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15 Aug 2005

Volume 98, Issue 4, Articles (04xxxx)

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Redshift of the light emission from highly strained In0.3Ga0.7As/GaAs quantum wells by dipole δ doping

Y. Fu, S.-M. Wang, X.-D. Wang, and A. Larsson

J. Appl. Phys. 98, 043501 (2005); http://dx.doi.org/10.1063/1.2008351 (5 pages) | Cited 2 times

Online Publication Date: 16 August 2005

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We have studied theoretically the energy band structures and optical properties of highly strained dipole δ-doped In0.3Ga0.7As/GaAs single quantum wells. Including dopant diffusion effect, strain in the quantum well, spin-orbital interactions, and many-body effects, the self-consistent calculations of the eight-band k∙p model and the Poisson equation show that the dipole δ doping induces an electric field across the In0.3Ga0.7As quantum well by the Stark effect so that both the interband transition energy and the wave-function overlap between the ground-state electrons and holes are reduced. Applying an external bias across the quantum well partially cancels the built-in electric field and reduces the wavelength redshift. The calculated material gain peak is close to the experimental lasing wavelength.
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78.67.De Quantum wells
61.72.uj III-V and II-VI semiconductors
73.21.Fg Quantum wells
71.20.Nr Semiconductor compounds
66.30.J- Diffusion of impurities
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Jq Electro-optical effects
71.15.-m Methods of electronic structure calculations

Effect of the surface-plasmon resonance on the emission properties of rhodamine 6G infiltrated in synthetic opals

Keiji Ishikawa and Tatsuya Okubo

J. Appl. Phys. 98, 043502 (2005); http://dx.doi.org/10.1063/1.2001157 (4 pages) | Cited 9 times

Online Publication Date: 16 August 2005

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We investigate the spectrally narrowed emission (SNE) from rhodamine 6G infiltrated in synthetic opals enhanced by the surface-plasmon resonance effect of Ag particles anchored on the internal surface of the synthetic opals. At a larger number density of Ag particles, SNE is observed at a lower pump intensity, and the intensity is reduced to one-tenth without Ag. The enhancement factor is qualitatively reproduced by theoretical calculations as a function of the amount of Ag particles. These results indicate that the enhancement is caused by the surface-plasmon resonance.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.55.Kz Solid organic materials

High-fluence Si-implanted diamond: Optimum implantation temperature for SiC formation

H. Weishart, F. Eichhorn, V. Heera, B. Pécz, Á. Barna, and W. Skorupa

J. Appl. Phys. 98, 043503 (2005); http://dx.doi.org/10.1063/1.2009073 (6 pages) | Cited 5 times

Online Publication Date: 18 August 2005

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In this paper the authors investigate the effect of implantation temperature on the structural properties of diamond implanted with high fluences of Si between 5.3×1017 Si cm−2 and 1×1018 Si cm−2. In order to reduce radiation-induced damage and to enhance SiC formation the implantations were performed at elevated temperatures in the range from 900 to 1200 °C. Subsequently, all samples were annealed for 10 min at 1500 °C in a rf-heated furnace. X-ray diffraction revealed the formation of cubic SiC nanocrystallites in a buried layer inside the implanted diamond. The implantation-induced damage was assessed by analyzing graphitization of the surface-near layer using Raman spectroscopy. With increasing Si fluence the implantation-induced damage rises and the nearly perfect alignment of the formed SiC crystallites within the host diamond lattice deteriorates. However, raising the implantation temperature from 900 to 1000 °C reduces the damage in the diamond and increases the amount, size, and epitaxial alignment of the crystalline SiC precipitates. Further increase of the implantation temperature gives no improvement in the quality of the SiC-rich layer. Instead, the damaged diamond converts into graphite and the formation of SiC crystallites is obstructed.
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81.07.Bc Nanocrystalline materials
81.05.Hd Other semiconductors
61.72.up Other materials
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Hv Other nonmetallic inorganics

Defects introduced into electroplated Cu films during room-temperature recrystallization probed by a monoenergetic positron beam

