bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability of visible luminescence from porous silicon
Authors: Batstone J. L. , Tischler M. A. , Collins R. T.
Published: July 2002

The stability of the luminescence from porous Si has been improved by rapid thermal oxidation. As-prepared and oxidized samples have been compared by cathodoluminescence and photoluminescence. Electron beam excitation resulted in rapid decay of the porous Si emission from as-prepared samples. Photoluminescence measurements from as-prepared samples in oxygen showed a similar degradation. In contrast, the rapid thermal oxidized samples showed a dramatic improvement in stability under either electron beam or photoexcitation.
Voltage noise properties of Nb-(fine Nb wires)-NbN thin film short weak links
Authors: Hatle M. , Kondo T. , Hamasaki K.
Published: July 2002

We have fabricated superconductive Nb-(fine Nb wires)-NbN short weak links. We find that their quasiparticle characteristics can be well explained using the theory of T. M. Klapwijk, G. E. Blonder, and M. Tinkham [Physica B and C 109 & 110B 1657 (1982)] based on the Andreev reflection phenomenon at two independent normal metal-superconductor interfaces for the case of a negligible effective barrier potential. For such devices, there is found no measurable excess noise associated with the Andreev reflection itself and device voltage noise clearly exhibits both thermal and shot noise limits. Although the device structure is fundamentally different, in the whole studied range of bias voltages, the voltage noise properties of our short weak links are found to be qualitatively comparable to those of small-area tunnel junctions.
Excess currents and voltages in superconducting junctions
Authors: Kleinsasser A. W.
Published: July 2002

Current-voltage characteristics which do not asymptotically approach those in the normal state at large voltages are an important feature of many superconducting junctions. Such devices are said to exhibit excess or deficit currents or voltages. Simple expressions for such currents are derived and their implications are discussed, pointing out the importance of studies of temperature dependence in such cases.
High temperature operation of InGaAsP/InP heterostructure lasers and integrated back facet monitors fabricated by chemically assisted ion beam etching
Authors: Dzioba Steven , Jatar S. , Herak T. V. , Cook John P. D. , Marks J. , Jones T. , Shepherd F. R.
Published: July 2002

Chemically assisted ion beam etching (CAIBE) has been used to etch InGaAsP/InP ridge laser facets. Smooth, vertical facets 4 μm deep have been etched using Ar/Cl2 CAIBE with a beam voltage of 440 V and a beam current density of 0.08 mA/cm2. Room temperature and high temperature (85 °C) L-I characteristics and device performance have been evaluated, as well as the performance of integrated back facet monitors. Output powers of 9.5 mW from the laser and a monitor current of 3.75 mA have been obtained.
Migration enhanced epitaxy growth of GaAs on Si with (GaAs)1−x (Si2)xGaAs strained layer superlattice buffer layers
Authors: Rao T. Sudersena , Nozawa K. , Horikoshi Y.
Published: July 2002

(GaAs)1−x(Si2)x/GaAs strained-layer superlattices (SLS) have been used as buffer layers to reduce the dislocation density in GaAs grown on Si by migration enhanced epitaxy (MEE). Double-crystal x-ray diffractograms of GaAs on Si grown using MEE with 3 packets of 5 period (GaAs)1−x(Si2)x/GaAs SLS buffer layers, exhibited a GaAs (004) peak full width at half maximum value of 150 arcsecs. The cross-sectional transmission electron microscopy investigations revealed extensive threading dislocation bending at each interface of (GaAs)1−x(Si2)x and GaAs, making the SLS highly efficient. The observed highly effective dislocation bending, we believe is due to a combined effect of built-in strain in the SLS and the relatively high elastic stiffness constant of (GaAs)1−x(Si2)x alloys. Plan-view transmission electron microscopy studies indicated dislocation densities <5×105 cm−2 at a distance of 0.2 μm from the surface of GaAs on Si.
Reduction of secondary defect density by C and B implants in GexSi1−x layers formed by high dose Ge implantation in (100) Si
Authors: Lombardo S. , Priolo F. , Campisano S. U. , Lagomarsino S.
Published: July 2002

(100) oriented Si substrates were implanted with 70 keV Ge ions at a dose of 3×1016 cm−2, corresponding to a Ge peak concentration of ≊15 at. %. Annealing at 1100 °C for 10 s forms a large density of secondary defects (dislocation loops). A 30 keV C implant at a dose of 3×1015 cm−2 on the Ge implanted samples suppresses the formation of secondary defects after the annealing. In GexSi1−x layers implanted with 30 keV B at a dose of 2.5×1015 cm−2, a dense dislocation network after annealing is present. Therefore C is much more effective in the suppression of secondary defects than B. In addition, it is shown that good epitaxial quality can be obtained in the heavily B doped GexSi1−x layers amorphizing a 2 μm thick surface layer by high energy Si implants prior to annealing.
Direct measurement of size fluctuation in reverse-mesa etched quantum wire structures by the atomic force microscope
Authors: Notomi M. , Nakao M. , Tamamura T.
Published: July 2002

By means of atomic force microscopy, we have directly measured, for the first time, size fluctuations in InGaAs/InP quantum wire structures fabricated by e-beam lithography and reverse-mesa wet etching. Based on a statistical analysis of the measured data, we discuss the standard deviation of the lateral size of wire structures. The results clearly indicate that the size fluctuations in the wire patterns are predominantly small compared to those in the original mask patterns. This is attributed to the formation of crystallographic facet during the reverse-mesa wet etching.
Effect of electron heating on electron capture cross section in very small metal-oxide-semiconductor transistors
Authors: Shi Z. M. , Miéville J.-P. , Dutoit M.
Published: July 2002

