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27 Jul 1998

Volume 73, Issue 4, pp. 423-552

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Effect of crystal phases on refractive index profiles of annealed proton-exchanged waveguides in X-cut LiTaO3

D. B. Maring, R. F. Tavlykaev, R. V. Ramaswamy, Yu. N. Korkishko, V. A. Fedorov, and J. M. Zavada

Appl. Phys. Lett. 73, 423 (1998); http://dx.doi.org/10.1063/1.122220 (3 pages) | Cited 4 times

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A complete structural phase diagram of annealed proton-exchanged X-cut LiTaO3 is presented, to relate refractive index change to proton-induced lattice deformation. From this diagram, explanations for the previously observed phenomena of index increase upon annealing and index decrease with increasing proton concentration (above a certain value) are derived. We have analyzed the evolution of index profiles during postexchange annealing, describing how the presence of multiple phases within a waveguide can lead to large index variations and buried index profiles. Finally, we identify at least two high-concentration phases that exhibit large temporal instabilities. © 1998 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects

White light emission from exciplex in a bilayer device with two blue light-emitting polymers

Ching-Ian Chao and Show-An Chen

Appl. Phys. Lett. 73, 426 (1998); http://dx.doi.org/10.1063/1.121888 (3 pages) | Cited 107 times

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Bilayer polymer light-emitting diodes with two blue light-emitting materials, poly(N-vinylcarbazole) (PVK) and poly(2-dodecyl-p-phenylene) (C12O-PPP), can emit blue or white light, depending on the solvent used in the fabrication of the second layer, C12O-PPP. If hexane (the nonsolvent for PVK) is used, the device emits blue light as a single layer device with C12O-PPP. However, if toluene (the cosolvent for the two polymers) is used, the device emits white light originating from an exciplex emission at the bilayer interface in addition to the exciton emission from C12O-PPP. At low temperatures, the intensity of the exciplex emission drops and that of the exciton emission becomes dominant. © 1998 American Institute of Physics.
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85.60.Jb Light-emitting devices
71.35.-y Excitons and related phenomena

Thick lens model for self-focusing in Kerr medium

Yu-Chuan Chen and Wei-Zhu Lin

Appl. Phys. Lett. 73, 429 (1998); http://dx.doi.org/10.1063/1.121889 (3 pages) | Cited 3 times

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An asymmetric “thick-lens” model for self-focusing in Kerr medium of finite thickness is presented by introducing a complex curvature radius of a Gaussian beam in nonlinear medium and a transfer matrix for the transition from linear to nonlinear medium. With this model the linear ABCD-matrix formalism can be extended to nonlinear optical systems with a clear physical insight. The modulation of the cavity transverse mode of a resonator containing a Kerr medium is characterized by the asymmetry of the “thick lens.” The intracavity small-signal relative spot size variation outside as well as inside the Kerr medium can be calculated efficiently with the “thick-lens”-like matrix formalisms. Criteria for the design and optimization of a Kerr-lens mode-locked laser resonator with a hard or soft aperture are predicted. © 1998 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.79.Bh Lenses, prisms and mirrors

Third harmonic generation through coupled second-order nonlinear optical parametric processes in quasiperiodically domain-inverted Sr0.6Ba0.4Nb2O6 optical superlattices

Yong-yuan Zhu, R. F. Xiao, J. S. Fu, G. K. L. Wong, and Nai-ben Ming

Appl. Phys. Lett. 73, 432 (1998); http://dx.doi.org/10.1063/1.121890 (3 pages) | Cited 18 times

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A one-dimensional quasiperiodically domain-inverted optical superlattice has been designed and fabricated in a strontium barium niobate (Sr0.6Ba0.4Nb2O6) single-crystal plate. A third harmonic output generated through coupled second-order nonlinear parametric processes with a conversion efficiency of about 1.6% was obtained when both the second harmonic and the third harmonic were simultaneously quasiphase matched in the crystal. © 1998 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Mp Nonlinear optical crystals
78.66.Nk Insulators

Control of microcavity effects in full color stacked organic light emitting devices

P. E. Burrows, V. Khalfin, G. Gu, and S. R. Forrest

Appl. Phys. Lett. 73, 435 (1998); http://dx.doi.org/10.1063/1.121891 (3 pages) | Cited 33 times

