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15 Sep 2000

Volume 88, Issue 6, pp. 3113-3785

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Relaxation in glassforming liquids and amorphous solids

C. A. Angell, K. L. Ngai, G. B. McKenna, P. F. McMillan, and S. W. Martin

J. Appl. Phys. 88, 3113 (2000); http://dx.doi.org/10.1063/1.1286035 (45 pages) | Cited 81 times

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The field of viscous liquid and glassy solid dynamics is reviewed by a process of posing the key questions that need to be answered, and then providing the best answers available to the authors and their advisors at this time. The subject is divided into four parts, three of them dealing with behavior in different domains of temperature with respect to the glass transition temperature, Tg, and a fourth dealing with “short time processes.” The first part tackles the high temperature regime T>Tg, in which the system is ergodic and the evolution of the viscous liquid toward the condition at Tg is in focus. The second part deals with the regime T∼Tg, where the system is nonergodic except for very long annealing times, hence has time-dependent properties (aging and annealing). The third part discusses behavior when the system is completely frozen with respect to the primary relaxation process but in which secondary processes, particularly those responsible for “superionic” conductivity, and dopart mobility in amorphous silicon, remain active. In the fourth part we focus on the behavior of the system at the crossover between the low frequency vibrational components of the molecular motion and its high frequency relaxational components, paying particular attention to very recent developments in the short time dielectric response and the high Q mechanical response. © 2000 American Institute of Physics.
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61.43.Fs Glasses
01.30.Rr Surveys and tutorial papers; resource letters
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.20.Lc Time-dependent properties; relaxation
61.43.Dq Amorphous semiconductors, metals, and alloys
66.30.H- Self-diffusion and ionic conduction in nonmetals
63.50.-x Vibrational states in disordered systems
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Atomic force microscope based patterning of carbonaceous masks for selective area growth on semiconductor surfaces

Adrian Avramescu, Akio Ueta, Katsuhiro Uesugi, and Ikuo Suemune

J. Appl. Phys. 88, 3158 (2000); http://dx.doi.org/10.1063/1.1287763 (8 pages) | Cited 5 times

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Carbonaceous masks for selective growth on GaAs substrates were fabricated with high resolution by anodization with an atomic force microscope (AFM). Mask deposition is made by a 15-kV accelerated electron-beam irradiation in a scanning electron microscope. The local anodization of the carbonaceous film under intense electric field is investigated and the main factors for improving resolution and reproducibility are discussed. The “edge effect” of the anodized region, revealed in the electric-field distribution at the tip–water–film interfaces is identified as the main factor responsible for the resolution degradation during patterning. Short forward bias pulse for anodizing the carbonaceous film and the subsequent reverse bias pulse for neutralizing the space charge, locally accumulated during the forward bias, are shown to be effective for the higher pattern resolution and also for deepening the patterning depth. Based on the analysis, a modulated-amplitude pulsed bias mode is proposed and is demonstrated to bring a significant improvement in the resolution and the aspect ratio of patterns made by the anodization. Carbonaceous masks ready for selective area growth of semiconductors alloys were fabricated with the pattern resolution of ∼26 nm, limited by the curvature of AFM cantilever tips. © 2000 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
82.45.-h Electrochemistry and electrophoresis
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
85.40.Sz Deposition technology
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Population inversion in an optically pumped single quantum well

T. J. Green and W. Xu

J. Appl. Phys. 88, 3166 (2000); http://dx.doi.org/10.1063/1.1287604 (4 pages) | Cited 5 times

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An optically pumped intersubband laser generator is proposed in which the continuum states above an Al0.2Ga0.8As–GaAs–Al0.2Ga0.8As single quantum well with a width of L=17 nm serve as the highest level in a four-level laser system. The design allows much greater flexibility in the choice of pumping source and simplifies considerably the device fabrication. We have obtained the electronic subband structure of the proposed device and utilized a simple rate equation approach to examine the electron density in different states under optical pumping. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
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Simulation of pulsed high-frequency breakdown in hydrogen

