bluuebunny/crossref_metadata_2025 huggingface dataset:
A-Si:H Ambipolar Diffusion Length and Effective Lifetime Measured by Flying Spot Technique (FST)
Authors: Vieira M. , Martins R. , Fortunato E. , Soares F. , Guimaraes L.
Published: March 2011

The determination of the ambipolar diffusion length, L*, and the effective lifetime, τ*, in p/i and a-Si:H Schottky barriers (ITO/p/a-Si:H/Al-Si; Cr/a-Si:H/Cr/Ag) have been determined by Flying Spot Technique, FST. This technique consists in the transient analysis of the photocurrent/photopotential induced by a laser beam that moves perpendicularly to the structure with a constant motion ratio, at different velocities. Taking into account the competition between the diffusion/drift velocities of the excess carriers and the velocity of the flying spot, it is possible to solve the transport equations and to compute separately L* and τ*, from the asymmetrical distribution responses.
Diffraction Studies of Water Under Pressure
Authors: Neilson G.W.
Published: March 2011

During the past decade, improvements in experimental techniques and computer simulation methods have led to a more comprehensive understanding of the properties of water [1]. Foremost amongst these are X-ray and neutron diffraction which provide information directly of the microscopic structure [2]. Such information is in the form of a structure factor F(k) and its real space Fourier transformation G(r). F(k) and G(r) can be used to test the various models of water used in computer simulation studies. G(r) can also provide a basic picture of the short range structure of water characterised by interparticle separations and coordination numbers.
High Pressure Studies of Liquid Crystalline Transitions
Authors: Shashidhar R.
Published: March 2011

Some of the important results emerging from our recent investigations
on liquid crystals at high pressure are presented. In particular the following topics will be discussed:
i) The relation between Pm, the maximum pressure of smectic stability, and the temperature range of the nematic phase in reentrant nematogenic compounds.
ii) Piezothermal studies in the vicinity of the smectic A-nematic transition in 8 OCB.
iii) The effect of molecular ordering on the pressure behaviour of the nematic-isotropic transition in reentrant nematic mixtures.
iv) The first observation of a multicritical point in a single component liquid crystal.
Pressure and Temperature Effects on the Raman Spectra of Aqueous Micellar Solutions of Sodium Oleate
Authors: Wong P.T.T. , Mantsch H.H.
Published: March 2011

Sodium oleate is practically insoluble in water at room temperature. Yet, when heated above the critical micellization temperature (cmt), its solubility increases rapidly and an isotropic optically clear micellar solution is formed. Upon cooling below the critical coagelization temperature (cct), the micellar phase transforms to an opaque curd, the coagel phase. The structural changes and the nature of this phase transition are, however, not well characterized.
High Temperature, High Pressure Absorption Spectra of Uranyl Chloride Solutions Under Shock Conditions
Authors: Ewald Arnold H.
Published: March 2011

In 1960 David and Ewald [1] developed a technique for photographing the absorption spectra of solutions under shock wave conditions. A photograph of the spectrum of a uranyl nitrate solution exposed to a shock wave of 75 kbar showed the absorption to extend beyond 500 nm, the long wavelength limit for uranyl solutions under ordinary conditions. A.H. Ewald (unpublished, 1963) found that at room temperature pressure up to 6 kbar had no appreciable effect on absorption. Bell and Biggers [2,3] published an analysis of the spectrum of uranyl perchlorate solutions. The longest wavelength absorption band was at 486 nm but Bell [4] later found bands at 508 and 531 nm. The intensity of these very weak bands increased when the solution was heated to 95° C, and they were interpreted as “hot bands” due to absorption from an excited ground state. This paper reports new absorption measurements made on uranyl solutions heated to 250°C at low pressure and offers an interpretation of the effect observed in the shock experiments.
Photoluminescence of Bis-Tetrabutylammonium Tetrabromomanganate to 440 K and 3 Kbar
Authors: VöGele H.P. , TöDheide K.
Published: March 2011

The absorption and emission spectra and the phosphorescence decay time of bis-tetrabutylammonium tetrabromomanganate-(II) were measured to 440 K and 3 kbar. In addition the melting pressure of the salt and its viscosity and electrical conductivity at normal pressure were determined as functions of temperature.
Phase Transitions in Solid Methane Up to 60 Kbar
Authors: Trappeniers N.J.
Published: March 2011

Solid methane has been a favourite subject for the study of phase transitions ever since the discovery by Clusius [1] of the phase transition α → β at 20.4 K in CH4. The reasons for the sustained interest in solid CH4may be attributed to the following facts. i. The CH4molecule has an almost spherical shape with a slight TDanisotropy. As a result, CH4crystallizes below 90.7 K into a plastic crystal, α, of cubic symmetry, exhibiting almost complete rotational freedom of the molecules. ii. The CH4molecule is very small in size with a low moment of inertia (I × 1040g cm2= 5.34 in CH4and 10.64 in CD4), leading to a large rotational kinetic energy and related quantum effects at low temperature. iii. The protons in CH4and the deuterons in CD4carry a nuclear spin resp. Ip = 1/2 and I. = 1, which gives rise to spin-isomerism. Thus, CH4has three spin varieties, meta (A1, In = 2), ortho (T2, in = 1) and para (E, In = 0). The isomerism may be expected to have profound influence on the phase diagram of solid methane.
Metastability in the H2O and D2O Systems at High Pressure
Authors: Piermarini G. J. , Munro R. G. , Block S.
Published: March 2011