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We model a three-color stacked organic light emitting device (SOLED) and determine the influence of microcavity effects on the color saturation of the layered, light emitting elements. Using the model, we design and demonstrate a SOLED with good color saturation and minimal viewing angle effects. The Commission Internationale de L’Éclairage chromaticity coordinates for the red, green, and blue subpixels of the SOLED are (0.68, 0.32), (0.32, 0.53), and (0.14, 0.19), respectively. The full color SOLED opens a path to full color, lightweight displays utilizing vertically stacked color elements to maximize the resolution and aperture ratio of the display. © 1998 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems

Photoluminescence from gas-suspended SiOx nanoparticles synthesized by laser ablation

David B. Geohegan, Alex A. Puretzky, Gerd Duscher, and Stephen J. Pennycook

Appl. Phys. Lett. 73, 438 (1998); http://dx.doi.org/10.1063/1.121892 (3 pages) | Cited 49 times

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Time-resolved photoluminescence (PL) spectra are reported for gas-suspended 1–10 nm diameter SiOx particles formed by laser ablation of Si into 1–10 Torr He and Ar. Three spectral bands (1.8, 2.5 and 3.2 eV) similar to PL from oxidized porous silicon were measured, but with a pronounced vibronic structure. Particle size and composition were determined with Z-contrast transmission electron microscopy imaging and high resolution electron energy loss spectroscopy linescans of individual nanoparticles. Maximized violet (3.2 eV) PL from the gas-suspended nanoparticles was correlated with an ex situ SiO1.4 overall particle stoichiometry. Cryogenically-collected gas-suspended nanoparticles produced web-like-aggregate films exhibiting very weak PL. Standard anneals restored strong PL bands without vibronic structure, but otherwise in agreement with the PL measured from the gas-suspended nanoparticles. © 1998 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.66.Jg Amorphous semiconductors; glasses
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.65.-b Surface treatments
78.47.-p Spectroscopy of solid state dynamics
79.20.Kz Other electron-impact emission phenomena

Raman spectra of the ordered vacancy compounds CuIn3Se5 and CuGa3Se5

C. Rincón, S. M. Wasim, G. Marín, J. M. Delgado, J. R. Huntzinger, A. Zwick, and J. Galibert

Appl. Phys. Lett. 73, 441 (1998); http://dx.doi.org/10.1063/1.121893 (3 pages) | Cited 33 times

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The optical vibrational modes of the ordered vacancy compounds CuIn3Se5 and CuGa3Se5 have been obtained by Raman spectra at various temperatures. The totally symmetric A1 mode appears around 155 and 167 cm−1 in CuIn3Se5 and CuGa3Se5, respectively. All the lines observed, except the B1 modes, present a reduction in their frequencies by about 10% as compared to the corresponding values in the CuInSe2 and CuGaSe2 chalcopyrites. This is due to the presence in these compounds of an array of vacancies occupying particular sites in the cation sublattice. These tend to relax the stretching forces thus reducing the vibrational frequencies. © 1998 American Institute of Physics.
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78.30.Hv Other nonmetallic inorganics
61.72.J- Point defects and defect clusters
63.20.kp Phonon-defect interactions

Coherent terahertz radiation detection: Direct comparison between free-space electro-optic sampling and antenna detection

Y. Cai, I. Brener, J. Lopata, J. Wynn, L. Pfeiffer, J. B. Stark, Q. Wu, X. C. Zhang, and J. F. Federici

Appl. Phys. Lett. 73, 444 (1998); http://dx.doi.org/10.1063/1.121894 (3 pages) | Cited 41 times

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We compare the use of free-space electro-optic sampling (FSEOS) with photoconducting antennas to detect terahertz (THz) radiation in the range of 0.1–3 THz. For the same average THz power and low-frequency modulation, signal-to-noise ratio and sensitivity are better with antenna detection at frequencies smaller than 3 THz. When the modulation frequency is increased to more than 1 MHz in FSEOS, both detection schemes have comparable performance. Using a singular-electric-field THz emitter, we demonstrate the feasibility of a THz imaging system using real-time delay scanning in FSEOS and only 20 mW of laser power. © 1998 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
84.40.Ba Antennas: theory, components and accessories
85.60.-q Optoelectronic devices
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Noncontact excitation of high Q acoustic resonances in glass plates

Adrian C. Stevenson and Christopher R. Lowe

Appl. Phys. Lett. 73, 447 (1998); http://dx.doi.org/10.1063/1.121895 (3 pages) | Cited 8 times

