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15 Oct 2003

Volume 94, Issue 8, pp. 4743-5438

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Aluminum oxynitride at pressures up to 180 GPa

Toshimori Sekine, Xijun Li, Takamichi Kobayashi, Yasuyuki Yamashita, Parimal Patel, and James W. McCauley

J. Appl. Phys. 94, 4803 (2003); http://dx.doi.org/10.1063/1.1608476 (4 pages) | Cited 11 times

Online Publication Date: 30 September 2003

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Hugoniot equation-of-state data of shock compressed aluminum oxynitride (AlON), consisting of 64.1 mol% Al2O3⋅35.9 mol% AlN with a density of ∼3.68 g/cm3, have been determined to 180 GPa. The relationship between shock velocity (Us) and particle velocity (Up) is expressed by a straight line: Us(km/s)=8.08+0.761Up(km/s). Although there is no evidence of phase transition in the data, the determined Hugoniot of AlON has been compared with those of oxide spinels such as MgAl2O4 and Fe3O4. We discuss the systematics of high pressure phase transitions of spinels that indicate a phase transition to CaTi2O4-type phases. The phase transition to CaTi2O4-type structures implies that the recently discovered Si3N4 spinel also may be transformed into a CaTi2O4-type phase with increasing pressure. © 2003 American Institute of Physics.
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64.30.-t Equations of state of specific substances
62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions

Postgrowth annealing of defects in ZnO studied by positron annihilation, x-ray diffraction, Rutherford backscattering, cathodoluminescence, and Hall measurements

Z. Q. Chen, S. Yamamoto, M. Maekawa, A. Kawasuso, X. L. Yuan, and T. Sekiguchi

J. Appl. Phys. 94, 4807 (2003); http://dx.doi.org/10.1063/1.1609050 (6 pages) | Cited 61 times

Online Publication Date: 30 September 2003

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Defects in hydrothermal grown ZnO single crystals are studied as a function of annealing temperature using positron annihilation, x-ray diffraction, Rutherford backscattering, Hall, and cathodoluminescence measurements. Positron lifetime measurements reveal the existence of Zn vacancy related defects in the as-grown state. The positron lifetime decreases upon annealing above 600 °C, which implies the disappearance of Zn vacancy related defects, and then remains constant up to 900 °C. The Rutherford backscattering and x-ray rocking curve measurements show the improvement of crystal quality due to annealing above 600 °C. Although the crystal quality monitored by x-ray diffraction measurements is further improved after annealing at above 1000 °C, the positron lifetime starts to increase. This is due to either the formation of Zn vacancy related defects, or the change of the Zn vacancy charge state occupancy as a result of the Fermi level movement. The electron concentration increases continuously with increasing annealing temperature up to 1200 °C, indicating the formation of excess donors, such as oxygen vacancies or zinc interstitials. The cathodoluminescence measurements reveal that the ultraviolet emission is greatly enhanced in the same temperature range. The experimental results show that the ZnO crystal quality, electrical and optical characteristics are improved by postgrowth annealing from 600 to 1200 °C. The disappearance of Zn vacancy related defects contributes to the initial stage of improved crystal quality. © 2003 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters
78.70.Bj Positron annihilation
78.60.Hk Cathodoluminescence, ionoluminescence
72.20.My Galvanomagnetic and other magnetotransport effects
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)

Optical characterization of AlN/GaN heterostructures

V. V. Ursaki, I. M. Tiginyanu, V. V. Zalamai, S. M. Hubbard, and D. Pavlidis

J. Appl. Phys. 94, 4813 (2003); http://dx.doi.org/10.1063/1.1609048 (6 pages) | Cited 5 times

Online Publication Date: 30 September 2003

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AlN/GaN/sapphire heterostructures with AlN gate film thickness of 3–35 nm are characterized using photoreflectivity (PR) and photoluminescence (PL) spectroscopy. Under a critical AlN film thickness, the luminescence from the GaN channel layer near the interface proves to be excitonic. No luminescence related to the recombination of the two-dimensional electron gas (2DEG) is observed, in spite of high 2DEG parameters indicated by Hall-effect measurements. The increase of the AlN gate film thickness beyond a critical value leads to a sharp decrease in exciton resonance in PR and PL spectra as well as to the emergence of a PL band in the 3.40–3.45 eV spectral range. These findings are explained taking into account the formation of defects in the GaN channel layer as a result of strain-induced AlN film cracking. A model of electronic transitions responsible for the emission band involved is proposed. © 2003 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.20.At Surface states, band structure, electron density of states
78.20.-e Optical properties of bulk materials and thin films
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
71.35.-y Excitons and related phenomena

