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15 Jun 1994

Volume 75, Issue 12, pp. 7607-8246

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Excitonic polaritons in quantum‐confined systems and applications to optoelectronic devices

Toshio Katsuyama and Kensuke Ogawa

J. Appl. Phys. 75, 7607 (1994); http://dx.doi.org/10.1063/1.356592 (19 pages) | Cited 7 times

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An excitonic polariton is a complex quasiparticle that consists of a photon and an exciton. Excitonic polaritons have recently been shown to exist in quantum‐confined systems such as GaAs quantum wells. Based on the coherent coupling between the charged electron (hole) and light, the quantum‐confined excitonic polariton has the characteristics of large coherence length and large phase modulation under electric fields. Furthermore, because of the inherent large refractive index, the spatial shape of the guided mode of the excitonic polariton transmitted in such quantum‐confined waveguides is expected to be squeezed significantly. We discuss the characteristics of such excitonic polaritons and possible applications to ultrasmall optoelectronic devices.
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71.35.-y Excitons and related phenomena
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.66.Fd III-V semiconductors

Role of dynamical cooperativity for an enhanced isotope effect during transport

R. W. Rendell

J. Appl. Phys. 75, 7626 (1994); http://dx.doi.org/10.1063/1.356593 (7 pages) | Cited 3 times

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The effect of particle‐lattice interactions on the hopping of particles over a barrier in a double‐well system is studied within a simple microscopic model. The probability of escape becomes modified by the slow dynamics of the lattice and results in nonexponential relaxation. The macroscopic relaxation time is related to the local hopping time by a type of scaling relation which has been experimentally observed in a wide range of relaxation phenomena. In particular, the scaling relation is consistent with an enhanced isotope effect recently observed in comparing hydrogen and deuterium dispersive transport in irradiated metal‐oxide‐semiconductor devices. In these systems, the hydrogen locally deforms the oxide lattice as it hops and the evidence for a connection with the type of mechanism studied is discussed. The existence of a scaled relaxation time in the present model is demonstrated from numerical solutions and this is supported by the analytic properties of the kinetic equations for this class of systems.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Bk General theory, scattering mechanisms
05.60.-k Transport processes

High‐power proton beam‐matter interaction diagnostics by analysis of the hydrodynamic response of solid targets

K. Baumung, H. U. Karow, D. Rusch, H. J. Bluhm, P. Hoppé, G. I. Kanel, A. V. Utkin, and V. Licht

J. Appl. Phys. 75, 7633 (1994); http://dx.doi.org/10.1063/1.356594 (6 pages) | Cited 5 times

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The hydrodynamic response of thin planar targets to the ablative pressure pulse induced by a high‐power proton beam has been investigated experimentally at the Karlsruhe Light Ion Facility using time‐resolved laser‐Doppler velocimetry. An analytical acoustic model was established which allows a semiquantitative interpretation of the phenomena observed. Details in the measured ablation pressure history could be explained by the particularities of the proton beam. The evolution in time of the depth of the energy deposition zone deduced from our experiments is in good agreement with the proton energy and stopping range increase during the voltage rise of the generator pulse.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
41.75.Ak Positive-ion beams
62.50.-p High-pressure effects in solids and liquids

Double‐grating thin‐film devices based on second‐order Bragg interaction

Masoud Kasraian

J. Appl. Phys. 75, 7639 (1994); http://dx.doi.org/10.1063/1.356595 (14 pages) | Cited 2 times

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Four coupled‐mode equations describing the characteristics of the second‐order Bragg interaction are derived for the transverse electric mode of a dielectric film waveguide with periodic corrugations on both the film‐cover and the film‐substrate interfaces. The characteristics of the frequency‐selective filter, output coupler, input coupler, and distributed feedback laser are obtained. Proper choice of the design parameters leads to a frequency‐selective filter radiating neither in the cover nor in the substrate, a highly efficient output coupler radiating only in the cover, and an efficient input coupler exciting a guided wave only in one direction. Similarly, in the distributed feedback laser, a suitable choice of the parameters of the two gratings provides a mechanism for controlling the oscillation characteristics of the laser. The attractive feature of the double‐grating design is that the characteristics of the thin‐film devices are not very sensitive to small deviations of the grating parameters from their designed values.
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42.82.Et Waveguides, couplers, and arrays
42.55.Rz Doped-insulator lasers and other solid state lasers

