelides

Appl. Phys. Lett. 86, 112107 (2005); http://dx.doi.org/10.1063/1.1883710 (3 pages) | Cited 3 times

Online Publication Date: 8 March 2005

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The mechanisms responsible for exchange of hydrogen with deuterium at the Si–SiO2 interfaces are analyzed through first-principles calculations. The associated reaction barrier is found to be 1.94 eV, in agreement with experiments of Cheng et al. [IEEE Electron. Device Lett. 22, 203 (2001) ; Cheng et al.J. Appl. Phys. 90, 6536 (2001) ] that studied the kinetics of the phenomenon through electrical measurements. The substitution of hydrogen by deuterium can be limited by another possible process, the breakup of the D2 molecule to a pair of Si–D bonds, which has a similar barrier.
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82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Tr Kinetic isotope effects including muonium
82.30.Nr Association, addition, insertion, cluster formation

Electrical characteristics of GaN implanted with Si+ at elevated temperatures

Y. Irokawa, O. Fujishima, T. Kachi, S. J. Pearton, and F. Ren

Appl. Phys. Lett. 86, 112108 (2005); http://dx.doi.org/10.1063/1.1884744 (3 pages) | Cited 4 times

Online Publication Date: 9 March 2005

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Si+ implantation at multiple ion energies (30–360 keV) into GaN for n-type doping was carried out at substrate temperatures from 27 to 700 °C, followed by annealing at 1150–1400 °C for 5 min. At total doses of 2.0×1014 cm−2 (corresponding to an approximately uniform Si concentration of ∼ 4×1018 cm−3), the use of elevated implant temperature does not produce improved electrical characteristics. For anneal temperatures below ∼ 1300 °C, the resulting sheet resistance of the GaN implanted at 700 °C was approximately a factor of 2 higher than for room-temperature implantation, mainly through a lower sheet carrier density. At the higher annealing temperatures (>1300 °C), elevated implant temperature produced similar sheet resistances to implantation carried out at room temperature. For annealing at 1300 °C, the lowest sheet resistances (<700 Ω/◻) and highest activation efficiencies ( ∼ 65%) were obtained for implant temperatures <400 °C. The most plausible explanation is that at these doses, SiGa (i.e., donor state) site occupation is not a strong function of the initial amount of damage created by the implantation.
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73.61.Ey III-V semiconductors
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.50.Dn Low-field transport and mobility; piezoresistance
61.72.Cc Kinetics of defect formation and annealing
61.72.S- Impurities in crystals

Electrical spin injection in multiwall carbon nanotubes with transparent ferromagnetic contacts

S. Sahoo, T. Kontos, C. Schönenberger, and C. Sürgers

Appl. Phys. Lett. 86, 112109 (2005); http://dx.doi.org/10.1063/1.1882761 (3 pages) | Cited 35 times

Online Publication Date: 9 March 2005

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We report on electrical spin injection measurements on multiwall carbon nanotubes (MWNTs). We use a ferromagnetic alloy Pd1−xNix with x ≈ 0.7 which allows us to obtain devices with resistances as low as 5.6 kΩ at 300 K. The yield of device resistances below 100 kΩ, at 300 K, is around 50%. We measure at 2 K a hysteretic magneto-resistance due to the magnetization reversal of the ferromagnetic leads. The relative difference between the resistance in the antiparallel (AP) orientation and the parallel (P) orientation is about 2%.
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75.50.Cc Other ferromagnetic metals and alloys
72.25.Ba Spin polarized transport in metals
72.25.Mk Spin transport through interfaces
75.60.Jk Magnetization reversal mechanisms
75.47.Np Metals and alloys
75.70.Ak Magnetic properties of monolayers and thin films
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Surface recombination velocity of silicon wafers by photoluminescence

D. Baek, S. Rouvimov, B. Kim, T.-C. Jo, and D. K. Schroder

Appl. Phys. Lett. 86, 112110 (2005); http://dx.doi.org/10.1063/1.1884258 (3 pages) | Cited 4 times

Online Publication Date: 9 March 2005

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Photoluminescence (PL) and optical reflection measurements, obtained in the two-wavelength SiPHER PL instrument, are used to determine the surface recombination velocity of silicon wafers. Local measurements and contour maps are possible allowing surface recombination maps to be displayed. This instrument also allows doping and trap density measurements. Surface recombination velocities from 10 to 106 cm/s can be measured on low or high resistivity polished and epitaxial wafers.
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73.61.Cw Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
73.25.+i Surface conductivity and carrier phenomena
78.55.Ap Elemental semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uf Ge and Si
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