The pressure and temperature parameters which delineate the equilibrium thermodynamic stability fields of the liquid, VI and VII phases, includinq the triple point, were measured for the H2;0 and D2;0 systems over the pressure range, 0.8 to 2.4 GPa, and the temperature interval, 20 to 135 °C. The phenomenon of metastability associated with the liquid-VII phase boundary was observed during this work; and, subsequently, a metastable extension of this coexistence curve was determined from the liquid-VI-VII triple point down to 20 °C for both H2;0 and D2;0. The measurements were made by optical polarizing microscopy in conjunction with a diamond anvil cell equipped with a miniature resistance coil heatinq element. Pressures were measured by the ruby fluorescence method.
Effects of Viscosity, Temperature, and Rate of Rotation on the Operation of a Controlled-Clearance Piston Gauge
Authors: Sharma J.K.N. , Jain Kamlesh K. , Bean Vern E. , Welch B.E. , Lazos Ruben J.
Published: March 2011

The calculation of the pressure generated by a controlled clearance piston gauge depends upon the jacket pressure corresponding to zero clearance between the piston and cylinder, Pz;. The dependence of Pz; on the viscosity of the pressure transmitting fluid, the temperature, and the rate of piston rotation has been measured.

The value of Pz; is nearly independent of viscosity below 60 cp. Above 60 cp, Pz; depends strongly upon viscosity. Variations of Pz; with femperature and rate of rotation are more severe at figher viscosities.

These results are a clear indication that for the most accurate pressure measurements, a controlled-clearance piston gauge must be characterized using the same operational and environmental conditions with the same fluid as in normal operation.
Crack Decay into Edge Dislocations
Authors: Shmatov V. T.
Published: March 2011

The hydrostatic pressure in a sample, making it possible the emitting of edge dislocations by the cleavage crack, is estimated (few tens of kbars). The increase of temperature and small plastic deformation further the healing of cleavage cracks by the decay into dislocations.
On the Hydrostatic Extrusion of Non-Ferrous Metals
Authors: Häuβler G. , Schreiter G. , Schlegel J. , Hennig W.
Published: March 2011

The growing interest in the process of hydrostatic extrusion is reflected by numerous publications on experimental results, fundamental researches and theoretical studies (e. g., [1] to [20]). In recent years it was the increasing demand for new materials and semiproducts with special cross-section dimensions and properties that substantiated the necessity of defining the application of hydrostatic extrusion in the field of non-ferrous metallurgy. Thus, it is the aim of the researches carried out with the experimental hydrostatic extrusion press type QEH 12 recently installed by the Swedish company ASEA in the Forschungsinstitut für NE-Metalle Freiberg of the VEB Mansfeld Kombinat “Wilhelm Pieck” to solve problems of materials and deformation engineering and to develop new technologies of producing special semiproducts from non-ferrous metals.
Power Law Behavior of the Pressure Dependence of Expansivity in the Liquid Hexane as a Model for Liquids. Limit of Thermodynamic Stability
Authors: Pruzan Ph.
Published: March 2011

In this work a power lay is used to fit the isothermal pressure dependence of the expansivity α = V−1(∂V/∂T)p of liquid hexane. This functional form is also observed to fit the expansivity and the isothermal compressibility KT = −V−1(∂V/∂P)T data of the three liquids : hexane, argon, carbon dioxide.
PVT Measurements and Critical Parameters of Water
Authors: Hanafusa H. , Kawai K. , Sato H. , Uematsu M. , Watanabe K.
Published: March 2011

The PVT properties and vapor-pressures of water have been measured in the critical region by using a constantvolume apparatus immersed in the constant-temperature bath with the procedure of varying the sample mass along a prescribed isotherm. Ninety-one PVT and five vapor-pressure measurements along 11 isotherms cover the region of temperatures 643 to 673 K and of pressures 19.7 to 38.6 MPa, which corresponds to a density variation from 108 to 618 kg/m3. The experimental uncertainties of temperature, pressure and density are estimated 4 mK, 5 kPa and 0.04%, respectively. Based on these measurements, the critical parameters of water are proposed to be 647.061 K, 22.041 MPa and 322.4 kg/m3 by the scaling law analysis.
Apparatus for the Measurement of Isothermal and Adiabatic Compressibility of Gases up to 10 Kbar
Authors: Biswas S.N. , Muringer M.J.P. , Trappeniers N.J.
Published: March 2011

A pVT apparatus based on a combination of gas expansion and isochoric method and an ultrasonic apparatus for sound velocity measurements based on phase comparison pulse-echo technique have been developed for precise measurements of isothermal and adiabatic compressibility of gases at pressures up to 10 kbar and temperatures down to the melting line.
Investigation of the Phase Equilibria in the System Neon-Xenon Using a Diamond-Anvil System
Authors: Schouten J.A. , Van Den Bergh L.C. , Trappeniers N.J.
Published: March 2011

The critical line of a nearly ideal binary system generally moves from the critical point of one of the components directly to the critical point of the other component (curve 1 Fig. 1). In a less ideal system, however, the behaviour is quite different. In some cases the curves move from the critical point of the less volatile component (component 2) to lower temperatures and higher pressures (curve 2) and rise again to higher temperatures via a temperature minimum, the critical double point. In other systems, the critical temperature increases continuously from the critical point of the less volatile component when the pressure is increased (curve 3). We assume here that the critical line is not interrupted by the appearance of a solid phase.
Aqueous Mixtures with Nonpolar Gases at High Pressures and Supercritical Temperatures
Authors: Franck E.U.
Published: March 2011