A. Uedono, T. Suzuki, T. Nakamura, T. Ohdaira, and R. Suzuki

J. Appl. Phys. 98, 043504 (2005); http://dx.doi.org/10.1063/1.2009813 (5 pages) | Cited 9 times

Online Publication Date: 18 August 2005

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Positron annihilation was used to probe vacancy-type defects in electroplated Cu films deposited on Ta/SiO2/Si. Doppler broadening spectra of the annihilation radiation were measured for the Cu films during grain growth at room temperature (i.e., self-annealing). The line-shape parameter S increased during self-annealing, and the observed time dependence of S was well described by the Johnson-Mehl-Avrami-Kolmogorov kinetics. After self-annealing, the values of S were found to be larger than the S value for annealed pure Cu, suggesting that the positrons annihilated from the trapped state by vacancy-type defects in grains. From a comparison with the results of previous isochronal annealing experiments, the major species of defects introduced during self-annealing was found to be vacancy clusters. The size of these defects increased, but their concentration decreased, with increasing film thickness. In thicker Cu films, an enhanced flow of atoms and subsequent rapid grain growth cause such defect behavior.
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78.70.Bj Positron annihilation
78.66.Bz Metals and metallic alloys
61.80.Fe Electron and positron radiation effects
61.82.Bg Metals and alloys
61.72.J- Point defects and defect clusters

Superlattice in an interminiband resonance ac field

V. I. Litvinov and A. Manasson

J. Appl. Phys. 98, 043505 (2005); http://dx.doi.org/10.1063/1.2010619 (4 pages)

Online Publication Date: 18 August 2005

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We discuss the properties of miniband electrons in a superlattice illuminated by a strong electromagnetic field. If the ac field is in resonance with a two-miniband superlattice, gaps in the quasienergy spectrum appear. The gap is proportional to the Bessel function and oscillates with the ac electric field. The resonant ac driving force makes the quasienergy spectrum tunable and may decrease the critical dc field for electrical domains to form.
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73.21.Cd Superlattices
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Valence-band structures of layered oxychalcogenides, LaCuOCh (Ch = S, Se, and Te), studied by ultraviolet photoemission spectroscopy and energy-band calculations

Kazushige Ueda, Hideo Hosono, and Noriaki Hamada

J. Appl. Phys. 98, 043506 (2005); http://dx.doi.org/10.1063/1.2001749 (7 pages) | Cited 13 times

Online Publication Date: 18 August 2005

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To examine the electronic structure of the valence band, ultraviolet photoemission spectra of a series of layered oxychalcogenides, LaCuOCh (Ch = S, Se, and Te), were measured. The measurements were conducted using He II, He I, and Ne I excitation lines to observe the excitation energy dependence of the spectral shape. Energy-band calculations based on a full-potential linearized augmented plain-wave method were performed. The calculated density of states and partial density of states were compared to the observed photoemission spectra. Five bands were observed in the valence band of LaCuOCh, and Ne I radiation remarkably enhanced two of them. The energy dependence of the photoionization cross section of atomic orbitals indicated that the two enhanced bands were due to the Ch p states. Energy calculations were used to assign the remaining bands. The electronic structure of LaCuOCh was further discussed using molecular-orbital diagrams to visualize the (La2O2)2+ and (Cu2Ch2)2− layers as large donor-acceptor pairs. The energy-band calculation and molecular-orbital diagram analyses suggested that the main difference among the valence-band structures of LaCuOCh (Ch = S, Se, and Te) originates from the variations in the energy position of the Ch p bands. The observed spectra are consistent with the results of the band calculations and clearly show the energy variations in the Ch p bands with respect to spectral shape and excitation energy dependence.
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71.20.Ps Other inorganic compounds
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Electric-dipole spin-resonance signals related to extended interstitial agglomerates in silicon

T. Mchedlidze, S. Binetti, A. Le Donne, S. Pizzini, and M. Suezawa

J. Appl. Phys. 98, 043507 (2005); http://dx.doi.org/10.1063/1.2001750 (5 pages) | Cited 1 time

Online Publication Date: 18 August 2005

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Three electric-dipole spin-resonance signals, labeled TU7, TU8, and TU9, were detected after subjecting oxygen-rich silicon samples to two-step annealing procedures at 450 and 650 °C for prolonged times. The formation and structural evolution of large interstitial agglomerates, known as rodlike defects, occur in oxygen-rich silicon material during similar annealing procedures. Comparison of parameters and formation peculiarities of the defects, inferred from the investigation of the detected signals, with those previously reported for rodlike defects, allowed the assigning of the TU7, TU8, and TU9 spectra to the line-interstitial defects, the planar defects, and the dislocation dipoles, respectively. Correlations of the spin-resonance signals and peculiarities in the photoluminescence spectra for the samples are reported and analyzed.
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76.30.-v Electron paramagnetic resonance and relaxation
61.72.J- Point defects and defect clusters
78.55.Ap Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Deep-level defects in n-type 6H silicon carbide induced by He implantation