Experimental findings in support of atomic transport of hydrogen in silica

E. Hörnlund and G. Hultquist

J. Appl. Phys. 94, 4819 (2003); http://dx.doi.org/10.1063/1.1603350 (5 pages) | Cited 9 times

Online Publication Date: 30 September 2003

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Data supporting a view of both molecular and atomic transport of hydrogen in quartz is presented. By studying isotopic equilibration, it is shown that virtually all of the molecules diffusing through a 1.5 mm thick quartz membrane at 900 °C have undergone dissociation. The catalytic properties of platinum for the dissociation of H2 are used to increase the surface concentration of atomic hydrogen on a quartz membrane. It is found that the high surface concentration increases the total flux of hydrogen through the membrane. It is also found by comparison with literature data that diatomic molecules probably diffuse in two modes in quartz. We suggest that these two modes are one atomic and one molecular. © 2003 American Institute of Physics.
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66.30.J- Diffusion of impurities
82.39.Wj Ion exchange, dialysis, osmosis, electro-osmosis, membrane processes
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Fictive temperature dependence of density fluctuation in SiO2 glass

T. Watanabe, K. Saito, and A. J. Ikushima

J. Appl. Phys. 94, 4824 (2003); http://dx.doi.org/10.1063/1.1608477 (4 pages) | Cited 10 times

Online Publication Date: 30 September 2003

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Fictive temperature dependence of density fluctuation in SiO2 glass was investigated by the small-angle x-ray scattering measurement. The density fluctuation in SiO2 glass varies linearly to the fictive temperature. Contribution of structural relaxation to the density fluctuation is larger than that of phonons. Isothermal compressibility, relaxational isothermal compressibility and high-frequency adiabatic compressibility are estimated. If N, math, and Δ represent the number of SiO4/2 unit, average and difference from average, respectively, the density fluctuation in SiO2 glass is less than 3.6% as math/math. © 2003 American Institute of Physics.
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61.43.Fs Glasses
62.20.F- Deformation and plasticity
81.05.Kf Glasses (including metallic glasses)
78.70.Ck X-ray scattering

Enhancement of sp3 hybridized C in amorphous carbon films by Ar ion bombardment and Si incorporation

Hae-Suk Jung, Hyung-Ho Park, I. R. Mendieta, and D. A. Smith

J. Appl. Phys. 94, 4828 (2003); http://dx.doi.org/10.1063/1.1606511 (7 pages) | Cited 7 times

Online Publication Date: 30 September 2003

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We report an effective method of increasing the sp3 hybridization fraction in sputtered amorphous carbon (a-C) film by the combination of Ar ion bombardment and Si incorporation. In the deposition of an a-C film, Ar ion bombardment by controlling the applied bias voltage plays a role in creating high stress in film and causes the local bonding configuration to change to a sp3 hybridized bond. Simultaneously, the incorporated Si in an a-C network breaks the sp2 hybridized bonded ring and promotes the formation of a sp3 hybridized bond. This enhancement of the sp3 hybridized bonding characteristic is maximized for an a-C film with 23 at. % of Si and 100–150 V of applied bias voltage. In this region, the increase of resistivity, optical band gap, and mechanical hardness of a-C is attributed to the reduction of the sp2 hybridized bonded ring and increased fraction of the sp3 hybridized bond. However, at a higher bias voltage above 150 V, the enhancement effect is reduced due to the resputtering and thermally activated reconversion of a sp3 to a sp2 hybridized bond. © 2003 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Cd Deposition by sputtering
61.80.Jh Ion radiation effects
78.66.Nk Insulators
68.60.Bs Mechanical and acoustical properties
73.61.Ng Insulators

Modeling the absorption spectra of Er3+ and Yb3+ in a phosphate glass

John B. Gruber, Dhiraj K. Sardar, Bahram Zandi, J. Andrew Hutchinson, and C. Ward Trussell