Modeling of mixing in chemical oxygen‐iodine lasers: Analytic and numerical solutions and comparison with experiments

B. D. Barmashenko, A. Elior, E. Lebiush, and S. Rosenwaks

J. Appl. Phys. 75, 7653 (1994); http://dx.doi.org/10.1063/1.356596 (13 pages) | Cited 13 times

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The processes of iodine dissociation, population inversion, and lasing in the chemical oxygen‐iodine laser (COIL) are affected by the mixing between the flows of oxygen and injected iodine. The effect of mixing on the operation of the COIL is studied theoretically applying a simple one‐dimensional leaky stream tube model and the results are compared to available experimental data. The model enables the calculation of the iodine dissociation and the gain along the flow and of the lasing power, as a function of the iodine flow rate (nI2), the yield of singlet oxygen [O2(1Δ)] and the pressure in the cavity. Both the fraction of the dissociated iodine and the maximum gain are shown to be nonmonotonous functions of nI2. There is an optimal value of nI2, depending on the O2(1Δ) yield, the gas velocity, and the temperature in the cavity, for which the gain achieves its maximum and the iodine dissociation length its minimum. The model shows that the maximum nI2 for which lasing is possible is less than 5% of the oxygen flow rate. This result is in agreement with experimental data and cannot be explained by models based on the assumption of a premixed flow. Simple analytic expressions are derived for the optimal nI2, the characteristic length of iodine dissociation, the gain, and the lasing power. The calculated gain and lasing power are compared with available experimental results for both subsonic and supersonic COILs.
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42.55.Ks Chemical lasers
78.60.Ps Chemiluminescence
47.70.Fw Chemically reactive flows

Optical properties of disordered GaAs/(Al,Ga)As distributed Bragg reflectors

P. D. Floyd and J. L. Merz

J. Appl. Phys. 75, 7666 (1994); http://dx.doi.org/10.1063/1.356597 (3 pages) | Cited 5 times

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The variation of the reflectivity, stopband width, and penetration depth of disordered GaAs/(Al,Ga)As distributed Bragg reflectors (DBRs) is analyzed by simulating interdiffusion of Al and Ga at the interfaces within the DBR. The results show that important optical parameters are unchanged for short diffusion lengths, but drastically degrade for larger diffusion lengths. The results indicate the limits of thermal processing for device structures containing GaAs/AlGaAs DBRs.
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42.55.Px Semiconductor lasers; laser diodes
42.82.Gw Other integrated-optical elements and systems

Thermionic‐tunneling‐diffusion model of the laser current‐voltage and power characteristics

A. A. Grinberg

J. Appl. Phys. 75, 7669 (1994); http://dx.doi.org/10.1063/1.356598 (12 pages) | Cited 4 times

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An analytical model of the laser‐diode current‐voltage (I‐V) characteristics based on the generalized thermionic‐tunneling‐diffusion mechanism of carrier transport through heterointerfaces has been proposed. It is valid for any degree of the carrier distribution degeneracy, not only in the laser active region but in the cladding layers as well. The model combines the laser rate equations with current flow equations and permits the evaluating of power‐current and power‐voltage characteristics. It is assumed that the temperature of the electron‐hole gas in the active layer is different from the lattice temperatures. Under appropriate circumstances this allows one to consider the gas heating effect. In the present paper it is supposed that the temperature of the carriers in the laser active layer is proportional to the current in order to investigate the influence of heating on the laser I‐V and power characteristics. The sequence of steps which must be carried out in the application of the model is described in detail. Analysis of the formation of different current components is carried out for lasing and unlasing laser diodes using as an example the 1.3 μm laser based on an InGaAsP compound. The influence of the heating effect and leakage current on the low‐frequency linear response function is also presented.  
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.60.Jb Light-emitting devices

