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2 Aug 2004

Volume 85, Issue 5, pp. 701-848

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 807 (2004); http://dx.doi.org/10.1063/1.1777817 (3 pages)

Henry J. Liu and Kyeongjae Cho
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Experimental demonstration of a low-loss optical H-tree distribution using silicon-on-insulator microwaveguides

L. Vivien, S. Lardenois, D. Pascal, S. Laval, E. Cassan, J. L. Cercus, A. Koster, J. M. Fédéli, and M. Heitzmann

Appl. Phys. Lett. 85, 701 (2004); http://dx.doi.org/10.1063/1.1772515 (3 pages) | Cited 16 times

Online Publication Date: 27 July 2004

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The experimental demonstration of an optical H-tree distribution from one input to sixteen outputs compatible with the size of a microelectronic chip is reported. It is based on low-loss silicon-on-insulator rib submicron waveguides. Each branch is 1 cm long and includes four ultracompact T splitters and two mirrors allowing 90° direction changes. The mean value of the global losses has been measured and is found equal to 26 dB, which corresponds to a power of 2.6 μW at each output, for a 3 mW laser diode power at the input. This demonstration is an important step for on-chip optical clock distribution in complementary metal–oxide–Semiconductor integrated circuits.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers

Improved performance of 1.3 μm multilayer InAs quantum-dot lasers using a high-growth-temperature GaAs spacer layer

H. Y. Liu, I. R. Sellers, T. J. Badcock, D. J. Mowbray, M. S. Skolnick, K. M. Groom, M. Gutiérrez, M. Hopkinson, J. S. Ng, J. P. R. David, and R. Beanland

Appl. Phys. Lett. 85, 704 (2004); http://dx.doi.org/10.1063/1.1776631 (3 pages) | Cited 112 times

Online Publication Date: 27 July 2004

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The use of a high-growth-temperature GaAs spacer layer is demonstrated to significantly improve the performance of 1.3 μm multilayer self-assembled InAs∕InGaAs dot-in-a-well lasers. The high-growth-temperature spacer layer inhibits threading dislocation formation, resulting in enhanced electrical and optical characteristics. Incorporation of these spacer layers allows the fabrication of multilayer quantum-dot devices emitting above 1.3 μm, with extremely low room-temperature threshold current densities and with operation up to 105°C.
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42.55.Px Semiconductor lasers; laser diodes
68.65.Ac Multilayers
68.18.-g Langmuir-Blodgett films on liquids
78.60.Fi Electroluminescence
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.67.Hc Quantum dots

Integrated horns for improved side coupling into in-plane three-dimensional photonic crystal waveguides

Curtis Sell, Caleb Christensen, Jason Muehlmeier, Gary Tuttle, Zhi-Yuan Li, and Kai-Ming Ho

Appl. Phys. Lett. 85, 707 (2004); http://dx.doi.org/10.1063/1.1772860 (3 pages) | Cited 4 times

Online Publication Date: 27 July 2004

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We examine the frequency response and radiation patterns for horn antennas constructed into a three-dimensional layer-by-layer photonic crystal. These horns resemble a pyramidal cavity and can be built by omitting material during the construction or by removing material from the finished crystal. The horns can be used to couple electromagnetic waves that are incident on the surface of a photonic crystal into an in-plane waveguide within the crystal. The horns are of a design suitable for use at optical frequencies.
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84.40.Ba Antennas: theory, components and accessories
84.40.Az Waveguides, transmission lines, striplines

Lithium iodate nanocrystals in Laponite matrix for nonlinear optical applications

Jérémie Teyssier, Ronan Le Dantec, Christine Galez, Yannick Mugnier, Jacques Bouillot, and Jean-Claude Plenet

Appl. Phys. Lett. 85, 710 (2004); http://dx.doi.org/10.1063/1.1777411 (2 pages) | Cited 3 times