C. C. Ling, X. D. Chen, G. Brauer, W. Anwand, W. Skorupa, H. Y. Wang, and H. M. Weng

J. Appl. Phys. 98, 043508 (2005); http://dx.doi.org/10.1063/1.2014934 (6 pages) | Cited 4 times

Online Publication Date: 18 August 2005

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Defects in He-implanted n-type 6H–SiC samples have been studied with deep-level transient spectroscopy. A deep-level defect was identified by an intensity with a logarithmical dependence on the filling pulse width, which is characteristic of dislocation defects. Combined with information extracted from positron-annihilation spectroscopic measurements, this defect was associated with the defect vacancy bound to a dislocation. Defect levels at 0.38/0.44 eV (E1/E2), 0.50, 0.53, and 0.64/0.75 eV (Z1/Z2) were also induced by He implantation. Annealing studies on these samples were also performed and the results were compared with those obtained from e−-irradiated (0.3 and 1.7 MeV) and neutron-irradiated n-type 6H–SiC samples. The E1/E2 and the Z1/Z2 signals found in the He-implanted sample are more thermally stable than those found in the electron-irradiated or the neutron-irradiated samples.
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81.05.Hd Other semiconductors
71.55.Ht Other nonmetals
61.80.Jh Ion radiation effects
61.80.Fe Electron and positron radiation effects
61.82.Fk Semiconductors
78.70.Bj Positron annihilation
61.72.Cc Kinetics of defect formation and annealing
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations
61.72.J- Point defects and defect clusters

Competition between tensile and compressive stress mechanisms during Volmer-Weber growth of aluminum nitride films

Brian W. Sheldon, Ashok Rajamani, Abhinav Bhandari, Eric Chason, S. K. Hong, and R. Beresford

J. Appl. Phys. 98, 043509 (2005); http://dx.doi.org/10.1063/1.1994944 (9 pages) | Cited 27 times

Online Publication Date: 18 August 2005

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Stress evolution during molecular-beam epitaxy of AIN films was monitored with in situ curvature measurements. Changes in the growth rate produced large stress variations, with more tensile stress observed at higher growth rates. For example, at a growth temperature of 750 °C the instantaneous steady-state stress in films with similar grain sizes varied from −0.15 GPa at a growth rate of 90 nm/h, to approximately 1.0 GPa at a growth rate of 300 nm/h. To explain these results, we develop a kinetic model of stress evolution that describes both tensile and compressive mechanisms. The tensile component is based on a mechanism which is proposed here as an inherent feature of grain-boundary formation. The compressive component is based on our recent model of atom insertion, driven by the excess chemical potential of surface adatoms that is created by the growth flux. The combined model predicts that the stress is largely governed by the competition between tensile and compressive mechanisms, which can be conveniently described with a single parameter, α. The limiting values α→0 and α→+∞ correspond to previous models of compressive and tensile stresses, respectively.
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68.60.Bs Mechanical and acoustical properties
68.60.Wm Other nonelectronic physical properties
68.55.-a Thin film structure and morphology
68.47.Fg Semiconductor surfaces
61.72.Mm Grain and twin boundaries
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Diffraction measurement and analysis of slanted holographic polymer dispersed liquid crystal

Xiao Hong Sun, Xiao Ming Tao, Ting Jin Ye, Yau-Shan Szeto, and Xiao Yin Cheng

J. Appl. Phys. 98, 043510 (2005); http://dx.doi.org/10.1063/1.2010618 (5 pages) | Cited 7 times

Online Publication Date: 19 August 2005

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In this article, slanted holographic polymer dispersed liquid-crystal films are prepared by using a single-prism interferometer. Their diffraction characteristics are measured at various incident angles. Based on the coupled-wave theory of diffraction efficiency and incident angles, the grating period, film thickness, and slanted angle of the volume grating are derived. A good agreement is demonstrated between the experimental and theoretical results, and supported by scanning electron microscopy observation. The electrical switching behavior of the grating is also described. The diffraction efficiency changes from 65% to a stable value of 10% at an electric field of 33 V/μm. On the other hand, based on the theoretical prediction of diffraction efficiency, the optimum film thickness and Bragg grating period are determined, which sheds light on the implementation of our experiments.
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42.40.Eq Holographic optical elements; holographic gratings
42.70.Df Liquid crystals
42.79.Wc Optical coatings
42.79.Dj Gratings

Trap concentration dependence of percolation in doped small molecule organic materials

