bluuebunny/crossref_metadata_2025 huggingface dataset:
Breakdown characteristics of a laser-triggered pseudospark discharge
Authors: Chuaqui H. , Favre M. , Wyndham E. , Arroyo L. , Choi P.
Published: July 2002

Experimental observations are presented on the breakdown characteristics of a pseudospark discharge when a pulsed laser is used to illuminate the back surface of the cathode. The breakdown delay and jitter of the discharge are observed to be controlled by the laser. Observations are presented on the effect of the relative timing of the laser pulse with respect to the fast rising applied voltage. It is found that mJ illumination at up to tens of microseconds before the application of the voltage reduces significantly both delay to breakdown and jitter. High laser energy, applied after the voltage is established across the anode-cathode region, leads directly to breakdown with a delay of less than 100 ns.
Self-compensation through a large lattice relaxation in p-type ZnSe
Authors: Chadi D. J. , Chang K. J.
Published: July 2002

The energetics of self-compensation through atomic relaxation around acceptor impurities in ZnSe were examined via first principles total energy calculations. We find large charge state and impurity-dependent lattice relaxations for As and P acceptors which can account for the experimentally observed difficulties in obtaining low-resistivity p-type ZnSe from these dopants. A much smaller relaxation is found for Li.
Observation of soliton-like envelope modulations generated in an anisotropic quartz plate by metallic interdigital transducers
Authors: Planat M. , Hoummady M.
Published: July 2002

It is observed that the bulk acoustic wave radiation from interdigital transducers deposited on a quartz crystal plate is dispersive and nonlinear. Pulse instability, pulse narrowing, and pulse splitting suggestive of soliton behavior are reported for 25–100 ns duration pulses from a transducer with a 17.2 μm spatial period on a Y-cut, Z-propagating quartz substrate.
I
n s
i
t
u monitoring of silicon nitride surface temperature from rotational temperature of a nitrogen molecule during rf glow discharge processing
Authors: Ishihara Shin-ichiro , Otsuka Akira , Nagata Seiichi
Published: July 2002

The rotational temperature of a nitrogen molecule (N2) was observed to increase proportionally with the substrate-holder temperature in a capacitively coupled rf glow discharge system. The rotational temperature, equivalent to the gas temperature, from the second positive system of the emission spectrum of N2 increased with increasing the mixing ratio of hydrogen, which correlates with the deposition rate, optical band gap, and etching rate of silicon nitride (SiNx). This technique can be used for monitoring the temperature of a SiNx surface during glow discharge processing without any damage to the plasma.
Positive-streamer-like phenomena in point-plane corona gaps: Trichel pulses and high-pressure cathode sheath instabilities
Authors: Cernák Mirko , Hosokawa Tatsuzo , Inoshima Masayuki
Published: July 2002

Current pulse shapes have been measured in negative and positive corona discharges mostly in dry air. Negative corona Trichel pulses and pulses corresponding to the primary streamer/cathode contact in a positive point-plane gap were found to exhibit remarkable similarities, indicating a positive-streamer-like mechanism for the Trichel pulse development. High-frequency instabilities of the high-pressure filamentary glow discharge, which can be responsible for the arcing from freshly polished cathodes, were observed and attributed to local positive-streamer-like breakdowns of the cathode sheath.
Dynamic behavior of two-laser-induced bubbles in water
Authors: Tomita Y. , Shima A. , Sato K.
Published: July 2002

Two bubbles are simultaneously generated in water by focusing a Q-switched ruby laser. The dynamic behavior of the induced bubbles is investigated by means of high-speed photography. Consequently it is found that the bubble–bubble interaction is significantly influenced not only by the relative size of bubbles but also by the mutual distance between them. When two bubbles are axisymmetrically produced one behind the other near a rigid wall, we can observe a very interesting phenomenon, bubble splitting followed by bubble pinching.
Metal reactivity effects on the surface recombination velocity at InP interfaces
Authors: Rosenwaks Y. , Shapira Yoram , Huppert D.
Published: July 2002

Direct measurements of the surface recombination velocity (SRV) on etched InP(110) and at its interfaces with various metals deposited by thermal evaporation have been performed using ultrafast time-resolved photoluminescence. The results show that the original InP low SRV is retained when these surfaces are coverd with metals which tend to react with the semiconductor’s anion, such as Al, Cr, and Zn. On the other hand, the SRV increases sharply as a function of unreactive metal coverage, such as Cu, Au, and Ag. The SRV results are explained in terms of metal-induced interface states, whose position in the band gap and thus their cross section for recombination depends on the metal reactivity. The similarity of the SRV and the reported Schottky barrier height dependence on the metal-phosphorus heat of reaction is noted.
Application of a near coincidence site lattice theory to the orientations of YBa2Cu3O7−x grains on (001) MgO substrates
Authors: Hwang D. M. , Ravi T. S. , Ramesh R. , Chan Siu-Wai , Chen C. Y. , Nazar L. , Wu X. D. , Inam A. , Venkatesan T.
Published: July 2002

Various orientations of YBa2Cu3O7−x grains in polycrystalline films prepared on (001)MgO substrates by in situ laser deposition were determined using electron diffraction. Eight different types of in-plane orientations have been observed. These orientations agree well with the prediction of a simplified theory of near coincidence site lattice between YBa2Cu3O7−x and MgO. The YBa2Cu3O7−x grains were found to have a high probability of forming low angle or low Σ boundaries among themselves. These grain boundaries are of low energy and should exhibit a high connectivity of Cu-O-Cu chains. Therefore, YBa2Cu3O7−x thin films on MgO can attain a Tc of ∼90 K and a Jc of ∼106 A/cm2 at 77 K.
Effects of aluminum microstructure on electromigration using a new reactive ion etching and scanning electron microscopy technique
Authors: Wu Ken , Baerg William , Jupiter Peter
Published: July 2002