The effect of electron heating on random telegraph signals due to oxide traps in deep-submicron n-channel MOSFETs is shown. A simple theoretical model gives a good description of the observed results. The mean capture time depends on the local velocity and temperature of channel electrons near the trap. The difference between the forward and reverse mode (source and drain exchanged) provides an estimate of the trap location along the channel.
Inhibition of surface-related electrical breakdown of long p+-i-n+ silicon structures
Authors: Peterkin F. E. , Williams P. F. , Hankla B. J. , Buresh L. L. , Woodward S. A.
Published: July 2002

Semiconductors such as silicon and GaAs appear attractive for use in high voltage devices because of their high bulk dielectric strength. Typically, however, such devices fail at a voltage well below that expected due to a poorly understood, surface-related breakdown process. In this letter we present empirical results which show that such breakdown of long silicon p+-i-n+ devices can be inhibited by the application of weak visible or near-infrared illumination. These results suggest a technique for avoiding surface flashover in practical high voltage devices, and provide information about the physical mechanisms responsible for initiating flashover.
In situ preparation of YBa2Cu3Oy thin films without post-oxygenation cooling using opposed-targets magnetron sputtering
Authors: Teshima Hidekazu , Shimada Haruo , Imafuku Muneyuki
Published: July 2002

Superconducting YBa2Cu3Oy thin films have been successfully prepared in situ by the opposed-targets magnetron sputtering method without introducing oxygen into the sputtering chamber after deposition. Although the films were cooled down under 1 atm of nitrogen atmosphere after deposition, they showed zero resistance Tc as high as 88 K with a relatively sharp transition width ΔTc (90%–10%) of 2 K. This suggests that the growing films contain enough oxygen to show superconductivity, in other words, the possibility of forming the orthorhombic structure during growth. Further, the films showed lower Tc at 83.5 K when they were cooled down under oxygen. This unexpected result can be explained by the overdoping of holes in the Cu-O2 planes.
Terracing and step bunching in interfaces of molecular beam epitaxy-grown (Al)GaAs multilayers
Authors: Albrektsen O. , Meier H. P. , Arent D. J. , Salemink H. W. M.
Published: July 2002

The growth terraces in molecular beam epitaxy-grown AlxGa1−xAs multilayers are observed on the ultrahigh vacuum cleaved (110) cross-sectional plane using scanning tunneling microscopy. Under regular growth conditions on 2° off oriented vicinal surfaces, we observe step bunching of 2–8 atomic layers and a corresponding extension of the terrace length instead of monolayer steps. These results demonstrate that the roughness of quantum confinement layers can be studied down to the atomic scale in a direct way.
Directional coupler electro-optic modulator in AlGaAs/GaAs with low voltage-length product
Authors: Khan M. Nisa , Yang Wei , Gopinath Anand
Published: July 2002

An AlGaAs/GaAs ridge directional coupler electro-optic modulator with a voltage-length (VL) product of only 7.0 V mm (L=3.5 mm, V=2 V) is reported. The low VL product has resulted from the efficient electrode configuration as well as the large overlap between the optical and electrical fields in the waveguides. Propagation loss of 3.4 dB/cm and the measured I-V characteristics confirm that the contributions from the Franz–Keldysh, charge-carrier, and thermal effects are small. To our knowledge, this is the lowest VL product ever reported for an electro-optic directional coupler modulator utilizing the Pockels effect. An extinction ratio of 13 dB was measured for the modulator at 0.83 μm wavelength.
Strain and defect generation during interdiffusion of GaAs into Al0.5In0.5P
Authors: Thornton R. L. , Ponce F. A. , Anderson G. B. , Endicott F. J.
Published: July 2002

We present results on the analysis of the interdiffusion process of a discrete GaAs layer into an Al0.5In0.5P half space using Si doping as an agent for enhanced layer interdiffusion. We have observed enhanced interdiffusion on both column III and column V sites, with the column III interdiffusion coefficient exceeding the column V interdiffusion coefficient by two orders of magnitude. Due to the disparity between these diffusion coefficients, substantial defect producing strain is introduced by the interdiffusion process. We have shown that by modeling the resulting strain profiles and applying a generalization of a critical thickness analysis, the instability of such interdiffused structures can be understood.
Simultaneous multiple wavelength operation of a multistripe array grating integrated cavity laser
Authors: Poguntke K. R. , Soole J. B. D. , Scherer A. , LeBlanc H. P. , Caneau C. , Bhat R. , Koza M. A.
Published: July 2002

Simultaneous multiple-wavelength operation of a multistripe array grating integrated cavity laser is reported. We demonstrate simultaneous lasing from a single output port at 2, 3, and 4 discrete wavelengths, each independently selected from a comb of 9 wavelengths set at ∼2 nm intervals, from 1512 to 1528 nm. Signal cross talk is examined for the case of two-wavelength emission and found to be independent of the wavelength separation. The emission wavelengths were linearly spaced to within ±0.02 nm, while the comb’s central wavelength deviated by less than 2 nm from its design value. This is the highest wavelength linearity and accuracy so far recorded for a monolithic multiwavelength source.
Γ-X intervalley transfer in single AlAs barriers under hydrostatic pressure
Authors: Carbonneau Y. , Beerens J. , Cury L. A. , Liu H. C. , Buchanan M.
Published: July 2002

We have investigated the contribution of Γ-X intervalley transfer to the tunneling current in single AlAs barrier heterostructures grown on a GaAs substrate by measuring I-V characteristics at low temperature and under hydrostatic pressure up to 9 kbar. The application of hydrostatic pressure affects the contribution of the Γ-X transfer process to the total tunneling current at a given bias voltage. Experimental results are compared with current-voltage characteristics calculated with a model taking into account the Γ-X transfer at heterointerfaces. Only transfer processes involving the longitudinal X valley in AlAs are considered in the calculations. Very good agreement is found for low bias conditions at all pressures.
Enhancement of photoluminescence from DX centers in AlGaAs heterostructures
Authors: Livescu G. , Asom M. T. , Luther L. , Zilko J. L , Trapp K. D. C. , Finkman E.
Published: July 2002

