bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamic and photochemical stability of low interface state density Ga2O3–GaAs structures fabricated by in situ molecular beam epitaxy
Authors: Passlack Matthias , Hong Minghwei , Mannaerts Joseph P. , Opila Robert L. , Ren Fan
Published: July 2002

The thermodynamic and photochemical stability of Ga2O3–GaAs interfaces fabricated using in situ multiple-chamber molecular beam epitaxy has been investigated. The Ga2O3 films were deposited on clean, atomically ordered (100) GaAs surfaces using a molecular beam of gallium oxide. Thermally induced degradation of electronic interface properties such as interface recombination velocity S (5750±1250 cm/s) and interface state density Dit(mid-1010 cm−2 eV−1 range) has not been observed after rapid thermal annealing at 800 °C. Furthermore, no interface degradation has been detected during exposure to high intensity laser light. The preservation of excellent electronic interface properties and the absence of interfacial chemical reactions are attributed to AsxOy and elemental As free Ga2O3–GaAs interfaces.
Near infrared absorption and dark conductivity of K1−yLiyTa1−xNbxO3 crystal
Authors: Tong Xiaolin , Zhang Min , Yariv Amnon , Agranat Aharon , Hofmeister Rudolf , Leyva Victor
Published: July 2002

Absorption bands in the wave-number range of 3525–3470 cm−1 have been observed in K1−yLiyTa1−xNbxO3 (KLTN) doped crystals except in crystals doped with Cu and V. These absorption bands are attributed to the O–H vibration band. The hydrogen concentration in KLTN doped crystal is controllable either by doping or by heat treatment. The activation energy of hydrogen ion migration is between 0.6 and 0.7 eV in KLTN doped crystals. The [H +] ion is identified as responsible for fixing (screening) the holographically produced electronic grating.
Subpicosecond switch-off and switch-on of a semiconductor laser due to transient hot carrier effects
Authors: Elsässer M. , Hense S. G. , Wegener M.
Published: July 2002

Recently it has been shown that perturbation of an already operating semiconductor laser with an additional pump pulse may lead to an unusual ultrafast switch-off. This effect is due to transient carrier heating. Subsequent carrier cooling allows for switch-on after about two picoseconds. In vertical cavity lasers containing only a few quantum wells as the active medium, the recovery, however, is limited by the comparatively low gain in the cavity. Here we demonstrate experimentally that both switch-off and switch-on can exhibit subpicosecond time constants if a bulk semiconductor is used as the active medium.
Electrical properties and microstructures of Pt/Ba0.5Sr0.5TiO3/SrRuO3 capacitors
Authors: Izuha Mitsuaki , Abe Kazuhide , Koike Mitsuo , Takeno Shiro , Fukushima Noburu
Published: July 2002

Thin film polycrystalline Ba0.5Sr0.5TiO3 capacitors employing conductive perovskite oxide SrRuO3 as a bottom electrode were fabricated on Si substrates by rf-magnetron sputtering. Dielectric constants of these capacitors were observed to be 206, 214, and 146 for 60, 40, and 20 nm Ba0.5Sr0.5TiO3 (BSTO) thicknesses, respectively. The lowest SiO2 equivalent thickness of 0.54 nm was obtained for 20-nm-thick BSTO capacitors; their leakage current density was less than 1×10−7 A/cm2 for ±1.8 V bias. The cross-sectional transmission electron microscope observation revealed that BSTO and SrRuO3 (SRO) formed continuous columnar grains and showed epitaxial growth at the interface of BSTO/SRO within each column; this microstructure of the capacitors was tentatively designated “local epitaxial film.”
Photoluminescence microscopy of InGaN quantum wells
Authors: Herzog W. D. , Singh R. , Moustakas T. D. , Goldberg B. B. , Ünlü M. S.
Published: July 2002

Submicron spatial resolution photoluminescence is used to assess radiative efficiency and spatial uniformity of GaN/InGaN heterojunctions. Room temperature photoluminescence of multiple InGaN quantum wells with GaN barriers fabricated by electron-cyclotron resonance assisted molecular beam epitaxy was measured as a function of position on a facet perpendicular to the layer structure. Our high resolution studies reveal that the radiative recombination for the InGaN quantum wells is 50–60 times more efficient than for the underlying GaN film.
Second harmonic generation in periodically domain-inverted Sr0.6Ba0.4Nb2O6 crystal plate
Authors: Zhu Y. Y. , Fu J. S. , Xiao R. F. , Wong G. K. L.
Published: July 2002

Quasiphase-matched second harmonic generation (SHG) has been realized in periodically domain-inverted strontium barium niobate (Sr0.6Ba0.4Nb2O6, so-called SBN) crystal plate induced by an external electric field. Both the coercive field and Curie temperature have been determined through in situ observation of the second harmonic signals. The measured SHG conversion efficiency is about 10% at a fundamental wavelength of 977.8 nm.
Enhanced detection bandwidth for optical doppler frequency measurements using moving space charge field effects in GaAs multiple quantum wells
Authors: Wang Chen-Chia , Linke Richard A. , Nolte David D. , Melloch M. R. , Trivedi Sudhir
Published: July 2002

Moving space charge field (photo-emf) effects are observed in standard and low temperature grown GaAs multiple quantum well (MQW) samples in which dc photocurrents are generated by constant speed moving optical interference patterns. Experiments reveal an enhanced detection bandwidth for optical doppler frequency measurements compared to previously studied bulk II-VI and III-V materials due to the higher quantum efficiency and optical absorption of GaAs MQWs, in spite of their reduced carrier mobility-lifetime product values resulting mainly from the significantly shorter free carrier lifetimes. The high defect density of low temperature grown MQWs can also yield large field-of-view and, for optical ultrasound detections, high cutoff frequency.
Three-dimensional imaging of spin polarization of alkali-metal vapor in optical pumping cells
Authors: Young A. R. , Appelt S. , Ben-Amar Baranga A. , Erickson C. , Happer W.
Published: July 2002