The effects of microstructure on the electromigration of aluminum-1% silicon and titanium/aluminum-silicon films were studied using a new reactive ion etching/scanning electron microscopy technique. We found that the number of intersecting Al grain boundaries, called ‘‘triple points,’’ in the metal line plays an important role in determining the median-time-to-fail (MTTF) of the electromigration distribution. Our data shows that the electromigration MTTF increases by 6× or 8× when the number of triple points decreases by 3× or 5× on Al-Si or Ti/Al-Si metallization, respectively.
Observations of ultrafast nonlinear refraction in an InGaAsP optical amplifier
Authors: Grant R. S. , Sibbett W.
Published: July 2002

Spectral broadening due to self-phase modulation has been observed for ultrashort pulses propagating through an InGaAsP optical amplifier. This is not associated with gain saturation or absorption saturation, since it can be observed at the transparency current. At transparency, the broadening and structure of the spectra are symmetrical for pulses of approximately 27 ps duration, implying that the underlying nonlinearity has a relatively fast recovery time. The associated nonlinear index coefficient n2 is estimated to be approximately −2×10−11 cm2 W−1.
Enhancement of light-induced degradation in hydrogenated amorphous silicon due to carbon impurities
Authors: Unold Thomas , Cohen J. David
Published: July 2002

The effect of carbon impurities in a-Si:H samples at low concentrations (1 at. % to less than 0.1 at. %) has been investigated using capacitance profiling methods on samples whose carbon content was intentionally modulated spatially during growth. We have found a strong correlation between the secondary-ion mass spectroscopy determined carbon content and the susceptibility of these samples to light-induced metastable defect creation. No correlation was found with respect to the variation in total hydrogen content of these samples.
Epitaxial growth of InSb on sapphire by rf sputtering
Authors: Miyazaki T. , Mori M. , Adachi S.
Published: July 2002

InSb films have been deposited directly by rf sputtering on sapphire substrates. X-ray diffraction and scanning electron microscopy data are presented to show that the InSb layer on sapphire (0001) is epitaxial and grows with (111) parallel to the substrate surface. Optical absorption studies of the epitaxial film also reveal distinct spectral features which resemble these from bulk, single-crystal InSb.
Subpicosecond, freely propagating electromagnetic pulse generation and detection using GaAs:As epilayers
Authors: Warren A. C. , Katzenellenbogen N. , Grischkowsky D. , Woodall J. M. , Melloch M. R. , Otsuka N.
Published: July 2002

Using GaAs epilayers with arsenic precipitates (GaAs:As) as the photoconductive material in a broad-band optoelectronic terahertz beam system, we have generated and detected freely propagating, subpicosecond electromagnetic pulses. The receiver signal gave a measured integrated pulse width of 0.71 ps. Fast photoconductive rise times have been achieved which are characteristic of good mobility GaAs. In addition, the material exhibits a short ‘‘effective’’ carrier lifetime of several ps due to the embedded, closely spaced (about 20 nm) arsenic precipitates.
Pulsed organometallic beam epitaxy of complex oxide films
Authors: Duray S. J. , Buchholz D. B. , Song S. N. , Richeson D. S. , Ketterson J. B. , Marks T. J. , Chang R. P. H.
Published: July 2002

We report the results of a pulsed organometallic beam epitaxy (POMBE) process for growing complex oxide films at low background gas pressure (10−4–10−2 Torr) and low substrate temperature (600–680 °C) using organometallic precursors in an oxygen plasma environment. Our results show that POMBE can extend the capability of organometallic chemical vapor deposition to growing complex oxide films with high precision both in composition and structure without the need for post-deposition oxidation and heat treatments. The growth of phase-pure, highly oriented Y-Ba-Cu-O superconducting oxide films {[Tc (R=0)=90.5 K] and Jc (77 K, 50 K gauss)=1.1×105 A/cm2} is given as an example. Similar to the pulsed laser deposition process, the POMBE method has the potential for in situ processing of multilayer structures (e.g., junctions).
Electrical characteristics of paraelectric lead lanthanum zirconium titanate thin films for dynamic random access memory applications
Authors: Jones R. E. , Maniar P. D. , Olowolafe J. O. , Campbell A. C. , Mogab C. J.
Published: July 2002

Paraelectric lead lanthanum zirconium titanate (PLZT) films, 150 nm thick, were deposited using a spin-coat, sol-gel process followed by a 650 °C oxygen anneal. X-ray diffraction indicated complete conversion to the perovskite phase. Sputter-deposited platinum electrodes were employed with the PLZT films to form thin-film capacitors with the best combination of high charge storage density (26.1 μC/cm2 at 3 V and 36.4 μC/cm2 at 5 V) and leakage current density (0.2 μA/cm2 at 3 V and 0.5 μA/cm2 at 5 V ) reported to date. The electrical characteristics of these thin-film capacitors meet the requirements for a planar bit cell capacitor for 64-Mbit dynamic random access memories.
Textured diamond growth on (100) β-SiC via microwave plasma chemical vapor deposition
Authors: Stoner B. R. , Glass J. T.
Published: July 2002

Textured diamond films have been deposited on β-SiC via microwave plasma chemical vapor deposition preceded by an in situ bias pretreatment that enhances nucleation. Approximately 50% of the initial diamond nuclei appear to be aligned with the C(001) planes parallel to the SiC(001), and C[110] directions parallel to the SiC[110] within 3°. The diamond was characterized by Raman spectroscopy and scanning electron microscopy.
Microwave rf SQUID integrated into a planar YBa2Cu3O7 resonator
Authors: Zhang Y. , Mück M. , Bode M. , Herrmann K. , Schubert J. , Zander W. , Braginski A. I. , Heiden C.
Published: July 2002