PTx-phase diagrams and critical curves for binary aqueous systems are briefly discussed. New results of the two-phase boundary surface and the critical curve for the water-nitrogen system to 2500 bar and 400°C are presented as isotherms in the Px-plane. A new extended Carnahan-Starling and squarewell type equation permits calculations of spinodal isopleths of the water-methane system and a prediction of the critical curve. - Excess volumes of supercritical benzene-water mixtures are given as functions of composition and pressure. Excess Gibbs energies and activity coefficients are derived. For the same system the static dielectric constant was measured between 300 and 400 °C in the homogeneous supercritical fluid for all concentrations. At 400 °C and 2000 bar the dielectric constant of pure water is 20 and decreases steeply with the addition of benzene. Addition of water to benzene causes at first only a slow increase above the value of 2 (for pure benzene). A short discussion of the description of the dielectric constant of such polar-nonpolar mixtures for wide ranges of density is given. - The solubility of anthracene in high density water to 250 °C was measured spectroscopically. Data are given. The “enhancement factor” is high at low temperature but decreases to unity at 250 °C and a water density of 1 g . cm−3
X-Ray and Raman Studies of Interlayer Mixing in SimGem Superlattices
Authors: Bowman R. C. , Adams P. M. , Chang S. J. , Arbet-Engels V. , Wang K. L.
Published: March 2011

Interface mixing between the Ge and Si layers in symmetrically strained SimGem superlattices occurs during post growth thermal anneals. Interdiffusion coefficients were obtained from intensity changes in the low angle superlattice x-ray satellites on samples with nominal periodicities between 1.4nm and 5.6nm. A common activation energy of 3.0±0.1 eV was found. The bulk interdiffusion coefficients for SimGem were derived since measurements were made on samples with different layer thicknesses. Intermixing appears to occur by diffusion of Si atoms into the Ge layers via a vacancy mechanism. Raman scattering measurements support this process as well as the formation of Si1−xGex, alloy layers during the anneals.
Suppression of Interfacial Mixing by Sb Deposition in Si/Ge Strained-Layer Superlattices
Authors: Fujita K. , Fukatsu S. , Yaguchi H. , Igarashi T. , Shiraki Y. , Ito R.
Published: March 2011

We have studied interfacial mixing of Si/Ge strained-layer superlattices during Si molecular beam epitaxy. The mixing has been shown to be primarily due to the surface segregation of Ge atoms during Si overlayer growth. It has been found that only the Ge atoms on the topmost Ge layer dominantly segregate to the growing surface. It has also been found that the surface segregation of Ge is effectively suppressed by depositing Sb atoms on the Ge layers. It has been demonstrated that Si/Ge superlattices with abrupt Si/Ge interfaces can be grown by depositing Sb. The two state exchange model is used to discuss the surface segregation of Ge and the suppression of the segregation by Sb deposition.
Defect Centers Formed During Wet Oxidation of Si-Ge/Si Heterostructures
Authors: Zvanut M. E. , Carlos W. E. , Prokes S. M. , Stahlbush R. E.
Published: March 2011

Germanium incorporated oxide films formed by wet oxidation of SiGe substrates have been studied using Electron Paramagnetic Resonance. SiGe layers 400 nm thick were prepared by molecular beam epitaxy and oxidized in a steam ambient at 900° C. After a 10 Mrad x-ray irradiation, an oxide defect with a zero crossing at g=1.995 is observed. Comparison of the spectrum with that obtained from Ge-doped silica suggests that the defect observed in the thin film is an oxygen vacancy related defect, a Ge E' center.
Low Temperature Hydrogen Plasma Cleaning Processes of Si (100), Ge (100), and SixGe1−x (100)
Authors: Schneider T. P. , Aldrich D. A. , Cho J. , Nemanich R. J.
Published: March 2011

Wet chemical and in situ hydrogen plasma cleaning processes were studied and a low temperature cleaning process was developed for Si (100), Ge (100) and SixGe1−x (100) surfaces. A uv-ozone and HF based spin etch were used to initially remove contaminants and oxides from the Si (100) and SixGe1−x (100) surfaces. The Ge (100) surfaces were treated with deionized water prior to entry to UHV. Residual gas analysis (RGA) was used in the investigation of the surface removal process of the in situ H-plasma cleaning. Low Energy Electron Diffraction (LEED) and angle resolved UV-Photoemission Spectroscopy (ARUPS) were used to examine the surface structure and electronic states. The 2×1 LEED patterns were obtained for Si (100), Ge (100) and SixGe1−x (100) after cleaning at a maximum processing temperature of 300°C. By varying process conditions, the LEED showed the 1×1 and 2×1 surface diffraction patterns. The ARUPS spectra showed the electronic states and the chemistry of the cleaned surfaces.
X-Ray Study of Non-Periodic Si/SiGe Multilayers
Authors: Herzog H. -J. , Kibbel H. , Schäffler F.
Published: March 2011

X-ray diffraction is applied for the assessment of structural data such as lattice mismatch and layer thickness of MBE grown Si/Si1−xGex heterobipolar transistor and double-barrier resonant-tunneling structures. Rocking curves from the former structure show distinct features which are obviously correlated to the individual layer parameters. The diffraction profile of the resonant tunneling structure is not only more complicated because of the larger number of parameters but also due to the strong interference effects resulting from the layer set-up. For a determination of the structural parameters a comparison of the experimental diffraction pattern with simulated rocking curves is performed.
The Effect of Oxygen on the Thermal Stability of Si1−xGex Strained Layers Grown by Limited Reaction Processing
Authors: Noble D. B. , Hoyt J. L. , Kuo P. , Nix W. D. , Gibbons J. F. , Laderman S. S. , Turner J. E. , Rosner S. J. , Scott M. P.
Published: March 2011