Wieland Weise, Torsten Keith, Norwin von Malm, and Heinz von Seggern

J. Appl. Phys. 98, 043511 (2005); http://dx.doi.org/10.1063/1.2005378 (5 pages)

Online Publication Date: 19 August 2005

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The thermally stimulated current (TSC) technique is used to investigate the effect of doping of organic glassy thin films of the hole transport material N,N′-di(1-naphthyl)N,N′-diphenylbenzidine (α-NPD) with various concentrations of 4,4′,4″-tris(N-(1-naphthyl)-N-phenylamino)triphenylamine (1-NaphDATA). The mobility is estimated from current-voltage characteristics. At small dopant concentrations a TSC peak appears at about 200 K. Increasing the dopant concentration to about 4 vol % leads to a peak shift towards higher temperatures, related to decreasing mobility. When increasing the dopant concentration further, the peak shifts again to lower temperatures towards the peak position for pure 1-NaphDATA. The energy distribution of the trap structure is obtained utilizing the fractional TSC technique. In accordance to a higher-lying highest occupied molecular-orbital level of 1-NaphDATA as compared to the α-NPD matrix, the activation energy of a deep trap level of about 0.5 eV was reported previously for low doping concentrations up to a few percent. At higher dopant concentrations the deep traps vanish from the trap structure. The behavior can be interpreted as a change from a trap-controlled transport for small doping concentrations to a percolating transport on the dopant molecules themselves. It is shown that the onset of percolation at rather low concentrations can be explained by hopping including not only nearest neighbors.
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73.61.Ph Polymers; organic compounds
73.61.Jc Amorphous semiconductors; glasses
61.72.up Other materials
61.72.S- Impurities in crystals
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Dn Low-field transport and mobility; piezoresistance
71.55.Ht Other nonmetals

Crystallographic and luminescent properties of orthorhombic BaAl2S4:Eu powder and thin films

Philippe F. Smet, Jo E. Van Haecke, Roland L. Van Meirhaeghe, and Dirk Poelman

J. Appl. Phys. 98, 043512 (2005); http://dx.doi.org/10.1063/1.2012515 (6 pages) | Cited 8 times

Online Publication Date: 22 August 2005

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BaAl2S4:Eu thin films were prepared from a multilayered BaS:Eu/Al2S3 thin-film structure, deposited with electron-beam evaporation. Depending on the deposition and postdeposition annealing temperature, europium-doped BaAl2S4 thin films can show both an orthorhombic and the more common cubic crystal structure. The lattice constants of the orthorhombic BaAl2S4 are determined from powder-diffraction data. The photoluminescent properties of europium-doped orthorhombic and cubic BaAl2S4 powders are compared. The occurrence of both phases in thin films is discussed in terms of substrate and postdeposition annealing temperature. A temperature of 600 °C is sufficient to obtain the orthorhombic phase, and annealing at 900 °C leads to the cubic phase. The phase formation in the multilayered thin films is investigated by studying the crystallographic, optical, and photoluminescent properties.
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61.72.Cc Kinetics of defect formation and annealing
68.55.-a Thin film structure and morphology
78.55.Hx Other solid inorganic materials
78.66.Nk Insulators
61.66.Fn Inorganic compounds
61.72.up Other materials

Luminescence characteristics of pulsed-laser-ablated Y1.35Gd0.6O3:Eu3+ thin-film phosphors

Jong Seong Bae, Byung Kee Moon, Jung Hyun Jeong, Soung Soo Yi, and Jung Hwan Kim

J. Appl. Phys. 98, 043513 (2005); http://dx.doi.org/10.1063/1.2001728 (5 pages) | Cited 2 times

Online Publication Date: 22 August 2005

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Y2O3:Eu3+ and Y1.35Gd0.6O3:Eu3+ luminescent thin films were grown on Al2O3 (0001) and Si (100) substrates by a pulsed-laser deposition technique. Both films grown under different deposition conditions have been characterized using microstructural and luminescent measurements. The crystallinity, surface morphology, and photoluminescence of the films are highly dependent on the deposition conditions. The structural characterization carried out on the films grown on both substrates at the substrate temperature of 600 °C and oxygen pressure of 200 mTorr indicated that films were preferentially (222) oriented. In particular, the surface roughness of the thin films had a strong effect on the photoluminescence. The incorporation of Gd into the Y2O3 lattice induced a change of crystallinity, surface roughness, and a remarkable increase of photoluminescence. Due to a math‐math transition of Eu3+, the Y1.35Gd0.6O3:Eu3+ films emitted the radiation of red light with a 612‐nm wavelength, whose brightness was increased by a factor of 3.1 in comparison with that of Y2O3:Eu3+ films.
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78.55.Hx Other solid inorganic materials
78.66.Nk Insulators
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)

Ionic conduction in 70-MeV C5+-ion-irradiated poly(vinylidenefluoride-co-hexafluoropropylene)-based gel polymer electrolytes