J. Appl. Phys. 94, 4835 (2003); http://dx.doi.org/10.1063/1.1607523 (6 pages) | Cited 11 times

Online Publication Date: 30 September 2003

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Absorption spectra of Er3+ and Yb3+ ions, codopants in a phosphate glass, are reported at 8 K and at wavelengths between 350 and 1600 nm. Detailed structure appearing in the spectra, associated with individual multiplet states, 2S+1LJ, of Er3+(4f11) and Yb3+(4f13) is interpreted using a ligand-field coordination sphere model to characterize the microscopic environment surrounding the rare earth ions in multiple sites. Inhomogeneous broadening of the spectra is likely due to different configurations of PO4 tetrahedra clustered about a caged rare earth ion in the amorphous host. Similarity between the Er3+ spectrum in the glass and in the spectrum of single-crystal LiErP4O12, where Er3+ occupies sites of C2 symmetry, suggests that an averaged site symmetry of C2 is a reasonable approximation for Er3+ and Yb3+ ions in the phosphate glass. Calculated splitting of multiplet states by the ligand-field cluster model are compared with energy levels derived from the observed absorption peaks and well-defined shoulders. Inhomogeneous broadening of the spectra limit the precision in establishing the energy of the multiplet splittings, but the analysis is useful for modeling studies of the Er:Yb:phosphate glass as an eye-safe laser (1.53 μm). The splitting of the Yb3+(4f13)2FJ states is determined using parameters obtained from the Er3+ set by means of the three-parameter theory. No adjustments were made to the Yb3+ parameters that predict multiplet splittings in reasonable agreement with experimental data. © 2003 American Institute of Physics.
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78.40.Pg Disordered solids
71.70.Ch Crystal and ligand fields

Formation of self-assembled epitaxial nickel nanostructures

H. Zhou, D. Kumar, A. Kvit, A. Tiwari, and J. Narayan

J. Appl. Phys. 94, 4841 (2003); http://dx.doi.org/10.1063/1.1609046 (6 pages) | Cited 17 times

Online Publication Date: 30 September 2003

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Highly orientated nickel magnetic nanoparticles were obtained by pulsed laser deposition technique on silicon (100) substrate using epitaxial titanium nitride film as the template. These nanoparticles have been characterized by conventional and high-resolution transmission electron microscopy, scanning transmission electron microscopy Z-contrast imaging, and x-ray diffraction techniques. The results have shown that the growth of nickel on epitaxially grown titanium nitride follows a three-dimensional island growth mechanism. The predominant orientation of nickel islands observed is Ni(100)∥TiN(100)∥Si(100), the so-called “cube-on-cube” orientation relation. The islands are faceted with a truncated pyramidal shape and bounded by (111) planes at sides and (100) plane at the top. Islands with nontruncated pyramidal shape were also found in some samples, but with rotational orientation relations, where the nickel crystal rotates with an approximate angle of 90° with respect to one of TiN 〈110〉 directions parallel to the interface. The appearance of this rotational epitaxial growth did not show any obvious deposition temperature dependence in the range of 400–650 °C, rather it seemed to be closely related to the crystalline quality of TiN template. The actual size of islands varies from a few nanometers to tens of nanometers, depending on the deposition time and temperature. The three-dimensional growth of nickel islands and the island faceting could be explained by the surface energy anisotropy of both nickel and titanium nitride. © 2003 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.70.Ak Magnetic properties of monolayers and thin films
61.46.-w Structure of nanoscale materials
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
68.35.Md Surface thermodynamics, surface energies
75.50.Cc Other ferromagnetic metals and alloys

Gd on GaN(0001) surface: Growth, interaction, and Fermi level movement

Wende Xiao, Qinlin Guo, Qikun Xue, and E. G. Wang

J. Appl. Phys. 94, 4847 (2003); http://dx.doi.org/10.1063/1.1609636 (6 pages) | Cited 4 times

Online Publication Date: 30 September 2003

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Growth, interfacial reaction, and Fermi level movement of Gd on n-type GaN(0001)-(1×1) surface are studied using x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and low-energy-electron diffraction. Gd grows in a layer-by-layer-like mode and reacts with the substrate at the interface, leading to formation of metallic Ga at room temperature. A downward Fermi level movement is observed, and the resultant Schottky barrier height is 1.5 eV. Annealing promotes further diffusion and an interfacial Gd–Ga exchange reaction, reducing the Schottky barrier height. © 2003 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
73.40.Ns Metal-nonmetal contacts
79.60.Jv Interfaces; heterostructures; nanostructures
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.Cc Kinetics of defect formation and annealing