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The applications of magnetic direct generation, a noncontact technique for generating acoustic waves, are limited by poor transduction efficiency. This letter describes an approach for substantially improving the transduction efficiency by application of a transduction format, enhanced direct magnetic generation, that utilizes continuous wave resonances and thin film generation. Glass plates coated with thin films of aluminium have been used as free-standing acoustic cavities to generate resonances with high transduction efficiencies and Q factors. These acoustic resonances have been excited without mechanical contact and their origin and characteristics are discussed with respect to resonances in 530 μm thick aluminized silica plates. The consequences of magnetic direct generation applied to thin metal films, as opposed to bulk metal, are also discussed, particularly with respect to high operating frequencies and acoustic Q factors. It is possible that novel sensors and time standards may be constructed by exploiting this approach. © 1998 American Institute of Physics.
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43.25.Gf Standing waves; resonance
43.38.Ar Transducing principles, materials, and structures: general
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Bond-orientational order in sheared dense flows of inelastic hard spheres

Piroz Zamankhan, William Polashenski, Hooman Vahedi Tafreshi, Pertti J. Sarkomaa, and Caroline L. Hyndman

Appl. Phys. Lett. 73, 450 (1998); http://dx.doi.org/10.1063/1.121896 (3 pages) | Cited 3 times

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Three-dimensional bond-orientational order is studied using computer simulations with 4296 hard, monodisperse inelastic spheres flowing in a Couette geometry at a high shear rate. At an average volume fraction close to 0.6, a state with extended correlations in the orientations of particle clusters starts to develop for rough particles after sufficiently long run times. However, no clear evidence of crystallization is found in the system. Further tests of a sheared system comprised of smooth, inelastic spheres reveal crystallization consistent with the previous experimental observations. © 1998 American Institute of Physics.
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47.15.Fe Stability of laminar flows
47.27.-i Turbulent flows
61.20.Ja Computer simulation of liquid structure

High-frequency electron beam modulation in a diode with an active plasma cathode

Ya. E. Krasik, A. Dunaevsky, and J. Felsteiner

Appl. Phys. Lett. 73, 453 (1998); http://dx.doi.org/10.1063/1.121897 (3 pages) | Cited 9 times

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We have carried out experiments with an active plasma cathode showing the possibility to generate a modulated electron beam with a repetition rate of 2 Hz without the use of a high-frequency power supply. The modulation of the beam current amplitude reaches values ≥ 30%. This modulation is found to have a frequency of 325±5 MHz for a discharge capacitor of 1 nF and a duration ≥ 1 μs. In addition, the modulated electron beam is accompanied by electromagnetic radiation with the same frequency. We suggest that this high-frequency modulation is caused by electron oscillations within the potential well which is created inside the cathode structure by the positive potential of the plasma. © 1998 American Institute of Physics.
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41.75.Fr Electron and positron beams
07.77.Ka Charged-particle beam sources and detectors
52.59.Mv High-voltage diodes

Precise control of atomic nitrogen production in an electron cyclotron resonance plasma using N2/noble gas mixtures

Z. Y. Fan and N. Newman

Appl. Phys. Lett. 73, 456 (1998); http://dx.doi.org/10.1063/1.121898 (3 pages) | Cited 13 times

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The atomic nitrogen flux and impacting ion kinetic energy are two important parameters which influence the quality of deposited nitride films using reactive growth. In this letter, a method is described to control the flux and kinetic energy of atomic and molecular nitrogen ions using an electron cyclotron resonance plasma with N2/Ar and N2/Ne gas mixtures. The results clearly show that the addition of neon to nitrogen plasma can remarkably enhance the production rate of atomic nitrogen due to Penning ionization involving the metastable state of Ne. In contrast, the addition of argon significantly decreases the rate. © 1998 American Institute of Physics.
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34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)
31.50.Df Potential energy surfaces for excited electronic states
52.50.Dg Plasma sources
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Destruction of ozone-depleting substances in a thermal plasma reactor

A. B. Murphy and T. McAllister

Appl. Phys. Lett. 73, 459 (1998); http://dx.doi.org/10.1063/1.121899 (3 pages) | Cited 9 times