We present detailed images of the Rb polarization in a high-pressure optical pumping cell. Images taken at high magnetic field strengths (≈37 G) yield precise information on the relative occupation probability of the hyperfine Zeeman sublevels. Low-field (⩽4 G) images yield very high resolution (less than 1 mm) maps of the spatial distribution of the Rb polarization. For optical pumping in the presence of high-pressure buffer gases, the measured populations of the hyperfine magnetic sublevels are shown to be well described by a spin temperature, even though the Rb–Rb spin exchange rate is much smaller than the rates of optical pumping or electron-randomizing Rb–Xe collisions in the buffer gas.
High frequency properties of Fe–Cr–Ta–N soft magnetic films
Authors: Jin S. , Zhu W. , van Dover R. B. , Tiefel T. H. , Korenivski V. , Chen L. H.
Published: July 2002

High frequency magnetic properties of a new, soft magnetic Fe–Cr–Ta–N alloy film have been investigated. Thin films with a composition of Fe-4.6% Cr-0.2% Ta-7.4% N (in atomic %) were prepared by reactive sputtering in a nitrogen-containing atmosphere. The films, most likely nanocrystalline, exhibit excellent soft magnetic properties in the as-deposited condition without any post heat treatment, e.g., Hc as low as 1.2 Oe (95.3 A/m) and 4πMs∼20 kG. The easy-axis M–H loop is square. The hard-axis loop is linear and closed, with the anisotropy field Ha=20–100 Oe (1.59–7.95 kA/m). By virtue of their high 4πMs and relatively high Ha, these soft magnetic films exhibit high permeability and low loss in the GHz frequency range with the undesirable ferromagnetic resonance interference suppressed to beyond 2 GHz.
Identification and optimization of advanced phosphors using combinatorial libraries
Authors: Sun Xiao-Dong , Gao Chen , Wang Jingsong , Xiang X.-D.
Published: July 2002

A combination of thin-film deposition and physical masking steps were used to generate libraries of the rare earth activated refractory metal oxides, Gd(La,Sr)AlOx. Systematic variation of composition and processing conditions afforded tricolor phosphors with the following nominal compositions, (Gd0.46Sr0.31)Al1.23OxF1.38:Eu0.062+ (green), La0.5Al1.5Ox:Eu0.042+ (blue), and Gd0.77Al1.23Ox:Eu0.063+ (red), which had quantum efficiencies of ⩾94%, ≃60%, and ⩾93%, respectively at λmaxex. The high quenching temperatures (250–350 °C), good chromaticities and refractory nature of these phosphors are desirable features for display applications.
Impact ionization coefficients in GaInP p–i–n diodes
Authors: Ghin R. , David J. P. R. , Hopkinson M. , Pate M. A. , Rees G. J. , Robson P. N.
Published: July 2002

Impact ionization coefficients have been deduced from photomultiplication measurements performed on Ga0.52In0.48P p–i–n diodes with nominal intrinsic region thicknesses of 1 .0, 0.7, and 0.2 μm. The results indicate that β, the hole ionization coefficient, is slightly greater than α, the electron ionization coefficient at low fields, and they both become effectively equal at high fields. α and β are also found to be significantly lower than GaAs across the range of electric fields studied, with correspondingly higher breakdown voltages.
Enhanced Jc and improved grain-boundary properties in Ag-doped YBa2Cu3O7−δ films
Authors: Selvam P. , Seibt E. W. , Kumar D. , Pinto R. , Apte P. R.
Published: July 2002

A large increase (∼8×) in critical current density, Jc, was achieved for in situ laser ablated YBa2Cu3O7−δ–Ag films. High-resolution Auger electron spectroscopic investigation indicates that the Ag-doped films are stoichiometric with a relatively low grain-boundary extension (8 nm) in contrast to undoped YBa2Cu3O7−δ films (32 nm). Further analysis suggests that the doped film contains a much lower silver content (<0.15 wt %) than in the target material (5 wt %). These observations are in excellent agreement with the temperature dependence of Jc, the room-temperature resistivity, and the surface resistance results. Thus, Jc enhancement in Ag-doped films can be attributed to their superior properties, viz., improved microstructure characteristics and the reduced resistive grain boundaries.
Oxygen aggregation in Czochralski-grown silicon heat treated at 450 °C under compressive stress
Authors: Emtsev V. V. , Andreev B. A. , Misiuk A. , Jung W. , Schmalz K.
Published: July 2002

It has been established that the oxygen aggregation processes in Czochralski-grown silicon (Cz–Si) at 450 °C are strongly affected by high hydrostatic pressure. We observed the enhanced production of shallow thermal donors with ionization energies of 30–40 meV and deep donors at ≈EC−0.1 eV under a pressure of 1 GPa. In contrast, the concentration of the well-known double thermal donors was found to be much less than that in Cz–Si heat treated without stress. The latter effect may be associated with the involvement of self-interstitials in their formation. The enhanced production of other thermal donors is thought to be caused by increasing diffusivity of oxygen under the high stress.
Excitation of a single molecule on the surface of a spherical microcavity
Authors: Norris D. J. , Kuwata-Gonokami M. , Moerner W. E.
Published: July 2002

We use the optical resonance of a spherical microcavity (quality factor ∼106) to excite a single molecule. By attaching a p-terphenyl crystal doped with pentacene and terrylene molecules to a dielectric sphere, we detect individual molecules excited by the near field of the cavity. A low-temperature optical microscope is utilized to image the emission from the single molecule, determine its position on the sphere surface, and measure its absorption linewidth. These results demonstrate the feasibility of single-molecule cavity quantum electrodynamics.
Hot electron relaxation dynamics in ZnSe
Authors: Mehendale Manjusha , Sivananthan S. , Andreas Schroeder W.
Published: July 2002