Stress development in sputtered NiO thin films during heat treatment

W. Brückner, R. Kaltofen, J. Thomas, M. Hecker, M. Uhlemann, S. Oswald, D. Elefant, and C. M. Schneider

J. Appl. Phys. 94, 4853 (2003); http://dx.doi.org/10.1063/1.1609052 (6 pages) | Cited 5 times

Online Publication Date: 30 September 2003

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Nickel oxide thin films with a thickness of 100 nm were deposited on oxidized silicon wafers by rf magnetron sputtering from a NiO target in an Ar (nonreactive case) and an Ar+O2 atmosphere with various oxygen contents (reactive cases). The as-deposited films possess high compressive stresses (up to 3700 MPa) which decrease irreversibly during annealing between 150 and 500 °C. Compositional and microstructural analyses were performed on as-deposited and annealed films by means of electron probe microanalysis, transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, thermal-desorption spectrometry, and magnetization measurements. All as-deposited thin films consist of NiOx with x ranging between about 1.15 and 1.27. These oxygen-excess films are thermally unstable. They decompose during heat treatment into thermally more stable, oxygen-poorer NiO and/or metallic Ni. This decomposition is the reason for the observed irreversible stress changes. © 2003 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
81.15.Cd Deposition by sputtering
68.60.Dv Thermal stability; thermal effects
68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
68.37.Lp Transmission electron microscopy (TEM)
79.60.Dp Adsorbed layers and thin films
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Atomic structure of random and c-axis oriented YMnO3 thin films deposited on Si and Y2O3/Si substrates

Yong Tae Kim, Ik Soo Kim, Seong Il Kim, Dong Chul Yoo, and Jeong Yong Lee

J. Appl. Phys. 94, 4859 (2003); http://dx.doi.org/10.1063/1.1604460 (4 pages) | Cited 6 times

Online Publication Date: 30 September 2003

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We have studied the atomic structure of YMnO3 deposited on Si and Y2O3 with high-resolution transmission electron microscopy and fast Fourier transforms-filtered lattice image analysis during furnace and rapid thermal annealing (RTA) processes. For the YMnO3/Si, it is found that the YMnO3 layer is c-axis oriented with an amorphous bottom region after furnace annealing at 850 °C for 1 h. In contrast, after RTA at 850 °C for 3 min the bottom region forms YMnO3 polycrystalline layer with the {math2math2} plane parallel to the surface. When an Y2O3 layer is interposed between YMnO3 and Si, a c-axis oriented YMnO3 layer grows on a [111]-oriented Y2O3 layer. Memory window and leakage current density of the c-axis YMnO3/[111] Y2O3 bilayers are strongly improved due to an aligned [0001] unipolar axis. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.72.Cc Kinetics of defect formation and annealing
85.50.Gk Non-volatile ferroelectric memories

Selectively excited photoluminescence of GaAs1−xNx single quantum wells

X. D. Luo, P. H. Tan, Z. Y. Xu, and W. K. Ge

J. Appl. Phys. 94, 4863 (2003); http://dx.doi.org/10.1063/1.1609047 (3 pages) | Cited 2 times

Online Publication Date: 30 September 2003

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GaAsN bulk and GaAsN/GaAs single quantum wells grown by molecular beam epitaxy are studied by selectively excited photoluminescence (PL) measurements. A significant difference is observed in the PL spectra when the excitation energy is set below or above the band gap of GaAs for the GaAsN/GaAs quantum well samples, while the spectral features of GaAsN bulk are not sensitive to the excitation energy. The observed difference in PL of the GaAsN/GaAs quantum well samples is attributed to the exciton localization effect at the GaAsN/GaAs interfaces, which is directly correlated with the transfer and trap processes of the photogenerated carriers from GaAs into GaAsN through the heterointerfaces. This interface-related exciton localization effect can be greatly reduced by a rapid thermal annealing process, making the PL be dominated by the intrinsic delocalized transition in GaAsN/GaAs. © 2003 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.67.De Quantum wells
61.72.Cc Kinetics of defect formation and annealing
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Temperature and thickness dependence of molecular orientation of α-sexithienyl on Cu(111)