Online Publication Date: 27 July 2004

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A Laponite clay-based lithium iodate nanocomposite have been synthesized for nonlinear optical applications. After addition of lithium iodate aqueous solution to a colloidal suspension of Laponite JS, thin layers are elaborated from this sol using dip-coating technique. After drying and heat treatments between 150 and 220°C, LiIO3 crystallizes in the matrix with nanometer size. As a result of their strong dipolar moment, the LiIO3 crystals can be orientated under an external electric field during nucleation. Planar waveguides have been elaborated on glass substrates and studied using m-lines spectroscopy. The experimental nonlinear optical response has been compared to predictions of a model and an effective nonlinear coefficient deff=1.4 pm∕V has been measured.
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42.79.Gn Optical waveguides and couplers
42.65.-k Nonlinear optics
82.70.Kj Emulsions and suspensions
42.70.Mp Nonlinear optical crystals
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Gh Other heat and thermomechanical treatments

Highly efficient triggered emission of single photons by colloidal CdSe∕ZnS nanocrystals

X. Brokmann, E. Giacobino, M. Dahan, and J. P. Hermier

Appl. Phys. Lett. 85, 712 (2004); http://dx.doi.org/10.1063/1.1775280 (3 pages) | Cited 41 times

Online Publication Date: 27 July 2004

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We demonstrate the realization of a highly efficient triggered source of single photons emitted by colloidal CdSe∕ZnS nanocrystals at room temperature. Under pulsed excitation, the fluorescence of single nanocrystals excited close to saturation exhibits a perfect antibunching and the probability to detect a single emitted photon per excitation pulse reaches 3%, comparable to the best values reported for other emitters. Without any correction, the probability of simultaneously emitting two photons is 25 times lower than for a faint pulsed laser. Combined with recent reports on the reduction of fluorescence intermittency, these results indicate that CdSe∕ZnS nanocrystals are promising single-photon sources.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
82.70.Dd Colloids

Improving the performance of a neodymium aluminium borate microchip laser crystal by resonant pumping

Z. D. Luo, Y. D. Huang, M. Montes, and D. Jaque

Appl. Phys. Lett. 85, 715 (2004); http://dx.doi.org/10.1063/1.1775281 (3 pages) | Cited 12 times

Online Publication Date: 27 July 2004

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Laser action at 1.06 μm from a neodymium aluminium borate microchip laser crystal has been demonstrated under 4F3∕2 direct excitation at 882 nm. We have found that the laser slope efficiency increases from 50% up to 70% when resonant pumping is used instead of the traditional 4I9∕2→4F5∕2( 808 nm) pumping. We conclude that the reduction in the pump-induced heat generation achieved by resonant pumping is at the origin of this improvement.
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42.55.Rz Doped-insulator lasers and other solid state lasers
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Synergism between low-energy neutral particles and energetic ions in the pulsed glow discharge deposition of diamond-like carbon films

I. V. Afanasyev-Charkin and M. Nastasi

Appl. Phys. Lett. 85, 718 (2004); http://dx.doi.org/10.1063/1.1775876 (3 pages) | Cited 6 times

Online Publication Date: 27 July 2004

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Diamond-like carbon films were deposited using pulsed glow discharge deposition at 4 kV. The duty factor was varied and all other parameters were kept constant. It was shown that the contribution of neutral particles to the total number of deposition atoms is much larger than that of energetic ions. At the same time, there is a relationship between the deposition of neutral particles and ion bombardment. The sticking coefficient of the neutral particles in proportional to the flux of energetic ions and does not exceed 5×10−4 for the deposition parameters used in our experiment.
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68.55.A- Nucleation and growth
81.15.Jj Ion and electron beam-assisted deposition; ion plating
52.80.Hc Glow; corona
61.80.Jh Ion radiation effects

Pulsed inductively coupled plasmas as a method to recoup uniformity: Three-dimensional modeling study

Pramod Subramonium and Mark J. Kushner

Appl. Phys. Lett. 85, 721 (2004); http://dx.doi.org/10.1063/1.1776617 (3 pages) | Cited 2 times