A. Lacoste, L. L. Alves, C. M. Ferreira, and G. Gousset

J. Appl. Phys. 88, 3170 (2000); http://dx.doi.org/10.1063/1.1288510 (12 pages) | Cited 5 times

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We present a simulation of the breakdown stage of high-power, short-pulse high-frequency discharges in hydrogen, produced when an electric field of the form E(t)=EmaxIW(1−e−t/τ)sin(ωt) is applied to a cylindrical resonant cavity. Typical discharge operating conditions considered are applied powers 1–15 kW, gas pressures 0.1–20 Torr, cavity diameter of 25.71 cm, tube radius of 0.8 cm, field frequency ω/2π=1.12 GHz, pulse width tP=10 μs, and rising times τ of a few microseconds. Under these conditions, discharge breakdown occurs before the electric field reaches its maximum amplitude EmaxIW, this situation corresponding to the so-called increasing wave (IW) regime. The simulation is based on a Monte Carlo model to calculate the breakdown times, tb, and fields, Eb, for different field rising slopes EmaxIW/τ≃10−1−103 V cm−1 ns−1. The results obtained show that a breakdown criterion based on the electron energy balance (εgain=εloss, where εgain and εloss are, respectively, the mean electron energy gain and loss) yields excellent agreement between calculated and measured values of tb and Eb, while the classical particle rate balance criterion (νgain=νloss, where νion and νloss are, respectively, the mean electron production and loss frequencies) is satisfied only at pressures below 0.5 Torr. It is further shown that: (i) the IW limit for long breakdown times (tb≃τ→∞) corresponds to the continuous wave regime; and (ii) there is an equivalence between pulsed excitation, with pulse width tP, and IW regimes, for short breakdown times such that tb=tP≪τ. © 2000 American Institute of Physics.
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52.80.Pi High-frequency and RF discharges

Spectroscopic study of ionizing and recombining plasma in a stationary plasma source

S. Namba, M. Goto, H. Tsuboi, T. Oda, and K. Sato

J. Appl. Phys. 88, 3182 (2000); http://dx.doi.org/10.1063/1.1289042 (8 pages) | Cited 3 times

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A hot cathode, which is composed of La2O3–W needles, has been constructed and tested in a modified arc discharge source in order to produce a high-density plasma by large discharge current. No damage of needles was found after 100 h at a discharge current of 300 A. Characteristics of generated helium plasmas have been investigated by spectroscopic observations. The electron density has been found to be ≧2×1014 cm−3 at a discharge current 100 A with this cathode. Experimental results were analyzed with calculations based on a collisional radiative model including an effect of radiation trapping. As a result, generated plasmas were shown to be classified into two groups by the pressure of neutral helium, that is, an ionizing plasma and recombining plasma. In low temperature recombining plasma, population inversions between He+ ion n=2 and the higher excited levels have been obtained. © 2000 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.-b Plasma properties
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.50.Dg Plasma sources

Radiation trapping of the Hg 185 nm resonance line

K. L. Menningen and J. E. Lawler

J. Appl. Phys. 88, 3190 (2000); http://dx.doi.org/10.1063/1.1289050 (8 pages) | Cited 15 times

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The decay rate of the Hg 61P1 level was measured as a function of cold spot temperature (Hg density) and buffer gas pressure in cylindrical, sealed fused silica cells. The decay rates were obtained using a time-resolved laser-induced 185 nm fluorescence experiment with multi-step excitation. Cold spot temperatures from 25 to 100 °C were studied. The Hg densities for this temperature range and with no buffer gas yield the lowest possible decay rates due to radiation trapping with partial frequency redistribution. Decay rates with argon buffer gas pressures of 3 and 30 Torr were also studied. The results are in agreement with published data from a discharge afterglow experiment. Monte Carlo simulations of radiation transport in the cells, including the effects of hyperfine and isotope structure, the effects of foreign gas broadening, and partial frequency redistribution are compared to the experimental data. Reasonably good agreement is obtained, however there is evidence of quenching of Hg 61P1 atoms in collisions with ground state Hg and Ar atoms. An analytic formula for the fundamental mode trapped decay rate of the 61P1 level, which is applicable over a substantial region of parameter space, was devised from the Monte Carlo results. © 2000 American Institute of Physics.
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37.10.De Atom cooling methods
37.10.Gh Atom traps and guides
32.50.+d Fluorescence, phosphorescence (including quenching)
31.50.Df Potential energy surfaces for excited electronic states
32.30.Rj X-ray spectra
31.30.Gs Hyperfine interactions and isotope effects
32.70.Jz Line shapes, widths, and shifts
34.50.-s Scattering of atoms and molecules