We fabricated and characterized microwave rf SQUIDs integrated into a planar, S-shaped λ/2 microstrip resonator. This 3 GHz resonator was fabricated from a pulsed-laser-deposited YBa2Cu3O7 epitaxial film. The SQUID structures incorporated double step-edge junctions and had a loop inductance of 120 pH. Such unoptimized SQUIDs operated between 4.2 and 85 K with dV/dΦ=18–20 μV/Φ0 at 77 K. At that temperature, the energy resolution of (8±2)×10−29 J/Hz above 0.1 Hz (in the best samples) was limited by the white noise, SΦ1/2=(7±1)×10−5 Φ0/Hz1/2. Optimization may increase dV/dΦ and improve the energy resolution by up to an order of magnitude.
Residue-free reactive ion etching of β-SiC in CHF3/O2 with H2 additive
Authors: Steckl A. J. , Yih P. H.
Published: July 2002

Longer term CHF3/O2 reactive ion etching of β-SiC thin films on Si required for heterostructure fabrication results in the formation of columnar residues in the etched regions which prevent proper device operation. Using Auger electron spectroscopy, the formation of the residues has been correlated with the sputter deposition of Al particles from the plasma electrode onto the SiC surface and the subsequent micromasking effect. A low-level (∼10%) addition of H2 gas to the CHF3/O2 plasma was found to completely prevent the formation of residues in the etched regions. Possible mechanisms responsible for the prevention of residues include the formation of volatile Al-H compounds and the enhanced etching of the C-rich surface.
High density, ultrafine precipitates in YBa2Cu3O7−x thin films prepared by plasma-enhanced metalorganic chemical vapor deposition
Authors: Lu P. , Li Y. Q. , Zhao J. , Chern C. S. , Gallois B. , Norris P. , Kear B. , Cosandey F.
Published: July 2002

Thin films of yttrium-rich YBa2Cu3O7−x with c-axis orientation prepared by plasma-enhanced metalorganic chemical vapor deposition have been examined by high-resolution transmission electron microscopy. Yttria precipitates smaller than 50 (Å) in size have been identified in the matrix. They are uniformly distributed, have a high density as large as 1024 per cubic meter and are oriented with respect to the matrix. The magnetic field dependence of the critical current density of the thin films indicates that the yttria precipitates are effective flux pinning centers.
Low threshold current InGaAs/GaAs/GaInP lasers grown by gas-source molecular beam epitaxy
Authors: Zhang G. , Näppi J. , Vänttinen K. , Asonen H. , Pessa M.
Published: July 2002

Strained-layer InGaAs/GaAs/GaInP separate confinement heterostructure single-quantum well lasers have been fabricated using gas-source molecular beam epitaxy. A threshold current density as low as 72 A/cm2 was achieved for a broad-area, uncoated Fabry–Perot laser with a cavity length of 1200 μm. The internal quantum efficiency and internal waveguide loss were 91% and 8.8 cm−1, respectively. A high characteristic temperature, 140 K, was obtained.
Construction of silicon nanocolumns with the scanning tunneling microscope
Authors: Ostrom R. M. , Tanenbaum D. M. , Gallagher Alan
Published: July 2002

Voltage pulses to a scanning tunneling microscope (STM) are used to construct silicon columns of 30–100 Å diameter and up to 200 Å height on a silicon surface and on the end of a tungsten probe. These nanocolumns have excellent conductivity and longevity, and they provide an exceptional new ability to measure the shapes of nanostructures with a STM. This construction methodology and these slender yet robust columns provide a basis for nanoscale physics, lithography, and technology.
Comparative study of minority electron properties in p+-GaAs doped with beryllium and carbon
Authors: Lovejoy M. L. , Melloch M. R. , Lundstrom M. S. , Keyes B. M. , Ahrenkiel R. K. , de Lyon T. J. , Woodall J. M.
Published: July 2002

Minority electron properties in p+-GaAs doped with beryllium (Be) and with carbon (C) are reported. Measurements of essentially identical responses for structures differing only in dopant element demonstrate that the diffusivity (Dn) and the diffusion lengths (Ln) are the same in p+-GaAs doped to ∼1019 cm−3 with Be- and C-dopants. Zero-field time-of-flight analysis yields Dn=35 cm2/s and internal quantum efficiency analysis yields Ln=2.4 μm, which implies a lifetime that is approximately at the estimated radiative limit. In addition, the majority Hall mobility was also found to be identical for the Be- and C-doped material.
Voltage-current characteristics of a high Tc superconducting field effect device
Authors: Xi X. X. , Doughty C. , Walkenhorst A. , Mao S. N. , Li Qi , Venkatesan T.
Published: July 2002

The source-drain voltage-current characteristics of a high Tc field-effect device consisting of a YBa2Cu3O7−x/SrTiO3/Au multilayer structure are measured. Similarities of the V-I curves to those of a metal-oxide-semiconductor field-effect transistor (MOSFET) are observed. However, we emphasize that the superconducting channel exhibits significantly lower dissipation in comparison with the inversion layer in a MOSFET. The device has a 50 Å thick YBa2Cu3O7−x channel layer (Tc=43 K) with a high critical current density Jc (5 K) over 1×105 A/cm2. A transconductance of over 0.2 mS/mm and a voltage gain of 0.9 are obtained in the device.
Structural properties of partially relaxed InxGa1−xAs layers grown on (100) and misoriented GaAs substrates
Authors: Maigné P. , Roth A. P.
Published: July 2002