Online Publication Date: 27 July 2004

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High plasma density sources such as inductively plasmas (ICPs) are commonly used for microelectronics fabrication. Design constraints often result in systems which have asymmetric gas pumping which can in turn produce azimuthal nonuniformities in plasma properties. These asymmetries are reinforced by a positive feedback between nonuniformities in conductivity and power deposition. In this letter, we discuss computational results from a three-dimensional model for pulsed operation of ICPs sustained in argon as a means to recoup azimuthal symmetry of plasma properties which may result from asymmetric pumping. We found that azimuthally asymmetric plasma properties produced by continuous operation gradually become more uniform during pulsed operation due to the interruption of the positive feedback and allowing interpulse diffusion to smooth asymmetries.
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52.50.Dg Plasma sources
52.25.Fi Transport properties
52.65.-y Plasma simulation
52.77.-j Plasma applications
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Finite size effects in stress analysis of interconnect structures

I. C. Noyan, Conal E. Murray, Jay S. Chey, and Charles C. Goldsmith

Appl. Phys. Lett. 85, 724 (2004); http://dx.doi.org/10.1063/1.1776331 (3 pages) | Cited 12 times

Online Publication Date: 27 July 2004

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Conventional formulations of thermal stress evolution in interconnect structures usually ignore the interface integrity between the various levels. In this letter we present thermal and residual stress versus temperature data from simple copper thin-film structures on silicon. The results indicate that interconnection models which assume fully elastic behavior and perfectly bonded interfaces may yield inaccurate predictions of the thermo-mechanical response for feature sizes smaller than 10 μm.
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68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
85.40.Ls Metallization, contacts, interconnects; device isolation
81.40.Gh Other heat and thermomechanical treatments
68.35.Ct Interface structure and roughness

Evaluation of the discrete energy levels of individual ZnO nanorod single-quantum-well structures using near-field ultraviolet photoluminescence spectroscopy

T. Yatsui, J. Lim, M. Ohtsu, S. J. An, and G.-C. Yi

Appl. Phys. Lett. 85, 727 (2004); http://dx.doi.org/10.1063/1.1776338 (3 pages) | Cited 19 times

Online Publication Date: 27 July 2004

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Spatially and spectrally resolved photoluminescence imaging of individual ZnO∕ZnMgO nanorod single-quantum-well structures (SQWs) with a spatial resolution of 55 nm was performed using the optical near-field technique with a metallized UV fiber probe. Using excitation power density-dependent photoluminescence spectra of a ZnO∕ZnMgO SQW nanorod, we observed the discrete energy levels in a ZnO quantum-well layer.
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73.21.Fg Quantum wells
68.65.Fg Quantum wells
78.67.De Quantum wells
78.55.Et II-VI semiconductors
61.46.-w Structure of nanoscale materials

Disorder and Urbach energy in hydrogenated amorphous carbon: A phenomenological model

G. Fanchini and A. Tagliaferro

Appl. Phys. Lett. 85, 730 (2004); http://dx.doi.org/10.1063/1.1776633 (3 pages) | Cited 26 times

Online Publication Date: 27 July 2004

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We develop a phenomenological model describing the structural and topological effects of the disorder in hydrogenated amorphous carbons (a-C:H), through the analysis of the Raman G-peak width and the optical absorption spectra, providing information on the densities of electronic π ad π* states (πDOS). We show that the Urbach energy is not related to topological disorder but to the Gaussian width (σπ) of the πDOS, peaked at ±Eπ energies above∕below the Fermi level. σπ, on its turn, is not related in a straightforward manner to the disorder. The disorder is better represented by the σπ∕Eπ ratio, expressing the disorder-induced narrowing of the Tauc optical gap.
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71.23.An Theories and models; localized states
73.20.At Surface states, band structure, electron density of states
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Deformation behavior of ion-irradiated polyimide