Vibrations of AT‐cut quartz strips of narrow width and finite length

P. C. Y. Lee and Ji Wang

J. Appl. Phys. 75, 7681 (1994); http://dx.doi.org/10.1063/1.356599 (15 pages) | Cited 6 times

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A system of one‐dimensional equations of motion for AT‐cut quartz strip resonators with narrow width and for frequencies up to and including the fundamental thickness shear is deduced from the two‐dimensional, first‐order equations for piezoelectric crystal plates by Lee, Syngellakis, and Hou [J. Appl. Phys. 61, 1249 (1987)] by expanding the mechanical displacements and electric potentials in a series of trigonometric functions of the width coordinate. By neglecting the piezoelectric coupling and the weak mechanical coupling through c56, four groups of coupled equations of motion are obtained. For the equations of each group, closed form solutions are obtained and the traction‐free conditions at four edges are accommodated. Dispersion curves and frequency spectrum are computed for quartz strips. The predicted frequency as a function of the length‐to‐thickness ratio and as a function of the width‐to‐thickness ratio of the quartz strips is compared with experimental data with good agreement.
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43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound
62.30.+d Mechanical and elastic waves; vibrations
77.65.Fs Electromechanical resonance; quartz resonators

Thermal waves in materials with linearly inhomogeneous thermal conductivity

Jan Fivez and Jan Thoen

J. Appl. Phys. 75, 7696 (1994); http://dx.doi.org/10.1063/1.356600 (4 pages) | Cited 24 times

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The problem of plane thermal waves in media with linearly varying thermal conductivity κ in the absence of internal heat sources is rigorously solved in terms of Bessel functions. An exact solution in the presence of an internal heat source arising from optical absorption is also presented. Focus is on the semi‐infinite solid. In particular, an inverse calculation procedure is outlined that is able to yield, in a very fast way, a linear κ profile that reveals the most important aspects of the actual profile.
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44.30.+v Heat flow in porous media
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

Circular streamline model of shaped‐charge jet and slug formation with asymmetry

J. P. Curtis and R. J. Kelly

J. Appl. Phys. 75, 7700 (1994); http://dx.doi.org/10.1063/1.356601 (10 pages) | Cited 5 times

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The formation of a jet as a result of the collapse of a shaped charge liner in the presence of asymmetry is considered. The development of a satisfactory analytic formation model based on the assumption of incompressible fluid flow requires the solution of the classically indeterminate problem of the collision of two unequal streams. A method of closing the problem is presented. It rests on the assumptions that there is a stagnant core region and that the flows of material from the impinging streams into the jet and slug turn by following circular streamlines with no decrease in speed. Balances of the centrifugal forces with the pressure in the stagnant core, relations derived from the flow geometry, the equation of mass conservation, and Bernoulli’s law provide the mathematical statement of the problem. These equations are manipulated to produce a reduced set of four equations in four unknowns, enabling a solution to be determined. This analytic solution predicts that both the jet and the slug are deflected by the same acute angle from the line of bisection of the angle between the impinging streams. The percentages of material in each stream which turn to form the jet are the same. The new model recovers analytically the classical Birkhoff, MacDougall, Pugh, and Taylor [J. Appl. Phys. 19, 563 (1948)] jet formation model in the symmetric case. It also yields the correct analytic result for the head‐on collision of two streams of equal speeds but differing widths. More generally the model predicts an approximately linear dependence of the off‐axis jet velocity component on the percentage difference in the stream speeds and a similar dependence for the widths. The predicted absolute values of the off‐axis velocity are greater for a given difference in the stream speeds than for the same percentage difference in the widths. Finally, fair agreement with some previous experimental work on the collision of streams of unequal widths is demonstrated.
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47.40.-x Compressible flows; shock waves
47.27.wg Turbulent jets

Enhanced saturation of sputtered amorphous SiN film frameworks using He‐ and Ne‐Penning effects

Iwao Sugimoto, Satoko Nakano, and Hiroki Kuwano

J. Appl. Phys. 75, 7710 (1994); http://dx.doi.org/10.1063/1.356602 (8 pages) | Cited 10 times

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Optical emission spectroscopy reveals that helium and neon gases enhance the nitridation reactivity of the nitrogen plasma by Penning effects during magnetron sputtering of the silicon target. These excited nitrogen plasmas promote the saturation of frameworks of the resultant silicon nitride films. X‐ray photoelectron spectroscopy, electron spin resonance, and x‐ray diffraction analyses provide insight into the structure of these films, and thermal desorption mass spectroscopy reveals the behavior of volatile species in these films.
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68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
52.40.Mj Particle beam interactions in plasmas