Profile control in BF3 plasma doping

Dixon T. K. Kwok, Paul K. Chu, and Chung Chan

J. Appl. Phys. 88, 3198 (2000); http://dx.doi.org/10.1063/1.1288012 (4 pages) | Cited 10 times

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Plasma doping (PD) is an alternative technique to form shallow junctions in deep-submicrometer microelectronic devices. Previous studies have demonstrated that PD produces shallow junctions with better efficiency than those by conventional low energy beam-line doping (BD). In addition, even though cross-sectional transmission electron microscopy reveals that the surface layer is amorphized after high dose BF3 PD or BD implantation, PD samples show less residual defects after rapid thermal annealing. For ultrashallow junctions, doping profiles with a high dopant concentration near the surface are required for the formation of low resistant contacts. In this article, we demonstrate the use of nonideal voltage pulse shape in achieving advantageous doping profiles that are difficult to obtain via BD. By performing particle-in-cell (PIC) simulation, we derive the ion energy distributions for different sample voltage pulse shapes for BF3 PD. Comparison of the PD boron depth profiles simulated by PIC and an assumed Gaussian implant profile to the BD boron depth profiles simulated by TRIM shows a low energy component that does not exist in BD samples. The rise and fall time of the sample voltage pulse contributes to the overall energy distribution since a long rise or fall time increases the low energy component. We postulate that these low energy ions may also change the nature of the amorphized layer and are one of the reasons for the reduction of residual defects after rapid thermal annealing. The preferred sample voltage pulse for plasma doping is suggested to be a short one with a relatively long rise and fall time. This is something that is very difficult to achieve by beam-line ion implantation. © 2000 American Institute of Physics.
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61.72.uf Ge and Si
61.82.Fk Semiconductors
61.72.S- Impurities in crystals
61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Energy coupling in a diode with a dielectric-gridded cathode

A. Lahav, V. Berezovsky, and L. Schächter

J. Appl. Phys. 88, 3202 (2000); http://dx.doi.org/10.1063/1.1288702 (6 pages) | Cited 1 time

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It is shown experimentally that electrostatic coupling between the ferroelectric “capacitor” and the anode-cathode gap controls the emission process in ferroelectric cathode. Three main quantities were demonstrated to be directly correlated to the energy stored in the ferroelectric: the energy in the diode, the diode impedance, and the delay of the peak (anode) current relative to the triggering time of the ferroelectric. The polarity of the triggering voltage does not seem to have a significant impact on the performance of the diode. © 2000 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors
82.45.-h Electrochemistry and electrophoresis

Absolute densities of long lived species in an ionized physical vapor deposition copper–argon plasma

Y. Andrew, I. Abraham, J. H. Booske, Z. C. Lu, and A. E. Wendt

J. Appl. Phys. 88, 3208 (2000); http://dx.doi.org/10.1063/1.1289219 (12 pages) | Cited 12 times

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Optical absorption spectroscopy has been used to measure absolute, average gas phase densities of neutral copper, ground and metastable states, and neutral argon, metastable and resonance states, in an ionized physical vapor deposition plasma. Spectroscopic measurements were carried with a xenon arc lamp as a high intensity, continuum light source, and an optical multichannel detector. Copper radiative transitions in the wavelength range of 324.8–510.6 nm and argon radiative transitions in the 706.7–811.5 nm range were employed. The curve of growth method has been used to calculate the absolute line average densities from fractional absorption data. For a copper–argon plasma of neutral pressure 30 and 10 mTorr copper metastable state densities were found to lie in the range of 1010–1012 cm−3. Comparison of these densities with neutral copper densities derived from independent measurements of neutral copper flux at the substrate indicate gas phase temperatures greater than 1500 K under certain experimental conditions. These values of inferred temperatures indicate the copper metastable state density to be significant in comparison with neutral copper ground state densities at 10 and 30 mTorr with radio frequency heating power of 1 kW. The concentrations of argon 4s sublevels of the first excited state were found to be in the range of 4.5×108–1.5×1011 cm−3 for the experimental conditions studied. The ordering of the relative densities of the argon 4s sublevels and the variation of the lumped first excited state with experimental parameters are discussed. © 2000 American Institute of Physics.
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52.25.-b Plasma properties
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Series operation of direct current xenon chloride excimer sources

Ahmed El-Habachi, Wenhui Shi, Mohamed Moselhy, Robert H. Stark, and Karl H. Schoenbach