S. O. Kucheyev, T. E. Felter, M. Anthamatten, and J. E. Bradby

Appl. Phys. Lett. 85, 733 (2004); http://dx.doi.org/10.1063/1.1776618 (3 pages) | Cited 8 times

Online Publication Date: 27 July 2004

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We study nanoindentation hardness, Young’s modulus, and tensile strength of polyimide (Kapton H) films bombarded with MeV light ions in the predominantly electronic stopping power regime. Results show that, for all the ion irradiation conditions studied, bombardment increases the hardness and Young’s modulus and decreases the tensile strength. These changes depend close to linearly on ion fluence and superlinearly (with a power-law exponent factor of ∼1.5) on electronic energy loss. Physical mechanisms of radiation-induced changes to mechanical properties of polyimide are discussed.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
62.20.D- Elasticity
61.80.Jh Ion radiation effects
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness
68.35.Gy Mechanical properties; surface strains

Determination of cations distribution in Mn3O4 by anomalous x-ray powder diffraction

Yanan Xiao, Dale E. Wittmer, Fujio Izumi, Susan Mini, Tim Graber, and P. James Viccaro

Appl. Phys. Lett. 85, 736 (2004); http://dx.doi.org/10.1063/1.1776326 (3 pages)

Online Publication Date: 27 July 2004

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The oxidation states of Mn at two different crystallographic sites in the distorted spinel structure of Mn3O4 were determined by the approach of anomalous synchrotron x-ray powder diffraction. The real parts of anomalous scattering factors for the two Mn sites were refined from a series of powder diffraction patterns collected at the vicinity of K absorption edge of Mn. The results of Rietveld refinements showed that the two distinct cation sites can obviously be distinguished from each other and that Mn2+ ions occupy the tetrahedral site and Mn3+ ions are located at the octahedral site.
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61.66.Fn Inorganic compounds
78.70.Dm X-ray absorption spectra

Anisotropic thermoelectric properties in layered cobaltite AxCoO2 (A=Sr and Ca) thin films

Tsutomu Kanno, Satoshi Yotsuhashi, and Hideaki Adachi

Appl. Phys. Lett. 85, 739 (2004); http://dx.doi.org/10.1063/1.1776310 (3 pages) | Cited 17 times

Online Publication Date: 27 July 2004

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We have fabricated epitaxial thin films of layered cobaltite AxCoO2 (A=Sr and Ca) on sapphire substrates by rf magnetron sputtering. The grown phase in the AxCoO2 films was found to be a monoclinic β-phase of primitive layered cobaltites and the epitaxial orientation of the film could be controlled by the surface plane of the substrates. The resistivity parallel to the CoO2 layers ρ∥ for the β-SrxCoO2 is as low as 2 mΩ cm at room temperature and shows metallic behavior. The ratio of perpendicular resistivity ρ⊥ to ρ∥ increases from 20 at room temperature to 90 at 3 K. More isotropic nature was observed in the Seebeck coefficient. Parallel Seebeck coefficients S∥ of AxCoO2 are approximately 60 μV∕K at room temperature and the perpendicular S⊥ are about half of S∥.
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68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
73.61.Ng Insulators
73.50.Lw Thermoelectric effects
68.55.A- Nucleation and growth

Photovoltage characterization of CuAlO2 crystallites

Th. Dittrich, L. Dloczik, T. Guminskaya, M. Ch. Lux-Steiner, N. Grigorieva, and I. Urban

Appl. Phys. Lett. 85, 742 (2004); http://dx.doi.org/10.1063/1.1776611 (3 pages) | Cited 21 times