Selectively excited room-temperature photoluminescence spectra of InGaAs-GaAs-AlGaAs quantum well heterostructures reveal a broad line at midgap energies originating in the Si doped AlGaAs. When carriers are photoexcited directly in the wells, this line is dramatically enhanced at the expense of the quantum well line, indicating carriers escape from the wells. The broad emission and its enhancement can be explained in terms of recombination between electrons trapped at DX centers in AlGaAs and holes transferred into AlGaAs from the neighboring wells. We also observe the broad emission by direct over-the-gap photoexcitation of very highly doped Si:AlGaAs. The doping dependence consistently correlates this line to DX centers.
Broadband optical parametric amplification in LiB3O5
Authors: Mao Hongwei , Wu Baichang , Chen Chuangtin , Zhang Daiqin , Wang Peilin
Published: July 2002

The study on broadband infrared parametric amplification in a lithium triborate (LBO) crystal is reported. By using optical parametric amplification in LBO, the picosecond (ps) infrared (IR) laser pulse with a bandwidth of 165 nm has been generated. The energy of broadband laser pulse train is 9.4 μJ, and the pulse duration is 20 ps.
Novel cross-correlation technique for characterization of subpicosecond pulses from mode-locked semiconductor lasers
Authors: Choi Kyoo Nam , Taylor Henry F.
Published: July 2002

A diagnostic technique for repetitively pulsed lasers which is simple in application but provides subpicosecond temporal resolution is described. The method uses cross-correlation in a scanned Michelson interferometer, the electrical output of which is produced by a low-speed photodiode and a lock-in amplifier. A measurement on an actively mode-locked semiconductor laser emitting near a wavelength of 0.845 μm indicated a pulse width of 258±44 fs and a phase memory time for pulses in a train of 1.47 ns.
Influence of the stoichiometry in the site distribution of Cr3+ ions in LiNbO3
Authors: Macalik B. , Bausá L. E. , García Solé J. , Jaque F.
Published: July 2002

In this letter the influence of the stoichiometry ([Li]/[Nb] ratio) on the R absorption lines of Cr3+ in LiNbO3 has been investigated. It is shown that Cr3+ ions occupy the Li+ and Nb5+ lattice sites but their relative distribution is modified by changing the melt composition ([Li]/[Nb] ratio). It has been also concluded that the defects associated to the nonstoichiometry (antisites and Nb vacancies) of the crystal host are responsible for the incorporation of Cr3+ ions into the LiNbO3 matrix.
Structural and electrical properties of BaTiO3 thin films grown on p-InSb substrate by metalorganic chemical vapor deposition at low temperature
Authors: Kim T. W. , Jung M. , Kim H. J. , Yoon Y. S. , Kang W. N. , Yom S. S.
Published: July 2002

Metalorganic chemical vapor deposition of BaTiO3 on p-InSb (111) using Ba(tmhd)2, Ti(OC3H7)4, and N2O via pyrolysis at low (∼300 °C) temperature was performed to produce high-quality BaTiO3/p-InSb (111) interfaces and BaTiO3 insulator gates with dielectric constants of high magnitude. Raman spectroscopy showed the optical phonon modes of a BaTiO3 thin film. The stoichiometry of the BaTiO3 film was investigated by Auger electron spectroscopy. Transmission electron microscopy showed that the BaTiO3 films had local epitaxial formations. Room-temperature capacitance-voltage measurements clearly revealed metal-insulator-semiconductor behavior for the samples with the BaTiO3 insulator gates, and the interface state densities at the BaTiO3/p-InSb interfaces were approximately high 1011 eV−1 cm−2 at the middle of the InSb energy gap. The dielectric constant determined from the capacitance-voltage measurements was as large as 743. These results indicate that the BaTiO3 layers grown at low temperature can be used for both high-density dynamic-memory and high-speed applications.
Photoluminescence, Raman scattering, and infrared absorption studies of porous silicon
Authors: Seo Y. H. , Lee H.-J. , Jeon H. I. , Oh D. H. , Nahm K. S. , Lee Y. H. , Suh E.-K. , Lee H. J. , Kwang Y. G.
Published: July 2002

Porous silicon layers prepared by anodic dissolutions of silicon wafers in aqueous HF solutions reveal either crystalline phase or intermediate phase between microcrystalline and amorphous phases, depending on the anodization conditions. The configurations of hydrogen and oxygen atoms near the surface of microstructures are directly related to the light emitting characteristics of porous silicon layers. We observed that oxidation leads to the shifts of SiHn stretching modes to higher frequencies and enhanced photoluminescence intensity, which can be correlated with a charge transfer within O—Si—H bonds. We also observed that chemical treatments in trichloroethylene have similar effects as thermal oxidation.
Determination of atomic density profiles in synthetic multilayers by anomalous x-ray diffraction
Authors: Tang Zizhou , Xu Zengli , Kevan S. D. , Novet Tom , Johnson David C.
Published: July 2002

We report a simple and nondestructive method to determine directly the spatial profiles of the constituent elements in a synthetic multilayered material with a resolution of 10–20 Å. This has been accomplished by measuring the x-ray diffraction Bragg peak intensities over a large range of energies, and interpreting these data using a dynamical theory to deduce the first few Fourier coefficients of the relevant spatial profiles. We present initial results for Ti-Si multilayer samples grown by thermal deposition. These results demonstrate extensive interdiffusion of the silicon into the titanium layers, even without annealing.
Precipitates in YBa2Cu3O7−δ thin films annealed at low oxygen partial pressure
Authors: Hou S. Y. , Phillips Julia M. , Werder D. J. , Tiefel T. H. , Fleming R. M. , Marshall J. H. , Siegal M. P.
Published: July 2002