Si1−xGex layers containing 2×1020 oxygen atoms/cm3 exhibit an enhancement in thermal stability when compared to similar films (comparable Ge content and thickness) with 2 orders of magnitude less oxygen. X-ray measurements of the lattice constants in the strained films indicate that the oxygen does not substantially change the amount of strain in the layers. A prediction of the effect of oxygen based on solid solution strengthening theory is shown to be consistent with experimental annealing results. In addition, experimental measurements of slower misfit dislocation velocities in the layers with high oxygen content compared to those measured in films with low oxygen content, support the idea of solid solution strengthening. It is therefore likely that oxygen impedes the kinetics of dislocation formation.
Wet Oxidation of Epitaxial Ge.36Si.64 on (100)Si
Authors: Liu W. S. , Bai G. , Nicolet M-A. , Chern C. H. , Arbet V. , Wang K. L.
Published: March 2011

The thermal oxidation of epitaxial Ge.36Si.64 on (100)Si is investigated experimentally for a wet ambient at 700°C and 1000°C. A pure silicon dioxide layer with pile-up of Ge behind the oxide is formed at 1000°C. At 700°C, however, both Ge and Si are oxidized. The Ge is included uniformly into the oxide layer without changing the initial Ge/Si ratio. The result at 1000°C follows the thermodynamical picture which predicts the same result at 700°C also, contrary to observation. The different result at 700°C is due to kinetic constraints which can be explained by different activation energies for the rate of the oxidation reaction and for the Ge or Si diffusivities in GeSi.
MBE Growth and Characterization of SxGe1−x Multilayer Structures on Si (100) for Use as a Substrate for GaAs Heteroepitaxy
Authors: Posthill J. B. , Malta D. P. , Venkatasubramanian R. , Sharps P. R. , Timmons M. L. , Markunas R. J. , Humphreys T. P. , Parikh N. R.
Published: March 2011

Investigation has continued into the use of SixGe1−x multilayer structures (MLS) as a buffer layer between a Si substrate and a GaAs epitaxial layer in order to accommodate the 4.1% lattice mismatch. SixGe1−x 4-layer and 5-layer structures terminating in pure Ge have been grown using molecular beam epitaxy. Subsequent GaAs heteroepitaxy has allowed evaluation of these various GaAs/SixGe1−xMLS/Si (100) structures. Antiphase domain boundaries have been eliminated using vicinal Si (100) substrates tilted 6° off-axis toward [011], and the etch pit density in GaAs grown on a 5-layer SixGe1−x MLS on vicinal Si (lOO) was measured to be 106 cm−2.
Deep Luminescence from ‘Relaxed’ Si1−xGex Epitaxial Layers
Authors: Davies Gordon , Higgs Victor , Kubiak Richard , Powell Adrian , Whall Terry , Parker Evan
Published: March 2011

In MBE Si1−xGex which is grown to thicknesses greater than the critical thickness hc, the dislocation-related luminescence peaks Dl and D2 have energies which are independent of x up to x ≈ 0.3, and then decrease, as observed in LPE Si1−xGex. In MBE Si1−xGex layers grown to thicknesses less than hc, post-growth annealing produces dramatic changes in the luminescence, giving spectra as from relaxed alloy, even though the relaxation determined by X-rays is negligible. These results establish photoluminescence as a sensitive diagnostic tool for detecting dislocations in Si1−xGe*.
Raman Study of Strain and Confinement Effects in Si/Ge Strained Layer Superlattices Under Hydrostatic Pressure
Authors: Sui Zhifeng , Herman Irving P. , Bevk Joze
Published: March 2011

The effects of strain and confinement on optical phonons in a Si12Ge4 strained layer superlattice grown by MBE on c-Si (001) were studied as a function of hydrostatic pressure (T = 295 K) using Raman scattering. The change of phonon frequency with pressure, dω/dP, for the principal quasi-confined LO mode in the Ge layers is found to be significantly smaller than that for bulk crystalline Ge because the magnitude of biaxial strain decreases in the Ge layers with added pressure and because the Grüneisen parameter of the confined mode is smaller than that of the Γ-point optical phonon. More generally, it is noted that the magnitude of biaxial strain in many strained layer superlattices initially decreases with the application of hydrostatic pressure, making the structures more stable.
Initial Oxidation of MBE-Grown Si Surfaces
Authors: Igarashi T. , Yaguchi H. , Fujita K. , Fukatsu S. , Shiraki Y. , Ito R. , Hattori T.
Published: March 2011

We investigated the initial oxidation of MBE-grown Si (100) surfaces with atomic flatness using x-ray photoemission spectroscopy (XPS) and reflection high energy electron diffraction (RHEED). It was found that the MBE-grown surfaces are inert and hardly oxidized even after exposure to molecular oxygen up to 1500 Langmuir (L) at room temperature. At elevated temperatures, the surface oxidation was substantially promoted. On the contrary, the surface oxidation was found to be substantiated on a deliberately corrugated Si surface prepared by low temperature MBE growth, even at room temperature.
Intersubband Absorption in the Conduction Band of Si/Si1−xGex Multiple Quantum Wells
Authors: Hertle H. , Schuberth G. , Gornik E. , Abscreiter G. , Schäffler F.
Published: March 2011

The intersubband absorption of electrons in modulation doped Si/Si1−xGex multiple quantum wells has been observed [1]. Various samples with different well widths and carrier densities have been studied. Narrow absorption lines are observed in waveguide geometry. Self consistent subband calculations are in good agreement with the experimental values.
High Mobility Two-Dimensional Electron Gas in Modulation-Doped Si/SiGe Heterostructures
Authors: Wang P. J. , Meyerson B. S. , Ismail K. , Fang F. F. , Nocera J.
Published: March 2011