Online Publication Date: 27 July 2004

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The delafossite phase of CuAlO2 has been prepared by ion exchange reaction at 475°C. The samples were characterized by x-ray diffraction, transmission electron microscopy, electron diffraction, transient and spectral photovoltage (PV), and diffuse reflectance spectroscopy. The produced CuAlO2 crystallites are p-type and of high electronic quality, i.e., no electronic transitions induced by deep states in the forbidden gap have been observed by PV. The temperature dependence of the optical band gap of CuAlO2 was measured between 80 and 600 K. The band gap of CuAlO2 approximated to 0 K amounts to 3.61 eV. The quenching of the PV signal is thermally activated with an activation energy of 1.8 eV.
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72.40.+w Photoconduction and photovoltaic effects
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Gh Other heat and thermomechanical treatments
68.37.Lp Transmission electron microscopy (TEM)

Evidence from atomistic simulations of fluctuation electron microscopy for preferred local orientations in amorphous silicon

S. V. Khare, S. M. Nakhmanson, P. M. Voyles, P. Keblinski, and J. R. Abelson

Appl. Phys. Lett. 85, 745 (2004); http://dx.doi.org/10.1063/1.1776614 (3 pages) | Cited 14 times

Online Publication Date: 27 July 2004

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Simulations from a family of atomistic structural models for unhydrogenated amorphous silicon suggest that fluctuation electron microscopy experiments have observed orientational order of paracrystalline grains in amorphous silicon. This order may consist of correlations in the orientation of nearby paracrystalline grains or anisotropy in the grain shape. This observation makes a natural connection to the known growth modes of microcrystalline silicon and may be useful for other materials systems.
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68.55.-a Thin film structure and morphology
61.43.Bn Structural modeling: serial-addition models, computer simulation

Structure formation upon reactive direct current magnetron sputtering of transition metal oxide films

J. M. Ngaruiya, O. Kappertz, S. H. Mohamed, and M. Wuttig

Appl. Phys. Lett. 85, 748 (2004); http://dx.doi.org/10.1063/1.1777412 (3 pages) | Cited 22 times

Online Publication Date: 27 July 2004

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A comparative study of reactive direct current magnetron sputtering for different transition metal oxides reveals crystalline films at room temperature for group 4 and amorphous films for groups 5 and 6. This observation cannot be explained by the known growth laws and is attributed to the impact of energetic particles, originating from the oxidized target, on the growing film. This scenario is supported by measured target characteristics, the evolution of deposition stress of the films, and the observed backsputtering.
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81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
61.05.cm X-ray reflectometry (surfaces, interfaces, films)

Sphalerite–rock salt phase transition in ZnMnSe heterostructures

D. Litvinov, D. Gerthsen, A. Rosenauer, B. Daniel, and M. Hetterich

Appl. Phys. Lett. 85, 751 (2004); http://dx.doi.org/10.1063/1.1775285 (3 pages) | Cited 6 times

Online Publication Date: 27 July 2004

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We report on the investigation of epitaxial MnSe layers grown on ZnSe by transmission electron microscopy. MnSe∕ZnSe superlattices (SLs) with different nominal MnSe thicknesses tMnSe between 2 and 20 monolayers (MLs) were investigated, which were grown by molecular-beam epitaxy on GaAs(001) substrates. Composition profiles of the SLs were evaluated by the measurement of local (002) lattice parameters in growth direction. A MnSe deposition between 2 and 4 MLs on ZnSe leads to the formation of intermixed Zn1−xMnxSe layers with sphalerite structure and a Mn concentration x increasing from 50% to 90%. For MnSe layers with a thickness between 6 and 20 ML, we observe 5–10 nm small MnSe inclusions with a rock salt structure embedded in sphalerite Zn1−xMnxSe with approximately 90%Mn.
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68.65.Cd Superlattices
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
68.55.A- Nucleation and growth
64.70.K- Solid-solid transitions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Effective optical manipulation of the charge state and emission intensity of the InAs∕GaAs quantum dots by means of additional infrared illumination

E. S. Moskalenko, K. F. Karlsson, V. Donchev, P. O. Holtz, B. Monemar, W. V. Schoenfeld, and P. M. Petroff

Appl. Phys. Lett. 85, 754 (2004); http://dx.doi.org/10.1063/1.1773374 (3 pages)