A combined plasma‐surface model for the deposition of C:H films from a methane plasma

A. von Keudell and W. Möller

J. Appl. Phys. 75, 7718 (1994); http://dx.doi.org/10.1063/1.356603 (10 pages) | Cited 62 times

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The deposition of C:H layers by an electron‐cyclotron‐resonance plasma from methane was investigated. C:H was deposited at a methane pressure of 1.6 Pa and a substrate temperature between room temperature and 700 K. The film composition, morphology, and structure were investigated by high‐energy ion beam analysis and scanning electron microscopy. A combined plasma‐surface model for thin‐film deposition is proposed, which includes the electron‐induced dissociation of methane in the plasma and a growth model. The dominant reactions for film growth are the adsorption of the radical CH3, the direct incorporation of the ions, and the etching reactions with atomic hydrogen from the plasma. A consistent description for the deposition of hydrocarbon layers emerges. It compares favorably with measurements on the temperature dependence of the film growth and the influence of variable gas flow through the reactor on the growth rate and the film morphology.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
52.40.Hf Plasma-material interactions; boundary layer effects

Morphologies and photoluminescence of porous silicon under different etching and oxidation conditions

Chi‐Huei Lin, Si‐Chen Lee, and Yang‐Fang Chen

J. Appl. Phys. 75, 7728 (1994); http://dx.doi.org/10.1063/1.356604 (9 pages) | Cited 15 times

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It is found from scanning electron microscopy that the porous silicon samples fabricated under different conditions exhibit different morphologies. Some of them show islands or cracks, but the rest appear to be smooth. It is proposed that the formation of the islands and the cracks depends on the porosity of the porous silicon samples and result from the shrinkage of the porous structure. The photoluminescence spectra of the porous silicon samples also depend on the etching conditions. The peak position of the photoluminescence shifts to higher energy with increasing the porosity of the samples or by rinsing the samples in deionized water for a long time. However, in certain situations the photoluminescence peak shifts to lower energy after the samples are placed in air for a couple of days. It is proposed that not only the quantum size effect but also the transition between oxide levels contribute to the photoluminescence of the porous silicon.
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78.55.Hx Other solid inorganic materials
81.65.-b Surface treatments
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Interaction of α‐radiation induced defects with Pd‐related deep levels in silicon

Asghar A. Gill, N. Zafar, M. Zafar Iqbal, and N. Baber

J. Appl. Phys. 75, 7737 (1994); http://dx.doi.org/10.1063/1.356605 (8 pages) | Cited 4 times

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Results of a detailed deep level transient spectroscopy study of Pd‐doped p+n Si diodes irradiated with 5.48 MeV α particles are presented, which also include investigations of isochronal annealing behavior of the deep level spectra up to a temperature of 350–400 °C. An extended comparison with results obtained on reference samples as well as with previously published results of deep level studies on Pd‐doped samples (unirradiated) and on undoped α‐irradiated samples provides valuable information, since the same starting material is used in all these studies. It is observed that, in general, the Pd‐related deep levels increase in concentration upon irradiation at the expense of α‐radiation‐induced levels. In particular, the A center sharply decreases in concentration upon post‐irradiation annealing with a corresponding increase in the concentration of the dominant Pd‐related level. The results also show that, contrary to the previously held belief, two well‐known Pd‐related levels at Ec−0.37 eV and Ec−0.59 eV are not states of the same defect and an off‐center/on‐center substitutional Pd‐vacancy model for the defects corresponding to Ec−0.18 eV and Ec−0.22 eV Pd‐related levels cannot explain new data presented here. In the reference (undoped, heat treated) samples, a few levels are observed after α‐irradiation or post‐irradiation annealing which were not detected in the untreated diodes, pointing to their relationship to quenched‐in defects. A new annealed‐in hole level H(α‐Pd) at Ev+0.27 eV is observed which seems to be a complex of Pd with some α‐irradiation‐induced defect.
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61.80.Jh Ion radiation effects
71.55.Cn Elemental semiconductors