J. Appl. Phys. 88, 3220 (2000); http://dx.doi.org/10.1063/1.1288699 (5 pages) | Cited 33 times

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Stable, direct current microhollow cathode discharges in mixtures of hydrochloric acid, hydrogen, xenon, and neon have been generated in a pressure range of 200–1150 Torr. The cathode hole diameter was 250 μm. Sustaining voltages range from 180 to 250 V at current levels of up to 5 mA. The discharges are strong sources of xenon chloride excimer emission at a wavelength of 308 nm. Internal efficiencies of approximately 3% have been reached at a pressure of 1050 Torr. The spectral radiant power at this pressure was measured as 5 mW/nm at 308 nm for a 3 mA discharge. By using a sandwich electrode configuration, consisting of five perforated, alternate layers of metal and dielectric, a tandem discharge—two discharges in series—could be generated. For an anode–cathode–anode configuration the excimer irradiance, recorded on the axis of the discharge, was twice as large as that of a single discharge. The extension of this basic tandem electrode structure to a multiple electrode configuration allows the generation of high irradiance excimer sources. Placing such a structure with a string of microhollow cathode discharge into an optical resonator promises to lead to a direct current microexcimer laser. © 2000 American Institute of Physics.
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52.80.Hc Glow; corona

Study of x-ray emission from a table top plasma focus and its application as an x-ray backlighter

F. N. Beg, I. Ross, A. Lorenz, J. F. Worley, A. E. Dangor, and M. G. Haines

J. Appl. Phys. 88, 3225 (2000); http://dx.doi.org/10.1063/1.1287220 (6 pages) | Cited 48 times

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A study of a 2 kJ, 200 kA, table top plasma focus device as an intense x-ray source is reported. The x-ray yield from a number of gases, (deuterium, nitrogen, neon, argon, and xenon) is measured as a function of filling pressure and in neon as a function of anode length. In gases with Z<18, the plasma implodes to form a uniform cylindrical column, whereas for Z⩾18, the plasma consists of a number of hot spots. A maximum x-ray yield of 16.6 J and pulse length of 10–15 ns was obtained in neon. The x-ray emission was established to be due to H- and He-like line radiation. The temperature estimated from spectroscopic observations was about 300–400 eV at an electron density of (3–5)×1020 cm−3 in neon. At low pressures in neon, hard x-ray radiation, presumably due to electron beams was dominant. Mesh images of different wire materials were recorded at the optimum pressure in neon as a proof of principle for x-ray backlighting. © 2000 American Institute of Physics.
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52.55.Ez Theta pinch
52.75.-d Plasma devices
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors

An electron impact cross section set for CHF3

Mark J. Kushner and Da Zhang

J. Appl. Phys. 88, 3231 (2000); http://dx.doi.org/10.1063/1.1289076 (4 pages) | Cited 12 times

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Trifluoromethane, CHF3, is used for plasma etching of silicon compounds for microelectronics fabrication, and so there is interest in developing computer models for plasmas sustained in CHF3. Recent measurements of electron swarm parameters, and electron impact dissociation and ionization cross sections, have provided a sufficient basis to develop a working electron impact cross section set for CHF3. Such a cross section set is reported here. We found that increased energy losses from dissociative electronic excitation processes were required to reproduce experimental ionization coefficients. The cross sections for attachment are small with there being some uncertainty in their magnitude at low energies. The cross sections were used in a plasma equipment model for an inductively coupled plasma reactor and compared to discharges sustained in C2F6. For otherwise identical operating conditions, plasmas sustained in CHF3 had higher electron and lower negative ion densities. © 2000 American Institute of Physics.
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34.80.Ht Dissociation and dissociative attachment
34.80.Gs Molecular excitation and ionization
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
52.65.-y Plasma simulation
52.25.Jm Ionization of plasmas
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Relation between the molecular orientations of a very thin liquid crystal layer and an underlying rubbed polyimide film

