bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron velocity saturation in quantized silicon carbide inversion layers
Authors: Gámiz F. , Roldán J. B. , López-Villanueva J. A. , Carceller J. E.
Published: July 2002

Results of electron mobility calculations at room temperature in quantized cubic silicon carbide (β-SiC) inversion layers are reported. A comparison with silicon mobility curves is provided. Drift velocities both at room and higher temperatures are calculated by Monte Carlo simulations including electron quantization and Coulomb scattering, in addition to phonon and surface roughness scattering. We have also observed that steady-state drift velocity curves show a maximum that decreases as the transverse electric field increases, due to the greater importance of intervalley scattering with respect to polar phonon scattering.
Enhancement of deep acceptor activation in semiconductors by superlattice doping
Authors: Schubert E. F. , Grieshaber W. , Goepfert I. D.
Published: July 2002

The thermal activation of acceptors in wide-gap semiconductors can be very low due to large acceptor activation energies. It is shown that superlattice doping, i.e., the composition modulation of a uniformly doped ternary semiconductor, can enhance the acceptor activation by more than one order of magnitude.
Investigation of transverse Peltier effect on top-seeded melt textureYBa2Cu3O7−δ
Authors: He Z. H. , Ma Z. G. , Li Q. Y. , Luo Y. Y. , Zhang J. X. , Meng R. L. , Chu C. W.
Published: July 2002

The transverse Peltier effect is investigated on the top-seeded melt texture superconductor YBa2Cu3O7−δ (YBCO). By restricting the heat absorbing or evolving on one of the sample’s surfaces, the Peltier heat flow is converted into a temperature difference for measurement. The temperature difference is found proportional to the current applied, which is in accordance with the prediction of transverse Peltier effect. Based on a simplified model, the difference of the Seebeck coefficients between the ab plane and the c axis, |Sab−Sc|, is about 35 μV/K. It is in good agreement with that of large single crystal [I. Terasaki, Y. Sato, S. Tajima, S. Miyamoto, and S. Tanaka, Physica C 235-240, 1413 (1994)]. The transverse Peltier effect is verified. This supports the idea that the off-diagonal thermoelectric effect is responsible for the anomalously high laser-induced transient transverse voltage on the oriented YBCO superconducting thin films.
Enhancement of the 77 K irreversibility field and critical current density of (Bi,Pb)2Sr2Ca 2Cu3Ox tapes by manipulation of the final cooling rate
Authors: Parrell J. A. , Larbalestier D. C. , Riley G. N. , Li Q. , Parrella R. D. , Teplitsky M.
Published: July 2002

By manipulating the cooling rate from the final heat treatment, we have raised the 77 K, self-field critical current density (Jc) of multifilament (Bi,Pb)2Sr2Ca2Cu3Ox (2223) tapes by a factor of 3, and the irreversibility field (H*) by more than 50%. The Jc of samples cooled in 7.5% O2 from their reaction temperature of 825 °C increased from ∼8 to ∼24 kA/cm2 and H*(77 K) increased from ∼120 to ∼200 mT as the cooling rate was decreased from 5 to 0.016 °C/min. The results unambiguously show that the flux pinning properties of 2223 tapes can be improved by simple changes in wire processing.
Voltage shift and deformation in the hysteresis loop of Pb(Zr,Ti)O3 thin film by defects
Authors: Lee Eun Gu , Wouters Dirk J. , Willems Geert , Maes Herman E.
Published: July 2002

Voltage shift and deformation in the hysteresis loop of Pb(Zr,Ti)O3 (PZT) capacitors have been studied by varying the annealing temperature after patterning the top sputter-deposited Pt electrode using reactive ion etch (RIE) with Ar gas. It was observed that the hysteresis loop of the film was seriously deformed by both sputtering and RIE induced defects. Voltage shift and polarization suppression can be explained by the charge trapping at electrode interfaces and at defect levels in the film, respectively. Space charges trapped at defect levels in the film suppress polarization parallel to poling direction, however, enhance polarization opposite to the poling direction.
The structural symmetry of epitaxial Tl2Ba2CuO6+δ thin films
Authors: Ren Z. F. , Wang J. H. , Miller D. J.
Published: July 2002

Epitaxial films of Tl2Ba2CuO6+δ (Tl-2201) have been prepared on SrTiO3 by sputtering and postdeposition annealing. The films were deposited onto (100)SrTiO3 single crystal substrates by rf magnetron sputtering and then annealed using a two-step process. The annealed films typically exhibit transition temperatures of about 11 K. Subsequent reannealing to optimize the oxygen doping in the film results in an increase in the transition temperature, and optimally reannealed films exhibit transition temperatures of about 83 K. The crystal structure of these films has been studied by x-ray diffraction and transmission electron microscopy. These results indicate that both the annealed (Tc=11 K) and optimally reannealed samples (Tc=83 K) have a tetragonal crystal structure. This structural information is crucial in evaluating recent measurements on these films to determine the electron pairing symmetry (d wave or s wave) in high-Tc superconductors.
YBa2Cu3O7−δ/NdBa2Cu3O7−δ/YBa2Cu3O7−δ edge junctions and SQUIDS
Authors: Oh B. , Choi Y. H. , Moon S. H. , Kim H. T. , Min B. C.
Published: July 2002