We have studied the precipitates in YBa2Cu3O7−δ(YBCO) thin films grown by the BaF2 process in pO2=4 Torr and 700 °C. While stoichiometric films result in BaCuO2 surface precipitates, we have found Y2Cu2O5 precipitates embedded in the matrix of the same film. Off stoichiometric films with Ba/Y<1.5 have a precipitate-free surface but with higher abundance of Y2Cu2O5 in the film matrix. The estimated densities of the two precipitates favor a stoichiometric YBCO film matrix. This behavior is not explainable in terms of phase equilibria and is attributed to kinetic effects. The electrical properties of the films degrade as the Ba/Y ratio deviates from 2.00.
In situ Cr gettering in polycrystalline silicon sheets obtained by edge-defined film-fed growth
Authors: Pivac B. , Borghesi A. , Sassella A. , Kalejs J. , Bathey B. R.
Published: July 2002

Gettering of Cr during the growth of silicon sheets from a Cr-doped melt is observed when the solid/liquid interface region is exposed to CO or CO2 gases. The gettering occurs within a region about 1-μm wide at the surface of the crystal, where a large accumulation of carbon and oxygen is detected. Mechanisms for carbon and oxygen participation in forming gettering sites for Cr are examined.
Two classes of recombination behavior as studied by the technique of the electron beam induced current: NiSi2 particles and misfit dislocations in Ni contaminated n-type silicon
Authors: Kittler M. , Seifert W. , Radzimski Z. J.
Published: July 2002

The recombination activity of well-defined NiSi2 precipitates and of misfit dislocations in Ni contaminated Si samples has been investigated using the technique of the electron-beam-induced current in dependence on sample temperature and beam current. Individual NiSi2 precipitates are found to show a high recombination activity, increasing slightly with temperature and decreasing with increasing beam current. On the other hand, misfit dislocations are nearly inactive at room temperature and increase their activity upon cooling the sample. The experimental findings are discussed in terms of recombination activity controlled by either defect charging or shallow centers.
Auger electron spectroscopy of molecular beam epitaxially grown GaAs surfaces exposed to trimethylgallium
Authors: Ohno H. , Goto S. , Nomura Y. , Morishita Y. , Watanabe A. , Katayama Y.
Published: July 2002

In situ Auger electron spectroscopy is employed to study the dynamics of the desorption process of carbon and its related species from clean molecular beam epitaxially grown GaAs surfaces exposed to trimethylgallium under the conditions where atomic layer epitaxy takes place by metalorganic molecular beam epitaxy. The direct real time spectroscopic observation of the surfaces by Auger electron spectroscopy shows that, after exposure to trimethylgallium, the initial carbon signal intensity exponentially decreases with an activation energy of 1.3 eV and reaches a steady state level.
Reactively sputtered titanium nitride films for submicron contact barrier metallization
Authors: Dixit G. A. , Wei C. C. , Liou F. T. , Zhang H.
Published: July 2002

Titanium nitride (TiN) is widely used as a barrier metal for submicron metallization because of its superior thermal stability. Various methods of forming TiN films have been explored. Oxygen passivation of the grain boundaries of the TiN and stoichiometry of the TiN are reported to be the dominant factors in achieving good barrier properties. We report on the structure property correlation of the TiN barrier metal films.
Improved electron beam pattern writing in SiO2 with the use of a sample heating stage
Authors: Pan Xiaodan , Broers Alec N.
Published: July 2002

In previous electron beam direct-write SiO2 experiments [D. R. Allee and A. N. Broers, Appl. Phys. Lett. 57, 2271 (1990); D. R. Allee, C. P. Umbach, and A. N. Broers, J. Vac. Sci. Technol. B 9, 2838 (1991)], contamination has always been formed during exposure as a result of the high electron dose required by the SiO2 process. Not only does this contamination need to be removed prior to development of the patterns in SiO2, but it also causes additional electron beam scattering and can therefore be a factor limiting the resolution of the SiO2 process. In this letter, we report improved pattern writing in SiO2 through the use of a sample heating stage. The SiO2 sample is heated in situ at ∼200 °C during exposure. This eliminates the formation of contamination and, as a result, decontamination is not needed and the exposed oxide can be developed immediately after exposure. Using this writing process, trenches on 10.8 nm periods have been demonstrated in SiO2.
Scaleable stagnation-flow reactors for uniform materials deposition: Application to combustion synthesis of diamond
Authors: McCarty K. F. , Meeks E. , Kee R. J. , Lutz A. E.
Published: July 2002

We describe two inherently scaleable geometries for chemical-vapor-deposition and heat-transfer processes that are based on stagnation flows. The ‘‘coflow’’ and ‘‘trumpet-bell’’ designs result in radially uniform fluxes to surfaces and they optimize the use of reagents. Using a trumpet-bell burner, we have grown uniform films of diamond from a substrate-stabilized flat flame of C2H2/H2/O2.
Cross-sectional scanning tunneling microscopy of electrodeposited metal oxide superlattices
Authors: Golden T. D. , Raffaelle R. P. , Switzer J. A.
Published: July 2002

We have used scanning tunneling microscopy to characterize cleaved cross sections of Pb-Tl-O superlattices. The metal oxide ceramic superlattices were electrodeposited from a single solution, with layer thicknesses as small as 1.5 nm. The lattice parameter of the fcc fluorite-type oxides is approximately 0.536 nm. Modulation wavelengths were determined using Fourier analysis of the STM images and found to be in good agreement with Faraday calculations and x-ray diffraction measurements. The STM is especially well suited for the measurement of modulation wavelengths that are too large to measure by x-ray diffraction, but too small to measure by scanning electron microscopy.
Chemical vapor deposition of rough-morphology silicon films over a broad temperature range
Authors: Dana S. S. , Anderle M. , Rubloff G. W. , Acovic A.
Published: July 2002