Naoki Ito, Kenji Sakamoto, Ryuichi Arafune, and Sukekatsu Ushioda

J. Appl. Phys. 88, 3235 (2000); http://dx.doi.org/10.1063/1.1288696 (7 pages) | Cited 12 times

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By polarized infrared absorption spectroscopy, we have determined the relation between the molecular orientation of a rubbed polyimide film and that of a very thin liquid crystal (LC) layer (approximately a monolayer of 8CB molecules) in contact with the polyimide film. The molecular orientation of the rubbed polyimide film was determined by fitting theoretically the incident angle dependence of the infrared absorption for molecular vibrations polarized parallel to the length of the polymer. Approximately a monolayer of 8CB molecules was deposited on a rubbed polyimide film with previously measured molecular orientation. The molecular orientation of this LC layer was also determined by polarized infrared absorption. We found that the LC molecules and the polyimide chains are oriented, on average, along the rubbing direction and tilted up from the surface, and that the molecular order of the LC layer is higher than that of the underlying rubbed polyimide film. © 2000 American Institute of Physics.
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61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
68.15.+e Liquid thin films
78.30.C- Liquids
78.66.Qn Polymers; organic compounds

Influence of impurities on the optical damage of KTiOPO4 crystals

C. Zaldo, J. Carvajal, R. Solé, F. Díaz, D. Bravo, and A. Kling

J. Appl. Phys. 88, 3242 (2000); http://dx.doi.org/10.1063/1.1288014 (7 pages) | Cited 4 times

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Optical damage has been induced in doped c-cut KTiOPO4 (KTP) crystals by low intensity (I0⩽0.1 W/cm2) continuous-wave illumination with ultraviolet (λ=364 nm) light. The presence of two growth sectors with different sensibility to optical damage has been observed and it is related to their different impurity concentrations. Impurities shift the optical absorption edge of KTP to lower energy and make the induced damage more stable at room temperature. The damage saturation depends on the ultraviolet power density and on the impurity concentration. It has also been observed that some impurities (W and others) change their valence due to ultraviolet irradiation. A dynamic model considering the excitation of electrons from donors and their release from traps is proposed. The model allows us to describe the main features of the optical damage and erasure kinetics. © 2000 American Institute of Physics.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators
71.55.Ht Other nonmetals
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Magnetic resonance investigations of defects in Ga14N and Ga15N

M. W. Bayerl, N. M. Reinacher, H. Angerer, O. Ambacher, M. S. Brandt, and M. Stutzmann

J. Appl. Phys. 88, 3249 (2000); http://dx.doi.org/10.1063/1.1289226 (5 pages) | Cited 2 times

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The influence of the nitrogen nuclear spin on the optically detected magnetic resonance and electron spin resonance signatures of the intrinsic shallow donor and a deep defect causing the characteristic yellow luminescence have been studied on wurtzite GaN epitaxial layers grown by plasma induced molecular beam epitaxy with isotopically pure 14N and 15N. In particular, the linewidth of the deep defect signal is observed to be independent of the nitrogen isotope. The missing effect of the different nuclear spin properties of the 14N and 15N isotopes is discussed in view of current microscopic models for the yellow luminescence in GaN. © 2000 American Institute of Physics.
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71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
76.70.Hb Optically detected magnetic resonance (ODMR)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Si self-interstitial injection from Sb complex formation in Si

J. Fage-Pedersen, P. Gaiduk, J. Lundsgaard Hansen, and A. Nylandsted Larsen

J. Appl. Phys. 88, 3254 (2000); http://dx.doi.org/10.1063/1.1289234 (6 pages) | Cited 12 times

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It has recently been established that Si self-interstitials are generated during annealing of high-concentration Sb layers in Si. In the present work, we make use of samples grown with molecular-beam epitaxy. We monitor, at different times and temperatures, the diffusion enhancement or retardation of deep B or Sb marker layers next to a 1.1×1020 cm−3 Sb box, as well as the formation of Sb precipitates within the box. It is concluded that the interstitials are not associated with precipitate growth, but that they are generated from formation of Sb-vacancy complexes, primarily involving 2 Sb atoms. © 2000 American Institute of Physics.
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61.72.J- Point defects and defect clusters
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing
81.05.Cy Elemental semiconductors
64.75.-g Phase equilibria
61.72.Yx Interaction between different crystal defects; gettering effect