D. Saikia, A. Kumar, F. Singh, D. K. Avasthi, and N. C. Mishra

J. Appl. Phys. 98, 043514 (2005); http://dx.doi.org/10.1063/1.2030417 (6 pages) | Cited 2 times

Online Publication Date: 22 August 2005

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In an attempt to increase the Li+-ion diffusivity, poly(vinylidenefluoride-co-hexafluoropropylene)-(propylene carbonate+diethyl carbonate)-lithium perchlorate gel polymer electrolyte system has been irradiated with 70-MeV C5+-ion beam of nine different fluences. Swift heavy-ion irradiation shows enhancement in ionic conductivity at lower fluences and decrease in ionic conductivity at higher fluences with respect to unirradiated gel polymer electrolyte films. Maximum room-temperature (303 K) ionic conductivity is found to be 2×10−2 S/cm after irradiation with a fluence of 1011 ions/cm2. This interesting result could be attributed to the fact that for a particular ion beam with a given energy, a higher fluence provides critical activation energy for cross linking and crystallization to occur, which results in the decrease in ionic conductivity. X-ray-diffraction results show decrease in the degree of crystallinity upon ion irradiation at low fluences ( ⩽ 1011 ions/cm2) and increase in crystallinity at higher fluences (>1011 ions/cm2). Analysis of Fourier-transform infrared spectroscopy results suggests the bond breaking at a fluence of 5×109 ions/cm2 and cross linking at a fluence of 1012 ions/cm2 and corroborate conductivity and x-ray-diffraction results. Scanning electron micrographs exhibit increased porosity of the polymer electrolyte after ion irradiation.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
61.80.Jh Ion radiation effects
78.35.+c Brillouin and Rayleigh scattering; other light scattering
64.70.D- Solid-liquid transitions
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Reactions of SiCl groups in amorphous SiO2 with mobile interstitial chemical species: Formation of interstitial Cl2 and HCl molecules, and role of interstitial H2O molecules

Koichi Kajihara, Masahiro Hirano, Linards Skuja, and Hideo Hosono

J. Appl. Phys. 98, 043515 (2005); http://dx.doi.org/10.1063/1.2005383 (9 pages) | Cited 8 times

Online Publication Date: 23 August 2005

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Reactions of the network-bound chloride (SiCl) groups in amorphous SiO2 (a-SiO2 or SiO2 glass) with mobile interstitial oxygen (O2), water (H2O), and hydrogen (H2) molecules thermally loaded from ambient atmosphere and with mobile radicals created by exposure to F2 laser light (λ = 157 nm,hν = 7.9 eV) were investigated. Reactions of the SiCl groups with O2 and H2O produce interstitial chlorine (Cl2) and hydrogen chloride (HCl) molecules, respectively. An infrared-absorption band appearing at ∼ 2815 cm−1 is assigned to the interstitial HCl. The SiCl groups do not react with H2 below 400 °C. However, sequential gas loading first with O2, then with H2 leads to the production of interstitial H2O, which decomposes the SiCl groups into HCl. Furthermore, the formation of the interstitial HCl with exposure to F2 laser light, most likely due to the cracking of the Si–Cl bonds with photogenerated hydrogen atoms (H0), was demonstrated. These findings yield a general picture of the reactions of the chlorine-related species in a-SiO2 and demonstrate the significant influence of even minor amounts (<1018 cm−3) of interstitial H2O on defect formation and annihilation processes.
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82.30.-b Specific chemical reactions; reaction mechanisms
61.43.Fs Glasses
78.35.+c Brillouin and Rayleigh scattering; other light scattering

A multiphase equation of state of three solid phases, liquid, and gas for titanium

S. Pecker, S. Eliezer, D. Fisher, Z. Henis, and Z. Zinamon

J. Appl. Phys. 98, 043516 (2005); http://dx.doi.org/10.1063/1.2006226 (12 pages) | Cited 3 times

Online Publication Date: 23 August 2005

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A multiple-phase equation of state of the α phase, β phase, ω phase, liquid, and gas for titanium is presented. This equation of state is thermodynamically consistent, based on a three-term semiempirical model for the Helmholtz free energy. The parameters of the free energy are first evaluated from the experimental data and solid-state theoretical calculations. Then, the values of the parameters are adjusted using a numerical minimization scheme based on the simplex algorithm, to values that best reproduce measured phase diagrams and other experimental data. The predicted phase diagram shows a compression-induced β-ω transition, up to a β-ω-liquid triple point at ∼ 45 GPa and ∼ 2200 K. For pressures above this triple point, the melting occurs from the ω phase. Moreover, no β-ω transition is predicted along the Hugoniot curve starting at STP conditions.
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64.30.-t Equations of state of specific substances
65.40.G- Other thermodynamical quantities
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.30.Bx Phase diagrams of metals, alloys, and oxides
64.70.K- Solid-solid transitions
64.70.D- Solid-liquid transitions
64.60.Kw Multicritical points