YBa2Cu3O7−δ (YBCO) Josephson junctions in a ramp edge geometry with NdBa2Cu3O7−δ (NBCO) barriers were fabricated by pulsed laser deposition on (100) SrTiO3 substrates. The barrier layer thicknesses were d=100, 200, and 300 Å . The I–V characteristics of YBCO/NBCO/YBCO junctions changed from the resistively shunted junction type to flux-creeplike behavior as temperature decreased. Shapiro steps due to the ac Josephson effect clearly developed under microwave irradiation. The interface between the superconducting (YBCO) and the normal layer (NBCO) turned out to be fairly clean with small interface resistance. The mean value of the measured IcRn product for junctions with 100-Å-thick barriers was 71±34 μV at 77 K. The normal coherence length of the NBCO barrier material was ∼40 Å. The SQUIDs, made of superconductor–normal metal–superconductor junctions, showed voltage modulation at 77 K.
Quasi-optical submillimeter-wave mixers with NbN/AlN/NbN tunnel junctions
Authors: Uzawa Yoshinori , Wang Zhen , Kawakami Akira
Published: July 2002

We demonstrate low-noise heterodyne mixing with NbN/AlN/NbN tunnel junctions in the submillimeter-wave region. The prepared junction size was 1 μm in diameter and the current density was about 20 kA/cm2, supplying a small ωCJRN product (ωCJRN=3 at 300 GHz). The mixer used a lens-coupled log-period antenna and an integrated tuning circuit which incorporated a radial short stub tuner for resonating out the junction capacitance. The junctions showed good dc I–V characteristics, excellent submillimeter-wave responses and sensitive heterodyne mixing responses. From 254 to 350 GHz the average receiver noise temperature measured using the standard Y-factor method was about 250 K double sideband (DSB). The lowest receiver noise temperature, 200 K (DSB), was obtained around 303 GHz.
A novel procedure for measuring the absolute current density profile of a focused gallium-ion beam
Authors: Wang J. B. , Wang Y. L.
Published: July 2002

A simple and sensitive method has been developed for measuring the absolute current density profile of a focused gallium-ion beam down to six orders of magnitude below its peak intensity. This method exploits both physical sputtering and a chemical etch-stop mechanism that occurs on Si(100) substrates after Ga-ion implantation. Sputtering creates craters on the substrate while the ion implanted area becomes insoluble in aqueous NaOH. This etch-stop layer can be used as negative resistance for creating hillocks on the substrate. By measuring the topographs of sputtered craters and etched hillocks using atomic force microscopy, the absolute current density profile of the focused ion beam is deduced.
X-ray diffraction and nuclear magnetic resonance studies of Y2Fe17
Authors: Shen N. X. , Zhang Y. D. , Budnick J. I. , Hines W. A. , Lyver R. , Buschow K. H. J.
Published: July 2002

X-ray structure analysis and 89Y nuclear magnetic resonance (NMR) measurements are presented for the hexagonal and rhombohedral phases of Y2Fe17. The rhombohedral structure has one Y site (designated 6c) and the hexagonal structure has two Y sites (designated 2b and 2d). By combining the x-ray and NMR results, the hyperfine fields corresponding to the three Y sites in these two phases are obtained. Furthermore, a deconvolution of the NMR spectrum for 89Y in the hexagonal Y2Fe17 phase shows that a disordering exists, resulting in an occupancy for the Y 2b sites of approximately 71%.
An InAlAs/InGaAs metal-oxide-semiconductor field effect transistor using the native oxide of InAlAs as a gate insulation layer
Authors: Grudowski P. A. , Chelakara R. V. , Dupuis R. D.
Published: July 2002

We report the growth, fabrication, and electrical characterization of InAlAs/InGaAs n-type depletion-mode, metal-oxide-semiconductor field effect transistors (MOSFETs) utilizing the thermally formed native oxide of InAlAs as a gate insulating layer. The native oxide of InAlAs, consisting mostly of aluminum–oxygen complexes, is formed in an elevated temperature environment with water vapor as the oxidizing species. This native oxidation process is similar to that used to oxidize other aluminum-containing compounds in the GaAs-based material system, such as AlGaAs and InAlP. The InGaAs MOSFETs having a gate length ∼8 μm exhibit a maximum gm∼6 mS/mm.
Growth of epitaxial SrS:Eu,Sm films by pulsed laser deposition
Authors: Piqué A. , Mathur M. , Moses J. , Mathews S. A.
Published: July 2002

High quality epitaxial SrS:Eu,Sm thin films have been deposited on (111) and (001) BaF2, (001) Gd3Ga5O12, and (001) MgO oriented substrates by pulsed laser deposition (PLD) in vacuum and H2S partial pressures. Structural evaluation of the SrS films showed them to be highly oriented along the (001) direction when deposited on (001) BaF2 or (001) MgO substrates, with a rocking angle full width half-maximum (FWHM) of about 0.5° for the SrS (002) peak on both substrates. The φ scans of the (111) SrS peak of these films indicated a high degree of in-plane epitaxy as well, with no signs of high angle grain boundaries. For the films grown on MgO substrates, the infrared stimulated luminescence was measured as a function of deposition temperature and found to depend on the film’s degree of crystallinity. These results indicate that PLD is a viable technique for the growth of highly epitaxial photoluminescent SrS:Eu,Sm thin films.
Second harmonic generation from beta barium borate (β-BaB2O4) thin films grown by metalorganic chemical vapor deposition
Authors: Studebaker D. B. , Stauf G. T. , Baum T. H. , Marks T. J. , Zhou H. , Wong G. K.
Published: July 2002

Thin films of beta barium borate (β-BaB2O4) have been deposited by metalorganic chemical vapor deposition on fused silica, sapphire, platinum, and silicon substrates. Deposition conditions were optimized to reproducibly grow films with the c axis normal to the substrate. Second harmonic generation measurements have been made on selected films. The films grown on fused silica exhibit a maximum χeff(2) of 0.78 pm/V, and on single-crystal sapphire, 1.6 pm/V.
Electron cyclotron resonance plasma assisted sputter deposition of boron nitride films
Authors: Rao G. Mohan , Krupanidhi S. B.
Published: July 2002

