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31 May 1999

Volume 74, Issue 22, pp. 3245-3412

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Monte Carlo simulation of reentrant reflection high-energy electron diffraction intensity oscillation observed during low-temperature GaAs growth

Haruyuki Yasuda and Hideo Ohno

Appl. Phys. Lett. 74, 3275 (1999); http://dx.doi.org/10.1063/1.123318 (3 pages) | Cited 5 times

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Reentrant behavior of intensity oscillation of reflection high-energy electron diffraction (RHEED) observed during low-temperature GaAs homoepitaxy on GaAs (001) substrates is studied by a Monte Carlo simulation using cubic solid-on-solid configuration. By assuming that an excess As overlayer acts as surfactant which enhances the migration of Ga adatoms at low temperature, temperature as well as V/III ratio dependence of step density oscillation (i.e., RHEED intensity oscillation) is successfully reproduced. © 1999 American Institute of Physics.
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Fx Diffusion; interface formation
68.08.-p Liquid-solid interfaces
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Light emission properties of crystalline SiO2 coated with LiNbO3/LiTaO3 multilayers

X. L. Wu and G. G. Siu

Appl. Phys. Lett. 74, 3278 (1999); http://dx.doi.org/10.1063/1.123319 (3 pages) | Cited 8 times

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Photoluminescence (PL) properties of the crystalline SiO2 coated with LiNbO3/LiTaO3 multilayers were studied using the 514.5 nm line excitation. The 2.25 eV PL band observed at room temperature can be Gaussian divided into two subbands at 2.19 and 2.30 eV, which can be clearly resolved in the 77 K PL spectrum. The 2.30 eV band is z polarized with a polarization degree of 0.25 and its intensity has a linear dependence on the excitation power. No similar behavior was observed for the 2.19 eV band. Spectral analysis indicates that the two PL bands arise from optical transitions of the self-trapped excitons and E′ defect pairs in the crystalline SiO2 surface, which are induced by the photorefractive effect of the coated multilayers. © 1999 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.66.Nk Insulators
42.79.Wc Optical coatings
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.Aa Frenkel excitons and self-trapped excitons
73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.55.Ht Other nonmetals

Local vibrational modes in Mg-doped GaN grown by molecular beam epitaxy

A. Kaschner, H. Siegle, G. Kaczmarczyk, M. Straßburg, A. Hoffmann, C. Thomsen, U. Birkle, S. Einfeldt, and D. Hommel

Appl. Phys. Lett. 74, 3281 (1999); http://dx.doi.org/10.1063/1.123320 (3 pages) | Cited 45 times

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Local vibrational modes in the region of the acoustic and optical phonons are reported for Mg-doped GaN grown by molecular beam epitaxy. The modes, studied by Raman spectroscopy, appear in addition to the known modes in the high-energy region around 2200 cm−1. We suggest disorder-activated scattering and scattering from Mg-related lattice vibrations to be the origin of the low-energy modes. Our assignment is supported by calculations based on a modified valence-force model of Kane. Temperature-dependent measurements between 4 and 300 K exclude an electronic Raman-scattering mechanism. We also report a new line at 2129 cm−1 and discuss the origin of all five observed high-energy modes. © 1999 American Institute of Physics.
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63.20.Pw Localized modes
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
61.72.S- Impurities in crystals
68.60.Wm Other nonelectronic physical properties

Reflection high-energy electron diffraction intensity oscillation during layer-by-layer oxidation of Si(001) surfaces

Heiji Watanabe, Toshio Baba, and Masakazu Ichikawa

Appl. Phys. Lett. 74, 3284 (1999); http://dx.doi.org/10.1063/1.123308 (3 pages) | Cited 5 times

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We have studied initial layer-by-layer oxidation of Si(001)-2×1 surfaces by using reflection high-energy electron diffraction (RHEED). We observed an intensity oscillation and a change in the streaky profile of a specular reflection spot in RHEED patterns during initial oxidation. These results indicate that layer-by-layer oxidation of Si surfaces is promoted by nucleation and lateral growth of two-dimensional oxide islands. We have also confirmed that a 1-monolayer-thick oxide has an ordered structure originating from the initial 2×1 reconstruction. © 1999 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.65.Mq Oxidation

Quantitative characterization of GaN quantum-dot structures in AlN by high-resolution transmission electron microscopy

M. Arlery, J. L. Rouvière, F. Widmann, B. Daudin, G. Feuillet, and H. Mariette

Appl. Phys. Lett. 74, 3287 (1999); http://dx.doi.org/10.1063/1.123321 (3 pages) | Cited 55 times