Manabu Kiguchi, Genki Yoshikawa, and Koichiro Saiki

J. Appl. Phys. 94, 4866 (2003); http://dx.doi.org/10.1063/1.1609637 (5 pages) | Cited 15 times

Online Publication Date: 30 September 2003

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Atomic and electronic structures of α-sexithienyl(6 T) films grown on Cu(111) were studied by near edge x-ray absorption fine structure (NEXAFS) and S 1s x-ray photoemission spectroscopies. The polarization dependent NEXAFS indicated highly ordered arrays of 6 T molecules, with their molecular long axes parallel to the surface, at substrate temperatures lower than 300 K. On the other hand, their molecular long axes became normal to the surface at 360 K, while they initially adsorbed with their long axes parallel to the surface. The film thickness and substrate temperature dependence of the molecular orientation is discussed in terms of the van der Waals interaction between 6 T and Cu(111) and the kinetics of the growth process. It is demonstrated that the molecular orientation of the promising organic semiconductor 6 T can be controlled by substrate temperature. © 2003 American Institute of Physics.
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68.55.A- Nucleation and growth
79.60.Dp Adsorbed layers and thin films
78.70.Dm X-ray absorption spectra

Observation of reflection high-energy electron diffraction oscillation during metalorganic-molecular-beam epitaxy of AlAs and control of carbon incorporation

Sasikala Ganapathy, Makoto Kurimoto, Periyasamy Thilakan, Kasturi Uesugi, Ikuo Suemune, Hideaki Machida, and Norio Shimoyama

J. Appl. Phys. 94, 4871 (2003); http://dx.doi.org/10.1063/1.1606515 (5 pages) | Cited 4 times

Online Publication Date: 30 September 2003

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The in situ observation of reflection high-energy electron diffraction (RHEED) oscillations during the metalorganic-molecular-beam epitaxy deposition of AlAs and AlGaAs epitaxial layers is reported. In situ RHEED oscillations as well as atomic force microscopy measurements confirmed the layer-by-layer growth of the AlAs as well as the AlGaAs layers on GaAs substrates. RHEED oscillation was successfully applied to the precise control of the AlAs/GaAs superlattices and of the alloy compositions in the AlGaAs alloys. High-resolution x-ray diffraction and Hall effect measurements revealed the unintentional doping of carbon into the AlGaAs layers, but it was found that the increase in the V/III ratio is able to reduce the carbon incorporation. © 2003 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.61.Ey III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
68.37.Ps Atomic force microscopy (AFM)

Brillouin scattering in planar waveguides. I. Numerical model

A. Chiasera, M. Montagna, F. Rossi, and M. Ferrari

J. Appl. Phys. 94, 4876 (2003); http://dx.doi.org/10.1063/1.1607519 (6 pages) | Cited 2 times

Online Publication Date: 30 September 2003

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A model for the calculation of Brillouin spectra in planar waveguides is presented. The electromagnetic field in a mode of a planar waveguide is a current wave along the guide and a standing wave across the guide with an evanescent tail in the substrate. The modal electromagnetic field can be calculated if the refractive index profile across the waveguide is known. The model for the calculation of Brillouin spectra considers the spatial distribution of the exciting field in the mode, a simple spatial dependence of the elasto-optic coefficients, through the value of the refractive index, and neglects the refraction of phonons. A single parameter, i.e., the sound velocity, is necessary to calculate as many spectra as is the number of modes in the waveguide. Examples of step index waveguides of different thicknesses and of graded-index waveguides are calculated and the results are compared with those of a simpler model based on a ray-tracing approach. In multimode waveguides with a step index profile, it turns out that longitudinal phonons produce two main peaks with an energy separation which increases with the mode index m. In graded-index waveguides, m−1 peaks of comparable intensities may appear. © 2003 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.79.Ry Gradient-index (GRIN) devices
42.15.Dp Wave fronts and ray tracing

Brillouin scattering in planar waveguides. II. Experiments

A. Chiasera, M. Montagna, E. Moser, F. Rossi, C. Tosello, M. Ferrari, L. Zampedri, S. Caponi, R. R. Gonçalves, S. Chaussedent, A. Monteil, D. Fioretto, G. Battaglin, F. Gonella, P. Mazzoldi, et al.