Boron nitride films have been deposited on p-type silicon substrates by rf sputtering in the presence of an electron cyclotron resonance (ECR) plasma at a temperature of 450 °C. Structural phases were identified using IR spectroscopy and electrical characterization was carried out in the metal-insulator-semiconductor configuration. It was shown that the presence of ECR plasma enhanced the formation of cubic phase at substrate temperature as low as 450 °C, along with hexagonal phase. The dielectric constant was found to be 6–8 and the resistivity was about 1012 Ω cm. The capacitance-voltage characteristics indicated good electronic interface with the presence of ECR plasma, with the density of states of about 1.18×1012 eV−1 cm−2. The density of states was found to be higher by a factor of 2 in the absence of ECR plasma.
Enhanced electro-optic coefficient of nonlinear optical polymer using liquid contact poling
Authors: Tang Huajun , Taboada John M. , Cao Guohua , Li Liqiang , Chen Ray T.
Published: July 2002

The value of electro-optic coefficient r33 of an electro-optic (EO) polymer film depends on the polarization density achieved after the electric poling process. In this letter, we report a high temperature liquid contact poling method which provides a poling field as high as 250 V/μm in LD-3 EO polymer film with less surface damages. The r33 value was measured to be 18 pm/V at 633 nm which is 40°/V higher than the previous reported datum. Such a high poling field and therefore larger r33 value are not achievable through either contact poling or corona poling.
Frequency doubling in gallium-lanthanum-sulphide optical glass with microcrystals
Authors: Pruneri V. , Kazansky P. G. , Hewak D. , Wang J. , Takebe H. , Payne D. N.
Published: July 2002

Second harmonic generation in gallium-lanthanum-sulphide (Ga:La:S) and germanium sulphide + Ga:La:S glasses is investigated. It is shown that microcrystals of Ga:La:S and α phase of gallium-sulphide (α-Ga2S3), whose presence in the glass matrix is revealed by energy dispersive spectroscopy and x-ray diffraction analysis, are responsible for the frequency doubling process.
Lineshape, linewidth and spectral density of parametric x-radiation at low electron energy in diamond
Authors: Freudenberger J. , Genz H. , Morokhovskii V. V. , Richter A. , Morokhovskii V. L. , Nething U. , Zahn R. , Sellschop J. P. F.
Published: July 2002

Applying an absorber technique, the experimental shape and width of a parametric x-radiation line has been determined. The 9 keV radiation was produced by bombarding a diamond crystal of 55 μm thickness with electrons of 6.8 MeV. The variance of the spectral line distribution was found to depend on the tilt angle of the crystal and to have a magnitude of σ=51 eV. Simulations based on a Monte Carlo method exhibit that the observed variance is mainly influenced by multiple scattering of electrons passing through the crystal (≈43 eV) and the finite detector opening (≈18 eV), leaving for the intrinsic linewidth a value of the order of 1 eV. The spectral density of the line was found to be J≈10−7 photons/(electron×sr×eV).
Postgrowth hydrogen treatments of nonradiative defects in low-temperature molecular beam epitaxial Si
Authors: Chen W. M. , Buyanova I. A. , Ni W.-X. , Hansson G. V. , Monemar B.
Published: July 2002

Influence of postgrowth hydrogen treatments on nonradiative recombination centers in undoped and B-doped Si epilayers, grown by molecular beam epitaxy at low temperatures, are studied by optical detection of magnetic resonance. Hydrogen passivation of the dominant nonradiative defects in undoped Si is shown to be rather effective, whereas in the B-doped Si epilayers the effects of the hydrogen treatment of the same defects are found to be only marginal. Possible mechanisms for this are discussed. Information on two new nonradiative defects is provided.
Preparation and termination of well-defined CdTe(100) and Cd(Zn)Te(100) surfaces
Authors: Heske C. , Winkler U. , Neureiter H. , Sokolowski M. , Fink R. , Umbach E. , Jung Ch. , Bressler P. R.
Published: July 2002

Polar (100) surfaces of commercial CdTe and Cd(Zn)Te single crystals were prepared by ion sputtering and annealing at different temperatures and under Te flux, Cd flux, or in ultrahigh vacuum. Various surface reconstructions with high structural order were obtained. Soft x-ray photoemission investigations of the Cd and Te 3d surface core-level shifts were employed to derive the surface termination, revealing Cd-terminated surfaces for most preparations and various reconstructions. The results suggest that sputter/annealing cycles are suitable for the preparation of highly ordered and uniformly terminated substrates for semiconductor heterojunctions on CdTe and Cd(Zn)Te without the need of an additional buffer layer.
CH
3
detection in a low-density supersonic arcjet plasma during diamond synthesis
Authors: Loh Michael H. , Cappelli Mark A.
Published: July 2002

We report on the measurement of methyl radical (CH3) densities in a low-density supersonic arcjet plasma used in the synthesis of diamond films. Single-pass, high-sensitivity ultraviolet (UV) absorption spectroscopy has been employed to study the X(2A2″)→B(2A1′) transition of the methyl radical near 216 nm. The minimum detectable CH3 density is found to be ∼4×1013 cm−3, which corresponds to a fractional absorption of 2×10−3 at a gas temperature of 1200 K. The dependence of the measured methyl column density on pressure and CH4/H2 flow ratio has been studied. The results are used to revise our previous estimates of the reactive “sticking” coefficient for CH3, and we now find that it is of order 10−2 under conditions where we have previously documented the growth of high quality diamond films.
Experimental test of models of radio-frequency plasma sheaths
Authors: Sobolewski M. A.
Published: July 2002