Growth of rough polycrystalline silicon films has been achieved on SiO2 surfaces over a broad temperature range (≥100 °C) using SiH4 chemical vapor deposition at low pressures (mTorr range), with smaller grain structure and roughness length scale achieved at lower temperatures. Rough morphology over a broad temperature range is attributed to the combination of nucleation-controlled initial growth (on SiO2) and domination of growth by surface reaction (cf. gas phase).
Step ordering during fractional-layer superlattice growth on GaAs(001) vicinal surfaces by metalorganic chemical vapor deposition
Authors: Saito H. , Uwai K. , Tokura Y. , Fukui T.
Published: July 2002

Step ordering during fractional-layer superlattice (FLS) growth is observed by trans- mission electron microscopy. A cross-sectional transmission electron micrograph of an (AlAs)1/2(GaAs)1/2FLS shows that the steps of unequal spacings observed on a GaAs surface develop a sequence of uniformly spaced steps of single monolayer height during the growth. Comparison of the observed FLS structure with a numerical simulation based on the assumption of unequal incorporation probabilities of adatoms into up steps and down steps shows that a net flux into the up steps 2%–4% larger than that into the down steps is enough to reproduce the FLS growth. It is demonstrated that the FLS growth provides a unique opportunity to observe the step ordering process directly and determine the anisotropy of diffusion quantitatively.
Effect of hydrogen treatment upon silicon surface investigated with the multiple internal reflection infrared spectroscopy
Authors: Zhong L. , Ling L. , Shimura F.
Published: July 2002

Multiple internal reflection infrared (MIR-IR) spectroscopy is used to study native oxide on silicon wafers which were annealed at 1200 °C in a hydrogen ambient. MIR-IR spectra of native oxide are dominated by a peak at 1230 cm−1, which shifts 10 to 1220 cm−1 for the samples with hydrogen treatment. A mechanism behind the shift is discussed according to the central force model, which suggests a 0.8% reduction in the distance between silicon atoms in the oxide. It is proposed that the introduction of hydrogen gives rise to a lattice contraction in the silicon substrate, and in turn, in the native oxide, which causes the MIR-IR absorption shift.
Type-II second-harmonic generation and sum-frequency mixing in uniform KTiOPO4 channel waveguides
Authors: Risk W. P. , Lau S. D. , Fontana R. , Lane L. , Nadler Ch.
Published: July 2002

Type-II second-harmonic generation was investigated in channel waveguides fabricated in potassium titanyl phosphate (KTiOPO4) crystals by ion exchange. The birefringence of the guided-wave structure was used to provide phasematching. A green (509 nm) output power of 0.25 mW was produced by frequency doubling the 1018-nm output of a titanium:sapphire laser; this power is 200 times greater than what would be obtained in the corresponding bulk interaction. Phasematching for second-harmonic generation was found to have broad tolerances with respect to temperature and wavelength. Blue light at 483 nm was produced by sum-frequency mixing of 1064-nm and 883-nm light.
Preparation of Pb(Zr0.54Ti0.46)O3 thin films on (100)Si using textured YBa2Cu3O7−δ and yttria-stabilized zirconia buffer layers by laser physical vapor deposition technique
Authors: Tiwari P. , Zheleva T. , Narayan J.
Published: July 2002

We have fabricated high-quality 〈00l〉 textured Pb(Zr0.54Ti0.46)O3 (PZT) thin films on (001)Si by interposing 〈00l〉 textured YBa2Cu3O7−δ (YBCO) and yttria-stabilized zirconia (YSZ) buffer layers using pulsed laser deposition (KrF excimer laser, λ=248 nm, τ=20 ns). The YBCO layer provides a seed for PZT growth and can also act as an electrode for the PZT films, whereas YSZ provides a diffusion barrier as well as a seed for the growth of YBCO films on (001)Si. These heterostructures were characterized using x-ray diffraction, high-resolution transmission electron microscopy, and Rutherford backscattering techniques. The YSZ films were deposited in oxygen ambient (∼9×10−4 Torr) at 775 °C on (001)Si substrate having 〈001〉 YSZ//〈001〉Si texture. The YBCO thin films were deposited in situ in oxygen ambient (200 mTorr) at 650 °C. Temperature and oxygen ambient for the PZT deposition were optimized to be 530 °C and 0.4–0.6 Torr, respectively. The laser fluence to deposit this multistructure was 2.5–5 J/cm2. The 〈00l〉 textured perovskite PZT films showed a dielectric constant of 800–1000, a saturation polarization of 37.81 μC/cm2, remnant polarization of 24.38 μC/cm2, and a coercive field of 125 kV/cm. The effects of processing parameters on microstructure and ferroelectric properties of PZT films and device implications of these structures are discussed.
Surface treatment of a–axis EuBa2Cu3O7−y thin films by an electron cyclotron resonance ion beam
Authors: Asano H. , Asahi M. , Kimachi Y.
Published: July 2002