The ultrafast relaxation dynamics of hot electrons, initially photoexcited with an excess energy of 300 meV, are monitored in a high-quality ZnSe epilayer grown on a GaAs substrate by exploiting the intrinsic interferrometric asymmetric Fabry–Perot sample structure. The results are consistent with the expected characteristic electronic LO-phonon emission time of 40–50 fs and provide evidence for the influence of the “hot phonon effect”(or “LO-phonon bottleneck”) on the electron cooling dynamics at carrier densities above ∼3×1017 cm−3.
Sheath dynamics observed in a 13.56 MHz-driven plasma
Authors: Mahony C. M. O. , Al Wazzan R. , Graham W. G.
Published: July 2002

We have established, through time correlated plasma emission and electrode and plasma potential measurements, that the near electrode emission observed in asymmetric capacitively coupled 13.56 MHz-driven hydrogen plasmas is caused by field reversal that leads to sheath collapse. Near-electrode emission has now been observed in Ar and He. The field reversal appears to be due to collision-induced electron drag.
Efficient, polarization-independent, reflective liquid crystal phase grating
Authors: Titus C. M. , Bos P. J.
Published: July 2002

A reflective liquid crystal diffraction grating is proposed which makes use of the maximum available surface area. The structure consists of alternating stripes, each a twisted-nematic domain with surface orientation perpendicular to that of its neighbors. All domains have the same twist sense. This device yields, in principle, 100% diffraction efficiency independent of incident polarization.
Polarity of (00.1) GaN epilayers grown on a (00.1) sapphire
Authors: Seelmann-Eggebert M. , Weyher J. L. , Obloh H. , Zimmermann H. , Rar A. , Porowski S.
Published: July 2002

The polarity is found to be a key parameter for the growth of high quality epitaxial GaN films on sapphire (00.1) substrates. A model is suggested which may consistently explain the observed influence of the process parameters on the polar orientation of the epitaxial film. A simple etching technique is proposed for quick distinction of the film polarity. The assignment of the etching behavior to the proper crystal structure is achieved by an analysis of the respective two-dimensional photoelectron diffraction patterns.
Direct observation of Si lattice strain and its distribution in the Si(001)–SiO2 interface transition layer
Authors: Kim Young Pil , Choi Si Kyung , Kim Hyun Kyong , Moon Dae Won
Published: July 2002

In the transition layer of the Si(001)–SiO2 interface, Si lattice strain and its distribution were directly observed by medium energy ion scattering spectroscopy for thermal and ion beam oxides. The strain was in the vertical direction, and the maximum values at the SiO2 side of the transition layer were 0.96% and 2.8% for the thermal and ion beam oxides, respectively.
Local stress measurements in laterally oxidized GaAs/AlxGa1−xAs heterostructures by micro-Raman spectroscopy
Authors: Landesman J. P. , Fiore A. , Nagle J. , Berger V. , Rosencher E. , Puech P.
Published: July 2002

Lattice deformation induced in surface GaAs layers by the selective lateral oxidation of buried AlxGa1−xAs layers was determined from the energy shift of the GaAs phonon line in Raman spectra excited with a focused laser beam. The procedure included a correction for the laser beam induced heating effects. The surface GaAs layer was found under small tensile stress in the oxidized regions of our samples with respect to the unoxidized regions. The deformation is 8×10−4 and is the same, within experimental error, for heterostructures incorporating pure AlAs layers or Al0.98Ga0.02As. Strong differences in Raman efficiency, as well as in photoluminescence efficiency, were observed for different samples, which are discussed in terms of the GaAs/oxide interface nonradiative recombination efficiency.
On the behavior of deuterium in ultrathin SiO2 films upon thermal annealing
Authors: Baumvol I. J. R. , Gusev E. P. , Stedile F. C. , Freire F. L. , Green M. L. , Brasen D.
Published: July 2002

Following the observation of the large isotopic effect in D2 passivated gate dielectrics [J. Lyding, K. Hess, and I. C. Kizilyalli, Appl. Phys. Lett. 68, 2526 (1996)], we studied the behavior of deuterium in ultrathin SiO2 films by nuclear reaction analysis techniques. Accurate concentrations of deuterium in the films, deuterium depth distributions, and deuterium removal from the film upon thermal annealing in vacuum have been examined. For D2 passivated films, we found rather high concentrations of deuterium near the SiO2/Si interface, well above both the solubility of deuterium in silica and the maximum concentration of electrically active defects at the interface. Our results suggest a complex multistep mechanism of thermally activated deuterium removal from the film, which probably consists of D detrapping, diffusion, and desorption steps.
Photoluminescence of erbium-implanted GaN and in situ-doped GaN:Er
Authors: Hansen D. M. , Zhang R. , Perkins N. R. , Safvi S. , Zhang L. , Bray K. L. , Kuech T. F.
Published: July 2002

The photoluminescence of in situ-doped GaN:Er during hydride vapor phase epitaxy was compared to an Er-implanted GaN sample. At 11 K, the main emission wavelength of the in situ-doped sample is shifted to shorter wavelengths by 2.5 nm and the lifetime is 2.1±0.1 ms as compared to 2.9±0.1 ms obtained for the implanted sample. The 295 K band edge luminescence of the in situ-doped sample was free of the broad band luminescence centered at 500 nm which dominated the spectrum of the implanted sample. Reversible changes in the emission intensity of the in situ-doped sample upon annealing in a N2 versus a NH3/H2 ambient indicate the probable role of hydrogen in determining the luminescence efficiency of these samples.
Angle-resolved energy distributions of laser ablated silver ions in vacuum
Authors: Hansen Tue N. , Schou Jo/rgen , Lunney James G.
Published: July 2002