Photon absorption in the Restrahlen band of thin films of GaN and AlN: Two phonon effects

Jianyong Yang, Gail J. Brown, Mitra Dutta, and Michael A. Stroscio

J. Appl. Phys. 98, 043517 (2005); http://dx.doi.org/10.1063/1.2034648 (5 pages) | Cited 3 times

Online Publication Date: 24 August 2005

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Würtzite semiconductors exhibit strong carrier-phonon coupling as well as strong Restrahlen-related absorption of radiation due to the interaction with optical phonons. For the GaN and AlN würtzites studied here, the optical phonon frequencies fall in the infrared region. With the transverse-optical phonon frequency ωt, and longitudinal-optical phonon frequency ωl, when light with frequencies ωt<ω<ωl is incident on a GaN or AlN film, the resonance with optical phonons will lead to strong absorption. In this paper, these effects are modeled and studied experimentally. Our studies show that the absorption is so strong that it is still significant even when the sample thickness is reduced to the submicron level. It is also found experimentally and theoretically that, not only the first harmonic, but also the second harmonic of the phonon frequency leads to strong absorption. Theoretical comparisons with experimental data and predicted transmission versus the energy of the incident light for different film thicknesses are presented.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
63.20.K- Phonon interactions

Annealing behavior between room temperature and 2000 °C of deep level defects in electron-irradiated n-type 4H silicon carbide

G. Alfieri, E. V. Monakhov, B. G. Svensson, and M. K. Linnarsson

J. Appl. Phys. 98, 043518 (2005); http://dx.doi.org/10.1063/1.2009816 (5 pages) | Cited 28 times

Online Publication Date: 24 August 2005

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The annealing behavior of irradiation-induced defects in 4H-SiC epitaxial layers grown by chemical-vapor deposition has been systematically studied by means of deep level transient spectroscopy (DLTS). The nitrogen-doped epitaxial layers have been irradiated with 15-MeV electrons at room temperature and an isochronal annealing series from 100 to 2000 °C has been performed. The DLTS measurements, which have been carried out in the temperature range from 120 to 630 K after each annealing step, revealed the presence of six electron traps located in the energy range of 0.45–1.6 eV below the conduction-band edge (Ec). The most prominent and stable ones occur at Ec−0.70 eV (labeled Z1/2) and Ec−1.60 eV(EH6/7). After exhibiting a multistage annealing process over a wide temperature range, presumably caused by reactions with migrating defects, a significant fraction of both Z1/2 and EH6/7 (25%) still persists at 2000 °C and activation energies for dissociation in excess of 8 and ∼ 7.5 eV are estimated for Z1/2 and EH6/7, respectively. On the basis of these results, the identity of Z1/2 and EH6/7 is discussed and related to previous assignments in the literature.
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81.05.Hd Other semiconductors
61.72.Cc Kinetics of defect formation and annealing
71.55.Ht Other nonmetals
61.80.Fe Electron and positron radiation effects
61.82.Fk Semiconductors
71.20.Nr Semiconductor compounds
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Pulsed-laser-deposited p-type ZnO films with phosphorus doping

Veeramuthu Vaithianathan, Byung-Teak Lee, and Sang Sub Kim

J. Appl. Phys. 98, 043519 (2005); http://dx.doi.org/10.1063/1.2011775 (4 pages) | Cited 46 times

Online Publication Date: 24 August 2005

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We report the preparation of p-type ZnO thin films on Al2O3(0001) substrates with phosphorus doping by pulsed laser deposition using Zn3P2 as the dopant source material. The results of the Hall effect measurements taken at room temperature indicate that the 3‐mol % phosphorus-doped ZnO films thermally annealed at temperatures between 600 and 800 °C under an O2 atmosphere exhibit p-type behavior with a hole concentration of 5.1×1014−1.5×1017 cm−3, a hole mobility of 2.38−39.3 cm2/V s, and a resistivity of 17−330 Ω cm. The low-temperature (15 K) photoluminescence results reveal that the peak related to the neutral-acceptor bound exciton (A0,X) emission at 3.358 eV is only observed in the films showing p-type behavior. Our results not only demonstrate that there is a narrow temperature window for rapid thermal annealing in which phosphorus-doped p-type ZnO films can be obtained, but also suggest that the use of Zn3P2 can provide an effective approach to the preparation of p-type ZnO films.
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81.05.Dz II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
61.72.uj III-V and II-VI semiconductors
73.61.Ga II-VI semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
71.35.-y Excitons and related phenomena
61.72.Cc Kinetics of defect formation and annealing