An electron cyclotron resonance (ECR) ion beam has been utilized for a developing surface cleaning process of high-Tc superconducting thin films. By means of silver-contact resistivity measurements, and ex situ surface analysis using x-ray photoelectron spectroscopy (XPS) and reflection high-energy electron diffraction (RHEED), the effects of ECR treatment on an air-exposed surface of a-axis EuBa2Cu3O7−y (EBCO) films are examined. Ag/EBCO contacts are made with exposure of the EBCO surface to an ECR oxygen ion beam with ion current densities of 100 μA/cm2 at room temperature for about 30 min and the in situ deposition of silver. The contacts, which are not annealed in oxygen, exhibit low contact resistivity in the 10−8–10−7 Ω cm2 range. These values are about five orders of magnitude lower than those of samples fabricated without ECR treatment. Based on XPS and RHEED data, change in the EBCO surface caused by ECR treatment is surmised.
Experimental and theoretical evidence for As—H bond cleavage in the decomposition of primary arylarsines
Authors: Foster Douglas F. , Glidewell Christopher , Cole-Hamilton David J.
Published: July 2002

Decomposition of 2-CH3C6H4AsD2 in vacuo at 600–1000 °C gives toluene, which is deuterated with 0, 1, 2, or 3 D atoms in the methyl group. Theoretical studies suggest that this distribution of D atoms can only occur if the primary process for decomposition of the primary arsine is As—D bond cleavage and if this is followed by reductive elimination to give As and toluene or by rearrangement of CH3C6H4AsD⋅ to DHAsC6H4CH2⋅, which then abstracts D from another 2-CH3C6H4AsD2 molecule.
The process limitation for forming Ti silicided shallow junction by BF2+ implantation into thin polycrystalline Si films and subsequent Ti silicidation
Authors: Juang M. H. , Lin C. T. , Jan S. T. , Cheng H. C.
Published: July 2002

Excellent shallow p+n junctions have been formed by implanting BF2+ ions into thin polycrystalline Si films and subsequent annealing; these junctions which show a leakage of 1 nA/cm2 and a junction depth of about 0.05 μm. An anomalous boron diffusion occurs when subsequent silicidation is carried out. Silicidation using 300-Å Ti just slightly affected the junction profile. However, the junction is considerably deepened for 600-Å Ti silicidation, yielding a resulting depth of about 0.11 μm. The large boron redistribution is attributed to the point defects induced by silicidation. Hence, proper silicide thickness should be chosen to retain the junction profile as well as to reduce the parasitic source/drain resistance.
Enhanced giant magnetoresistance in Fe/Cr multilayer films by Cr alloying of the Fe layers
Authors: Chen L. H. , Tiefel T. H. , Jin S. , Van Dover R. B. , Gyorgy E. M. , Fleming R. M.
Published: July 2002

The effect of the Cr alloying addition to the Fe layers in the Fe/Cr superlattice films [Fe(15 Å)/Cr(tÅ)]30), (t=8–20) on the magnetoresistance behavior has been investigated. The alloyed superlattice films exhibited significantly improved giant magnetoresistance effect (ΔR/R∼12.2% at 4.2 K) as compared to the unalloyed Fe/Cr multilayer films (ΔR/R∼6.9%). Both films exhibit ΔR/R dependence on the thickness of the Cr layer with the maximum ΔR/R occurring at ∼10 Å thickness. The M-H loops indicate that antiferromagnetic coupling exists in both films, which is believed to be responsible for the observed giant magnetoresistance. The improvement in ΔR/R in the Cr-alloyed superlattice films is attributed to the stronger spin-dependent scattering of conduction electrons.
Effect of ultraviolet irradiation upon the recombination lifetime of silicon wafers covered with a dielectric film
Authors: Zhong L. , Ando K. , Tsuya H. , Shimura F.
Published: July 2002

The effect of UV irradiation upon the recombination lifetime of silicon covered with chemical vapor deposition (CVD) oxide has been studied using a laser-microwave photoconductance (LM-PC) technique. It is found that the lifetime changes little after the first UV irradiation, but dramatically decreases following thermal annealing at 500 K for 1 h. Moreover, the lifetime can be cycled up and down by repeated irradiation and thermal annealing. A comparison is made of the UV irradiation effect upon the lifetime of silicon wafers covered with a variety of different dielectric films. It is suggested that UV rechargeable defects are present in a CVD oxide film, like in native oxide and CVD nitride, but are absent in thermal oxide. Finally, it is emphasized that the noncontact LM-PC technique can be a powerful tool to characterize the defects in dielectric films on silicon wafers.
In situ fabrication of InP-based optical waveguides by excimer laser projection
Authors: Matz R. , Heydel R. , Göpel W.
Published: July 2002

We describe the preparation of InGaAsP/InP optical rib waveguides by maskless excimer laser projection etching. The process is based on the spontaneous chemical reaction of Cl2 etch gas with the InP surface at room temperature and subsequent laser-induced chloride evaporation. The spatial resolution is at least 1 μm. A typical etch rate is 0.45 nm/pulse or 540 nm/min at 20 Hz pulse repetition rate. Due to smooth surfaces, the optical attenuation of laser-etched waveguides is equivalent to that of conventionally etched guides. To demonstrate the utility of the process, we have also designed and successfully fabricated directional couplers from the same waveguide type according to the effective index method.
Space- and time-resolved investigation of short wavelength x-ray laser in Li-like Ca ions
Authors: Xu Zhizhan , Fan Pinzhong , Lin Lihuang , Li Yaolin , Wang Xiaofang , Lu Peixiang , Li Ruxin , Han Shensheng , Sun Lan , Qian Aidi , Shen Baifei , Jiang Zhiming , Zhang Zhengquan , Zhou Jinzhi
Published: July 2002

We have demonstrated the soft x-ray amplification for lithium-like Ca17+ 4f-3d transition at 57.7 Å with 900 ps, 1.05 μm drive laser pulse. The spatial distribution of the gain coefficient and temporal history of the lasing line emissions were also obtained.
Measurement of residual stress in MgO thin films on GaAs by electron microscopy
Authors: De Graef Marc , Clarke David R.
Published: July 2002