The energy distributions of ions ablated from silver in vacuum have been measured in situ for pulsed laser irradiation at 355 nm. We have determined the energy spectra for directions ranging from 5° to 75° with respect to the normal in the intensity range from 100 to 400 MW/cm2. At the highest intensity and for angles close to the normal, the highest ion energy measured exceeds 500 eV. However, the energy distributions are shifted strongly towards low energies with increasing angle.
Humidity-dependent impedance in porous spinel nickel germanate ceramic
Authors: Hogan M. J. , Brinkman A. W. , Hashemi T.
Published: July 2002

The spinel ceramic material nickel germanate, Ni2GeO4, has been found to exhibit a humidity-dependent impedance. A change in the magnitude of the impedance at 100 Hz, from 108 Ω at 20% RH to 104 Ω at 98% RH, at 298 K, is typical. The effect of frequency on the complex impedance has been investigated over the frequency range 10 mHz–10 MHz, using the technique of impedance spectroscopy. The observed impedance spectra show two regions, indicative of an ionic-charge transport process and a charge transfer to the electrodes, suggesting that at high levels of humidity conduction is essentially electrochemical.
Dynamics of polarization loss in (Pb, La)(Zr, Ti)O3 thin film capacitors
Authors: Jenkins I. G. , Song T. K. , Madhukar S. , Prakash A. S. , Aggarwal S. , Ramesh R.
Published: July 2002

We report results of high-speed polarization relaxation measurements in ferroelectric thin film capacitors. Polarization relaxation has been reported to occur in two distinct time regimes, one for relaxation times in the range of a few milliseconds and a second for longer relaxation times. We find that the polarization relaxation in the first regime is governed by at least two different physical processes, namely depoling fields and the activation field for switching. Using prototypical epitaxial PbZr0.2Ti0.8O3 and Pb0.9La0.1Zr0.2Ti0.8O3 test capacitors, we demonstrate the effect of film microstructure and switching speed on the relaxation dynamics in the first regime.
Hybrid ferromagnetic/semiconductor Hall effect device
Authors: Reijniers J. , Peeters F. M.
Published: July 2002

The diffusive classical transport of a two-dimensional electron gas (2DEG) in a Hall cross, subjected to a locally inhomogeneous magnetic field resulting from an in plane magnetized ferromagnetic film deposited above the 2DEG, is investigated. The magnetic field profile in the 2DEG is obtained analytically and the Hall resistance is calculated for various configurations. Our results are in good agreement with the recent experimental results of Johnson et al. [Appl. Phys. Lett. 71, 974 (1997)] on a novel magnetoelectronic device. The output of the device scales inversely with both the size of the voltage and the current probes.
Spin-dependent tunneling in discontinuous Co–SiO2 magnetic tunnel junctions
Authors: Sankar Sandra , Berkowitz A. E. , Smith David J.
Published: July 2002

Discontinuous magnetic tunnel junctions (DMTJs) are an alternate system to the magnetic tunnel junctions (MTJ) currently being considered for magnetoresistance (MR) sensors. The DMTJs are easier to fabricate and more robust than the MTJs. The nominal film structure is SiO2(20 Å)/Co(tCo)/SiO2(30 Å)/Co(tCo)/SiO2(20 Å), in which the thin Co layers are discontinuous, in the form of nanoparticles. Magneto-transport measurements were made perpendicular to the film plane on macroscopic junctions for in-plane applied magnetic fields. The results, for these films with only two magnetic layers, are similar to those of the discontinuous multilayers previously reported. The MR response is relatively sharp and almost linear at low magnetic fields and is reproducible from one junction to another. This MR (defined as ΔV/Vmax) is weakly temperature dependent with a maximum between 4 and 300 K. The MR and the magnetization at low temperature suggest ferromagnetically coupled particles, which switch in lower magnetic fields than noninteracting particles.
Dynamics of phonon-assisted tunneling in a silicon degenerate pn junction
Authors: Richardson W. H.
Published: July 2002

The charge distribution and junction voltage on an indirect-band-gap semiconductor tunnel junction (that is in parallel with a resistor and current source) were obtained by solution of the master equation. Expressions for the tunneling rate in a silicon degenerate pn junction are presented. Phonon-assisted tunneling permits relaxation of a requirement (that the external resistance be much larger than the resistance quantum) for the observation of single electron tunneling oscillations. Consequently, that process may enable observation of such oscillations in practical single junction circuits.
The effect of the Si/N treatment of a nitridated sapphire surface on the growth mode of GaN in low-pressure metalorganic vapor phase epitaxy
Authors: Haffouz S. , Lahrèche H. , Vennéguès P. , de Mierry P. , Beaumont B. , Omnès F. , Gibart P.
Published: July 2002

In this letter, we studied the effect of the high-temperature Si/N treatment of the nitridated sapphire surface followed by the deposition of a low-temperature GaN nucleation layer on the growth mode of GaN in low-pressure metalorganic vapor phase epitaxy. It was shown that the nucleation layer, initially flat and continuous, converts to wide isolated truncated hexagonal islands having {1–101} facet planes and a top (0001) plane, after heating up to 1150 °C. The coalescence of these GaN islands yields a reduction of the total number of extended defects from the 1010–1011 cm−2 range usually obtained down to the low 109 cm−2 range for the best samples.
Diagnostic technique for measuring plasma parameters near surfaces in radio frequency discharges
Authors: Rauf Shahid , Kushner Mark J.
Published: July 2002