Thermal response of Ru electrodes in contact with SiO2 and Hf-based high-k gate dielectrics

H.-C. Wen, P. Lysaght, H. N. Alshareef, C. Huffman, H. R. Harris, K. Choi, Y. Senzaki, H. Luan, P. Majhi, B. H. Lee, M. J. Campin, B. Foran, G. D. Lian, and D.-L. Kwong

J. Appl. Phys. 98, 043520 (2005); http://dx.doi.org/10.1063/1.2012510 (6 pages) | Cited 6 times

Online Publication Date: 24 August 2005

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A systematic experimental evaluation of the thermal stability of Ru metal gate electrodes in direct contact with SiO2 and Hf-based dielectric layers was performed and correlated with electrical device measurements. The distinctly different interfacial reactions in the Ru/SiO2, Ru/HfO2, and Ru/HfSiOx film systems were observed through cross-sectional high-resolution transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy with electron-energy-loss spectra, and energy dispersive x-ray spectra analysis. Ru interacted with SiO2, but remained stable on HfO2 at 1000 °C. The onset of Ru/SiO2 interfacial interactions is identified via silicon substrate pitting possibly from Ru diffusion into the dielectric in samples exposed to a 900 °C/10-s anneal. The dependence of capacitor device degradation with decreasing SiO2 thickness suggests Ru diffuses through SiO2, followed by an abrupt, rapid, nonuniform interaction of ruthenium silicide as Ru contacts the Si substrate. Local interdiffusion detected on Ru/HfSiOx samples may be due to phase separation of HfSiOx into HfO2 grains within a SiO2 matrix, suggesting that SiO2 provides a diffusion pathway for Ru. Detailed evidence consistent with a dual reaction mechanism for the Ru/SiO2 system at 1000 °C is presented.
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84.32.Tt Capacitors
66.30.Ny Chemical interdiffusion; diffusion barriers
64.75.-g Phase equilibria
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
79.20.Uv Electron energy loss spectroscopy
68.37.Lp Transmission electron microscopy (TEM)

Er3+ fluorescence in rare-earth aluminate glass

Richard Weber, Scott Hampton, Paul C. Nordine, Thomas Key, and Richard Scheunemann

J. Appl. Phys. 98, 043521 (2005); http://dx.doi.org/10.1063/1.2034080 (9 pages) | Cited 1 time

Online Publication Date: 25 August 2005

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Er3+ ion fluorescence was excited with a 980-nm pump laser in Er-doped rare-earth aluminate (REAl) glasses with Er-dopant concentrations from 0.5–30 mol % (oxides basis). The spectral and decay characteristics were measured at ∼ 1550 nm from Er3+ math and at ∼ 2750 nm from Er3+ math. Red and green light emissions were also observed, from Er3+ math and math+math, respectively. The fluorescence decay rates are described by a model that yields an accurate fit of results at Er concentrations from 0.5 to 7 mol %. The radiative lifetime of Er3+ math in Er:REAl glass is 6.12±0.26 ms. Hydroxyl ion quenching occurs at a rate given by 9.88×10−20 aOHnEr Hz, where aOH is the glass absorption coefficient (in cm−1) at a wavelength of 2950 nm and nEr is the total Er ion concentration. The math upconversion rate constant increases with the Er concentration to 1.35+0.05×10−18 cm3/s at and above 7-mol % Er2O3. Er3+ math fluorescence decays primarily by multiphonon quenching to math, at 7700±800 Hz, a rate that is slightly less than in tellurite glasses. The addition of 20-mol % silica to the glass has only a small influence on the fluorescence decay rates and greatly improves glass formation from the liquid to allow melting and casting of Er-doped REAl glass from platinum crucibles. The application of these Er-doped glasses in laser and optical device applications is briefly discussed.
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78.55.Qr Amorphous materials; glasses and other disordered solids
78.66.Jg Amorphous semiconductors; glasses
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.S- Impurities in crystals

Large positive and negative Goos-Hänchen shifts from a weakly absorbing left-handed slab

Li-Gang Wang and Shi-Yao Zhu

J. Appl. Phys. 98, 043522 (2005); http://dx.doi.org/10.1063/1.2034084 (4 pages) | Cited 21 times

Online Publication Date: 25 August 2005

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We theoretically show that the Goos-Hänchen (GH) shifts [ F. Goos and H. Hänchen, Ann. Phys. 1, 333 (1947) ] of the TE- and TM-polarized beams reflected from a slab of the weakly absorbing left-handed material can be large positive near the resonant transmission if the absorption of the slab is sufficiently weak. The GH shift of the TM-polarized reflected beam can be large negative or positive near the Brewster angle.
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42.70.-a Optical materials
42.25.Bs Wave propagation, transmission and absorption
42.25.Ja Polarization
42.25.Gy Edge and boundary effects; reflection and refraction