Radiotracer identification of a Ta-related deep level in 4H–SiC

J. Grillenberger, N. Achtziger, R. Sielemann, and W. Witthuhn

J. Appl. Phys. 88, 3260 (2000); http://dx.doi.org/10.1063/1.1289484 (6 pages) | Cited 7 times

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To identify tantalum-related deep levels, deep level transient spectroscopy (DLTS) measurements were performed on Ta-implanted n-type 4H–silicon carbide. The DLTS spectra of samples implanted with stable 181Ta exhibit one dominating peak representing a trap energy of about ET=EC−0.67 eV. Due to superimposed signals of intrinsic defects, the exact value depends on the annealing conditions. To achieve a definite assignment of this peak to tantalum, the radioactive isotope 177Ta was recoil implanted into n-type 4H–SiC. DLTS spectra measured subsequently during the nuclear decay of 177Ta to 177Hf reveal a trap with decreasing concentration according to the elemental transmutation. This effect definitely proofs the identification of a Ta-related level at 0.68 eV below the conduction band edge. There is no further DLTS peak of time-dependent height, indicating that there is no deep level of Hf in the part of the band gap investigated. © 2000 American Institute of Physics.
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71.55.Ht Other nonmetals
61.72.up Other materials

Ultrasonic attenuation in Zr41Ti14Cu12.5Ni10−xBe22.5Cx (x=0,1) bulk metallic glasses under high pressure

Wei Hua Wang, R. J. Wang, F. Y. Li, M. X. Pan, Z. C. Qin, D. Q. Zhao, Y. X. Zhuang, and Y. Zhang

J. Appl. Phys. 88, 3266 (2000); http://dx.doi.org/10.1063/1.1289237 (3 pages) | Cited 1 time

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The pressure dependence of ultrasonic attenuation in Zr41Ti14Cu12.5Ni10−xBe22.5Cx (x=0,1) bulk metallic glasses has been studied up to 0.5 GPa by using a pulse echo overlap method. The effect of carbon addition on the attenuation is also investigated. Some unique characteristics of the ultrasonic attenuation are found and compared with those of other glasses. The origin of the anomalous attenuation behavior is discussed. © 2000 American Institute of Physics.
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62.65.+k Acoustical properties of solids
81.05.Kf Glasses (including metallic glasses)
62.50.-p High-pressure effects in solids and liquids

Preparation and transport properties of polycrystalline Bi and Bi–SiO2 nanocomposites

F. Brochin, B. Lenoir, X. Devaux, R. Martin-Lopez, and H. Scherrer

J. Appl. Phys. 88, 3269 (2000); http://dx.doi.org/10.1063/1.1289079 (7 pages) | Cited 11 times

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Bismuth–silica nanocomposites and polycrystalline bismuth were prepared via powder metallurgy in order to study the influence of silica inclusions on the thermoelectric properties of bismuth. Bi–SiO2 powders containing from 0.5 to 15 vol. % of silica and pure Bi powders were produced by an arc-plasma processing. Transmission electron microscopy investigations revealed the presence of a nanometric silica shell around the Bi grains. The powders were cold pressed and sintered close to the melting temperature of bismuth. The bulk microstructures are very different for the bismuth and the Bi–SiO2 nanocomposites because silica, which is primarily dispersed at grain boundaries, inhibits the grain growth during sintering. The electrical resistivity was measured from 5 to 300 K, while the thermoelectric power and the thermal conductivity were measured from 65 to 300 K on both polycrystalline bismuth and Bi–SiO2 samples containing 0.5, 4, and 15 vol. % of silica, respectively. The transport properties are mainly discussed with regard to the microstructures. In spite of a strong reduction of the thermal conductivity for the nanocomposites, the thermoelectric figure of merit is not improved compared to bismuth due to a dominating concurrent increase of the electrical resistivity resulting from a finite-size effect. © 2000 American Institute of Physics.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Tm Composite materials
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.05.Mh Cermets, ceramic and refractory composites
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
72.20.Fr Low-field transport and mobility; piezoresistance