We report an x-ray diffraction study of partially relaxed In(0.20)Ga(0.80)As layers grown simultaneously on (100) GaAs substrates and misoriented GaAs substrates. We have measured the magnitude and direction of the tilt between (100) InGaAs and GaAs planes, as well as the relaxation coefficients in 〈011〉 directions. Our results show that in many respects, the misorientation of the substrates strongly influences the relaxation of the mismatch strain. The magnitude of the tilt is always larger on misoriented substrates and approximately twice the value measured on flat substrates. The direction of the tilt changes with increasing thickness and the two directions are always 135° apart from one type of substrate to the other. In addition, for thin layers, the residual strain is about five times larger on misoriented substrates but becomes comparable for both orientations, when the layers relax further.
Determination of electron recombination parameters in GaAs/AlGaAs quantum wells by impedance spectroscopy
Authors: Luc F. , Rosencher E. , Vinter B.
Published: July 2002

We show that the capture process between a three-dimensional (3D) gas and a two-dimensional quantum well are unambiguously characterized by impedance spectroscopy. The contact layer of an asymmetrical semiconductor-insulator-semiconductor diode provides the 3D gas to the conduction band of an AlGaAs barrier which interacts near thermal equilibrium with a GaAs quantum well (QW). This approach is validated by an excellent agreement between experimental results and theoretical expectations regarding the influence of electric field and temperature. We show that the natural quantity which describes this recombination is the recombination velocity in the QW, which is found to be ≊8×104 cm/s for a 60 Å GaAs/Al0.22Ga0.78As quantum well at 100 K for an electric field of 3 kV/cm, which corresponds to a capture probability of 0.013. Results indicate a decrease of the recombination velocity in the quantum well with an increasing applied electric field.
Excess-Si related defect centers in buried SiO2 thin films
Authors: Warren W. L. , Fleetwood D. M. , Shaneyfelt M. R. , Schwank J. R. , Winokur P. S. , Devine R. A. B.
Published: July 2002

Using electron paramagnetic resonance (EPR) and capacitance-voltage measurements we have investigated the role of excess-silicon related defect centers as charge traps in separation by the implantation of oxygen materials. Three types of EPR-active centers were investigated: oxygen vacancy Eγ′ centers (O3≡Si• +Si≡O3), delocalized Eδ′ centers, and D centers (Si3≡Si•). It was found that all of these paramagnetic centers are created by selective hole injection, and are reasonably ascribed as positively charged when paramagnetic. These results provide the first experimental evidence for (1) the charge state of the Eδ′ center, and (2) that the D center is an electrically active point defect in these materials.
Effect of thermal resistivity on the catastrophic optical damage power density of AlGaInP laser diodes
Authors: Fujii Hiroaki , Ueno Yoshiyasu , Endo Kenji
Published: July 2002

We show that the low catastrophic optical damage power density observed for AlGaInP laser diodes (LDs) (1/2 to 1/2.9 that of AlGaAs LDs) is mainly attributable to the high thermal resistivities of the materials (5.5 times higher than for AlGaAs LDs) by using a thermal runaway model calculation.
Near-equilibrium growth of thick, high quality beta-SiC by sublimation
Authors: Shields Virgil B. , Fekade Konjit , Spencer Michael G.
Published: July 2002

A close spaced near-equilibrium growth technique was used to produce thick, high quality epitaxial layers of beta-silicon carbide. The process utilized a sublimation method to grow morphologically smooth layers. The beta silicon carbide growth layers varied from about 200 to 750 μm in thickness. Chemical vapor deposition grown, 2–10 μm, beta silicon carbide films were used as seeds at 1860 and 1910 °C growth temperatures. The respective average growth rates were 20 and 30 μm per hour. The layers are p-type with a 3.1×1017 cm−3 carrier concentration. Electrical measurements indicate considerable improvement in the breakdown voltage of Schottky barriers on growth samples. Breakdown values ranged from 25 to 60 V. These measurements represent the highest values reported for 3C-SiC.
Ultraviolet ozone induced oxidation of epitaxial Si1−xGex(111)
Authors: Agarwal A. , Patterson J. K. , Greene J. E. , Rockett A.
Published: July 2002

Exposure of Si1−xGex(111) to ultraviolet light in air at room temperature is shown, using angle-resolved x-ray photoelectron spectroscopy and preferential etching, to lead to the formation of a two-phase oxide consisting of SiO2 and GeO2. Segregation of Ge was not observed at either the alloy/oxide or oxide/vapor interface. The oxidation rate was found to increase with increasing Ge content in the alloy.
Electric-field measurements in 13.56 MHz helium discharges
Authors: Greenberg K. E. , Hebner G. A.
Published: July 2002

Laser excitation of helium singlet Rydberg states results in fluorescence emanating from many other states including those in the triplet system. By monitoring this fluorescence, it is possible to observe the Stark broadening of the Rydberg states in the presence of an electric field. This technique can be used to measure electric fields in 13.56 MHz parallel-plate discharges with a high degree of spatial and temporal resolution.
Crossed fluxes technique for pulsed laser deposition of smooth YBa2Cu3O7−x films and multilayers
Authors: Strikovsky M. D. , Klyuenkov E. B. , Gaponov S. V. , Schubert J. , Copetti C. A.
Published: July 2002

A system with two interacting plasma fluxes for the deposition of high-temperature superconductor films is presented. This system prevents the appearance of particles on a film surface, and permits one to obtain YBa2Cu3O7−x films with the surface defect concentration as low as 104 cm−2, a high critical temperature of 90 K, and a critical current density of 4×106 A/cm2 at 77 K. It is shown that high morphological quality films are obtained at a specific target-substrate distance.
Structure of Au ultrafine particles in silica glass: X-ray diffraction study
Authors: Fukumi Kohei , Chayahara Akiyoshi , Makihara Masaki , Fujii Kanenaga , Hayakawa Junji , Satou Mamoru
Published: July 2002