The ion current and sheath impedance were measured at the radio-frequency-powered electrode of an asymmetric, capacitively coupled plasma reactor, for discharges in argon at 1.33–133 Pa. The measurements were used to test the models of the radio frequency sheath derived by Lieberman [IEEE Trans. Plasma Sci. 17, 338 (1989)] and Godyak and Sternberg [Phys. Rev. A 42, 2299 (1990)], and establish the range of pressure and sheath voltage in which they are valid.
Unusual strain relaxation in SiGe/Si heterostructures
Authors: Lyakas M. , Parnis D. , Kaplan W. D. , Zolotoyabko E. , Eizenberg M. , Demuth V. , Strunk H. P.
Published: July 2002

Si 1−x Ge x films (x=0.22) epitaxially grown by ion beam-sputter deposition on (001) Si substrates were subjected to rapid and conventional thermal annealings at different temperatures. Strain measurements carried out by means of high-resolution x-ray diffraction exhibited strongly nonmonotonous strain dependencies on the annealing time. We observed short-time and long-time relaxation modes with activation energies of 4.6 and 1.3 eV, respectively, and unexpectedly, an additional mode of strain recovery at intermediate time durations with an activation energy of 1.6 eV. This behavior was attributed to processes that involve {113} two-dimensional defects, i.e., agglomerates of interstitials, which were identified by means of transmission electron microscopy.
Photorefractive grating fixing in KNbO3 by ferroelectric domains
Authors: Cudney R. S. , Bernasconi P. , Zgonik M. , Fousek J. , Günter P.
Published: July 2002

We report observations of photorefractive grating fixing in potassium niobate at room temperature by means of ferroelectric domains. A grating is recorded while the crystal is simultaneously depoled. By repoling the crystal, the presence of a latent grating is revealed. This fixed grating diffracts light with an efficiency which increases when an electric field is subsequently applied and when it is uniformly illuminated. We explain these observations qualitatively using a previously developed model that involves charge compensation by domain walls, and a new aspect that invokes the creation of new trap sites at the ferroelectric domain walls.
The role of hydrogen in nitrogen-containing diamondlike films studied by photoelectron spectroscopy
Authors: Souto S. , Alvarez F.
Published: July 2002

The influence of H on the local structure of N-containing amorphous diamondlike films (a-CNx:H) is reported. The samples were prepared by rf sputtering of graphite in a N2, Ar, and H2 atmosphere. The chemical bonding of C and N atoms was inferred by analyzing the C 1s and N 1s electronic core-level by x-ray photoelectron spectroscopy. Hydrogen free films present N 1s peaks with a “doublet”, located at 398.2–400.5 eV. When H is introduced in the preparation chamber, the doublet evolves to a single wider band located at 399.1 eV. This new band becomes dominant when increasing H2 partial pressure, completely hiding the original structure. High H2 partial pressure interrupts the growing network formed by N and C due to the attachment of H to N and/or C. Furthermore, the experimental results suggest that the possibility of formation of the C3N4 phaselike is inhibited by the presence of hydrogen.
Laue x-ray diffraction from heterostructures: CdF2–CaF2 superlattices on Si(111)
Authors: Kyutt R. N. , Khilko A. Yu. , Sokolov N. S.
Published: July 2002

X-ray diffraction measurements have been carried out on epitaxial superlattices (SLs) in symmetric Laue geometry. High quality pseudomorphic CdF2/CaF2 SLs on Si(111) have been used as samples. Satellites, due to periodic variations of structural factor value, are revealed at ω-scanning rocking curves. A comparison of information about SL provided by diffraction in Bragg and Laue geometries is presented. The possibility of direct determination of SL structural parameters is discussed.
Grating coupled infrared modulator at normal incidence based on intersubband transitions
Authors: Duboz J. Y. , Berger V. , Laurent N. , Adam D. , Nagle J.
Published: July 2002

An infrared modulator based on intersubband transitions in GaAs/AlGaAs quantum wells and working at normal incidence has been fabricated. The coupling is provided by a diffraction grating and the modulation is observed in the nondiffracted order transmitted by the modulator. Modulation depths are increased by a factor of 3 compared to the same structure used without grating at Brewster angle. The results are in excellent agreement with our calculations of near field diffraction in an anisotropic quantum well region.
Characterization of Ti2+/Ti3+ donor level in ZnSe by isothermal capacitance transient spectroscopy
Authors: Okada H.
Published: July 2002

The thermally ionized process of the Ti2+/Ti3+ donor level in Ti-doped ZnSe crystals grown by the vertical gradient freezing method was first analyzed with detailed isothermal capacitance transient spectroscopy. The ionization enthalpy and an apparent electron capture cross section of the trap observed from the Arrhenius plot of the emission time constant were 1.058±0.005 eV and (1.03±0.15)×10−12 cm2, respectively. The temperature dependence of the capture cross section of the ionized Ti3+ state revealed a lattice relaxation energy of 0.29±0.03 eV. The real depth of the donor level was determined to be 0.77 eV below the conduction band.
Pure silicon plasma in a helicon plasma deposition system
Authors: Durandet A. , Davis C. A. , Boswell R. W.
Published: July 2002

A plasma containing only silicon atoms and ions has been obtained by electron-beam evaporation of solid silicon through a helicon rf plasma source. The density of the silicon plasma in the diffusion chamber is 3–5×1010 cm−3, and the electron temperature 12 eV. These plasma conditions correspond to a predicted deposition rate from silicon ions of 230±60 nm/min, comparable to the deposition rate of 250 nm/min obtained using the same evaporation conditions, without generating a plasma. The large contribution of silicon ions, the high deposition rate, and the absence of other species such as hydrogen or argon, leads to novel conditions for plasma assisted deposition.
Effects of lattice mismatch due to partially relaxed buffer layers in InGaAs/AlGaAs strain balanced quantum well modulators
Authors: Neilson D. T. , Wilkinson L. C. , Goodwill D. J. , Walker A. C. , Vögele B. , McElhinney M. , Pottier F. , Stanley C. R.
Published: July 2002