A plasma diagnostic technique for measuring the electron density, electron temperature, and ion current near a surface in radio frequency (rf) discharges is proposed. The sensor uses a small wire probe to determine the plasma potential and a small metal electrode to measure the current and voltage profiles. The values of current, sheath voltage, and time derivative of sheath voltage at three distinct points during the rf cycle are used in conjunction with an analytical sheath model to determine the plasma parameters. The technique is demonstrated by implementing the diagnostic in a computer model of an inductively coupled plasma reactor which has an rf biased substrate. Although any three disjoint sets of measurements can ideally be used, a sensitivity analysis is used to show that certain sets may be more suitable in experimental systems where noise is present.
Hot electron emission lithography
Authors: Poppeller M. , Cartier E. , Tromp R. M.
Published: July 2002

We have developed an electron lithography method, hot electron emission lithography, which is capable of printing integrated circuits with an exposure time of only a few seconds. The basic design and fabrication of the patterned electron emitting mask made by standard metal–oxide–semiconductor technology will be discussed, and its applicability in a simple 1:1 e-beam stepper will be demonstrated. Patterns with a minimum feature size of 160 nm have been printed successfully. Further improvements in resolution to 50 nm appear to be possible.
Guiding characteristics of an acoustic standing wave in a piezoelectric tube
Authors: Fauser C. M. , Gaul E. W. , Le Blanc S. P. , Downer M. C.
Published: July 2002

Propagation of an He–Ne laser beam through a gas filled piezoelectric tube is used to characterize the guiding properties of a radially driven acoustic standing wave. Impedance matched driving at 1 MHz of the 5-cm-long piezotube yields radial density perturbations of 0.005 at 40 V driving voltage. The frequency spectrum of the cavity resonances is used to measure the damping of the standing wave due to shear viscosity in Ar.
Room-temperature diffusivity of self-interstitials and vacancies in ion-implanted Si probed by in situ measurements
Authors: Coffa Salvatore , Libertino Sebania
Published: July 2002

We have determined the room-temperature diffusivity of self-interstitials and vacancies in Si. Silicon p+−n junctions were realized in n-type epitaxial Si wafers, having an O and C content ⩽1015/cm3, and implanted at room temperature with 2.5 MeV He ions to fluences in the range 1×109–1×1012/cm2. The junctions were reverse biased at −30 V, in order to embody the entire damage profile of the ion in the depletion layer, and in situ leakage measurements were performed during and just after implantation. It is found that the leakage current increases monotonically during implantation while, at the beam turn off, it decreases by about a factor of 2 for times as long as 1 day. Ex situ deep level transient spectroscopy measurements show that the main contribution to leakage current is due to the deep levels introduced in the band gap by phosphorous–vacancy and divacancy complexes. This allowed us to associate the leakage current reduction at the beam turn off to the recombination of vacancy-type complexes by residual free interstitials. When, for a fixed fluence, the ion flux is increased, an initial faster transient, lasting up to ∼1000 s, is observed and has been attributed to the annihilation of residual free vacancies. Diffusivity values of 1.5×10−15 and 3.0×10−13 cm2/s for interstitials and vacancies, respectively, have been achieved from the analysis of these data.
Photoluminescence of localized excitons in pulsed-laser-deposited GaN
Authors: Cazzanelli M. , Cole D. , Donegan J. F. , Lunney J. G. , Middleton P. G. , O’Donnell K. P. , Vinegoni C. , Pavesi L.
Published: July 2002

Continuous-wave photoluminescence (PL) and time-resolved photoluminescence of gallium nitride layers grown by pulsed laser deposition are compared. The temperature dependence of the photoluminescence decay time and the PL-integrated intensity allows a determination of radiative and nonradiative time constants of GaN. We find that luminescence peaks centered at 3.360 and 3.305 eV at low temperature can be attributed to recombination of excitons localized at extended defects. The photoluminescence radiative lifetime at room temperature is on the order of tens of ns.
Suppression of boron penetration by polycrystalline Si1−x−yGexCy in metal–oxide–semiconductor structures
Authors: Chang C. L. , Sturm J. C.
Published: July 2002

A polycrystalline Si1−x−yGexCy layer grown by rapid thermal chemical vapor deposition has been used as a thin intermediate layer on top of the thin gate oxide in a metal–oxide–semiconductor structure with boron-doped polycrystalline silicon as the gate electrode. Although boron readily penetrated through the Si1−x−yGexCy and accumulated in it, boron penetration across the gate oxide into the substrate was greatly suppressed compared to that in structures without Si1−x−yGexCy layer. Our work suggests that the addition of carbon reduced the chemical potential of boron in polycrystalline Si1−x−yGexCy, compared to that in polycrystalline silicon or polycrystalline Si1−xGex. We have also observed no gate depletion effects with the use of poly-Si1−x−yGexCy layers in both p+ and n+ gate doping.
Change in electromechanical properties of 0.9PMN:0.1PT relaxor ferroelectric induced by uniaxial compressive stress directed perpendicular to the electric field
Authors: Zhao J. , Glazounov A. E. , Zhang Q. M.
Published: July 2002

It was shown that the uniaxial compressive stress applied perpendicular to the electric field strongly changes the dielectric and electromechanical properties of relaxor ferroelectric 0.9PMN:0.1PT at temperatures around its dielectric constant maximum, Tm. This includes: (i) a shift of the temperature of the electric field induced phase transition into the ferroelectric state and a depoling temperature to higher values which brings a large hysteresis in the material response to the electric field, and (ii) the symmetry breaking in the plane perpendicular to the direction of the electric field (3-axis). Using this symmetry breaking, from the ratio of the effective piezoelectric coefficients in the field biased state, d32/d31, the size of the micropolar regions at temperatures near Tm was estimated.
Thermally induced threefold upconversion emission enhancement in nonresonant excited Er3+/Yb3+-codoped chalcogenide glass
Authors: dos Santos P. V. , Gouveia E. A. , de Araujo M. T. , Gouveia-Neto A. S. , Sombra A. S. B. , Medeiros Neto J. A.
Published: July 2002