We report record-high electron mobilities obtained in the Si/SiGe alloy system via single-junction n-type modulation-doped Si/Si0.7Ge0.9 heterostructurcs grown by the ultra-high vacuum chemical vapor deposition technique. Peak electron mobilities as high as 1,800 cm2/Vs, 9,000 cm2/Vs and 19,000 cm2/Vs were measured at room temperature, 77K and 1.4K, respectively. These high mobilities resulted from excellent Si/SiGe interfacial properties by employing a compositional graded Si/SiGe superlattice prior to the growth of a thick S0.7Ge0.3 buffer, which brought about a dramatic reduction of the threading dislocation density in the active Si channel. Two thin phosphorous-doped layers were incorporated in the SiGe barrier and at its surface to supply electrons to the Si channel and to suppress the surface depletion, respectively. The transport properties of these heterostructurcs were determined to be those of a two dimensional electron gas at Si/SiGe heterointerfaces at low temperatures.
Columnar Structure Growth by Silicon Molecular Beam Epitaxy
Authors: Xie Y. H. , Gilmcr G. H. , Fitzgerald E. A. , Michel J.
Published: March 2011

Si columnar structures were fabricated using Si MBE on Si substrates with column sizes in the order of ∼ 100 Å. The objective is to explore a viable approach to fabricate quantum wire structures. The growth of the structures, which was due to the growth instability, was an excellent example of a self-limiting process. The dependence of column morphology on the critical parameters, e.g., Si molecular beam incident angle, substrate temperature, substrate rotation, speed, etc., were demonstrated. Comparison between the experimental and the computer simulation results demonstrated the importance of the latent heat related atom migration as compared to the normal surface diffusion at low substrate temperatures and several A/s beam fluxes. A substrate temperature window (≈125°C) was observed which allowed the fabrication of crystalline micro-columns on Si (100) substrates. RHEED studies indicated that the crystalline micro- columns were heavily twined. The twinning phenomenon was also observed in the computer simulation results and interpreted as a result of the reduction in twin formation energy due to the extremely small dimension of the columns. Thermal stability of the columnar structures is discussed. Finally, photoluminescence studies and some potential applications are also discussed.
Molecular Beam Epitaxial Growth of Very High Mobility Two-Dimensional Electron Gases in Si/GeSi Heterostructures
Authors: Xie Y. H. , Fitzgerald E. A. , Mii Y. J. , Monroe D. , Thiel F. A. , Weir B. E. , Feldman L. C.
Published: March 2011

We report the fabrication of modulation doped Si/Gex Si1−x heterostructures by molecular beam epitaxy. The samples are characterized by Rutherford backscattering spectrometry, cross-sectional transmission electron microscopy, electron beam induced current, Hall measurement, and the magnetoresistance (Shubnikov-de Haas) measurements. Threading dislocation densities of = 106cm−2 are observed for relaxed Ge0.3Si0.7 films on Si (100). The modulation doped structures fabricated on these Ge0.3 Si0.7 films contain two-dimensional electron gases with mobilities ranging from 60,000 to 96,000 cm2/V - s at 4.2 K.
Reduction of p+-n+ Junction Tunneling Current for Base Current Improvement in Si/SiGe/Si Heterojunction Bipolar Transistors
Authors: Matutinović-Krstelj Ž , Prinz E. J. , Schwartz P. V. , Sturm J. C.
Published: March 2011

A reduction of parasitic tunneling current by three orders of magnitude in epitaxial p+-n+ junctions grown by Rapid Thermal Chemical Vapor Deposition (RTCVD) compared to previously published ion implantation results is reported. These results are very important for the reduction of base current in scaled homojunction and Si/SiGe/Si heterojunction bipolar transistors. High reduction in tunneling currents allows higher limits to transistor base and emitter dopings. Significant tunneling was observed when the doping levels at the lighter doped side of the junction were of the order of 1×1019cm−3 for both Si/Si and SiGe/Si devices. These results were confirmed by I-V measurements performed at different temperatures. Since the tunneling current is mediated by midgap states at the junction, these results demonstrate the high quality of the epitaxial interface.
Silicon Germanium Heterobipolar Transistor Structures with Extremely High Base Doping
Authors: Kasper E. , Kibbel H. , König U.
Published: March 2011

The complete layer sequence of a SiGe-HBT including the emitter contact is grown by Si-MBE. The base doping level was increased from 1018/cm3 up to 1020/cm3 which resulted in very low intrinsic base sheet resistivities (0.27 kΩ/□ for a 50 nm base). With a base Ge content x = 32 % the highest current gain β=5000 could be obtained. A SiGe spacer between base and collector improved the DC-characteristics considerably.
Channel Profile Engineering of MOSFETs using Delta Doping
Authors: Wood Andrew C. G. , O'Neill Anthony G.
Published: March 2011

The influence of the location, dose and width of the doping spike in a delta doped MOSFET is investigated theoretically. Calculations are performed for a range of n and p type 5M0SFETS, and the importance of each design parameter of the device is assessed. The optimum device has a delta layer around 2 0nm deep, with a sheet doping density around 1012cm−2 for the pMOSFET and 5.1011cm−2 for the nMOSFET. The effect of diffusion of the dopant during processing on the device performance is also considered, and it is found that this causes a shift in the threshold voltage of the device. The layer width should ideally be kept below 5nm.
Subsurface Growth of CoSi2 by Deposition of Co on Si-Capped CoSi2 Seed Regions
Authors: Fathauer R. W. , George T. , Pike W. T.
Published: March 2011