This letter describes the performance of electro-absorption optical modulator structures, based on strain-balanced InGaAs/AlGaAs p-i-n multiple quantum wells (MQWs). It specifically considers the influence of lattice mismatch with the graded InGaAlAs buffer arising from unrelaxed material forming the substrate upon which the p-i-n structure is grown. We have shown that to achieve a lattice constant corresponding to the average for the MQW region, it is necessary to grade the buffer up to a higher indium concentration than the average indium concentration of the MQW. We have found that mismatched samples exhibit poorer modulation on the long wavelength side of the exciton peak as a result of a greater reduction in the exciton peak with applied field, and we attribute this to screening and nonuniform fields resulting from the ionization of defects at high fields. We have also shown that the similar effect induced by going to lower barrier potentials is relatively less important.
Observation of singly ionized selenium vacancies in ZnSe grown by molecular beam epitaxy
Authors: Setzler S. D. , Moldovan M. , Yu Zhonghai , Myers T. H. , Giles N. C. , Halliburton L. E.
Published: July 2002

Electron paramagnetic resonance (EPR) has been used to investigate singly ionized selenium vacancy VSe+ centers in ZnSe epilayers grown by molecular beam epitaxy (MBE). The study included undoped and nitrogen-doped films. Spectra taken at 8 K and 9.45 GHz, as the magnetic field was rotated in the plane from [100] to [010], showed an isotropic signal at g=2.0027±0.0004 with a linewidth of 5.8 G. In the two samples where this signal was observed, estimates of concentration were approximately 1.1×1017 and 6.3×1017 cm−3. The appearance of the EPR signal correlated with an increase in the Zn/Se beam equivalent pressure ratio (during growth) in undoped films and with an increase in the nitrogen concentration in doped films. We conclude that the singly ionized selenium vacancy may be a dominant point defect in many MBE-grown ZnSe layers and that these defects may play a role in the compensation mechanisms in heavily nitrogen-doped ZnSe thin films.
Thermally oxidized AlN thin films for device insulators
Authors: Chowdhury E. A. , Kolodzey J. , Olowolafe J. O. , Qiu G. , Katulka G. , Hits D. , Dashiell M. , van der Weide D. , Swann C. P. , Unruh K. M.
Published: July 2002

The structural, optical, and electronic properties of an insulating material prepared by the thermal oxidation of AlN thin films on Si have been studied by a number of different experimental techniques. The thermal oxidation at 1100 °C of reactively sputtered AlN films on Si wafers was found to result in the formation of an oxide with a relative Al to O concentration near Al2O3 with small amounts of incorporated N. The structure of the AlO:N oxide could be varied between amorphous and polycrystalline, depending on the preparation conditions, and the oxide surface was found to be approximately three time smoother than the as-sputtered AlN films. Metal–oxide–silicon capacitors had an oxide charge density of about 1011 cm−2, capacitance–voltage characteristics similar to pure SiO2, and a dielectric constant of 12.4. Infrared measurements yielded a refractive index of 3.9. These results indicate that thermally oxidized AlN films show promise as insulating structures for many integrated circuit applications, particularly for the case of III–V and group III–nitride based semiconductors.
Polarimetry of thin metal transmission gratings in the resonance region and its impact on the response of metal-semiconductor-metal photodetectors
Authors: Chen Erli , Chou Stephen Y.
Published: July 2002

The resonance behavior of metal transmission gratings and its impact on the response of metal-semiconductor-metal (MSM) photodetectors have been studied experimentally and theoretically. The metal gratings, with finger spacings in the subwavelength region of the visible light, were fabricated using e-beam lithography and lift-off. Strong resonances have been observed only in the S polarization. As a result, the light transmitted through a grating is primarily S polarized if the grating’s finger spacing is less than one-third of the wavelength of the incident light, but P polarized otherwise. Similar phenomenon has been observed in the response of MSM photodetectors since the fingers (electrodes) of an MSM photodetector basically form a grating. Theoretical simulations employing the rigorous modal-expansion theory fairly predict the observed phenomenon.
Many-body effects on modulation-doped InAs/GaAs quantum dots
Authors: Lee Joo In , Lee Hyung Gyoo , Shin Eun-joo , Yu Sungkyu , Kim Dongho , Ihm Gukhyung
Published: July 2002

The excitation intensity dependent photoluminescence spectra of various modulation-doped InAs/GaAs quantum dots exhibit the band filling and band-gap renormalization. From the time-resolved photoluminescence spectra, in addition to the interaction of the carriers in quantum dots with the remote ionized impurities in a GaAs barrier, the screening due to the two-dimensional charges is found to mainly affect the carrier lifetime in the modulation-doped quantum dots.
Polarization-dependent, laser-induced anisotropic photocrystallization of some amorphous chalcogenide films
Authors: Lyubin V. , Klebanov M. , Mitkova M. , Petkova T.
Published: July 2002

We report the observation of the influence of light polarization on the photocrystallization process and on the properties of crystallized films. Irradiation with linearly polarized He–Ne laser light results in the preparation of polycrystalline films with strong optical anisotropy (dichroism), the sign of which is determined by the direction of the electrical vector of light. The results obtained allow one to select from previously proposed mechanisms of photocrystallization. Large values of photoinduced dichroism in the films studied can be interesting for different applications of photoinduced anisotropy.
Rapid thermal annealing of spin-coated phosphoric acid films for shallow junction formation
Authors: Sivoththaman S. , Laureys W. , Nijs J. , Mertens R.
Published: July 2002