Structure of ultrafine gold particles embedded in silica glass has been studied by the x-ray diffraction method. It is found that the gold particles have an effective temperature factor of 1.84 Å−2 and include a few layers of plane faults. It is deduced that the gold particles in silica glass are highly defective owing to the mismatch of the thermal expansion coefficient.
Change of surface structure of thin silicon nitride layers during electron beam rapid thermal annealing
Authors: Markwitz A. , Baumann H. , Krimmel E. F. , Bethge K. , Grill W.
Published: July 2002

The surface of 〈100〉 Si specimens implanted at room temperature (RT) with 15N+2 ions at 10 keV with fluences of 5×1016 at./cm2 was subsequently annealed by electron beam rapid thermal annealing (EB-RTA) at temperatures between 900 and 1150 °C forming SiNx layers 25–20 nm thick. The modification in surface structure of these layers by EB-RTA was investigated by atomic force microscopy (AFM) and nuclear reaction analysis (NRA). The 15N depth profile measurement [15N(p,αγ)12C] at target tilt angles from 30° to 7° indicates a shift of the low energy edge which represents the SiNx sample surface. This shift is attributed to the shadowing effect of the SiNx sample surface. Detailed AFM analysis shows that the surfaces are covered with irregularly distributed vertical structures, being whiskers of ∼16 nm height. These structures become more pronounced with increasing annealing temperatures.
Thickness dependence of the electrical characteristics of chemical vapor deposited diamond films
Authors: Plano M. A. , Zhao S. , Gardinier C. F. , Landstrass M. I. , Kania D. R. , Kagan H. , Gan K. K. , Kass R. , Pan L. S. , Han S. , Schnetzer S. , Stone R.
Published: July 2002

The electrical characteristics of chemically vapor deposited (CVD) diamond films were measured as a function of film thickness. The samples studied were polycrystalline with the average grain size increasing from approximately 1 μm on the substrate side to approximately 30 μm on the growth surface for the thickest sample. Using time-resolved transient photoconductivity and charged-particle induced conductivity, the collection distance (d) that a free carrier drifts under the influence of an applied electric field was measured. Our data indicate that there is a gradient in the collection distance through the material. This gradient in electrical properties has implications for electronic uses of CVD diamond.
Electrical and optical properties of oxygen-ion hot-implanted GaAs layers
Authors: Yamazaki Hajime , Watanabe Kazuo
Published: July 2002

Oxygen-ion hot implantation into undoped GaAs has been investigated as fundamental research for the purpose of fabricating highly resistive isolation regions at lower temperatures. Hot implantation at 300 °C at an energy of 170 keV and a dose of 1×1015 cm−2 results in a sheet resistivity of 4×106 Ω/⧠ without post-implant annealing and 7.7×106 Ω/⧠ after annealing at 400 °C for 10 min. These values are about one order of magnitude higher than those obtained after implantation at the same energy and dose done at room temperature. This high resistivity of the hot-implanted layers is caused by both the removal of hopping conduction with an activation energy of 0.06 eV and the formation of 0.24–0.27 eV deep-level electron traps. The effective reduction in implantation damage resulting from hot implantation, which induces the removal of hopping conduction, is confirmed by laser Raman spectroscopy.
Improved thermal conductivity in isotopically enriched chemical vapor deposited diamond
Authors: Graebner J. E. , Hartnett T. M. , Miller R. P.
Published: July 2002

The thermal conductivity κ of an isotopically enriched (0.055% 13C) polycrystalline diamond plate made by chemical vapor deposition (CVD) has been measured for heat flowing in a direction either parallel (κ∥) or perpendicular (κ⊥) to the plane of the plate. The room-temperature conductivities (κ∥=21.8 and κ⊥=26 W cm−1 K−1) are higher than for any CVD diamond previously reported, and the κ⊥ value is higher than the best gem-quality single crystal with the natural abundance (1.1%) of 13C. Analysis of the temperature dependence of κ∥ reveals that the point-defect scattering of phonons is in fact significantly lower than expected for the natural abundance of 13C and that it is responsible for the improved conductivity. The observed anisotropy κ∥/κ⊥=0.84 at room temperature is associated with the anisotropic grain structure.
Heterojunction fabrication by selective area chemical vapor deposition induced by synchrotron radiation
Authors: Byun Dongjin , Hwang Seong-don , Dowben P. A. , Perkins F. Keith , Filips F. , Ianno N. J.
Published: July 2002

We have fabricated a B5C, boron-carbide/Si(111) heterojunction diode by the synchrotron radiation-induced decomposition of orthocarborane. This diode can be compared with similar boron-carbide/Si(111) heterojunction diodes fabricated by plasma enhanced chemical vapor deposition. The synchrotron radiation induced chemical vapor deposition is postulated to occur via the decomposition of weakly chemisorbed species and the results suggest that ‘‘real-time’’ projection lithography (selective area deposition) of boron-carbide devices is possible.
Room temperature spectral hole burning and elimination of photodarkening in sol-gel derived CdS quantum dots
Authors: Kang K. , Kepner A. D. , Hu Y. Z. , Koch S. W. , Peyghambarian N. , Li C.-Y. , Takada T. , Kao Y. , Mackenzie J. D.
Published: July 2002