Thermally induced threefold infrared-to-visible upconversion emission enhancement in Er3+/Yb3+-codoped Ga2S3:La2O3 chalcogenide glasses excited at 1.064 μm is reported. The times three upconversion efficiency enhancement was achieved by heating the sample in the temperature range of 23–155 °C, and is assigned to the temperature-dependent multiphonon-assisted anti-Stokes sideband excitation process of the ytterbium sensitizer. A theoretical analysis based upon rate equations considering the sensitizer absorption cross section as a function of the phonon occupation number in the host material exhibited very good agreement with experimental data.
Scanning room-temperature photoluminescence in polycrystalline silicon
Authors: Koshka Y. , Ostapenko S. , Tarasov I. , McHugo S. , Kalejs J. P.
Published: July 2002

Photoluminescence (PL) mapping was performed on polycrystalline silicon wafers at room temperature. Two PL bands are observed: (1) a band-to-band emission with a maximum at 1.09 eV, and (2) a deep “defect” luminescence at about 0.8 eV. PL mapping of 10 cm×10 cm wafers revealed inhomogeneity of the band-to-band PL intensity which could be correlated to the distribution of minority carrier diffusion length in the wafer bulk. We have also observed that the intensity of the 0.8 eV band is strongest along those grain boundaries where the band-to-band PL is suppressed as well as minority carrier diffusion length. The origin of the 0.8 eV luminescence band is discussed.
Evolution of {311} type defects in boron-doped structures: Experimental evidence of boron–interstitial cluster formation
Authors: Lilak A. D. , Earles S. K. , Law M. E. , Jones K. S.
Published: July 2002

Boron-doped well structures formed in Czochralski silicon are subjected to a self-implant and various anneals to form a population of type {311} defects. Quantitative transmission electron microscopy is then used to measure the residual interstitials trapped in the {311} defects as a function of boron concentration and anneal temperature. We have found a strong tendency for increased dissolution rates of {311} type defects at boron concentrations above 1018 cm−3, providing direct evidence for the formation of boron–interstitial clusters. By profiling the samples with secondary ion mass steptroscopy and comparing the results to spreading resistance measurements the degree of deactivation can be determined.
Electrical activation kinetics for shallow boron implants in silicon
Authors: Fiory A. T. , Bourdelle K. K.
Published: July 2002

Silicon implanted with boron at 1015 cm−2 dose and energies from 500 eV to 1 keV were annealed over wide variations in temperature and time to obtain process kinetics and thermal activation energies for shallow junction formation. Diffusion depths and carrier densities were determined by modeling sheet electrical transport. The thermal activation energy for the mean time to produce electrical activation is found to be 5.1±0.1 eV, while for the mean diffusivity it is found to be 4.1±0.1 eV. The 1 eV difference expresses quantitatively the particular advantage of spike thermal anneals at temperatures above 1000 °C.
Soft x-ray absorption of a buried SmCo film utilizing substrate fluorescence detection
Authors: Coulthard I. , Freeland J. W. , Winarski R. , Ederer D. L. , Jiang J. S. , Inomata A. , Bader S. D. , Callcott T. A.
Published: July 2002

Oxygen K-shell x-ray fluorescence was monitored from the MgO substrate of a metallic heterostructure system containing a buried SmCo permanent magnet layer. This fluorescence was utilized as a detector to record transmission yield spectra for the SmCo film at both the Co–L3,2 and Sm–M5,4 absorption edges. Ordinarily, traditional transmission yield spectroscopy in the soft x-ray regime is impossible to perform with films on single-crystal substrates. The measured intensity ratios agree with simulations to confirm the thickness information. The potential and limitations of this technique are discussed in comparison to standard total electron and fluorescence yield techniques and magnetic circular dichroism.
Effect of strain and associated piezoelectric fields in InGaN/GaN quantum wells probed by resonant Raman scattering
Authors: Wagner J. , Ramakrishnan A. , Obloh H. , Maier M.
Published: July 2002

The influence of pseudomorphic strain and resulting piezoelectric fields on In0.13Ga0.87N/GaN quantum wells has been studied by resonant Raman scattering. The A1(LO) phonon of In0.13Ga0.87N pseudomorphically strained to GaN is found to be downshifted in frequency by only 3 cm−1 with respect to GaN, which gives evidence for a near cancellation between the much larger frequency downshift of 10 cm−1 reported for unstrained In0.13Ga0.87N and a high-frequency shift of the A1(LO) phonon induced by the in-plane compressive strain. For excitation in resonance with the fundamental interband transition of the InGaN well, the intensity of first- and second-order scattering by the InGaN A1(LO) phonon was found to decrease with decreasing excitation power density, and thus increasing strength of the piezoelectric field. This finding is explained by a quenching of the excitonic enhancement in the resonance profile by the piezoelectric field.
Supercurrents in HgBa2CaCu2O6+δ and TlBa2CaCu2O7 epitaxial thin films
Authors: Gapud A. A. , Wu J. Z. , Fang L. , Yan S. L. , Xie Y. Y. , Siegal M. P. , Overmyer D. L.
Published: July 2002

The availability of high-quality epitaxial thin films of HgBa2CaCu2O6+δ (Hg-1212) and TlBa2CaCu2O7 (Tl-1212) with high critical current densities (Jc) has made it possible to examine and compare the Jc of these species. Results reveal that the Jc of 1212 species have very similar temperature behavior at low fields, strongly suggesting that the 30 K shift in critical temperature (Tc) induced by the exchange of Hg and Tl in the 1212 structure is due largely to a change in charge carrier density and/or electronic band structure.
Pulse separation control for mode-locked far-infrared p-Ge lasers
Authors: Muravjov A. V. , Strijbos R. C. , Fredricksen C. J. , Withers S. H. , Trimble W. , Pavlov S. G. , Shastin V. N. , Peale R. E.
Published: July 2002