Rapid thermal annealing (RTA) of spin-coated phosphoric acid (H3PO4) films on silicon substrates has been studied for the formation of shallow junctions. The junctions are characterized by spreading resistance profiling. Device quality, shallow (<0.2 μm), n+p junctions are formed by the resulting phosphorous diffusion with the junction depth and surface concentration depending on the RTA conditions. The films have been studied by Fourier transform infrared spectroscopy after various RTA treatments. The presence of P=O bonds in the films becomes evident after the RTA treatment at elevated temperatures (>750 °C), below which absorption bands originating from water species are noted. More than 15% efficient, shallow emitter, large-area (10 cm×10 cm) n+pp+ silicon solar cells are fabricated with a short-time processing using this rapid thermal processing technique.
Deep level capture barrier in molecular beam epitaxial grown AlAsySb1−y measured by isothermal capacitance transient spectroscopy
Authors: Johnstone D. K. , Yeo Y. K. , Hengehold R. L. , Turner G. W.
Published: July 2002

Improved isothermal capacitance transient spectroscopy (ICTS), which measures the entire capacitance transient as a function of time and temperature in a single temperature scan, has been implemented in a deep level trap analysis extending the characterization to include capture barrier measurement. This method eliminates inaccuracies introduced by narrow pulse widths that are difficult to reproduce accurately, providing capture barrier information more accurately and easily in addition to the usual deep level characteristics. A method of establishing ICTS experimental conditions and a method of analyzing the resulting data are described and applied to the investigation of deep levels in Te-doped AlAs0.07Sb0.93. The sample shows a single DX center trap having a deep level energy of 278 meV, a high temperature capture cross section of 1.3×10−12 cm2, and a capture barrier energy of 137 meV, clearly demonstrating the superior method of measuring a capture barrier.
Tailored superlattices containing distinct oxide and oxycarbonate blocks grown by pulsed laser deposition
Authors: Prellier W. , Mercey B. , Lecoeur Ph. , Hamet J. F. , Raveau B.
Published: July 2002

The synthesis of copper oxycarbonate superlattices comprised of two structural types that are observed in high Tc superconductors was achieved using the pulsed laser deposition (PLD) technique. These artificially layered materials consist of specific numbers of alternately stacked infinite layer SrCuO2 and oxycarbonate Ba2−xCaxCuO2CO3 blocks, and were grown on (110) NdGaO3 using two targets. From x-ray diffraction, it was found that several unit cells of SrCuO2 could be inserted between the layers of Ba2−xCaxCuO2CO3. These results demonstrate that a large series of new structures combining oxycarbonate with oxide components can be obtained using a multitarget PLD system.
Room temperature differential negative resistance in an Al/Zn0.61Cd0.39Se/n+-InP device
Authors: Shum Kai , Zhou J. , Zhang W. , Zeng L. , Tamargo M. C.
Published: July 2002

Experimental data are presented on the current–voltage characteristics of an Al/ZnCdSe/n+-InP device from 77 to 300 K. A strong negative differential resistance under forward bias was observed for temperature higher than 145 K. The peak-to-valley current ratio was measured to be 30 at room temperature. In the reverse bias region the device behaves as a leaky Schottky diode.
Photoconductor gain mechanisms in GaN ultraviolet detectors
Authors: Muñoz E. , Monroy E. , Garrido J. A. , Izpura I. , Sánchez F. J. , Sánchez-Garcı́a M. A. , Calleja E. , Beaumont B. , Gibart P.
Published: July 2002

GaN photoconductive detectors have been fabricated on sapphire substrates by metal organic vapor phase epitaxy and gas-source molecular beam epitaxy on Si (111) substrates. The photodetectors showed high photoconductor gains, a very nonlinear response with illuminating power, and an intrinsic nonexponential photoconductance recovery process. A novel photoconductor gain mechanism is proposed to explain such results, based on a modulation of the conductive volume of the layer.
Improved laser modulation response by frequency modulation to amplitude modulation conversion in transmission through a fiber grating
Authors: McAdams Matt , Peral Eva , Provenzano Dan , Marshall W. K. , Yariv Amnon
Published: July 2002

We have demonstrated that transmission through a fiber grating can increase the system response of a directly modulated semiconductor laser by over 7 dB at all modulation frequencies up to 25 GHz. When combined with dispersive optical fiber, the grating produced a system response that was larger, flatter, and had a larger bandwidth, providing a frequency-domain demonstration of dispersion compensation through an unchirped grating. The effect can be understood as frequency modulation to amplitude modulation conversion by the grating, and was accurately predicted by a Fourier domain analysis of the laser signal and grating.
Direct observation of the amphoteric behavior of Ge in InP modified by P co-implantation
Authors: Yu Kin Man , Ridgway M. C.
Published: July 2002

We have investigated the preferred substitution of Ge in InP by altering the local stoichiometry of the InP substrate. By co-implanting P with Ge to create a group V-rich environment, we directly observed an enhancement of the Ge substituting the In sublattice. A corresponding increase in the n-type conductivity by as much as three times was also observed in the Ge and P co-implanted sample. However, due to the altered local stoichiometry, the Ge solubility in InP was reduced by a factor of 2. The residual crystalline damage in the P co-implanted InP after annealing was also decreased due to the compensation of the nonstoichiometry related damage by the excess P in the middle of the implanted region.
Surface tensions and anchoring transitions of nematic liquid crystals on gradually oxidized substrates
Authors: Hubert Pascal , Galerne Yves
Published: July 2002