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GaN/AlN heterostructures grown by molecular beam epitaxy are studied by high-resolution transmission electron microscopy (HRTEM). The two-dimensional/three-dimensional Stranski–Krastanow growth mode transition of GaN allows the formation of GaN quantum-dot structures embedded in AlN. The nature of the wetting layer associated with these dots is determined by quantitative HRTEM analysis, based on comparison between interplanar distortion profiles of experimental and simulated images. This study demonstrates a low intermixing between GaN and AlN materials. Such result is also evidenced for the GaN dots. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Interpretation of x-ray photoelectron spectra of elastic amorphous carbon nitride thin films

B. C. Holloway, O. Kraft, D. K. Shuh, M. A. Kelly, W. D. Nix, P. Pianetta, and S. Hagström

Appl. Phys. Lett. 74, 3290 (1999); http://dx.doi.org/10.1063/1.123362 (3 pages) | Cited 25 times

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We report the synthesis and characterization of amorphous carbon nitride (CNx) thin films using a direct current magnetron reactive sputter system. Nanoindentation of the CNx films and amorphous carbon films deposited under similar conditions shows the CNx films are extremely elastic, that the addition of nitrogen fundamentally changes the mechanical properties of the films, and that traditional methods of calculating the hardness and Young’s modulus may not be valid. X-ray photoelectron spectroscopy (XPS) of the N(1s) and C(1s) core levels show multiple bonding arrangements. In a new interpretation of the XPS data, the two predominant N(1s) spectral features have been identified, based on comparison to reference data in the literature, as those belonging to nitrogen in a four-bond arrangement and nitrogen in a three-bond arrangement, independent of hybridization. The formation of a fourth bond allows nitrogen to substitute for C atoms in a carbon-based graphitic system without the formation of dangling bonds or unfilled states. The relationship between nitrogen incorporation in a carbon-based ring structure and measured film properties is rationalized based on previously published models. © 1999 American Institute of Physics.
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81.15.Cd Deposition by sputtering
61.43.Er Other amorphous solids
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.60.Bs Mechanical and acoustical properties
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
71.55.Ht Other nonmetals
68.55.-a Thin film structure and morphology

Effects of a low-energy ion beam on the growth of titanium nitride layers near the interface of a polyimide

Peter Abramowitz, Michael Kiene, and Paul S. Ho

Appl. Phys. Lett. 74, 3293 (1999); http://dx.doi.org/10.1063/1.123322 (3 pages) | Cited 6 times

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In this letter two different growth methods, reactive evaporation and ion-assisted reactive evaporation, were used to grow titanium nitride films on the polyimide biphenyl tetracarboxylic acid dianhydride-para phenylene diamine. The films were examined with x-ray photoemission spectroscopy and it was found that the chemical properties of the film depend on the distance from the polyimide/titanium nitride interface. While both techniques produced very similar films at distances greater than 5 nm from the interface, only the ion-assisted grown film had a significant amount of nitride near the interface. This is due to the ability of low-energy (100 eV) nitrogen ions to break the initial titanium/polyimide bonds which would otherwise prevent the growth of titanium nitride at the interface. © 1999 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
85.40.Ls Metallization, contacts, interconnects; device isolation
81.15.Jj Ion and electron beam-assisted deposition; ion plating
85.40.Sz Deposition technology
68.35.Ct Interface structure and roughness

Tapping-mode atomic force microscopy and phase-imaging in higher eigenmodes

Robert W. Stark, Tanja Drobek, and Wolfgang M. Heckl

Appl. Phys. Lett. 74, 3296 (1999); http://dx.doi.org/10.1063/1.123323 (3 pages) | Cited 40 times

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Tapping-mode atomic force microscopy (TM-AFM) is a powerful tool to study soft biological samples. Higher eigenmodes of the vibrating cantilever offer enhanced signal and smaller time constants increasing the sensitivity of the tapping probe as compared to conventional TM-AFM. The first five eigenmodes of a v-shaped silicon cantilever were investigated with respect to their suitability for imaging. Stable imaging was possible in the first and third modes. Phase imaging in the third mode was extremely sensitive to surface inhomogeneities and surface contamination particles not visible in standard TM-AFM. © 1999 American Institute of Physics.
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07.79.Lh Atomic force microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
87.64.Dz Scanning tunneling and atomic force microscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Dv Composition, segregation; defects and impurities

Optical properties of doped InGaN/GaN multiquantum-well structures

J. Dalfors, J. P. Bergman, P. O. Holtz, B. E. Sernelius, B. Monemar, H. Amano, and I. Akasaki

Appl. Phys. Lett. 74, 3299 (1999); http://dx.doi.org/10.1063/1.123324 (3 pages) | Cited 29 times