The residual stress in thin films of MgO deposited on GaAs is determined from the shape of characteristic diffraction bend contours, seen in the transmission electron microscope, in regions where the substrate was preferentially etched away leaving only the film. The residual stress in a MgO film deposited, by electron beam evaporation, at 450 °C, was found to be compressive with a magnitude of 176±8 MPa. This is opposite in sign to that expected on the basis of the thermal expansion and lattice mismatches.
Phenomenological theory of cuprate superconductivity
Authors: Rabinowitz Mario , McMullen T.
Published: July 2002

Reasonably good agreement with the superconducting transition temperatures of the cuprate high-Tc superconductors can be obtained on the basis of an approximate phenomenological theory. In this theory, two criteria are used to calculate the superconducting transition temperature. One is that the quantum wavelength is of the order of the electron-pair spacing. The other is that a fraction of the normal carriers exist as Cooper pairs at Tc. The resulting simple equation for Tc contains only two parameters: the normal carrier density and effective mass. We calculate specific transition temperatures for 12 cuprate superconductors.
Controlled misfit dislocation nucleation in Si0.90Ge0.10 epitaxial layers grown on Si
Authors: Watson G. Patrick , Fitzgerald Eugene A. , Xie Ya-Hong , Silverman Paul J. , White Alice E. , Short Kenneth T.
Published: July 2002

Misfit dislocation formation has been controlled during growth at 500 °C in strained, 720 nm Si0.90Ge0.10 on Si. The Si substrates were selectively Ge+ ion implanted and etched to form a series of mesas with stripes of implant damaged crystal. Misfit dislocations nucleated preferentially from the ion implanted regions during epitaxial layer growth, while other nucleation sources were inhibited by the low growth temperature and the etched trenches between mesas. Films were relaxed by as much as 35%. The epitaxial layers on some mesas were relaxed in essentially one 〈110〉 direction as well. Electron beam induced current images indicate that ion-implant activated misfit dislocations form before heterogeneous nucleation sources can operate, so that relaxation occurs in a more uniform manner.
Scanning tunneling microscopy observation of monolayer steps on GaAs(001) vicinal surfaces grown by metalorganic chemical vapor deposition
Authors: Kasu Makoto , Kobayashi Naoki , Yamaguchi Hiroshi
Published: July 2002

Using scanning tunneling microscopy (STM), we have observed monolayer steps for the first time on (001)GaAs vicinal surfaces grown by metalorganic chemical vapor deposition (MOCVD). The surface was passivated with As to protect it from air during the transfer from the MOCVD to the STM. We found that the monolayer step edges on the surface misoriented in the [110] direction undulate with about 2 times larger amplitude than the surface misoriented in the [1̄10] direction.
Theoretical gain of strained quantum well grown on an InGaAs ternary substrate
Authors: Ishikawa Hiroshi
Published: July 2002

Optical gain is calculated for a strained quantum well grown on a ternary In1−xGaxAs substrate which is now being developed. Using an In0.26Ga0.74As substrate we can design a strained quantum well for 1.3 μm laser with a large band gap InGaP or InGaAsP barrier layer. This gives a much deeper potential well when compared with that on an InP substrate and results in a high optical gain owing to the large subband energy separation provided by the deep well. The optical gain of the strained quantum well on the ternary substrate is shown to be higher by about 750 cm−1 when compared with that on an InP substrate.
Gain-guided laser diode having a curved-mirror-cavity with a low astigmatism
Authors: Toda A. , Kobayashi T. , Dohsen M. , Mori Y.
Published: July 2002

A gain-guided laser diode having a curved-mirror-cavity that has coaxial mirrors and a fan-shaped stripe structure has been fabricated by dry etching. Although gain guided, the laser has an astigmatism of 4.1 μm, which is very low compared to conventional laser’s. The threshold current of the laser is 35 mA, the longitudinal mode spectrum is multiple, and the transverse optical mode is fundamental. These results are comparable to conventional gain-guided lasers. Etched mirror laser diodes with flat facets have been stably operated over 1500 h under automatic-power control at a power of 3 mW/facet at 50 °C, without facet coating
Localization at imperfect interfaces and its role in optical spectra of quantum well structures
Authors: Jaros M. , Beavis A. W.
Published: July 2002

We present microscopic calculations that show that some of the novel features recently found in the luminescence spectra of quantum well structures (e.g., Si-SiGe, GaAs-GaAlAs, ZnSe-ZnCdSe) can be accounted for by electron localization at small interface islands.
Evidence for structural similarities between chemical vapor deposited and neutron irradiated SiO2
Authors: Devine R. A. B. , Marchand M.
Published: July 2002

Raman spectroscopy, infrared absorption, and refractive index measurements have been carried out on films of amorphous SiO2 deposited by plasma enhanced chemical vapor deposition from SiH4 and N2O gases. It is demonstrated that the films have physical characteristics different from those of thermally grown or bulk oxide. Comparison with the data obtained from neutron irradiated, bulk SiO2 leads to the conclusion that deposited oxides and heavily neutron irradiated oxides have a similar and unusual network structure. In this network the Si—O—Si bond angles are substantially reduced (∼10°) with respect to bulk and relaxed silica. The three membered ring density is significantly enhanced and there is a considerably larger fraction of free volume. These structures coincide with materials having a fictive temperature in excess of 2400 °C and it is argued that they are analogous to the porosil structure known in crystalline forms of SiO2.
Thermal conductivity in molten-metal-etched diamond films
Authors: Jin S. , Chen L. H. , Graebner J. E. , McCormack M. , Reiss M. E.
Published: July 2002