Intermediate anchorings of nematic liquid crystals onto substrates are now intensively studied essentially because of their potential display applications. Here, we use the active oxygen gas arising from a plasma reactor to realize progressive chemical modifications of glass substrates covered with silane. In this manner, the dispersive and nondispersive surface tensions of the substrate are gradually modified involving a continuous change in the differential wetting properties of the substrate with both parts of the liquid crystal molecules, and in the anchoring energy. Intermediate anchorings with tilted angles are thus obtained in the vicinity of an anchoring transition from the pseudohomeotropic to the planar alignment, where symmetry is broken.
Light-hole resonant tunneling through a tensile-strained GaAsP quantum well
Authors: Lampin J. F. , Mollot F.
Published: July 2002

We report the demonstration of resonant tunneling of holes through an AlAs/GaAs0.7P0.3 double-barrier heterostructure. The tensile strain in the quantum well is large enough to reverse the order of the light- and heavy-hole levels (the first light-hole level is the ground state). The I(V) characteristic of this structure is measured and compared to a standard AlAs/GaAs unstrained one. As expected, the peak current density of the first light-hole resonance and its peak-to-valley current ratio are enhanced (they reach 28 A/cm2 and 3.4:1 at 15 K). Negative differential resistance is observed up to 250 K.
Effects of O2 on the {113} defect formation in Si observed by in situ ultrahigh vacuum transmission electron microscopy
Authors: Koto K. , Takeda S. , Ichihashi T. , Iijima S.
Published: July 2002

The nucleation and growth of the {113} defects in floating zone Si have been observed in situ in a ultrahigh vacuum (UHV) transmission electron microscopy. After the surfaces of a Si foil are controlled, intense irradiation of 200 keV electrons proceeds at 400 or 500 °C in the base pressure of 1.0×10−7 Pa. We have found that the defect development changes prominently after O2 is injected in a specimen chamber. While O2 flows, the pressure is kept at about 5.0×10−5 Pa. This result has brought direct evidence for the effect of O2 on formation of the defects, since no other impurities are involved in the UHV environment.
Direct observation of stacking fault tetrahedra in ZnSe/GaAs(001) pseudomorphic epilayers by weak beam dark-field transmission electron microscopy
Authors: Fung K. K. , Wang N. , Sou I. K.
Published: July 2002

Using weak beam dark-field transmission electron microscopy, we have identified, by reference to stacking fault trapezoids, an additional crystal defect, a stacking fault tetrahedron, at the interface of ZnSe/GaAs(001) epilayers. Unlike the other stacking faults which are basically of uniform size, the size of stacking fault tetrahedra can vary by a few times, with a typical value of less than 10 nm. The stacking fault tetrahedron is a closed defect and does not extend very far from the interface. The density of the stacking fault tetrahedra is at least as high as that of the dominant stacking faults trapezoids.
Measurements of quasi-Fermi energies by scanning electron beam
Authors: Mil’shtein S.
Published: July 2002

Scanning electron microscopy dark voltage contrast (DVC) was used to define quasi-Fermi energies in a silicon p-n junction either under illumination or forward bias conditions. Quantitative DVC measurements have proven to be a precise method of locating quasi-Fermi levels (QFLs) in any operating device. By simultaneously using light and electron beams we have obtained accurate measurements of the position of QFLs by DVC in an illuminated p-n junction.
Luminescence study of band gap conversion in the SiGe material
Authors: Chen H. , Xie X. G. , Cheng W. Q. , Huang Q. , Zhou J. M.
Published: July 2002

We report a photoluminescence study of SiGe quantum dots formed by one, two, and five periods of Si[8 monolayer (ML)]/Ge(4 ML) superlattices. The peak of photoluminescence from one Ge layer is at 0.95 eV, but the one from two and five periods of superlattices jump to about 1.2 eV.
Sealing of AlAs against wet oxidation and its use in the fabrication of vertical-cavity surface-emitting lasers
Authors: Lim Dae Ho , Yang Gye Mo , Kim Jong-Hee , Lim Kee Young , Lee Hyung Jae
Published: July 2002

We have studied the process of sealing an exposed AlAs to prevent further wet oxidation. A critical step in this sealing process consists of the first wet oxidation for a short time at 408 °C in a steam environment of a previously room-ambient exposed AlAs surface. During this brief wet oxidation, a dense oxide surface barrier with a thickness of 1.1 μm is formed, which further blocks diffusing oxygen species during the second wet oxidation. The effectiveness of the sealing is demonstrated through its use as a mask against wet oxidation in the fabrication of oxide-confined vertical-cavity surface-emitting lasers.
Large infrared modulation depth obtained in the normal incidence reflection on a grating coupled with intersubband transitions
Authors: Duboz J. Y. , Berger V. , Laurent N. , Adam D. , Nagle J.
Published: July 2002

An infrared modulator based on intersubband transitions in GaAs/AlGaAs quantum wells, working at normal incidence, has been fabricated. The electro-optic modulation arises from electron transfer between coupled wells by applying an electric field to the device. The coupling between the light and quantum wells is provided by a metal diffraction grating. Modulation depths larger than 60% are observed at a 8.8 μm wavelength in the nondiffracted order reflected by the modulator. The performance measured at 80 K is limited by an incomplete electron transfer between wells.
Al–Al pair in silicon: Evidence for long-range hydrogen-enhanced aluminum migration
Authors: Abdullin Kh. A. , Mukashev B. N. , Gorelkinskii Yu. V.
Published: July 2002