Magnetism of ternary compounds RE6Fe13X; RE=Pr, Nd; X=Cu, Ag, Au, Zn, Cd, and Hg

F. Weitzer, A. Leithe‐Jasper, P. Rogl, K. Hiebl, A. Rainbacher, G. Wiesinger, W. Steiner, J. Friedl, and F. E. Wagner

J. Appl. Phys. 75, 7745 (1994); http://dx.doi.org/10.1063/1.356606 (7 pages) | Cited 18 times

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Novel compounds RE6Fe13X (X=Cu, Ag, Au, Zn, Cd, Hg) have been synthesized by arc melting (Cu, Ag, Au) or by reaction sintering (Zn, Cd, Hg), followed by heat treatment at 550 or 600 °C up to 350 h in evacuated silica capsules. From room temperature x‐ray powder diffraction analyses the alloys were found to crystallize with the ordered Nd6Fe13Si type. The Curie point of all the compounds is found to lie around room temperature. Due to their low magnetization values a ferrimagnetic coupling within the Fe sublattice is suggested. A canted RE‐spin structure cannot be ruled out. 57Fe Mössbauer spectra were recorded from the samples with X=Ag and Au. Additionally, 197Au spectra were taken from the two Au‐containing compounds. The 57Fe spectra are composed of various subpatterns, originating from the different Fe sites and were found to be essentially unaffected by the specific element RE and X. In all cases under investigation the spectra could only be fitted under the assumption of an easy axis of magnetization lying within the basal plane. The 197Au spectra reveal that the Au atoms predominantely occupy the 4a site.  
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75.30.-m Intrinsic properties of magnetically ordered materials
76.80.+y Mössbauer effect; other γ-ray spectroscopy
61.05.C- X-ray diffraction and scattering

Nitrogen effect in mechanical alloying of immiscible Cu‐V: Extended x‐ray absorption fine structure study

Kenji Sakurai, Chung Hyo Lee, Nariko Kuroda, Toshiharu Fukunaga, and Uichiro Mizutani

J. Appl. Phys. 75, 7752 (1994); http://dx.doi.org/10.1063/1.356607 (4 pages) | Cited 7 times

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A mixture of pure metallic powders of Cu and V has been mechanically alloyed by ball milling in a nitrogen atmosphere instead of a conventional inert gas. A strongly disordered phase of Cu30V70‐N was obtained, in spite of the immiscibility of Cu and V. The change of local structure around each atom was investigated by the extended x‐ray absorption fine structure technique. It was found that a nitriding reaction proceeds in the crystalline Cu‐V supersaturated solid solution, which is formed at the early stage.
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61.66.Dk Alloys
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Synchrotron radiation topography studies of twinning in NdP5O14 crystals

X. R. Huang, Z. W. Hu, S. S. Jiang, J. H. Jiang, Y. L. Tian, Y. Han, and J. Y. Wang

J. Appl. Phys. 75, 7756 (1994); http://dx.doi.org/10.1063/1.356608 (5 pages) | Cited 4 times

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An investigation of twin structures in NdP5O14 single crystals has been undertaken using white‐beam synchrotron x‐ray topography. The so‐called a‐type twins along the a axis are clearly revealed in the topographs. The displacements of the images that arise from the twins are directly measured in different topographs. With the measured values, the monoclinic distortion angle δ(δ=β−90°) is calculated, which is in good agreement with the unit cell parameters. A fine‐beam Laue diffraction pattern of the twin has also been taken which is well consistent with its simulation. From these results, the twin structures of NdP5O14 are discussed.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Mm Grain and twin boundaries
77.80.Fm Switching phenomena

X‐ray diffraction from laterally structured surfaces: Crystal truncation rods

M. Tolan, W. Press, F. Brinkop, and J. P. Kotthaus

J. Appl. Phys. 75, 7761 (1994); http://dx.doi.org/10.1063/1.356609 (9 pages) | Cited 19 times

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X‐ray‐diffraction measurements from single‐crystalline GaAs(001) surface gratings are presented. The experiments were performed using a three‐crystal diffractometer. The vicinity of the (004) Bragg reflection for five samples was investigated in detail. Model calculations based on the kinematical crystal truncation rod theory are able to explain all measurements quantitatively. Mesoscopic grating parameters as well as microscopic surface roughnesses of the samples were obtained from fits of the data. For three samples scanning electron microscope pictures were taken. The analysis of these pictures leads to the same mesoscopic parameters as obtained from x‐ray Bragg diffraction.
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61.05.cc Theories of x-ray diffraction and scattering
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology

Trapping of hydrogen impurities in helium‐implanted niobium and tantalum

P. Haussalo, J. Keinonen, U.‐M. Jäske, and J. Sievinen

J. Appl. Phys. 75, 7770 (1994); http://dx.doi.org/10.1063/1.356611 (4 pages) | Cited 6 times

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Trapping of hydrogen impurities at helium precipitates in helium‐implanted niobium and tantalum has been studied. The samples were implanted at room temperature with 100 keV 4He+ ions to doses of (0.6–36)×1016 cm−2. Some of the samples were postirradiated with 60 keV and 4 MeV protons, and annealed at elevated temperatures up to 1070 K. The helium and hydrogen concentration distributions were characterized simultaneously using the elastic‐recoil‐detection‐analysis technique. The hydrogen distributions were also measured by the nuclear resonance reaction 1H(15N,αγ) 12C. The observed hydrogen distributions show that defect‐hydrogen complexes at He bubbles are built from the ion‐irradiation‐induced and pre‐existing vacancies and pre‐existing hydrogen impurities migrated to the associated internal surfaces and that the hydrogen impurities saturate the surfaces. Recovery energies of about 2.1 eV in Nb and about 2.7 eV in Ta were observed for the hydrogen trapping defects.
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61.72.up Other materials
61.80.Jh Ion radiation effects
61.72.S- Impurities in crystals

Ion implantation into (x11)A‐oriented InP and GaAs (x≤4)

Mulpuri V. Rao, Harry B. Dietrich, P. B. Klein, Ayub Fathimulla, David S. Simons, and Peter H. Chi

J. Appl. Phys. 75, 7774 (1994); http://dx.doi.org/10.1063/1.356612 (5 pages) | Cited 1 time

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Si, Ge, and Be implantations were performed into (x11)A‐oriented semi‐insulating InP and GaAs substrates for x≤4. For comparison some of the implantations were also performed into (110)‐ and (100)‐oriented substrates. For 200 keV/5×1013 cm−2 Si and 200 keV/3×1013 cm−2 Ge implants after 850 °C/7 s annealing, the InP is always n type with similar sheet resistance independent of the substrate orientation. No in‐diffusion of Si or Ge was observed after annealing for any substrate orientation. Similar behavior was observed for Si implants in GaAs and for Si/B co‐implants in both InP and GaAs. Photoluminescence measurements were performed on the Si‐ and Si/B‐implanted InP and GaAs. For 30 keV/1.5×1014 cm−2 Be implants in both InP and GaAs, the in‐diffusion of Be in (311)A‐oriented substrates is less compared to the (100) material.
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61.72.uj III-V and II-VI semiconductors

Visible photoluminescence in Si+‐implanted silica glass

Tsutomu Shimizu‐Iwayama, Katsunori Fujita, Setsuo Nakao, Kazuo Saitoh, Tetsuo Fujita, and Noriaki Itoh

J. Appl. Phys. 75, 7779 (1994); http://dx.doi.org/10.1063/1.357031 (5 pages) | Cited 204 times

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We have investigated visible photoluminescence excited by Ar‐ion laser (488 nm, 2.54 eV) at room temperature from Si+‐implanted silica glass, as‐implanted and after subsequent annealing in vacuum. We found two visible luminescence bands: one peaked around 2.0 eV, observed in as‐implanted specimens and annealed completely after heating to about 600 °C, the other peaked around 1.7 eV observed only after heating to about 1100 °C, the temperature at which Si segregates from SiOx. It was found that the 2.0 eV band anneals parallel to the E′ centers, as detected by electron spin resonance studies. It was also found that Raman lines around 520 cm−1, due to Si—Si bonds, grow and that interference patterns are induced by annealing Si+‐implanted silica glass. Based on these studies, we ascribe the 2.0 eV band to the electron‐hole recombination in Si‐rich SiO2 and the 1.7 eV band to the electron‐hole recombination in the interface between the Si nanocrystal and the SiO2 formed by segregation of crystalline Si from SiOx.
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61.72.up Other materials
78.55.Hx Other solid inorganic materials
76.30.Lh Other ions and impurities