J. Appl. Phys. 94, 4882 (2003); http://dx.doi.org/10.1063/1.1607520 (8 pages) | Cited 1 time

Online Publication Date: 30 September 2003

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Silica–titania planar waveguides of different thicknesses and compositions have been produced by radio-frequency sputtering and dip coating on silica substrates. Waveguides were also produced by silver exchange on a soda-lime silicate glass substrate. Brillouin scattering of the samples has been studied by coupling the exciting laser beam with a prism to different transverse-electric (TE) modes of the waveguides, and collecting the scattered light from the front surface. In multimode waveguides, the spectra depend on the m mode of excitation. For waveguides with a step index profile, two main peaks due to longitudinal phonons are present, apart from the case of the TE0 excitation, where a single peak is observed. The energy separation between the two peaks increases with the mode index. In graded-index waveguides, m−1 peaks of comparable intensities are observed. The spectra are reproduced very well by a model which considers the space distribution of the exciting field in the mode, a simple space dependence of the elasto-optic coefficients, through the value of the refraction index, and neglects the refraction of phonons. A single-fit parameter, i.e., the longitudinal sound velocity, is used to calculate as many spectra as is the number of modes in the waveguide. © 2003 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.79.Ry Gradient-index (GRIN) devices

Arsenic incorporation into InGaAsP grown by low-pressure metalorganic vapor phase epitaxy using tertiarybutylarsine and tertiarybutylphosphine in N2 ambient

G. S. Huang, X. H. Tang, B. L. Zhang, and Swee Chuan Tjin

J. Appl. Phys. 94, 4890 (2003); http://dx.doi.org/10.1063/1.1610807 (6 pages) | Cited 3 times

Online Publication Date: 30 September 2003

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InxGa1−xAsyP1−y epilayers have been grown by low-pressure metalorganic vapor phase epitaxy (LPMOVPE) using tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) as group V precursors and nitrogen as the carrier gas. Arsenic incorporation into InxGa1−xAsyP1−y films grown by LPMOVPE as a function of the gas phase composition ratio and V/III ratio has been systematically studied. With optimized growth conditions, the arsenic composition of the epilayers does not change linearly with the TBA source flow. It is observed that the arsenic incorporation becomes saturated when the gas phase composition TBA/(TBA+TBP) increases to 0.4. The incorporation kinetics in MOVPE growth of InxGa1−xAsyP1−y alloy has been analyzed by using an adsorption-trapping model. The As composition (y) of the InxGa1−xAsyP1−y films varies with the TBA gas phase composition ξ=TBA/(TBA+TBP) according to the expression y=2Ns∗/aN0(1−e−θβξ). It is demonstrated that with the optimized growth conditions, TBA has a higher incorporation efficiency than TBP in MOVPE growth of InxGa1−xAsyP1−y films. © 2003 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
82.33.Ya Chemistry of MOCVD and other vapor deposition methods
68.55.A- Nucleation and growth

Optical, photoelectric, and photorefractive properties of Ti-doped CdTe crystals

Yu. P. Gnatenko, A. O. Borshch, N. Kukhtarev, T. Kukhtareva, I. O. Faryna, V. I. Volkov, P. M. Bukivskij, R. V. Gamernyk, V. I. Rudenko, S. Yu. Paranchych, and L. D. Paranchych

J. Appl. Phys. 94, 4896 (2003); http://dx.doi.org/10.1063/1.1610787 (8 pages) | Cited 9 times

Online Publication Date: 30 September 2003

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The photorefractive characteristics of Ti-doped CdTe semi-insulating crystals were measured. Additional optical and photoelectric measurement confirmed that titanium has advantages over other dopants and that this material has better characteristics for potential applications. The high optical holographic gain coefficient, Γ≈0.60 cm−1, low background absorption, kb≈0.2 cm−1, high optical quality and homogeneity, and almost monopolar (electronic) photoconductivity show that these materials can be effectively used for both optical and photoelectric applications in the near infrared region. Studies of the optical absorption and photodiffusion current made it possible to determine the nature and energy structure of impurity and intrinsic defects as well as to establish their role in the photorefractive effect. It is shown that the excited impurity 4T1(F) state is in resonance with the conduction band. As a result, autoionization of electrons to the conduction band under laser excitation takes place. An energy-level diagram, both of impurity and intrinsic defects, in the CdTe:Ti crystals was constructed. © 2003 American Institute of Physics.
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78.20.-e Optical properties of bulk materials and thin films
72.40.+w Photoconduction and photovoltaic effects
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
72.80.Ey III-V and II-VI semiconductors
71.55.Gs II-VI semiconductors
78.55.Et II-VI semiconductors
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Dose dependence of carrier and heat dynamics at an ion-implanted silicon surface measured using lens-free heterodyne transient grating method