Online Publication Date: 27 July 2004

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InAs quantum dots (QDs) at different levels of density have been studied by means of photoluminescence, when in addition to the main laser, a second infrared (IR) laser is employed to excite the QD. It is demonstrated that the IR laser considerably affects the QD charge state as well as the emission intensity level (an increase greater than fivefold was observed). These effects are explained in terms of separate generation of excess electrons and holes provided under dual-laser excitation. However, these effects progressively vanish with increasing QD density. The results obtained unambiguously imply that the emission intensity from the QD can be effectively enhanced by purely optical means.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
73.21.La Quantum dots
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Change of the electrical properties in Fe-Al2O3 granular films

M. A. S. Boff, S. R. Teixeira, J. E. Schmidt, and A. B. Antunes

Appl. Phys. Lett. 85, 757 (2004); http://dx.doi.org/10.1063/1.1775890 (2 pages) | Cited 4 times

Online Publication Date: 27 July 2004

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A systematic study of the electrical resistance as a function of the temperature was performed in Fe-Al2O3 granular thin films. Our findings revealed a nonlinear dependence of the current versus voltage in the low field regime at low temperature. The variable range hopping mechanism is the best description of the behavior of our samples. A change of the electronic properties can be observed depending on the direct current applied to the sample’s plane, and is related to different localization lengths.
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73.61.Ng Insulators
72.20.Ee Mobility edges; hopping transport

Gallium concentration dependence of room-temperature near-band-edge luminescence in n-type ZnO:Ga

T. Makino, Y. Segawa, S. Yoshida, A. Tsukazaki, A. Ohtomo, and M. Kawasaki

Appl. Phys. Lett. 85, 759 (2004); http://dx.doi.org/10.1063/1.1776630 (3 pages) | Cited 68 times

Online Publication Date: 27 July 2004

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We investigated the optical properties of epitaxial n-type ZnO films grown on lattice-matched ScAlMgO4 substrates. As the Ga doping concentration increased up to 6×1020 cm−3, the absorption edge showed a systematic blueshift, consistent with the Burstein–Moss effect. A bright near-band-edge photoluminescence (PL) could be observed even at room temperature, the intensity of which increased monotonically as the doping concentration was increased except for the highest doping level. It indicates that nonradiative transitions dominate at a low doping density. Both a Stokes shift and broadening in the PL band are monotonically increasing functions of donor concentration, which was explained in terms of potential fluctuations caused by the random distribution of donor impurities.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors
61.72.uj III-V and II-VI semiconductors

Removal of thick (>100 nm) InGaN layers for optical devices using band-gap-selective photoelectrochemical etching

E. D. Haberer, R. Sharma, A. R. Stonas, S. Nakamura, S. P. DenBaars, and E. L. Hu

Appl. Phys. Lett. 85, 762 (2004); http://dx.doi.org/10.1063/1.1776615 (3 pages) | Cited 24 times

Online Publication Date: 27 July 2004

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We report on band-gap-selective photoelectrochemical (PEC) etching of thick InGaN layers for use in optical devices, such as GaN microdisks, distributed Bragg reflectors, and two-dimensional photonic crystal membranes. Three InGaN sacrificial layer structures are studied: a 300 nm InGaN layer, an InGaN∕GaN superlattice, and an InGaN∕InGaN superlattice. Calculated equilibrium band diagrams of the epitaxial structures are used to explain the observed etching behavior. The strong piezoelectric-induced fields within the InGaN sacrificial layers are found to greatly affect carrier confinement and etching behavior. As a demonstration of the etching technique, a free-standing GaN microdisk on an InGaN post is fabricated.
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68.65.Cd Superlattices
81.65.Cf Surface cleaning, etching, patterning
77.65.-j Piezoelectricity and electromechanical effects
68.55.-a Thin film structure and morphology
82.45.Mp Thin layers, films, monolayers, membranes
64.60.F- Equilibrium properties near critical points, critical exponents
81.30.Dz Phase diagrams of other materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Influence of the hole injection layer on the luminescent performance of organic light-emitting diodes