Spectral hole burning at room temperature is used as a technique to compare optical nonlinearities of semiconductor quantum dot materials prepared by the sol-gel and glass fusion techniques. In an effort to understand the mechanism of photodarkening in quantum dots and assess its effect on optical nonlinearities, we prepared and characterized three representative samples with similar dot sizes. We found that photodarkening can be reduced substantially by controlling the media surrounding the dots. The sol-gel derived samples with 80 wt % SiO2 do not exhibit appreciable photodarkening while the melt-quenched glasses with 56 wt % SiO2 exhibit strong photodarkening effects at room temperature which results in reduction of their optical nonlinearity by a factor of ≂20 compared with the sol-gel derived samples.
Defect accumulation during ion irradiation of crystalline Si probed by in situ conductivity measurements
Authors: Battaglia A. , Coffa S. , Priolo F. , Spinella C.
Published: July 2002

We have used in situ conductivity measurements to investigate the defect evolution and accumulation in ion implanted crystalline Si. Upon irradiation at room temperature with 400 keV Si ions the initial conductivity (4×10−2 Ω−1 cm−1) decreases by about 4 orders of magnitude to a value of 2×10−6 Ω−1 cm−1, characteristic of intrinsic silicon, at a fluence of 1×1013/cm2 and then slowly increases at higher fluences. Deep level transient spectroscopy measurements, transmission electron microscopy analyses, and thermal annealings were performed on samples irradiated at various fluences. The data demonstrate that the strong conductivity decrease at low fluences is the result of a dopant compensation produced by deep levels introduced by divacancies and complex defects in the band gap. At higher fluences the conduction is dominated by electron hopping in a buried continuous amorphous layer produced by irradiation. These results are reported and discussed.
Kinetics of hydrogen interaction with SiO2-Si interface trap centers
Authors: Khatri R. , Asoka-Kumar P. , Nielsen B. , Roellig L. O. , Lynn K. G.
Published: July 2002

The effects of low temperature (≤700 °C ) annealing on the thermal dissociation of hydrogen-passivated interface trap centers of a SiO2-Si(100) system is studied using positron annihilation spectroscopy. The Si—H bonds dissociate with an activation energy of 2.60±0.06 eV. Assuming that the anneal generates trap centers with a single charge, positron measurements indicate that ∼4.5×108 trap centers/cm2 are created by a 600 °C anneal.
Formation mechanism of TiC by mechanical alloying
Authors: Liu Z. G. , Guo J. T. , Ye L. L. , Li G. S. , Hu Z. Q.
Published: July 2002

Titanium carbide (TiC) has been synthesized by mechanically alloying the elemental powder mixture of titanium and graphite at composition of Ti1−xCx (x=0.35, 0.43, 0.50). Under the employed milling condition, the formation of TiC has been found to undergo an abrupt, exothermic reaction. The final product is TiC for x=0.43 and 0.50, and TiC+Ti (small amount) for x=0.35. It is suggested that this reaction appears to be a self-sustained high-temperature synthesis process. The initial milling stage seems to be an incubation duration for the reaction, and the mechanical impacts to be the ignition of the following abrupt reaction. It is believed that this type of reaction is an important mechanism for mechanical alloying of the highly exothermic alloy systems.
Annealing study of electron irradiation-induced defects in SiGe alloys
Authors: Goubet J. J. , Stievenard D.
Published: July 2002

Isochronal annealing experiments on defects produced by 1.5 MeV electron irradiation at room temperature have been performed on n-type SiGe alloys. Two defects have been studied, labeled P1 and P2, with associated energy levels located at EC−0.32 eV and EC−0.49 eV, respectively, and capture cross sections equal to 1×10−15 cm2 and 2×10−15 cm2. P1 anneals out at 560 K and P2 at 470 K. A comparison with the defects known in Si and Ge allows us to propose the following identification: P1 is associated with the 0/− charge state of the divacancy (V–V)Si and P2 is associated with the 0/− charge state of the E center (P–VSi).
Cavity characteristics of selectively oxidized vertical-cavity lasers
Authors: Choquette Kent D. , Lear K. L. , Schneider R. P. , Geib K. M.
Published: July 2002

We show that a buried oxide layer forming a current aperture in an all epitaxial vertical-cavity surface emitting laser has a profound influence on the optical and electrical characteristics of the device. The lateral index variation formed around the oxide current aperture leads to a shift in the cavity resonance wavelength. The resonance wavelength under the oxide layer can thus be manipulated, independent of the as-grown cavity resonance, by adjusting the oxide layer thickness and its placement relative to the active region. In addition, the electrical confinement afforded by the oxide layer enables record low threshold current densities and threshold voltages in these lasers.
Defect distribution in low-temperature molecular beam epitaxy grown Si/Si(100), improved depth profiling with monoenergetic positrons
Authors: Szeles Cs. , Asoka-Kumar P. , Lynn K. G. , Gossmann H.-J. , Unterwald F. C. , Boone T.
Published: July 2002

The depth distribution of open-volume defects has been studied in Si(100) crystals grown by molecular beam epitaxy at 300 °C by the variable-energy monoenergetic positron beam technique combined with well-controlled chemical etching. This procedure gave a 10 nm depth resolution which is a significant improvement over the inherent depth resolving power of the positron beam technique. The epitaxial layer was found to grow defect-free up to 80 nm, from the interface, where small vacancy clusters, larger than divacancies, appear. The defect density then sharply increases toward the film surface. The result clearly shows that the nucleation of small open-volume defects is a precursor state to the breakdown of epitaxy and to the evolution of an amorphous film.
On the carrier mobility in forward-biased semiconductor barriers
Authors: Lundstrom Mark , Tanaka Shin’ichi
Published: July 2002