In this letter, we present results of electron paramagnetic resonance studies of new defects (labeled Si-AA15 and Si-AA16) incorporated aluminum atoms. The AA15 defect is created in hydrogen-doped silicon by low temperature (∼80 K) irradiation, and an Al27 (100% abundant, I=5/2) hyperfine interaction reveals the presence of two nearly equivalent aluminum atoms. Therefore, the appearance of the AA15 defect containing Al–Al pair is the first observation of hydrogen-enhanced long-range migration (at least of ∼100 lattice constants) of aluminum atom at low temperatures (<200 K). The AA15 center anneals out at room temperature. The AA16 center containing only one Al atom disappears at 200 K. Tentative models of AA15 and AA16 defects as an Al–Al 〈110〉-split interstitial and Al–H interstitial pair correspondingly are proposed.
Continuous control of the superconducting transition temperature from overdoped to underdoped regimes in tetragonal Tl2Ba2CuO6+δ thin films
Authors: Ren Z. F. , Wang J. H. , Miller D. J.
Published: July 2002

Epitaxial superconducting thin films Tl2Ba2CuO6+δ (Tl-2201) with a continuous range of doping levels have been synthesized. The films were made by rf magnetron sputtering and two-step postdeposition annealing, and their doping levels were controlled by varying the oxygen content through annealing in flowing argon. By annealing in flowing argon, the as-grown Tl-2201 thin films were changed continuously from the initially overdoped state, through the optimally doped state and then to the underdoped state. The normal state resistivity versus temperature curves of all the underdoped Tl-2201 thin films are convex, whereas those of the overdoped Tl-2201 thin films are all concave. Transmission electron microscopy bright-field images and selected area diffraction patterns of the 58 K underdoped Tl-2201 thin film showed neither twinning bands nor spot splitting associated with an orthorhombic crystal lattice. Therefore, it is concluded that underdoped Tl-2201 thin films are also tetragonal just like all the overdoped and optimally doped Tl-2201 thin films.
Electric-field-independent band gap superpositioning at 1.3 μm in an InGaAs–InAlAs strained-layer superlattice
Authors: Fritz I. J. , Hafich M. J. , Casalnuovo S. A.
Published: July 2002

We report on the electric-field dependent band-gap energy and near-gap absorption coefficient of a specially designed strained-layer superlattice (SLS) employing tensile strained quantum wells and having a band-gap wavelength near 1.3 μm. The SLS was grown by molecular-beam epitaxy on an InP substrate and consists of In0.43Ga0.57As wells (4.5-nm-thick) and In0.6Al0.4As barriers (6.75-nm-thick). For applied fields from zero up to at least 2.5×105 V/cm, the band-edge absorption exhibits a single peak, which we attribute to a field-independent superpositioning of the heavy- and light-hole ground states. This result agrees with tunneling resonance calculations, which predict these hole states to have the same zero-field energy and to undergo nearly identical Stark shifts. Absorption–coefficient changes of up to 104 cm−1 were readily achieved with applied biases under 15 V, suggesting potential applications to optical modulator devices.
Microwave plasma chemical vapor deposited diamond tips for scanning tunneling microscopy
Authors: Albin Sacharia , Zheng Jianli , Cooper John B. , Fu Weihai , Lavarias Arnel C.
Published: July 2002

Diamond microparticles were grown on etched tungsten wires using a microwave plasma-assisted chemical vapor deposition process. The apexes on cubo-octahedral particles bound by {100} and {111} facets were effectively used as tunneling tips for scanning tunneling microscopy. The atomically resolved surface image of highly oriented pyrolytic graphite was acquired. Tunneling characteristics revealed a higher electron emission from the diamond tips than that from the platinum–iridium tips. The same diamond tips were used to produce surface indentation and its image.
Highly-sensitive passive integrated optical spiral-shaped waveguide refractometer
Authors: Veldhuis G. J. , Lambeck P. V.
Published: July 2002

A passive integrated optical waveguide refractometer based on bendloss changes in a spiral-shaped channel waveguide is proposed and fabricated in Si3N4/SiO2 technology. The experimentally determined performance and the theoretical predictions, based on a simple model for so-called “whispering gallery modes,” agree very well. The minimum detectable refractive index change was measured to be Δn=1.3×10−5.
Ellipsometric monitoring of an oriented diamond nucleation process in bias-enhanced chemical vapor deposition
Authors: Hayashi Yasuaki , Li Xi , Nishino Shigehiro
Published: July 2002

The process of bias-enhanced nucleation of diamond has been monitored and analyzed by ellipsometry. The time evolution of optically equivalent thickness has been obtained and it has been confirmed with the help of x-ray photoelectron spectroscopy that four stages exist: they are carbonization, incubation, nuclei growth, and film growth. It has been considered, during the incubation stage, that carbonization and etching proceed simultaneously and that high density and oriented diamond nuclei are generated by the accelerated elimination of weak C–C bonds and the faster formation of sp3 C–C bonds in a substrate.
Optically induced current bistability in coupled quantum wells
Authors: Ramamurthi Anand V. , Srinivas Vivek , Hegde G. M.
Published: July 2002

We report the observation of bistability in the photocurrent and photoluminescence spectra of GaAs quantum well heterostructures. The excitation energy is nonresonant and above the band-gap energy of the barrier. A self-consistent calculation taking into account the rate equations governing the charge distribution in the wells is shown to result in the observed bistability which leads to a new class of optically bistable devices.
Microdefects in Al2O3 films and interfaces revealed by positron lifetime spectroscopy
Authors: Xu Jun , Somieski B. , Hulett L. D. , Pint B. A. , Tortorelli P. F. , Suzuki R. , Ohdaira T.
Published: July 2002

We have studied microdefects and interfaces of Al2O3 films on iron and nickel aluminide substrates using variable-energy positron lifetime spectroscopy. Di-vacancies, vacancy clusters, and microvoids were observed in the oxide scales. Their sizes and distributions were determined by the nature of the process used to synthesize the alumina film, and influenced by the composition of the alloy substrates. For oxide–iron aluminide interfaces, positron lifetimes are longer than those for the alumina layer itself, suggesting a greater defect concentration at such sites.