Single‐crystal elastic constants of fluorapatite, Ca5F (PO4)3

Michael C. Sha, Zhuang Li, and Richard C. Bradt

J. Appl. Phys. 75, 7784 (1994); http://dx.doi.org/10.1063/1.357030 (4 pages) | Cited 18 times

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The single‐crystal elastic stiffnesses of fluorapatite, Ca5F(PO4)3, have been measured by an ultrasonic technique. The values are: C11=152.0, C12=49.99, C13=63.11, C33=185.7, and C44=42.75 GPa. These results are compared with previously published values to resolve anisotropy contradictions and differences in magnitude. The apatite crystal structure is not very elastically anisotropic. It suggests that the elastic anisotropy of bone derives primarily from the hierarchical microstructure of that biocomposite and not from the anisotropy contribution of the apatite mineral component.
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62.20.D- Elasticity

Fast crystallizing GeSb alloys for optical data storage

J. Solis, C. N. Afonso, J. F. Trull, and M. C. Morilla

J. Appl. Phys. 75, 7788 (1994); http://dx.doi.org/10.1063/1.356584 (7 pages) | Cited 29 times

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A systematic study is presented on the optical and structural transformations induced in amorphous Ge1−xSbx alloys with Sb contents in the 0.71≤x≤0.91 range by irradiation with 250 ns laser pulses. The results show that only those films richer in Sb than the eutectics (x=0.85) show appreciable optical contrast upon irradiation. The dominant role of Sb in the performances of this family of alloys is analyzed. The transition from a low‐reflectivity amorphous phase to a high‐reflectivity extended solid solution of Ge in crystalline Sb is shown to be the key for a new generation of fast reversible optical storage materials in which amorphous‐crystalline cycling using ultrashort laser pulses is feasible.
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64.70.K- Solid-solid transitions
42.70.Ln Holographic recording materials; optical storage media
78.66.Jg Amorphous semiconductors; glasses

Measurements of thermal conductivity of diamond films by photothermal deflection technique

M. Bertolotti, G. L. Liakhou, A. Ferrari, V. G. Ralchenko, A. A. Smolin, Elena Obraztsova, K. G. Korotoushenko, S. M. Pimenov, and V. I. Konov

J. Appl. Phys. 75, 7795 (1994); http://dx.doi.org/10.1063/1.356585 (4 pages) | Cited 8 times

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The photothermal deflection technique has been used for contactless measurements of the thermal conductivity of thin polycrystalline diamond films grown in a dc arc discharge in different CH4/H2 mixtures. The thermal conductivity correlates inversely with amorphous sp2 carbon content in the films. Values of thermal conductivity in the range 2–5 W/cm K were obtained for ∼10‐μm‐thick diamond films deposited from gas mixtures containing methane percentages varying from 3% to 9%.  
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.60.-p Physical properties of thin films, nonelectronic

Computer simulation of electromigration in thin‐film metal conductors

J. T. Trattles, A. G. O’Neill, and B. C. Mecrow

J. Appl. Phys. 75, 7799 (1994); http://dx.doi.org/10.1063/1.356586 (6 pages) | Cited 16 times

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A model is presented for simulating electromigration in thin‐film metal conductors. The backfluxes are calculated explicitly in each of the grain boundaries using concentration and stress gradients resulting from the initial electromigration flux. The stress‐dependent diffusivity term is also directly included in the formulation. It is assumed that the main cause of the flux divergence is the grain structure of the conductor and that these divergences occur at the triple‐point junctions of the grain boundaries. Time‐to‐failure and classic resistometric analyses of five conductors are performed. Results indicate that current‐density exponent of n≊2 should be used in time‐to‐failure analysis. This is due to the localized stress migration and diffusion acting against the electromigration force throughout the period of the conductor lifetime. A direct correlation between the time to failure (TTF) and relative rate of resistance change Rrc was found when all conductors and stress conditions were considered together. This relationship is of the form TTF=0.223R−1.11rc and indicates that resistance measurements can be used in producing lifetime parameters for use in providing reliability rules for conductor design.
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66.30.Qa Electromigration
73.61.At Metal and metallic alloys
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