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A two-dimensional numerical model of the PLASCON™ plasma reactor is used to investigate the destruction of ozone-depleting substances in the reactor. The model includes electromagnetic, fluid dynamic and chemical kinetic phenomena. Calculated temperature, flow and species concentration fields within the plasma torch, the injection manifold and the reaction tube are presented for the case of the destruction of CFC-12 (CF2Cl2). Conversion of CFC-12 to CFC-13 (CF3Cl), a more stable ozone-depleting substance, is found to occur in the region close to the injection manifold, and to be unaffected by reaction tube geometry. CFC-13 is predicted to be the dominant ozone-depleting substance in the exhaust gas. The predictions of the model are found to be in good agreement with measurements of the exhaust gas composition. © 1998 American Institute of Physics.
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82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.65.-y Plasma simulation
52.75.Hn Plasma torches
52.30.-q Plasma dynamics and flow
82.20.Wt Computational modeling; simulation
52.25.-b Plasma properties
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Viscosity of eutectic Pd78Cu6Si16 measured by the oscillating drop technique in microgravity

I. Egry, G. Lohöfer, I. Seyhan, S. Schneider, and B. Feuerbacher

Appl. Phys. Lett. 73, 462 (1998); http://dx.doi.org/10.1063/1.121900 (2 pages) | Cited 25 times

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During the STS-83 Spacelab mission, a sample of Pd78Cu6Si16 was processed in the electromagnetic levitation facility TEMPUS. Surface oscillations of the levitated liquid droplet were excited, and frequency and damping of the oscillations were observed. Under microgravity conditions, the damping constant is simply related to the viscosity. This method was successfully applied. The experiments were performed in a temperature range of 400 K, including the eutectic temperature Te = 1033 K. At this temperature, our data agree well with those of S. K. Lee, K. H. Tsang, and H. W. Kui [J. Appl. Phys. 70, 4842 (1991)]. © 1998 American Institute of Physics.
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66.20.-d Viscosity of liquids; diffusive momentum transport

Thickness dependence of dielectric loss in SrTiO3 thin films

Hong-Cheng Li, Weidong Si, Alexander D. West, and X. X. Xi

Appl. Phys. Lett. 73, 464 (1998); http://dx.doi.org/10.1063/1.121901 (3 pages) | Cited 88 times

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We have measured the dielectric loss in SrTiO3 thin films grown on SrRuO3 electrode layers with thickness ranging from 25 nm to 2.5 μm. The loss depends strongly on the thickness but differently above and below T ≈ 80 K: as the thickness increases, the loss decreases at high temperatures but becomes higher at low temperatures. Our result suggests that, in the high temperature regime, the interfacial dead layer effect dominates while, in the low temperature regime, the losses related to the structural phase transition and quantum fluctuations are important. © 1998 American Institute of Physics.
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77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)

On the role of interface imperfections in thermoelectric nondestructive materials characterization

Jiangtao Hu and Peter B. Nagy

Appl. Phys. Lett. 73, 467 (1998); http://dx.doi.org/10.1063/1.121902 (3 pages) | Cited 12 times

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This letter draws attention to a previously unnoticed artifact associated with the most common type of thermoelectric nondestructive materials characterization technique. It is shown that contact heating between the specimen to be tested and the reference electrode gives rise to a considerable offset in the measured thermoelectric voltage. The resulting bias significantly reduces the feasibility of thermoelectric measurements in nondestructive testing applications that require sensitive materials discrimination, for example, to sort metals of similar alloying content, to distinguish similar grades of heat treatment, and to detect slight variations in the thermoelectric power of metals due to hardening, texture, fatigue, etc. It is also suggested that the demonstrated intrinsic sensitivity of the thermoelectric contact technique to imperfect interfaces could be exploited for nondestructive detection of tightly compressed but metallurgically not bonded interfaces in spot welds, diffusion bonds, and other types of solid-state bonds. © 1998 American Institute of Physics.
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81.70.Ex Nondestructive testing: electromagnetic testing, eddy-current testing
68.35.Gy Mechanical properties; surface strains
81.40.Gh Other heat and thermomechanical treatments

Wide viewing angle, homeotropic nematic liquid-crystal display controlled by effective field

S. H. Lee, H. Y. Kim, Y. H. Lee, I. C. Park, B. G. Rho, H. G. Galabova, and D. W. Allender

Appl. Phys. Lett. 73, 470 (1998); http://dx.doi.org/10.1063/1.121903 (3 pages) | Cited 11 times