High-precision measurement of azimuthal rotation of liquid crystals on solid substrates

I. Jánossy

J. Appl. Phys. 98, 043523 (2005); http://dx.doi.org/10.1063/1.2031927 (6 pages) | Cited 6 times

Online Publication Date: 25 August 2005

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A high-accuracy optical method for the determination of the rotation of the liquid-crystal director on solid substrates is reported. The measurements involve the use of a photoelastic modulator in conjunction with a white light source. The detection of the first and second harmonics of the light signal allows for the determination both of the director position and the twist deformation at the exit face of the cell. The method is illustrated by experiments on the liquid crystal penthylcyanobiphenyl aligned by polyimide layers. The importance of director gliding is pointed out as well.
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61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions
42.70.Df Liquid crystals
33.15.Bh General molecular conformation and symmetry; stereochemistry
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
78.40.Me Organic compounds and polymers
78.40.Dw Liquids

Analysis of thermohydraulic explosion energetics

Ralf Büttner, Bernd Zimanowski, Chris-Oliver Mohrholz, and Reiner Kümmel

J. Appl. Phys. 98, 043524 (2005); http://dx.doi.org/10.1063/1.2033149 (8 pages) | Cited 3 times

Online Publication Date: 25 August 2005

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Thermohydraulic explosion, caused by direct contact of hot liquids with cold water, represent a major danger of volcanism and in technical processes. Based on experimental observations and nonequilibrium thermodynamics we propose a model of heat transfer from the hot liquid to the water during the thermohydraulic fragmentation process. The model was validated using the experimentally observed thermal energy release. From a database of more than 1000 experimental runs, conducted during the last 20 years, a standardized entrapment experiment was defined, where a conversion of 1 MJ∕kg of thermal energy to kinetic energy within 700 μs is observed. The results of the model calculations are in good agreement with this value. Furthermore, the model was found to be robust with respect to the material properties of the hot melt, which also is observed in experiments using different melt compositions. As the model parameters can be easily obtained from size and shape properties of the products of thermohydraulic explosions and from material properties of the hot melt, we believe that this method will not only allow a better analysis of volcanic eruptions or technical accidents, but also significantly improve the quality of hazard assessment and mitigation.
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47.27.T- Turbulent transport processes
47.40.Nm Shock wave interactions and shock effects
82.33.Vx Reactions in flames, combustion, and explosions
91.40.Ft Eruption mechanisms
47.70.Fw Chemically reactive flows
47.55.Kf Particle-laden flows
05.70.Ln Nonequilibrium and irreversible thermodynamics

High quantum efficiency ultraviolet/blue AlGaN/InGaN photocathodes grown by molecular-beam epitaxy

D. J. Leopold, J. H. Buckley, and P. Rebillot

J. Appl. Phys. 98, 043525 (2005); http://dx.doi.org/10.1063/1.1999026 (5 pages) | Cited 6 times

Online Publication Date: 26 August 2005

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Enormous technological breakthroughs have been made in optoelectronic devices through the use of advanced heteroepitaxial-semiconductor crystal-growth techniques. This technology is being extended toward enhanced ultraviolet/blue single-photon detection through the design and fabrication of atomically tailored heteroepitaxial GaAlN/GaInN photocathode device structures. The AlGaN/InGaN system is ideal because the band gap can be tailored over an energy range from 0.8 to 6.2 eV and epitaxial thin-film layers can be grown directly on optically transparent sapphire substrates. Although a single p-type GaN layer activated with cesium can produce reasonably high quantum efficiency in the ultraviolet wave band, a more complex design is necessary to achieve high levels extending into the blue region. In the present work, band-gap engineering concepts have been utilized to design heterostructure photocathodes. The increased level of sophistication offered by this approach has been exploited in an attempt to precisely control photoelectron transport to the photocathode surface. Thin heterostructure layers designed for transmission-mode detection were fabricated by molecular-beam epitaxy. A quantum efficiency of 40% at 250 nm was achieved using a thin, compositionally graded GaN/InGaN layer, epitaxially grown on a sapphire substrate. Further improvements are anticipated through continued optimization, defect reduction, and more complex photocathode designs.
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85.60.Ha Photomultipliers; phototubes and photocathodes
85.60.Bt Optoelectronic device characterization, design, and modeling
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