Kenji Katayama, Masahiro Yamaguchi, and Tsuguo Sawada

J. Appl. Phys. 94, 4904 (2003); http://dx.doi.org/10.1063/1.1605255 (4 pages) | Cited 6 times

Online Publication Date: 30 September 2003

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The lens-free heterodyne transient grating method was shown to reveal the dynamics of photoexcited carriers and heat on the surface region of an ion-implanted silicon in the dose range of 1011–1015 cm−2. In addition to the fact that the detection limit of the dose was superior to that for conventional methods, several physical properties of the carrier and heat can be obtained by analyzing transient responses. Theoretical analysis provided the lifetime of carriers and thermal diffusion coefficients in the ion-implanted surface region. © 2003 American Institute of Physics.
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61.72.uf Ge and Si
61.80.Jh Ion radiation effects
66.30.Xj Thermal diffusivity
72.80.Cw Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.82.Fk Semiconductors
72.40.+w Photoconduction and photovoltaic effects
78.47.-p Spectroscopy of solid state dynamics

Viscosity and elastic constants of thin films of amorphous Te alloys used for optical data storage

J. Kalb, F. Spaepen, T. P. Leervad Pedersen, and M. Wuttig

J. Appl. Phys. 94, 4908 (2003); http://dx.doi.org/10.1063/1.1610775 (5 pages) | Cited 24 times

Online Publication Date: 30 September 2003

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The biaxial modulus and the linear coefficient of thermal expansion of sputtered amorphous Ge4Sb1Te5, Ge2Sb2Te5, and Ag0.055In0.065Sb0.59Te0.29 thin films were determined from stress versus temperature measurements on two different substrates. Viscous flow was measured by stress relaxation at constant temperature using wafer curvature measurements. The shear viscosity increased linearly with time, which can be attributed to bimolecular structural relaxation kinetics. The isoconfigurational activation energy was 1.94±0.09 eV for Ge4Sb1Te5, 1.76±0.05 eV for Ge2Sb2Te5, and 1.33±0.09 eV for AgInSbTe. These values scale with the absolute melting temperatures of the material. © 2003 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
42.70.Ln Holographic recording materials; optical storage media
62.20.D- Elasticity
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.60.Dv Thermal stability; thermal effects

Capillary condensation monitored in birefringent porous silicon layers

N. Künzner, E. Gross, J. Diener, D. Kovalev, V. Yu. Timoshenko, and D. Wallacher

J. Appl. Phys. 94, 4913 (2003); http://dx.doi.org/10.1063/1.1609643 (5 pages) | Cited 8 times

Online Publication Date: 30 September 2003

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We performed studies on the capillary condensation of various substances in optically anisotropic porous silicon layers. Their strong in-plane form birefringence has been utilized to analyze the polarization state of the transmitted light when molecules penetrate into the pores. The polarization state of the transmitted light is correlated with the filling fraction of the pores by an effective-medium model for anisotropic porous materials. The experimentally obtained adsorption/desorption isotherms show hysteresis typical for capillary condensation in porous materials. We discuss the shape of the hysteresis loops in the framework of the morphology of the layers. Pore-size distributions derived from adsorption/desorption isotherms are presented. © 2003 American Institute of Physics.
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78.20.Fm Birefringence
78.66.Db Elemental semiconductors and insulators
68.43.Mn Adsorption kinetics