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The electro-optic properties of a liquid-crystal display associated with a homeotropic to multidomainlike transition for a liquid crystal with a positive dielectric anisotropy have been investigated. The cell plates are prepared in such a way that, in the absence of an electric field, the liquid-crystal alignment is homeotropic. an electric field created by interdigitated electrodes on both substrates causes a director deformation of a multidomain type. The display shows wide viewing angle, excellent color characteristics, and a fast response time. The molecular director configuration, together with the electro-optic characteristics of the device, are discussed in this letter. © 1998 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems

Stress-induced amorphization at moving crack tips in NiTi

P. R. Okamoto, J. K. Heuer, N. Q. Lam, S. Ohnuki, Y. Matsukawa, K. Tozawa, and J. F. Stubbins

Appl. Phys. Lett. 73, 473 (1998); http://dx.doi.org/10.1063/1.121904 (3 pages) | Cited 22 times

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In situ fracture studies have been carried out on thin films of the NiTi intermetallic compound under plane stress, tensile loading conditions in the high-voltage electron microscope. Local stress-induced amorphization of regions directly in front of moving crack tips has been observed. The upper cutoff temperature, TC–Amax, for the stress-induced crystalline-to-amorphous transformation was found to be 600 K, identical to that for heavy ion-induced amorphization of NiTi and for ion-beam mixing-induced amorphization of Ni and Ti multilayer specimens. 600 K is also both the lower cutoff temperature, TA–Cmin, for radiation-induced crystallization of initially-unrelaxed amorphous NiTi and the lowest isothermal annealing temperature, TXmin, at which stress-induced amorphous NiTi crystallizes. Since TXmin should be TK, the ideal glass transition temperature, the discovery that TC–Amax = TA–Cmin = TXmin = TK implies that disorder-driven crystalline-to-amorphous transformations result in the formation of the ideal glass, i.e., the glassy state that has the same entropy as that of the defect-free crystal. As the glassy state with the lowest free energy, its formation can be understood as the most energetically-favored, kinetically-constrained response of crystalline alloys driven far from equilibrium. © 1998 American Institute of Physics.
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62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
64.70.K- Solid-solid transitions
65.20.-w Thermal properties of liquids
65.40.gd Entropy
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

Phase transition of C60 crystal in high temperature regime

Feng Yan and Ye-Ning Wang

Appl. Phys. Lett. 73, 476 (1998); http://dx.doi.org/10.1063/1.121905 (2 pages) | Cited 2 times

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The internal friction of the polycrystalline C60 films was measured in the temperature range of 320–620 K. Around 426 K, a λ-shaped internal friction peak was detected. The peak was interpreted in terms of another phase transition above the order-disorder phase transition temperature. © 1998 American Institute of Physics.
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64.70.K- Solid-solid transitions
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
68.60.Wm Other nonelectronic physical properties
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations

Luminescence characteristics of impurities-activated ZnS nanocrystals prepared in microemulsion with hydrothermal treatment

S. J. Xu, S. J. Chua, B. Liu, L. M. Gan, C. H. Chew, and G. Q. Xu

Appl. Phys. Lett. 73, 478 (1998); http://dx.doi.org/10.1063/1.121906 (3 pages) | Cited 83 times

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Cu-, Eu-, or Mn-doped ZnS nanocrystalline phosphors were prepared at room temperature using a chemical synthesis method. Transmission electron microscopy observation shows that the size of the ZnS clusters is in the 3–18 nm range. New luminescence characteristics such as strong and stable visible-light emissions with different colors were observed from the doped ZnS nanocrystals at room temperature. These results strongly suggest that impurities, especially transition metals and rare-earth metals-activated ZnS nanoclusters form a new class of luminescent materials. © 1998 American Institute of Physics.
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78.55.Et II-VI semiconductors
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization

Transmission electron microscopy of defects in GaN films formed by epitaxial lateral overgrowth

Akira Sakai, Haruo Sunakawa, and Akira Usui

Appl. Phys. Lett. 73, 481 (1998); http://dx.doi.org/10.1063/1.121907 (3 pages) | Cited 79 times