Shih-Fang Chen and Ching-Wu Wang

Appl. Phys. Lett. 85, 765 (2004); http://dx.doi.org/10.1063/1.1775282 (3 pages) | Cited 39 times

Online Publication Date: 27 July 2004

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We investigate the influence of the hole injection layer (HIL) on the performance of vapor-deposited tris-(8-hydroxyquinoline) aluminum-based organic light-emitting diodes. Four different HIL materials were used: 4,4′, 4″-tris{N,(3-methylphenyl)-N-phenylamino}-triphenylamine) (m-MTDATA), 4,4′, 4″-tris{N,-(2-naphthyl)-N-phenylamino}-triphenylamine, copper phthalocyanine, and oxotitanium phthalocyanine. In all cases, Alq3 acts as the emitting layer as well as electron-transporting layers. Evidence showed that m-MTDATA exhibits a dense film structure and fine surface morphology, leading to easier hole migration at the indium tin oxide/m-MTDATA and m-MTDATA/hole-transport layer junctions. It also possesses a shallow bulk trap level, providing more detrapping holes from the bulk trap states to highest occupied molecular orbital states for transporting in m-MTDATA. We suggest that these are the main contributing factors to the superior current density–voltage and luminance-voltage performance of this device.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Background charge fluctuation in a GaAs quantum dot device

S. W. Jung, T. Fujisawa, Y. Hirayama, and Y. H. Jeong

Appl. Phys. Lett. 85, 768 (2004); http://dx.doi.org/10.1063/1.1777802 (3 pages) | Cited 25 times

Online Publication Date: 27 July 2004

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We investigate background charge fluctuation in a GaAs quantum dot device by measuring 1∕f noise in the single-electron tunneling current through the dot. The current noise is understood as fluctuations of the confinement potential and tunneling barriers. The estimated potential fluctuation increases almost linearly with temperature, which is consistent with a simple model of the 1∕f noise. We find that the fluctuation increases very slightly when electrons are injected into excited states of the quantum dot.
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85.35.Gv Single electron devices
73.63.Kv Quantum dots
73.23.Hk Coulomb blockade; single-electron tunneling
72.70.+m Noise processes and phenomena

Increase of free carrier lifetime in nonpolar a-plane GaN grown by epitaxial lateral overgrowth

S. Juršènas, E. Kuokštis, S. Miasojedovas, G. Kurilčik, A. Žukauskas, C. Q. Chen, J. W. Yang, V. Adivarahan, and M. Asif Khan

Appl. Phys. Lett. 85, 771 (2004); http://dx.doi.org/10.1063/1.1777409 (3 pages) | Cited 7 times

Online Publication Date: 27 July 2004

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Carrier recombination dynamics in epitaxial a-plane GaN and fully coalesced epitaxial laterally overgrown (ELOG) a-plane GaN films has been studied by means of time-resolved photoluminescence under high photoexcitation. The results were compared with conventional c-plane GaN films grown under similar conditions. In a-plane GaN epilayers, the total efficiency of electron-hole plasma spontaneous luminescence decreases 20 times, whereas the luminescence decay time reduces from τLU=42 to τLU⩽10 ps in comparison with c-plane GaN films. Meanwhile, an essential increase in total emission efficiency (by more than two orders of magnitude) and an increase of the decay time up to τLU=430 ps have been observed for an ELOG a-plane sample in comparison with a-plane GaN films. This confirms a significant reduction of the nonradiative recombination rate for nonequilibrium carriers. Assuming a saturation of the nonradiative deep-level transitions, the room-temperature free-carrier lifetime of τ=910 ps for ELOG a-plane GaN sample was obtained, which indicates on an excellent quality of the a-plane ELOG GaN films.
Show PACS
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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