At a growth temperature of 800°C, Co deposited on Si (111) diffuses through a Si cap and exhibits oriented growth on buried CoSi2 grains, a process referred to as endotaxy. This occurs preferentially to surface nucleation of CoSi2 provided the thickness of the Si cap is less tfian a critical value between 100 and 200 nm for a deposition rate of 0.01 nm/s. Steady-state endotaxy is modeled under the assumption that the process is controlled by Co diffusion.
Low Temperature Growth of Group II–A Fluoride Layers on Silicon as Buffer for Heteroepitaxial IV–VI and II–VI Compound Semiconductors
Authors: Blunier S. , Zogg H. , Tiwari A. N. , Maissen C. , Weibel H. , Hoshino T. , Theodoropol S.
Published: March 2011

We present our new development of low temperature (<450°C) MBE growth of group II-a fluorides on Si (111) and infrared sensor fabrication in Pb1−xSnxSe grown on such fluoride layers. The stacked CaF2-BaF2 buffer helps to overcome the large lattice and thermal mismatch between the Si-substrate and the narrow gap chalcogenide. Despite a rather nominal quality of the low temperature grown CaF2 layer, the 200nm thick epitaxial BaF2 top layer is of good structural perfection as judged from RBS channelling yield, RHEED-patterns and microscopy. The fluoride buffers were successfully overgrown with Pb1−xSnxSe and small IR-sensor arrays with up to 10.5μm cut-off wavelength were fabricated in the layers. The performance of these sensors is as good as for sensors fabricated with the high temperature buffer layer growth process.
Gas Source Silicon Molecular Beam Epitaxy
Authors: Hirayama H. , Hiroi M. , Koyama K. , Tatsumi T. , Sato M.
Published: March 2011

Gas source silicon molecular beam epitaxial (Si-MBE) growth is microscopically governed by a disociative adsorption of silicon hydrides, such as Si2H6 source gas molecules on Si surface. The dissociative adsorption generates SiH species on the surface. From this hydride phase, hydrogen desorbs thermaly. The temperature dependence of the growth rate indicated that the hydrogen desorption from the SiH is the rate limiting step. In HBO2 Knudsen cell doping, B adsorbates block the surface migration. Such a blocking effect can be avoided by B2H6 gas dopant, because of the similar incorpration mechanism of B2H6 to that of Si2H6. However, in PH3 gas doping, a crystal quality degradation was observed at a high doping range due to the preferentially high sticking coefficient of PH3 and the resulting surface dangling bond termination. The selective epitaxial growth of a B doped layer using Si2H6 and B2H6 was applied to a novel structured base fabrication for super self-aligned selectively grown base transistor (SSSBT). A successful achievement of the SSSBT fabrication indicates the high potentiality of gas source Si-MBE to the sub-micron size ultra-high speed bipolar large scale integrated (LSI) circuits.
Epitaxial Growth of Perovskite Type Oxide Films OH Si Substrates
Authors: Ishiwara H. , Mori H. , Jyokyu K. , Ueno S.
Published: March 2011

Epitaxial growth conditions of perovskite type oxide films on Si substrates are theoretically considered from a viewpoint of lattice matching. Then, epitaxial growth of SrTiO3 films and BaTiO3 films on Si (100) substrates has been tried, in which in order to deoxidize the SiO2 layers on the substrates, thin Sr layers are deposited prior to deposition of the oxide films. It has been found from X-ray diffraction, reflection high energy diffraction, and Rutherford backscattering analyses that SrTiO3 films grow epitaxially on Si (100) substrates under the optimum conditions of the Sr layer thickness, deposition temperature, and annealing temperature.
Growth of Silicon-Germanium Alloys by Atmospheric-Pressure Chemical Vapor Deposition at Low Temperatures
Authors: Agnello P. D. , Sedgwick T. O. , Goorsky M. S. , Ott J. , Kuan T. S. , Scilla G. , Kesan V. P.
Published: March 2011

Dichlorosilanc and germane were used to grow silicon-germanium alloys at temperatures as low as 550°C at atmospheric pressure. Germanium mole fractions as high as 44% were obtained and the layers exhibit smooth surface morphology. Silicon-gcrmanium/silicon multilayers with abrupt hctero-intcrfaccs have been achieved. Cross Section Transmission Electron Microscopy, (XTEM) and High Resolution X-Ray Diffraction, (HRXRD) characterization of the hetero-interface abruptness will be presented. Recent results on two-dimensional (2-D) hole mobility structures grown by this technique will also be reported. Selective growth of silicon-germanium on oxide patterned silicon wafers was also demonstrated. A significant feature of the selective deposition is the lack of faceting at the oxide sidcwall, which has been commonly observed in high temperature silicon growth.
Experimental and Model Studies of Dopant Segregation During Growth of Silicon Films by Molecular Beam Epitaxy
Authors: Ni W. -X. , Hansson G. V. , Sundgren J. -E. , Markert L. C. , Greene J. E.
Published: March 2011

Dopant incorporation and surface segregation are studied for thermal Sb and Al cases. The values of the incorporation probability and the segregation ratio have been mainly determine by SIMS measurements. The doping kinetics is discussed using a multi-site model including high dopant surface coverage effects. The calculated results were in good agreement with experimental data.
Evaluation on Electromigration and Stressmigration of Metal Interconnections by Hardness Measurements
Authors: Nakagawa T. , Miyatake H. , Maeda T. , Kuroda K. , Tokushige N. , Inoue R. , Kudo J. , Ashida T.
Published: March 2011