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We have investigated by transmission electron microscopy (TEM) defect morphology and structure in GaN films formed using an epitaxial lateral overgrowth (ELO) technique on SiO2-mask/window-stripe-patterned GaN layers in hydride vapor-phase epitaxy. In this experiment, the regions overgrown on the SiO2 masks were thoroughly examined. Cross-sectional TEM clearly revealed characteristic defects along the [0001] direction in the overgrown region, which consisted of arrays of dislocations running along the mask stripe direction. These defects caused crystallographic tilting in that region near the mask with respect to the other region grown from the window area. We also observed, at the coalesced site on the mask, vertical repropagation of dislocations that had propagated laterally during ELO. The origin of the observed defects and their influence on the residual dislocation distribution near the film surface are discussed. © 1998 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
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Fracture phenomena in silicon imaged by infrared radiation from ejected small particles

E. Busch and D. Haneman

Appl. Phys. Lett. 73, 484 (1998); http://dx.doi.org/10.1063/1.121908 (3 pages) | Cited 2 times

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We have found that fracture of silicon wafer specimens without introduced flaws takes place with the ejection of many small particles that emit infrared radiation, which has been imaged with a sensitive CCD camera. The particles are of order micron dimensions, preventing surface-barrier separation of carriers excited by the bond breaking at cleavage. Furthermore, larger ejected particles can subsequently crack, allowing further ejection of small luminescent particles. The results show that a simple theory of spread of a pre-existing flaw can be a serious oversimplification of complex phenomena occurring at the onset of brittle cleavage. © 1998 American Institute of Physics.
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78.60.Mq Sonoluminescence, triboluminescence
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

Adatom diffusion at GaN (0001) and (0001) surfaces

Tosja Zywietz, Jörg Neugebauer, and Matthias Scheffler

Appl. Phys. Lett. 73, 487 (1998); http://dx.doi.org/10.1063/1.121909 (3 pages) | Cited 172 times

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The diffusion of Ga and N adatoms has been studied for the technologically relevant wurtzite (0001) and (0001) surfaces employing density-functional theory. Our calculations reveal a very different diffusivity for Ga and N adatoms on the equilibrium surfaces: While Ga is very mobile at typical growth temperatures, the diffusion of N is by orders of magnitude slower. These results give a very detailed insight of how and under which growth conditions N adatoms can be stabilized and efficiently incorporated at the surface. We further find that the presence of excess N strongly increases the Ga diffusion barrier and discuss the consequences for the growth of GaN. © 1998 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Soft breakdown fluctuation events in ultrathin SiO2 layers

E. Miranda, J. Suñé, R. Rodríguez, M. Nafría, and X. Aymerich

Appl. Phys. Lett. 73, 490 (1998); http://dx.doi.org/10.1063/1.121910 (3 pages) | Cited 28 times

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When an ultrathin (<5 nm) oxide is subjected to electrical stress, several soft-breakdown events can occur prior to the final dielectric breakdown. After the occurrence of such failure events, the current–voltage (I–V) characteristic corresponds to the superposition of highly conductive spots and background conduction through the undegraded capacitor area. In this conduction regime, the application of a low constant voltage gives rise to large leakage current fluctuations in the form of random telegraph signal. Some of these fluctuations have been identified with ON/OFF switching events of one or more local conduction spots, and not with a modulation of their conductance. The experimental soft-breakdown I–V characteristics are shown to be better understood if the spot conduction is considered to be locally limited by the silicon electrodes and not by the oxide. © 1998 American Institute of Physics.
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73.61.Ng Insulators
77.22.Jp Dielectric breakdown and space-charge effects
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
73.50.Td Noise processes and phenomena

Role of localized and extended electronic states in InGaN/GaN quantum wells under high injection, inferred from near-field optical microscopy

A. Vertikov, A. V. Nurmikko, K. Doverspike, G. Bulman, and J. Edmond

Appl. Phys. Lett. 73, 493 (1998); http://dx.doi.org/10.1063/1.121911 (3 pages) | Cited 32 times

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We report on spatially resolved optical measurements of high-quality InGaN/GaN multiple quantum wells under conditions of direct high optical injection (>1019 cm−3) using near-field optical microscopy in the collection mode. The spectral dependence of the spatial distribution of the photoluminescence indicates that the range of In-composition fluctuations reaches the 100-nm lateral scale. The spectra are dependent on the carrier injection level and reveal significant state filling effect. We sketch tentative conclusions about the In-cluster size distribution in terms of contributions to the radiative processes that involve localized and extended states, respectively, in the regime of electron–hole (e–h) pair densities at which present diode lasers operate. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.20.Fz Weak or Anderson localization
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
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