A simple one-speed solution to the Boltzmann equation is used to evaluate the mobility and diffusion coefficient for carriers in forward-biased semiconductor barriers. The analysis shows that although the average kinetic energy of carriers remains near thermal equilibrium, the mobility and diffusion coefficient are strongly reduced by the built-in field. Conventional macroscopic transport equations, which treat the carrier mobility and diffusion coefficient as single valued functions of the kinetic energy will improperly treat transport in forward-biased barriers. The results are important for the careful analysis of metal–semiconductor and heterojunction diodes.
Salient nonlinear optical properties of novel organic crystals comprising π-conjugated ketones
Authors: Kawamata Jun , Inoue Kuon , Inabe Tamotsu
Published: July 2002

Second-harmonic generation (SHG) properties of two novel organic crystals, i. e., 2,5- bis(benzylidene)cyclopentanone (BBCP) and 2,6-bis( p-methylbenzylidene)-4-tert-butylcyclo- hexanone (MBBCH), were studied. Based on an x-ray structural analysis, their SHG coefficients dij at 1.06 μm are determined by the Maker-fringe method as d14=7 pm/V for BBCP, and d31=15 pm/V, d32=12 pm/V, and d33=4 pm/V for MBBCH, respectively. Measurements on the refractive indices reveal that angle-tune phase matching in the form of both types I and II is possible, in particular, with a large efficiency for MBBCH, deff∼12 pm/V, which was confirmed experimentally.
Investigation of β-BaB2O4 as a Q switch for high power applications
Authors: Goodno G. D. , Guo Z. , Miller R. J. D. , Miller I. J. , Montgomery J. W. , Adhav S. R. , Adhav R. S.
Published: July 2002

A beta barium borate (β-BaB2O4 or BBO) crystal has been used to electro-optically Q switch both diode-pumped and lamp-pumped Nd:YLF laser systems, resulting in stable, high average power operation. Piezoelectric ringing was found to have negligible effects on the performance of the BBO Pockels cell at repetition rates up to 6 kHz. The high damage threshold and low insertion loss of BBO permitted operation up to average powers in excess of 6 kW/cm2, which makes a BBO Pockels cell well suited for high power, small mode volume operation, such as in diode-pumped solid state lasers. Based on typical diode-pumped laser parameters, BBO is expected to extend simple compact Q-switched operation of diode-pumped lasers to average powers of 30–100 W.
Carrier confinement by multiple quantum barriers in 1.55 μm strained GaInAs/AlGaInAs quantum well lasers
Authors: Fukushima T. , Shimizu H. , Nishikata K. , Hirayama Y. , Irikawa M.
Published: July 2002

Carrier confinement performance by multiple quantum barriers (MQB) is demonstrated in 1.55 μm strained GaInAs/AlGaInAs multiple quantum well (MQW) lasers grown by molecular beam epitaxy. The strained MQW lasers with MQB at p-side optical confinement layer show larger characteristic temperature and slope efficiency at high temperature than those without MQB. It is also shown that the MQW lasers with MQB have less spontaneous emission from the optical confinement layer than the lasers without MQB. As another important result, it is demonstrated for the first time that the MQW lasers with MQB have less dependency of the K factor on the temperature than the lasers without MQB. These results further verify the effective carrier confinement performance of GaInAs/AlInAs MQB structure.
Study of deep hole and electron traps in nitrogen-doped ZnSe by isothermal capacitance transient spectroscopy and deep level transient spectroscopy
Authors: Tanaka Kiyotake , Zhu Ziqiang , Yao Takafumi
Published: July 2002

Deep hole traps in N-doped p-type ZnSe epilayer grown by molecular-beam epitaxy have been studied using isothermal capacitance transient spectroscopy and deep level transient spectroscopy measurement (DLTS). Two hole traps with thermal activation energies of 0.68 and 0.85 eV were detected. These centers have large potential barrier heights in the carrier capture process. The thermal activation energies for the carrier capture were 0.23 eV on KT1 trap and 0.33 eV on KT2. These facts indicate that large lattice relaxation is induced in the hole capture/ emission processes. The deep electron trap related to active nitrogen doping was measured through comparison of the DLTS results from n-type ZnSe co-doped with chlorine and nitrogen with those from chlorine-doped n-type ZnSe. A deep electron trap associated with nitrogen doping with activation energy of 0.36 eV below the conduction band was found.
Fast-opening magnetic valve for high-pressure gas injection and applications to hydrogen pellet fueling systems
Authors: Milora S. L. , Combs S. K. , Foust C. R.
Published: July 2002

A fast, magnetically driven gas valve and its application to pneumatic-based solid hydrogen pellet injectors are described. The valve, which is equipped with a polyimide stem tip (hard seal) and a 5-mm-diam orifice, can open against working pressures up to 140 bar (2000 psi). Other unique features of this design include temperature- and radiation-resistant seals, a programmable output pressure pulse, and repetitive operation in excess of 20 Hz. A prototype valve has been used to propel frozen hydrogen isotope pellets to speeds of up to 1900 m/s.
Reconstruction of m=1 MHD modes from projections
Authors: Sauthoff N. R. , McGuire K. M. , von Goeler S.
Published: July 2002

Fluctuations with a dominant poloidal structure involving the intact displacement of the center of the discharge play a significant role in tokamak discharges. A technique for the deductive analysis of their structures, which involve multiple harmonics due to the multipole moments, is desired. This paper describes (1) a method for the inversion of line integral data from a single view of a rotating plasma based on a harmonic decomposition of the poloidal structure, and (2) some techniques for determining critical parameters by inspection. A simulation program generates sample data based on the assumption of a slowly evolving plasma with a displaced central hot spot and a plateau near the radius of the ‘‘q=1’’ surface. The sample data are decomposed into time windows to permit reconstruction of the profiles every few rotations. Results of the reconstructions are compared to the source data. Applicability of the techniques to experimental tokamak data is discussed.
Thermal imbalance errors and effective area in guarded hot plates
Authors: Pham Q. T. , Smith C. G.
Published: July 2002