Substantial thinning of chemical vapor deposited diamond films has been accomplished by a diffusional transfer of carbon atoms from diamond to molten rare-earth metals. Cerium and lanthanum are particularly useful because of their large liquid solubility of carbon. The perpendicular thermal conductivity of the processed diamond film (after removal of about 40 μm from the bottom surface) is remarkably improved from ∼14–15 to about 20–22 W/cm °C, a value approaching that of high-quality Type IIa single crystal diamond. The in-plane conductivity, on the other hand, is improved only slightly because of the anisotropic microstructure. The improvement in conductivity implies that few phonon scattering centers are introduced by the thinning process, for example, through grain boundary contamination by metal atoms.
Raman scattering from oval defects in GaAs epilayers
Authors: Khulbe P. K. , Dobal P. S. , Bist H. D. , Mehta S. K. , Muralidharan R. , Jain R. K.
Published: July 2002

Micro-Raman investigations have been carried out at various spots in and around oval defects in epitaxially grown 〈100〉 GaAs wafers. Changes in the crystalline orientation have been observed within the oval defect structure as compared to the normal region. However, the crystalline quality of these defects remain equally good. These oval defects also possess a deviation in stoichiometry, corroborating to the conclusions of other studies.
Very high two-dimensional electron gas concentrations with enhanced mobilities in selectively double-δ-doped GaAs/InGaAs pseudomorphic single quantum well heterostructures
Authors: Shieh H. M. , Hsu W. C. , Wu C. L.
Published: July 2002

In this letter a new type of GaAs/In0.25Ga0.75As/GaAs pseudomorphic single quantum well heterostructure by selectively double-δ-doping GaAs layers on both sides of the InGaAs channel grown by low-pressure metalorganic chemical vapor deposition is demonstrated. An extremely high two-dimensional electron gas concentration more than 1×1013 cm−2 with enhanced mobility of 2900 cm2/V s is achieved. This type of structure can easily break through the doping limitation in conventional heterostructures while keeping a high mobility.
Measurement of modulation saturation intensity in strain-balanced, undefected InGaAs/GaAsP modulators operating at 1.064 μm
Authors: Goossen K. W. , Cunningham J. E. , Santos M. B. , Jan W. Y.
Published: July 2002

We measure high modulation saturation intensities in both strain-relaxed InGaAs/GaAs multiple-quantum-well (MQW) modulators (107 kW/cm2) and strain-balanced InGaAs/GaAsP MQW modulators (31 kW/cm2) operating at 1.064 μm, measured with a Nd:YAG laser. This compares with 16 kW/cm2 for GaAs/Al0.3Ga0.7As thin barrier MQW modulators and 65 kW/cm2 for GaAs/Al0.02Ga0.98As shallow MQW modulators operating near 850 nm (reflection modulators). The advantage of the strain-balanced system is that it results in an undefected material with sharper excitonic features and better morphology compared to the strain-relaxed system. This study shows that the InGaAs/GaAsP system may be used to obtain long wavelength operation with these advantages without incurring an unreasonable penalty for high power operation due to the higher barriers.
Reliability of the electrical properties of the BF2+ ion implanted polycrystalline diamond film
Authors: Lee S. L. , Lin S. J. , Hwang J.
Published: July 2002

The resistance of the BF2+ ion implanted polycrystalline diamond film drifted higher with time when the diamond film was exposed in air. The reliable resistance of the implanted diamond film could be obtained after the heat treatment at high temperature under vacuum. Temperature dependence of the reliable resistance of the BF2+ ion implanted diamond film indicated two activation energies within the temperature range from room temperature to 400 °C. The effect of gas exposure on the resistance of the implanted diamond film was discussed.
Performance improvement in quantum well lasers by optimizing band gap offset at quantum well heterojunctions
Authors: Zhao B. , Chen T. R. , Shakouri A. , Yariv A.
Published: July 2002

We analyze the influence of the band gap offset at the quantum well (QW) heterojunctions on the performance of QW lasers. It is shown that, in addition to the strain, optimization of the band gap offset also leads to improved performance in QW lasers, especially in enabling a simultaneous attainment of ultralow threshold current and high speed. The improvement stems from the reduction of state filling in the QW lasers since the asymmetry between the conduction band and the valence band structures in the optical confining region is compensated by the corresponding optimal band gap offset at the QW heterojunctions. The results provide general guidelines to the design of high performance of QW lasers as well as suggest applications to other active laser devices.
Influence of oxygen concentration and annealing on morphology and electrical properties of semi-insulating polycrystalline silicon
Authors: Lombardo S. , Campisano S. U. , Baroetto F.
Published: July 2002

Semi-insulating polycrystalline silicon films, deposited by low-pressure chemical vapor deposition on oxidized Si substrates at O concentrations from 2 up to 35 at. % O, have been annealed at 920 °C for 30 min. Transmission electron microscopy revealed the presence of crystalline Si grains. The average Si grain radius decreases with O content going from ≊15 up to ≊2 nm, while electrical resistance increases with O concentration of almost four orders of magnitude. We attribute the resistance increase at large O contents to the presence of SiO2 shells, two monolayers thick, covering the Si grains. At these large O contents a noticeable increase in Si grain size and electrical conductance is observed in samples annealed at 1200 °C for 30 min. These results can be interpreted on the basis of thermal instability of the oxide shells. This assumption is supported by observations of native oxide breaking against high-temperature annealings.
Lithium-ion mobility improvement in floating-zone silicon by external gettering
Authors: Walton J. T. , Derhacobian N. , Wong Y. K. , Haller E. E.
Published: July 2002

Phosphorous diffusion for approximately 1 h at 950 °C is shown to be an effective gettering procedure to remove lithium-ion mobility reducing defects in floating-zone p-type silicon wafers. The removal of these defects, which can severely impede the movement of lithium ions in silicon wafers during lithium-ion compensation process, is crucial in the fabrication of silicon lithium-drifted radiation detectors.