Crystallization kinetics and structural aspects of TeGaSn amorphous alloys

M. Fontana, B. Arcondo, M. T. Clavaguera-Mora, N. Clavaguera, and J. M. Greneche

J. Appl. Phys. 88, 3276 (2000); http://dx.doi.org/10.1063/1.1288691 (9 pages) | Cited 1 time

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Cast and rapidly quenched samples of ternary system GaTeSn in the Te rich corner were studied by means of x-ray diffraction, 119Sn Mössbauer spectrometry at 77 K, and differential scanning calorimetry. The crystallization products, the activation energy, the crystallization enthalpy, and the crystallization and glass temperatures of the amorphous phases are reported. The addition of Sn to GaTe increases the glass forming range of the binary system and the thermal stability of the amorphous phase. In the crystalline samples the divalent Sn atoms are always surrounded by Te in octahedrally coordinated environments. It is observed that the addition of Sn, above a threshold concentration, stabilizes the high temperature phase Ga2Te5 at room temperature. The Mössbauer spectra obtained on amorphous samples indicate two kinds of environments at Sn sites: one ascribed to the octahedral coordination, the other one to Sn surrounded by Te with tetrahedral coordination. The Mössbauer results are related to the calorimetric measurements: the role of Sn to stabilize the amorphous structure is discussed. The first steps of the crystallization of pure Te are modeled assuming homogeneous nucleation followed by three-dimensional interface-controlled growth of the crystal. © 2000 American Institute of Physics.
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61.43.Dq Amorphous semiconductors, metals, and alloys
65.20.-w Thermal properties of liquids
65.40.gd Entropy
76.80.+y Mössbauer effect; other γ-ray spectroscopy
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

Raman spectra of Ge nanocrystals embedded into SiO2

A. V. Kolobov, Y. Maeda, and K. Tanaka

J. Appl. Phys. 88, 3285 (2000); http://dx.doi.org/10.1063/1.1289818 (5 pages) | Cited 9 times

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We start with an analysis of the Raman spectra of Ge nanocrystals obtained in previous studies and demonstrate that in many cases the observed experimental peak attributed to Ge in fact originates from the Si substrate. We further compare various experimental ways to separate the Ge signal from that of the substrate and suggest optimum conditions for such measurements. Finally, we demonstrate that upon the annealing of an amorphous Ge–Si–O film, Ge nanocrystals are formed. The nanocrystals are randomly oriented and Ge–Si mixing takes place only at the interface with the Si substrate. © 2000 American Institute of Physics.
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78.30.Am Elemental semiconductors and insulators
78.66.Jg Amorphous semiconductors; glasses

The shock Hugoniot of the intermetallic alloy Ti–46.5Al–2Nb–2Cr

Jeremy Millett, George T. (Rusty) Gray, and Neil Bourne

J. Appl. Phys. 88, 3290 (2000); http://dx.doi.org/10.1063/1.1288500 (5 pages) | Cited 16 times

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Plate impact experiments were conducted on a γ-titanium aluminide (TiAl) based ordered intermetallic alloy. Stress measurements were recorded using manganin stress gauges supported on the back of TiAl targets using polymethylmethacrylate windows. The Hugoniot in stress-particle velocity space for this TiAl alloy was deduced using impedance matching techniques. The results in this study are compared to the known Hugoniot data of the common alpha-beta engineering Ti-based alloy Ti-6Al–4V. The results of the current study on the intermetallic alloy TiAl support that TiAl possesses a significantly higher stress for a given particle velocity than the two-phase Ti–6Al–4V alloy. © 2000 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
64.30.-t Equations of state of specific substances

High spatial resolution thermal conductivity and Raman spectroscopy investigation of hydride vapor phase epitaxy grown n-GaN/sapphire(0001): Doping dependence