It is well known that the grain size of interconnections made from aluminum alloys affects electromigration and stressmigration tolerance. The hardness of three kinds of aluminum alloys is measured and it is shown that it has a strong correlation between the grain size of the aluminum alloy films. Stressmigration testing is done for those aluminum alloy films and it is found that the SM tolerance of aluminum films can be judged by the hardness of the films. Electromigration testing is also done and the results also confirm the correlation between EM tolerance and hardness of the aluminum films. Hardness measurements are simple and have the possibility of rough estimation of EM and SM tolerance. This method have the merit of saving time for life test.
Silicon Carbide Whisker Reinforced Aluminum with Improved Temperature Resistance due to the Use of a Phosphate Binder
Authors: Chiou Jeng-Maw , Chung D. D. L.
Published: March 2011

Silicon carbide whisker reinforced aluminum with improved temperature resistance, increased tensile strength and decreased coefficient of thermal expansion was obtained by using a phosphate binder instead of a commonly used silica binder for preparing the SiC whisker preform, to which liquid aluminum was infiltrated in order to form the composite. The composite is attractive for applications as a heat sink with a low coefficient of thermal expansion.
Numerical Simulation & Experimental Investigation of SMT Laser Microsoldering Thermal Process
Authors: Chunqing Wang , Yiyu Qian , Yihong Jiang
Published: March 2011

In this paper, a numerical simulation of thermal process in the SMT laser microsoldering joint has been developed, in which, the influence on thermal process of the factors such as the thermal conductivity variation of solder with temperature, light reflection coefficient of the lead wire surface, and heat exchange on the surface of SMT materials all have been considered. In order to carry this numerical calculation practice and prove it's results, the reflexive characteristic of light wave to the SMT materials has been gauged, and the dynamic temperature process of laser microjoint has been measured by a new experimental method which was invented by the authors.

The results of numerical simulation have been borne out by the tests, and the influences of heating parameters on thermal process has been analysed in this paper. The conclusions will be advantageous to the further study of the microjoint quality control in the SMT laser microsoldering.
Modelling and Characterization of Submicron P-Channel MOSFET's Locally Degraded by Hot Carrier Injection
Authors: Hassein-Bey A. , Cristoloveanu S.
Published: March 2011

The influence of the localized defective channel region formed by hot carrier injection on the basic characteristics of P-channel transistors is systematically investigated and modeled. A practical method of parameter extraction in stressed P-MOSFET's is proposed. It is based on the comparison of Ids(Vg) characteristics before and after stress in weak and strong inversion.
Impact of Oxygen during Post-Gate Processing on MOS Device Characteristics
Authors: Lee Steven S. , Lo G. Q. , Kwong D. L.
Published: March 2011

The effects of post-gate processing in N2+O2 (0˜40%) ambient (e.g., source/drain annealing, BPSG densification and reflow) on the initial MOS characteristics and reliability are discussed in this study. In comparison with processing in pure N2 ambient, it is found that processing in N2+O2-enriched ambient causes a significant, but, transient low-field breakdown of MOS capacitors on both n- and p-wells when electron injection occurs at the poly-gate/SiO2 interface. As a result, the p-channel MOSFETs with high concentration-O2 (˜40%) processing have an excess (i.e., two orders of magnitude) gate leakage current. The experimental results seem to suggest that the annealing in O2-enriched ambient (vs. pure N2 ambient) may induce positive charges near the poly-gate/SiO2 interface which reduce the electron tunneling barrier. Our results also suggest that the induced positive-charges are annihilated immediately upon the application of electric fields.
Enhanced Gate Oxide Reliability through Fluorine Incorporation and the Influence of Polysilicon Process Variations
Authors: MacWilliams K. P. , Lowry L. E. , Lin S. T. , Song M. , Cole R. , Brown S.
Published: March 2011

There has been some uncertainty as to the impact of fluorine (F) on SiO2 quality and reliability. Several laboratories have shown greatly enhanced quality and reliability with fluorinated oxides, while others have been unable to repeat the results. In addition, the laboratories which have shown enhanced reliability with the fluorinated oxides have differed in their interpretation of the mechanism by which the enhancement occurs. X-ray diffraction stress measurements, partial time dependent dielectric breakdown (TDDB) measurements, SIMS depth profiling, transmission electron microscopy, standard high/low frequency C-V measurements, and hot-carrier aging of variously processed MOSFETs have been used to investigate a variety of fluorinated films. We believe that the apparent lack of consistency of the effects of fluorine on MOSFET reliability between laboratories may be explained by slight variations in the gate polysilicon processing which result in variations in polysilicon morphology. The polysilicon morphology determines both mechanical stress and F diffusion which ultimately impacts interface state density and thus hot carrier reliability.
Properties of SiO2 Films Fabricated by Microwave ECR Plasma Processing with and without Energetic Particle Bombardment During Film Deposition. Part II: Electronic Properties
Authors: Chau T. T , Mejia S. R. , Kao K. C.
Published: March 2011

Silicon dioxide (SiO2) films were fabricated by microwave ECR plasma processing at 300°C, the range of the film thicknesses being 200 - 300 Å. Two groups of films were fabricated; group A with the substrates placed in a position directly facing the plasma so that the substrates as well as the on-growing films were subjected to bombardment of energetic particles produced in the plasma, and group B with the substrates placed in a processing chamber physically separated from the plasma chamber in order to prevent or suppress the damaging effects resulting from these energetic particle bombardment. It has been found that group A films are poor in both the capacitance-voltage (C-V) and the current-voltage (I-V) characteristics, possibly due to dust particles created by the gas phase reaction of SiH4 and ionic bombardment and radiation damage during film deposition. Group B films, on the other hands, exhibit good electronic properties. On the basis of their I-V and C-V characteristics, group B films yield an average breakdown strength of about 10 MV/cm, an oxide bulk charge density on the order of 1014 q/cm3 and an interface trap density on the order of 1011 cm−2 eV−1 which are approaching those of high quality thermally grown oxides and they are suitable for use as gate insulator for MOS devices.
Modulated Reflectance and Surface Topography Imaging: New Tools for Microelectronics Reliability
Authors: Smith W. Lee
Published: March 2011