Configurations, energies, and thermodynamics of the neutral MgH complex in GaN

A. F. Wright and S. M. Myers

J. Appl. Phys. 94, 4918 (2003); http://dx.doi.org/10.1063/1.1610232 (5 pages) | Cited 10 times

Online Publication Date: 30 September 2003

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Atomic configurations corresponding to local-energy minima for the neutral MgH complex in wurtzite GaN are identified using density-functional theory and the generalized-gradient approximation for exchange and correlation. MgH binding energies, H local-mode vibration frequencies, and configurational degeneracies for the six lowest-energy configurations are used, along with corresponding results for isolated H+, to compute equilibrium H state populations in Mg-doped GaN as a function of temperature. For a Mg concentration of 1×1019/cm3 and a H/Mg concentration ratio of 0.99, MgH is found to be the majority H species at room temperature with isolated H+ becoming the majority species at T≈550 °C. Among the MgH states, one is found to dominate at all temperatures. The dominant configuration consists of H at an antibonding site of a N neighbor of the substitutional Mg, with the Mg–N and N–H bonds nearly aligned and the N–H bond oriented at an angle of ∼109° with the c axis. The H stretch-mode frequency of the dominant state is consistent with the peak observed in Fourier-transform infrared reflection spectra from Mg-doped GaN samples. © 2003 American Institute of Physics.
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61.72.Yx Interaction between different crystal defects; gettering effect
71.55.Eq III-V semiconductors
71.15.Nc Total energy and cohesive energy calculations
78.30.Fs III-V and II-VI semiconductors
61.50.Lt Crystal binding; cohesive energy
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Anisotropy of optical properties of conjugated polymer thin films by spectroscopic ellipsometry

Maria Losurdo, Giovanni Bruno, and Eugene A. Irene

J. Appl. Phys. 94, 4923 (2003); http://dx.doi.org/10.1063/1.1610236 (7 pages) | Cited 13 times

Online Publication Date: 30 September 2003

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Optical properties of thin films of conjugated poly(arylenephenylene) polymers have been determined using variable angle spectroscopic ellipsometry. Dispersion of the complex refractive index parallel, N∥=(n∥+ik∥), and perpendicular, N⊥=(n⊥+ik⊥), to the film plane are reported for the photon energy range 1.5–5.0 eV. The energy dispersion in the optical properties has been analyzed using a three-phase model and Lorentzian dispersion functions for the polymers. The resonant frequencies of the Lorentzian oscillators describe the fundamental π-π∗ optical transition polarized parallel to the polymer chain and indicate additional optical transitions polarized perpendicular to the polymer chain that are introduced by interchain interactions. Dependence of the optical anisotropy and fundamental π-π∗ optical transition on the polymer backbone is discussed. © 2003 American Institute of Physics.
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78.66.Li Other semiconductors
78.66.Qn Polymers; organic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Temperature dependence of the radiative recombination coefficient of intrinsic crystalline silicon

T. Trupke, M. A. Green, P. Würfel, P. P. Altermatt, A. Wang, J. Zhao, and R. Corkish

J. Appl. Phys. 94, 4930 (2003); http://dx.doi.org/10.1063/1.1610231 (8 pages) | Cited 47 times

Online Publication Date: 30 September 2003

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The radiative recombination coefficient B(T) of intrinsic crystalline silicon is determined as a function of temperature over the temperature range 77–300 K. We observe that B(T) decreases as a function of temperature and we compare our results to previously published contradictory data from the literature. The radiative recombination coefficient is calculated from the absorption coefficient for band-to-band transitions, which we determine at different temperatures from photoluminescence spectra measured on planar high resistivity float zone silicon wafers. Photoluminescence spectra could be detected over a large range of more than five orders of magnitude, which allowed us to determine extremely low values of the absorption coefficient in the spectral range where absorption processes are accompanied by the simultaneous absorption of up to four phonons. © 2003 American Institute of Physics.
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71.20.Mq Elemental semiconductors
78.55.Ap Elemental semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Modeling plate impact response of particle–polymer composite

Duan Z. Zhang

J. Appl. Phys. 94, 4938 (2003); http://dx.doi.org/10.1063/1.1610235 (8 pages) | Cited 3 times

Online Publication Date: 30 September 2003

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A recently obtained constitutive relation [Zhang et al., Phys. Rev. E 66, 051806 (2002)] is used for polymers to model plate impact experiments on a composite material consisting of elastic particles and a polymer binder. The stress relaxation in the polymer is described by a kernel in a history integral. The kernel implies a 1/math stress relaxation for a short time t, and an exponential stress relaxation for a long time. It is found that the binder behavior, especially the stress relaxation at a short-time scale, plays an essential role in the wave dispersion observed during the experiments. Although it is difficult to implement the history dependent constitutive relation directly into a numerical calculation, a mathematical approximation of the kernel is found in the form resembling a prony series. The approximation enables easy implementation of the constitutive relation into numerical calculations. While the conventional use of a prony series requires a series of experiments to determine the parameters, in the present article, the parameters in the series expansion are uniquely determined by the kernel. Furthermore, not all the terms in the series are needed for a specific problem of interest. Only those terms with the relaxation times in the range of the time scales of the physical process are important. © 2003 American Institute of Physics.
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46.55.+d Tribology and mechanical contacts
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
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