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A systematic investigation of the photoluminescence spectra from InGaN/GaN multiquantum-well structures with different levels of Si doping in the quantum well has been carried out, in order to study the screening of the strain induced piezoelectric field and potential fluctuations. It is found that the emission energy strongly depends on the carrier concentration, originating from the doping or photogeneration. The observed strong shift with Si doping can only partly be explained by the screening of the piezoelectric field. The main shift is suggested to be related to the screening of the localization potentials. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
77.65.Ly Strain-induced piezoelectric fields

Solvent-induced phase transition in thermally evaporated pentacene films

D. J. Gundlach, T. N. Jackson, D. G. Schlom, and S. F. Nelson

Appl. Phys. Lett. 74, 3302 (1999); http://dx.doi.org/10.1063/1.123325 (3 pages) | Cited 101 times

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We report a solvent-induced phase transition in pentacene thin films, from a “thin film” phase to a bulk-like phase. X-ray diffraction indicates that as-deposited thermally evaporated pentacene films consist mainly of (001)-oriented pentacene with an elongated (001) plane spacing of 15.5±0.1 Å, and a minor amount with a (001) plane spacing of 14.5±0.1 Å. When such films are exposed to solvents such as acetone, isopropanol, or ethanol, the plane spacing of the entire layer shifts abruptly from the elongated (001) plane spacing to the bulk value and this shift is accompanied by a macroscopic change in film morphology. While molecular ordering is maintained as indicated by x-ray diffraction, thin film transistor performance is severely degraded, most likely as a result of the morphological changes in the film. © 1999 American Institute of Physics.
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64.70.K- Solid-solid transitions
68.55.-a Thin film structure and morphology
85.30.Tv Field effect devices

Irradiation-induced growth of nanoquasicrystals from amorphous matrix in the equilibrium immiscible Fe–Cu system

G. W. Yang, W. S. Lai, C. Lin, and B. X. Liu

Appl. Phys. Lett. 74, 3305 (1999); http://dx.doi.org/10.1063/1.123326 (3 pages) | Cited 26 times

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A microstructure of nanosized quasicrystals embedded in an amorphous matrix was formed in the Fe70Cu30 multilayered films upon room temperature 200 keV xenon ion irradiation. The initial Fe and Cu crystalline phases in the as-deposited multilayers transformed into a unique amorphous phase at a dose of 8×1014 Xe+ cm−2 and further irradiation, i.e., up to a dose of 5×1015 Xe+ cm−2, induced the growth of the quasicrystals in some local areas in the amorphous matrix. High-resolution electron microscopy examination revealed that the compositions of the quasicrystals and amorphous matrix were close to Fe50Cu50 and Fe70Cu30, respectively. Apparently, the above microstructure was formed through a two-step phase transition along the increase of ion dose and the amorphous-to-quasicrystal transition was discussed in terms of the similarity in the atomic configuration between the icosahedral and amorphous short-range orders. © 1999 American Institute of Physics.
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61.44.Br Quasicrystals
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.80.Jh Ion radiation effects
61.72.-y Defects and impurities in crystals; microstructure
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Evidence for relaxed and high-quality growth of GaN on SiC(0001)

F. Boscherini, R. Lantier, A. Rizzi, F. D’Acapito, and S. Mobilio

Appl. Phys. Lett. 74, 3308 (1999); http://dx.doi.org/10.1063/1.123327 (3 pages) | Cited 11 times

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By using polarization-dependent x-ray absorption spectroscopy at the Ga edge, we study the growth of GaN on SiC(0001) in the thickness range 0.7–150 nm. We find that the growth is always relaxed (i.e., nonpseudomorphic) even for the thinnest epilayers, i.e., below the expected critical thickness. No evidence is found for a mixed Ga/Si interface plane, while a C/N mixed interface plane cannot be ruled out. The results are discussed with reference to the electronic structure of the SiC/GaN heterojunction and in particular to band offsets and strain-induced piezoelectric polarization. © 1999 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.70.Dm X-ray absorption spectra
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.55.-a Thin film structure and morphology
73.20.At Surface states, band structure, electron density of states

High temperature proton implantation induced photosensitivity of Ge-doped SiO2 planar waveguides

P. J. Hughes, A. P. Knights, B. L. Weiss, S. Kuna, P. G. Coleman, and S. Ojha

Appl. Phys. Lett. 74, 3311 (1999); http://dx.doi.org/10.1063/1.123328 (3 pages) | Cited 11 times