New methods of probing beyond the limits of optical penetration have been developed using sensitive laser modulated reflectance techniques. Coupled with this subsurface defect detection method is a new surface topography imaging method. Together, these techniques nondestructively produce submicron-resolution images of surface and subsurface inhomogeneities in microelectronic structures. The measurables of these techniques are related to current reliability subjects. In interconnect metalization processes, defects such as stress- and electromigration-induced voids, precipitates of silicon or copper, sidewall notches, and hillocks and pits are images with these techniques. Sequential stressand-probe nondestructive testing allows the growth rate and other dynamical processes to be documerited. In silicon substrates, metal contamination and crystallographic defects are detected. In this talk, the measurement techniques are described and examples of their usage for VLSI reliability improvement are related.
Investigations of Residual Chlorine on Etched AlCu Metal Lines by Total Reflection X-Ray Fluorescence (TXRF)
Authors: Hockett R. S. , Herman M. H. , Mu X. C. , Ma Li-Jia
Published: March 2011

The present trend in the silicon IC industry is toward the replacement of AlSi metallization by AlCu(Si). However, the addition of Cu to Al(Si) increases the sensitivity of the metallization to moisture corrosion. Total reflection X-Ray Fluorescence (TXRF) with a detection limit in the 1012 atoms/cm2 range is used to measure the residual Cl on Al(Cu) as a function of processing. The results indicate that significant Cl can remain even after standard ash and chemical solvent resist removal. Furthermore, a need is identified to study some unexpected sources of Cl (e.g., air) and the chemistry of its removal from Al films, and this can be now be done easily using TXRF.
Metastable Pitting Corrosion of Aluminum, Al-Cu, and Al-Si Thin Films in Dilute HF Solutions and its Relevancy to the Processing of Integrated Circuit Interconnections
Authors: Scully J. R. , Peebles D. E.
Published: March 2011

We have investigated the pitting corrosion of Al, Al-Cu, and Al-Si thin films in dilute hydrofluoric acid solution. Additions of Cu and, to a lesser extent, Si cause an increase in open circuit potentials (OCP), pit densities and pit sizes as compared to pure Al. Pits in Al-Cu alloys are associated with Cu depleted grain boundaries which are galvanically coupled to adjacent θ-phase precipitates. Pits formed in Al-Si alloys are associated with the Al matrix which is galvanically coupled to Si nodules. θ-Al2Cu has different electrochemical characteristics than Al even though both maintain a thin Al surface oxide. θ-Al2Cu has a more positive OCP, above the average pit repassivation potential for pure Al. Since θ-Al2Cu supports cathodic reactions at enhanced rates compared to pure Al, its presence raises the potential of the adjacent pure Al grain boundary to values near its average breakdown potential and above its average repassivation potential. Metastable pitting is thus promoted.
Sub-Micron Contact Filling and Electromigration of Selfion-Enhanced Physical Vapor Deposited Aluminum Films
Authors: Hummel R. E. , Malone D. W.
Published: March 2011

The electromigration resistance, the sub-micron contact area filling capability, the crystal structure, the preferred orientation, and the CMOS device characteristics of self-ion-enhanced physical vapor deposited aluminum metallizations have been studied. It has been found that optimal conditions can be achieved by increasing the deposition rate and by applying some ionization and acceleration of the aluminum particles.
The AC-Indentation Technique and its Application to Al and Al-Si Coatings
Authors: Wu T.W.
Published: March 2011

An ac-microindentation technique, namely indenting with a small displacement modulation superimposed on an otherwise linear indenter motion, will be introduced. The basic principle and theory will also be illustrated by using a mechanical model to simulate the indenter behavior.

Other than being as capable as conventional indentation, the ac-technique acquires the unloading slope simultaneously and continuously with the penetration depth and applied load during an entire indentation process. With this extra information, the conversion between the total depth and plastic depth can be executed right after a single indentation, and in turn the hardness as well as. contact modulus depth profiles can be calculated. This is in contrast to the conventional indentation technique where a group of indentations associated with different maximum loads are required in order to achieve the same purpose. Furthermore, it also avoids the subjectivity in the selection of the fitting portions from the unloading stage of an indentation curve to extract the unloading slopes as well as the plastic penetration depths.

Another important advantage of using this ac-technique is the high sensitivity in detecting the indenter/surface contact. This advantage is very useful in the determination of the origins of penetration depths as well as in the investigation the evolution of the contact area, and both issues are very crucial in the microhardness calculations.

The strain rate effect on the hardness measurements of a 1 μm thick Al-2%Si coating has been demonstrated by using the ac-technique. As the indenter loading speed increases from 2.5 to 10 nm/sec, the measured hardness of the coating can be increased from ∼20% to ∼80% depending on the penetration depth, and the shallower the penetration depth the larger the increment is. However, the contact modulus depth profiles remain unchanged for all the indentation rates.
Laser Ultrasonic Measurement of Thin Film Elastic Properties
Authors: Bobbin Sarah E. , Wagner J. W. , Cammarata R. C.
Published: March 2011

A technique is presented for measurement of elastic properties of thin films from 0.001-0.025 mm in thickness. Lamb Waves were excited in free standing films with a pulsed Nd:YAG laser, and detected using heterodyne interferometry. Elastic properties were calculated from time-of-flight measurements. Variability in waveform structure with film thickness was observed, and interpreted with respect to extraction of elastic property information. An explanation is offered for changes in waveform structure, and common features are highlighted.