Active mode locking of the far-infrared p-Ge laser giving a train of 200 ps pulses is achieved via gain modulation by applying an rf electric field together with an additional bias at one end of the crystal parallel to the Voigt-configured magnetic field. Harmonic mode locking yields a train of pulse pairs with variable time separation from zero to half the roundtrip period, where pulse separation is electrically controlled by the external bias to the rf field.
Temporal development of the plasma composition of a pulsed aluminum plasma stream in the presence of oxygen
Authors: Schneider Jochen M. , Anders André , Brown Ian G. , Hjörvarsson Björgvin , Hultman Lars
Published: July 2002

We describe the temporal development of the plasma composition of pulsed aluminum plasma streams at various oxygen pressures. The plasma was formed with a vacuum arc plasma source and the time resolved plasma composition was measured with time-of-flight charge-to-mass spectrometry. The temporal development of the plasma composition as well as the Al average ion charge state was found to be a strong function of the oxygen pressure. Oxygen and hydrogen concentrations of up to 0.36 and 0.32, respectively, were found in the first 50 μs of the pulse at oxygen pressures of ⩾5×10−5 Torr. The average charge state of aluminum ions was found to vary from +1.2 to +2.5 depending on the oxygen pressure and the time elapsed after ignition of the arc. These results are of fundamental importance for the understanding of the evolution of the composition (through the plasma composition) and microstructure (through the Al ion flux energy) of alumina thin films produced by pulsed, reactive aluminum plasmas.
Performance and stability of Si:H p–i–n solar cells with i layers prepared at the thickness-dependent amorphous-to-microcrystalline phase boundary
Authors: Koval Randy J. , Koh Joohyun , Lu Z. , Jiao L. , Collins R. W. , Wronski C. R.
Published: July 2002

Systematic studies have been carried out on the transition from the amorphous to the microcrystalline phase in intrinsic Si:H as a function of the accumulated film thickness and the effect of this transition on p–i–n solar cell performance [J. Koh, Y. Lee, H. Fujiwara, C. R. Wronski, and R. W. Collins, Appl. Phys. Lett. 73, 1526 (1998)]. Guided by a deposition phase diagram obtained from real-time spectroscopic ellipsometry, cell structures having i layers deposited with different H2-dilution levels and thicknesses were investigated. For these structures, the fill factors are controlled by the bulk i layers. From the systematic changes in the fill factors, specifically their initial and degraded steady-state values and their degradation kinetics, the effects of the transition from the amorphous to the microcrystalline phase within the Si:H layers are identified, and insights are obtained into the properties of these structurally graded materials.
Room-temperature 1.3 μm emission from InAs quantum dots grown by metal organic chemical vapor deposition
Authors: Bloch J. , Shah J. , Hobson W. S. , Lopata J. , Chu S. N. G.
Published: July 2002

Using metal organic chemical vapor deposition, we have fabricated self-organized quantum dots that emit efficiently at 1.3 μm at room temperature. They are grown on GaAs and consist of InAs covered with an InGaAs cap layer. Their density is 2×1010 cm−2 as determined by transmission electron microscopy. Room-temperature photoluminescence shows a 36 meV broad line at 1.3 μm, corresponding to the quantum-dot ground state, with excellent uniformity across the wafer. The efficiency of this emission is reduced only by a factor of 4 with respect to low temperature showing the high quality of the sample.
Electron field emission from diamond-like carbon films deposited by electrolysis of methanol liquid
Authors: Kiyota H. , Araki H. , Kobayashi H. , Shiga T. , Kitaguchi K. , Iida M. , Wang H. , Miyo T. , Takida T. , Kurosu T. , Inoue K. , Saito I. , Nishitani-Gamo M. , Sakaguchi I. , Ando T.
Published: July 2002

Electron field emission has been studied with diamond-like carbon (DLC) films deposited from a liquid phase. The DLC films were deposited on Si substrate by electrolysis of methanol liquid. The field emission measurements were carried out with a parallel plate configuration using the deposited DLC films on Si substrate as a cathode, and an indium tin oxide (ITO) coated glass plate as an anode. We found several bright spots on a luminescent screen mounted on the ITO anode, indicating that the electrons are emitted from the isolated emission sites on the deposited DLC film. The emission current density is more than 10−7 A/cm2 at the electric field as low as 1.2 V/μm. This result suggests that the DLC film deposited from the liquid phase has a potential advantage for field emitter applications.
Microphotoluminescence mapping of packaging-induced stress distribution in high-power AlGaAs laser diodes
Authors: Martin E. , Landesman J. P. , Hirtz J. P. , Fily A.
Published: July 2002

Spatially resolved photoluminescence line scans were performed to determine the local stresses in AlGaAs laser diodes designed for high-power operation at 808 nm. In this approach, the sign and magnitude of the local stress are deduced from the spectral shift of the peak associated with band-to-band transitions in the n-type GaAs substrate. The sensitivity of the technique (minimal equivalent hydrostatic stress that can be detected) can reach 10 MPa or better. Correlations between solder-induced stress distribution in the devices and estimated lifetimes are demonstrated.
Electrical characteristics of Ta2O5 thin films deposited by electron beam gun evaporation
Authors: Mikhelashvili V. , Eisenstein G.
Published: July 2002