An analytical equation is derived for the error heat flow due to thermal imbalance between the hot plate and the guard in the case of an infinite strip. Finite element calculations show that the same equation can be used for circular plates with negligible error. The equation can also be extended to square plates if corner effects are neglected. By combining the present solution and a previous one by Woodside [Rev. Sci. Instrum. 28, 1033 (1957)], an expression is derived for the effect of the distortion of heat-flow lines near the gap even when thermal balance is obtained. The availability of this expression opens the possibility of using larger gaps than previously, to reduce thermal imbalance errors. The use of two-material specimens (test material over hot plate, insulant over guard and gap) would lessen thermal imbalance errors, material requirements, and edge effects.
Magnetic time-of-flight photoelectron spectrometer for mass-selected negative cluster ions
Authors: Cheshnovsky O. , Yang S. H. , Pettiette C. L. , Craycraft M. J. , Smalley R. E.
Published: July 2002

Design considerations and initial results are presented for a new type of time-of-flight photoelectron spectrometer which is particularly suited to the study of cold metal and semiconductor cluster anions prepared in a supersonic molecular beam. The desired cluster is extracted from the molecular beam, mass-selected after an initial time-of-flight, and decelerated as it enters the photoelectron spectrometer. Photoelectrons ejected from the cluster by an ArF excimer laser are collected with >98% efficiency in an intense pulsed magnetic field of carefully controlled divergence. This divergent field parallelizes the photoelectron trajectories and maps smoothly onto a low, uniform magnetic field which guides the electrons along a 234-cm flight tube leading to a microchannel-plate detector. The strong magnetic fields and simple, open design provide excellent rejection of stray photoelectrons in a clean, ultrahigh-vacuum environment. The UPS spectrum of Si20− is given as an example.
Analysis of Langmuir probe measurements from the Tandem Mirror Experiment Upgrade (TMX-U)
Authors: Buchenauer D. , Molvik A. W.
Published: July 2002

A nonlinear least-squares curve-fitting routine has been used to analyze single-tip Langmuir probe measurements from the Tandem Mirror Experiment Upgrade during high-density (≊1×1012 cm−3) operation. This procedure provided estimates of uncertainties (variances) in the electron temperature and plasma density due to noise in the probe current. The electron temperature and plasma potential inferred from the fit were found to increase with the upper cutoff voltage used above a certain voltage. This effect appears to be due to a departure of the electron current from an exponentially increasing function for probe positions inside the limiter radius only. The fitted values for electron temperature and plasma density are consistent with previous measurements obtained with a double-tipped probe and the fitted values of space potential indicate a linear relationship with electron temperature.
New polarization-modulation spectrometer for simultaneous circular dichroism and optical rotatory dispersion measurements. II. Design, analysis, and evaluation of a prototype model
Authors: Shindo Yohji , Mizuno Kazuko , Sudani Masahiro , Hayakawa Hiroshi , Ohmi Yasuhiro , Sakayanagi Nobuyuki , Takeuchi Norimasa
Published: July 2002

We have designed and constructed a prototype model of a new polarization-modulation spectrometer for simultaneous circular dichroism (CD) and optical rotary dispersion (ORD) measurements based on the results of our preliminary experiments. The Mueller matrix approach is used to analyze and evaluate important factors determining the performance of our new spectrometer. The CD and ORD base-line shifts are found to be an indicator representing the total performance of the spectrometer. The capability of our spectrometer in measuring CD and ORD signals is equal to that of commercially available CD and ORD spectropolarimeters in the wavelength range from 220 to 700 nm. Furthermore, our spectrometer has much faster speed of ORD measurement than the ORD spectropolarimeter of null-point detection type. Our spectrometer has also high sensitivity to both linear birefringence and linear dichroism measurements.
Electrochemical etching of Si(001) in NH4F solutions: Initial stage and {111} microfacet formation
Authors: Yau Shueh-Lin , Kaji Kazutoshi , Itaya Kingo
Published: July 2002

In situ scanning tunneling microscopy (STM) has been used to examine the etching of an n-Si(001) electrode in 0.1 M NH4F. Cathodic polarization facilitated chemical etching of Si(001) to give {111} microfacets as a result of the tendency of Si to form a monohydride terminated surface. Time-dependent in situ STM atomic images were obtained to demonstrate the preferential etching at the kinks and steps. From the results of the time-dependent imaging, local etching rates were evaluated for the specific crystallographic directions. A Si(001):H-(1×1) square structure was also obtained, demonstrating the presence of dihydride configuration in the beginning of the etching.
Scanning thermal imaging microscopy using composite cantilever probes
Authors: Nakabeppu O. , Chandrachood M. , Wu Y. , Lai J. , Majumdar A.
Published: July 2002

We have developed a simple technique of measuring surface temperature contrast with submicron spatial resolution. The technique uses the atomic force microscope (AFM) to scan a composite cantilever probe made of a thin metal film (aluminum or gold) deposited on a regular silicon nitride AFM probe. During tip-surface contact, heat flow through the tip changes the cantilever temperature which bends the cantilever due to differential thermal expansion of the two probe materials. An ac measurement is used to separate cantilever bending due to temperature and topography. To eliminate image distortion due to air heat conduction, thermal images of a biased resistor were obtained in vacuum (10−5 Torr). The images showed hot spots due to current crowding around voids in the heater and suggested a spatial resolution of 0.4 μm.
Cluster ion source for micromachining
Authors: Henkes P. R. W.
Published: July 2002

An ion source producing focused beams of accelerated carbon dioxide clusters is described, which improves on that used by us in previous work for structuring surfaces by sputtering.