D. I. Florescu, V. M. Asnin, Fred H. Pollak, R. J. Molnar, and C. E. C. Wood

J. Appl. Phys. 88, 3295 (2000); http://dx.doi.org/10.1063/1.1289072 (6 pages) | Cited 30 times

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We have measured high resolution thermal conductivity (κ) and Raman spectra {E2 mode [high frequency], A1 mode [longitudinal optical (LO)], and high frequency LO-plasmon coupled mode [LPP+]} at 300 K of three series of n-GaN/sapphire (0001) samples fabricated by hydride vapor phase epitaxy (HVPE). The former was determined with a scanning thermal microscope while the latter was obtained using a micro-Raman system, both having a spatial resolution of ≈2–3 μm. For all three sets of samples the thermal conductivity decreased linearly with log n, about a factor of two decrease in κ for every decade increase in n. Also, we found a correlation between film thickness and improved thermal conductivity. Furthermore, κ≈1.95 W/cm K for one of the most lightly doped samples (≈6.9×1016 cm−3), higher than previously reported κ≈1.7–1.8 W/cm K on lateral epitaxial overgrown (LEO) material with n≈(1–2)×1017 cm−3 [V. M. Asnin et al., Appl. Phys. Lett. 75, 1240 (1999)], κ=1.55 W/cm K on LEO samples using a third-harmonic technique [C. Y. Luo et al., Appl. Phys. Lett. 75, 4151 (1999)], and κ≈1.3 W/cm K on a HVPE sample [E. K. Sichel and J. I. Pankove, J. Phys. Chem. Solids 38, 330 (1977)]. The carrier concentration dependence of κ is similar to that of other semiconductors in a comparable temperature range. On a log–log scale the linewidth of the observed E2 Raman mode remained constant up to n≈1×1018 cm−3 and then increased linearly. The carrier concentration obtained from the LPP+ mode is less than the Hall effect determination. This is probably due to the fact that the latter measures n in both the epilayer and GaN/sapphire interfacial region [D. C. Look and R. J. Molnar, Appl. Phys. Lett. 70, 3377 (1997); W. Götz et al., Appl. Phys. Lett. 72, 1214 (1998)] while the Raman signal is primarily from the epilayer. © 2000 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
78.66.Fd III-V semiconductors
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
73.61.Ey III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
63.20.kk Phonon interactions with other quasiparticles
78.30.Fs III-V and II-VI semiconductors

Modeling electromigration-induced stress evolution and drift kinetics with a stress-dependent diffusivity

S. A. Chizhik, A. A. Matvienko, A. A. Sidelnikov, and J. Proost

J. Appl. Phys. 88, 3301 (2000); http://dx.doi.org/10.1063/1.1287760 (9 pages) | Cited 3 times

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Clement and Thompson have justified that it is necessary to take into account the stress dependence of atomic mobility when describing stress evolution in a metal conductor caused by electromigration [J. J. Clement and C. V. Thompson, J. Appl. Phys. 78, 900 (1995)]. In the present contribution the role of this dependence is considered in more detail, leading to qualitatively new results concerning stress evolution and drift kinetics. The stationary stress distribution over the length of the elastic zone of the conductor was shown to be nonlinear and asymmetrical at superthreshold conditions, with the zone of compressive stress being more extended than that of tensile stress. This also results in an asymmetrical pattern for plastic deformation, the hillocking zone being more extended than the voiding region at the cathode. The drift rate was shown to achieve its maximum value during the nonstationary stage of stress evolution and then to drop down to its stationary value. The duration of the nonstationary stage of stress evolution is proportional to the conductor length and inversely proportional to the current density. This is essentially different from the result obtained in all previous works. Our model also predicts that for conductors with a length much longer than the critical one, the nonstationary stage of stress evolution corresponds to a quasistationary stage for drift kinetics, during which a constant drift rate is observed. Finally, we will consider the consequences of taking into account the stress dependence of mobility when describing the effects of passivation and thermal stress on drift kinetics. © 2000 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Qa Electromigration
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
81.65.Rv Passivation
66.30.Dn Theory of diffusion and ionic conduction in solids

Optical absorption and Hall effect in (220) and (400) oriented polycrystalline silicon films

T. Kamiya, K. Nakahata, T. Sameshima, T. Watanabe, T. Mouri, and I. Shimizu

J. Appl. Phys. 88, 3310 (2000); http://dx.doi.org/10.1063/1.1288170 (6 pages) | Cited 8 times

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Carrier transport properties were investigated for polycrystalline silicon (poly-Si:H:F) films fabricated at 300 °C by 100 MHz plasma enhanced chemical vapor deposition from gaseous mixture of SiF4 and H2. Analysis of free carrier optical absorption (FCA) revealed that 1 μm thick (400) oriented phosphorus-doped poly-Si:H:F films with a carrier concentration of 5×1019 cm−3 had the average electron mobility in crystalline grains at 40 cm2/V s, while the electron mobility of the (220) oriented phosphorus-doped poly-Si:H:F films was only 12 cm2/V s. These results indicated that (400) oriented poly-Si:H:F films had excellent quality crystalline grains. Analyses of the FCA combined with Hall effect current measurements revealed that the electrical conductivity at grain boundaries of top doped films increased as the underlying film thickness increased from 0 to 280 nm for (400) oriented phosphorus-doped/undoped double layered samples, but grain boundaries still acted as large resistive regions limiting the effective conductivity. © 2000 American Institute of Physics.
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73.61.Cw Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
61.72.Mm Grain and twin boundaries
73.50.Dn Low-field transport and mobility; piezoresistance
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
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