We report electrical characteristics of Ta2O5 films deposited by a simple electron beam gun evaporator. We describe thickness-dependent characteristics for films with thicknesses of 7–130 nm. An equivalent SiO2 thickness of 3.5–4.5 nm for films whose leakage current density at an electric field of 106 V/cm is lower than 10−7 A/cm2 is demonstrated.
Completely 〈111〉-textured growth and enhanced ferroelectric properties of Pb(Ta0.05Zr0.48Ti0.47)O3 films on Pt/TiO2/SiO2/Si(001) using SrRuO3 buffer layer
Authors: Yin J. , Liu Z. G. , Wu Z. C.
Published: July 2002

Completely 〈111〉-textured Pb(Ta0.05Zr0.48Ti0.47)O3 (PTZT) films are grown on Pt/TiO2/SiO2/Si(001) substrates by pulsed-laser deposition using SrRuO3 as a buffer layer. It is argued that the small lattice-mismatch in (111) plane between Pt and SrRuO3 and the compatible perovskite structures for SrRuO3 and PTZT are responsible for the complete (111) orientation of PTZT films. The as-fabricated PTZT ferroelectric capacitor exhibits large remnant polarizations +Pr=18.4 μC/cm2, and −Pr=−16.0 μC/cm2, and very low leakage current as well. The excellent fatigue-resisting property of PTZT films in terms of the polarization degradation is demonstrated.
Pyroelectric Ba0.8Sr0.2TiO3 thin films derived from a 0.05 M solution precursor by sol–gel processing
Authors: Cheng Jian-Gong , Meng Xiang-Jian , Tang Jun , Guo Shao-Ling , Chu Jun-Hao
Published: July 2002

Tetragonal Ba0.8Sr0.2TiO3 thin films with large columnar grains 100–200 nm in diameter have been prepared on Pt/Ti/SiO2/Si substrates using a 0.05 M solution precursor by sol–gel processing. The ferroelectric phase transition in the prepared Ba0.8Sr0.2TiO3 thin films is broadened, and suppressed to 40 °C with a maximum dielectric constant of εr (100 kHz)=680. The observed low dissipation factor tan δ=2.6% and high pyroelectric coefficient p=4.586×10−4 C/m2 K at 33 °C render the prepared Ba0.8Sr0.2TiO3 thin films promising for uncooled infrared detector and thermal imaging applications.
Electron diffusion length and escape probabilities for cesiated and hydrogenated polycrystalline diamond photocathodes
Authors: Niigaki M. , Hirohata T. , Mochizuki T. , Uchiyama S. , Kan H. , Hiruma T.
Published: July 2002

Electron diffusion lengths and escape probabilities from cesiated and hydrogenated polycrystalline diamond photocathodes were estimated by comparing the photoemission spectral response characteristics between the experimental and calculated data. As a result, the diffusion length for the polycrystalline diamond film used in this study was estimated to be as long as approximately 50 nm. Estimated escape probabilities of 0.8 and 0.2 were also obtained for cesiated and hydrogenated surfaces, respectively. The results suggest that the cesiated surface has a true negative electron affinity while the hydrogenated surface has an effective negative electron affinity.
Thermal conductivity and electromechanical property of single-crystal lead magnesium niobate titanate
Authors: Zhu Da-Ming , Han P. D.
Published: July 2002

Thermal conductivity of a single-crystal lead magnesium niobate titanate-(1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 with x=0.34 has been studied at temperatures from 20 to 320 K and in an applied electric field. The thermal conductivity of the crystal is similar to that of a typical amorphous solid both in the temperature dependence and in magnitude. The electric field dependence of the thermal conductivity and strain show an abrupt change at about 15 kV/cm, which is interpreted as due to a field-induced phase transformation in the crystal.
Influence of a thin AlAs cap layer on optical properties of self-assembled InAs/GaAs quantum dots
Authors: Arzberger M. , Käsberger U. , Böhm G. , Abstreiter G.
Published: July 2002

The influence of an AlAs cap layer with a thickness of a few monolayers on the optical properties of molecular beam epitaxy-grown InAs/GaAs self-assembled quantum dots is investigated. The capping of the InAs islands with a thin AlAs layer before the overgrowth by GaAs leads to a blueshift of the photoluminescence at a substrate temperature TS=480 °C, but to a significant redshift at TS=530 °C. This indicates that the InAs/GaAs intermixing caused by In segregation at TS=530 °C can be considerably reduced by a thin AlAs capping layer. This leads to deeper potential wells due to the higher In content in the quantum dots which results in a room-temperature photoluminescence at about 1.3 μm.
Vacuum emission and breakdown characteristics of a planar He–Xe microdischarge
Authors: Postel Olivier B. , Cappelli Mark A.
Published: July 2002

Vacuum emission, breakdown, and current–voltage characteristics of a large surface area-to-volume ratio planar dc microdischarge have been measured for different He–Xe mixtures in the range of 10%–100% Xe and pressures in the range of 60–500 Torr. The electrical measurements show that the Paschen breakdown curves and the current–voltage characteristics are primarily controlled by the xenon concentration in the mixture. A study of the vacuum ultraviolet emission of xenon atoms at 147 nm and of xenon dimers at 150 nm normalized to the discharge power reveals the presence of local maxima in the emitted intensity as a function of discharge pressure and xenon concentration, indicative of complex excited-state atomic and excimer kinetic processes.
Fabrication of a Josephson junction using an atomic force microscope
Authors: Song Insang , Kim Byong Man , Park Gwangseo
Published: July 2002

A Josephson junction was fabricated by inducing a selective surface modification on a YBa2Cu3O7−y strip with an atomic force microscope (AFM). The surface modification in the field of conductive AFM tip results in the controlled growth of protrusions across the entire strip. By properly regulating the extent of AFM modification, we achieved a Josephson junction. The self-radiation power of about 50 pW at a resonant frequency of 22 GHz was detected from this junction, which is in excellent agreement with the Josephson frequency-voltage relationship.