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The possibility of using keV proton implantation at 800 °C to enhance the photosensitivity of Ge-doped silica has been investigated. Room temperature implantation induced defects indicated by absorption at ultraviolet (UV) (<200 nm) and visible wavelengths (>550 nm) were annealed during implantation at 800 °C to leave stable photosensitive neutral oxygen vacancy (NOV) centers with an absorption peak at ∼ 240 nm. The stable NOV defects were photochemically bleached after UV exposure, a process which is accompanied by a change in UV absorption. Positron annihilation spectroscopy demonstrated the effectiveness of implantation at 800 °C in annealing the implantation induced damage. © 1999 American Institute of Physics.
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42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
61.82.Ms Insulators
61.80.Jh Ion radiation effects
61.72.up Other materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.70.Bj Positron annihilation
61.72.J- Point defects and defect clusters

Study of wet treatment of polyimide by sum-frequency vibrational spectroscopy

Doseok Kim and Y. R. Shen

Appl. Phys. Lett. 74, 3314 (1999); http://dx.doi.org/10.1063/1.123329 (3 pages) | Cited 21 times

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A polyimide surface treated with a strong NaOH solution for improvement of adhesion with metals was investigated using ultraviolet absorption and sum-frequency vibrational spectroscopy. Conversion of imide groups to amide groups at the polyimide surface was observed. This conversion and subsequent etching of the polyimide film by the solution seems to be more effective in the amorphous part of the film. Drying of the film converts the surface amides back to imides. © 1999 American Institute of Physics.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.Cf Surface cleaning, etching, patterning
63.50.-x Vibrational states in disordered systems
78.40.Me Organic compounds and polymers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Deformation of carbon nanotubes in nanotube–polymer composites

C. Bower, R. Rosen, L. Jin, J. Han, and O. Zhou

Appl. Phys. Lett. 74, 3317 (1999); http://dx.doi.org/10.1063/1.123330 (3 pages) | Cited 193 times

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Composites of uniaxially oriented multiwalled carbon nanotubes embedded in polymer matrices were fabricated and investigated by transmission electron microscopy. In strained composite films, buckling was ubiquitously observed in bent nanotubes with large curvatures. By analyses of a large number of bent nanotubes, the onset buckling strain and fracture strain were estimated to be ≈5% and ⩾18%, respectively. The buckling wavelengths are proportional to the dimensions of the nanotubes. Examination of the fracture surface showed adherence of the polymer to the nanotubes. © 1999 American Institute of Physics.
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81.40.Lm Deformation, plasticity, and creep
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
62.20.F- Deformation and plasticity
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Optical microscopy of electronic and structural properties of epitaxial laterally overgrown GaN

A. Kaschner, A. Hoffmann, C. Thomsen, F. Bertram, T. Riemann, J. Christen, K. Hiramatsu, T. Shibata, and N. Sawaki

Appl. Phys. Lett. 74, 3320 (1999); http://dx.doi.org/10.1063/1.123331 (3 pages) | Cited 31 times

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Local strain relaxation as well as inhomogeneous impurity incorporation in epitaxial laterally overgrown GaN (ELOG) structures is microscopically characterized using spectrally resolved scanning cathodoluminescence (CL) and micro-Raman spectroscopy. We correlate the different CL emission spectra with results of spatially resolved Raman-scattering experiments sensing the local strain and free-carrier concentration. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.60.Hk Cathodoluminescence, ionoluminescence
68.60.Bs Mechanical and acoustical properties
78.30.Fs III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.15.Kk Vapor phase epitaxy; growth from vapor phase
63.20.kk Phonon interactions with other quasiparticles
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Direct transition at the fundamental gap in light-emitting nanocrystalline Si thin films

Toshihiko Toyama, Yoshihiro Kotani, Akihito Shimode, and Hiroaki Okamoto

Appl. Phys. Lett. 74, 3323 (1999); http://dx.doi.org/10.1063/1.123332 (3 pages) | Cited 9 times

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Optical transitions at the fundamental gaps of 1.20–1.37 eV are observed at 293 K directly by electroreflectance (ER) spectroscopy in nanocrystalline Si (nc-Si) thin films, from which photoluminescence (PL) with dominant peak energies of 1.65–1.75 eV is observed. Also observed by ER are optical transitions at 2.2 and at 3.1–3.4 eV. With a decrease in the mean crystal size from ∼3 nm to below 2 nm, the transition energy of the fundamental gap is increased and the ER signal is intensified. The band-gap widening would be due to quantum confinement in Si nanocrystals, and the increased signal indicates the appearance of direct transitions. In conjunction with the ER results, the PL mechanisms have been discussed. © 1999 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
78.66.Jg Amorphous semiconductors; glasses
78.20.Jq Electro-optical effects
71.20.Mq Elemental semiconductors
81.05.Cy Elemental semiconductors
61.46.-w Structure of nanoscale materials
73.22.-f Electronic structure of nanoscale materials and related systems
81.07.-b Nanoscale materials and structures: fabrication and characterization
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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