bluuebunny/crossref_metadata_2025 huggingface dataset:
Velocity Overshoot And Ballistic Electron Transport In Wurtzite Indium Nitride
Authors: Foutz B. E. , O'leary S. K. , Shur M. S. , Eastman L. F. , Bhapkar U. V.
Published: April 2011

Using an ensemble Monte Carlo approach, ballistic transport and velocity overshoot effects are examined in InN and compared with those in GaN and GaAs. It is found that the peak overshoot velocity is in general greater than both GaN and GaAs. Furthermore, the velocity overshoot in InN occurs over distances in excess of 0.4 μm, which is comparable to GaAs but is significantly longer than the overshoot in GaN. These strong overshoot effects, combined with a high peak drift velocity, large low-field mobility, and large saturation drift velocity, should allow InN based field effect transistors to outperform their GaN and GaAs based counterparts.
Theory of Interfaces and Surfaces of Wide-Gap Nitrides
Authors: Rapcewicz Krzysztof , Nardelli Marco Buongiorno , Bungaro Claudia , Briggs E. L. , Bernholc J
Published: April 2011

The results of extensive theoretical studies of the properties of interfaces and surfaces of the wide-gap III-V nitride semiconductors are reviewed. The phenomena that we have investigated include band offsets and transport properties in nitride-based devices, surface reconstruction energetics and adsorbate-substrate interactions. In the modelling of realistic blue-laser multiquantum well structures such as In0.2Ga0.8N/In1−xGaxN (x > 0.8) superlattices, pyro- and piezo-electric effects are found to be strong enough to reduce the interband recombination rate and limit the efficiency of an actual device. We have also studied the influence of growth conditions and surface polarity upon the morphology of (0001) GaN surfaces, which are the primary growth faces. The charge transfer between the Ga and N atoms in GaN and the very large electronegativity of nitrogen are found to play decisive roles in determining the stable reconstructions. The behavior of Mg at the Ga-terminated (0001) surface has also been investigated. We find that Mg in the Gasubstitutional site is preferred to adatom sites on the surface. Further, our results suggest that Mg prefers to segregate to the surface.
Band Offsets In GaN/AlN and AlN/SiC Heterojunctions
Authors: Binggeli Nadia , Ferrara Philippe , Baldereschi Alfonso
Published: April 2011

We have investigated the structural trends of the band offsets in GaN/AlN and AlN/SiC heterojunctions using the ab initio pseudopotential method. In the zincblende GaN/AlN (100), (110), and (111) heterojunctions, the band offsets are relatively insensitive to interface orientation. Bulk strain effects, however, can modify the offset by as much as 0.4 eV in coherently strained AlN/GaN and GaN/AlN (100) junctions. The band alignment in the heterovalent AlN/SiC (110) and (111) heterojunctions depends on the geometry and stoichiometry of the interface. Valence band offsets as high as 2.5 eV are obtained for neutral AlN/SiC(11) junctions with a mixed Al/Si interface layer and as low as 1.3 eV with a mixed N/C layer. Atomic relaxation plays a major role in determining the offset. The change from zincblende (111) to wurtzite (0001) crystal structure in GaN/AlN and AlN/SiC heterojunctions selectively affects the conduction band offset, and has only a minor influence on the valence discontinuity.
Valence Band Parameters for Wurtzite GaN and InN
Authors: Yeo Y. C. , Chong T. C. , Li M. F.
Published: April 2011

Theoretical studies and design of quantum well lasers employing InGaN require material parameters for both GaN and InN. However, the Luttinger-like effective-mass parameters for InN are currently unavailable. In this work, we extract effective-mass parameters for wurtzite GaN and InN from their electronic band structures calculated using the Empirical Pseudopotential Method (EPM). We obtain the electron and hole (including the heavy- (HH), light- (LH), and crystal-field split-off (CH) holes) effective-masses at the Γ point in the kz and the in-plane kx-ky plane) directions using a parabolic fit. In addition, the hole effective-mass parameters are derived using the 6×6 effective-mass Hamiltonian and the k.p method. Our results will be useful for material design in wide-gap nitride-based semiconductor lasers containing InGaN.
Doping, Activation of Impurities, and Defect Annihilation in Gan by High Pressure Annealing
Authors: Suski T. , Jun J. , Leszczynski M. , Teisseyre H. , Grzegory I. , Porowski S. , Baranowski J. M. , Rocket A. , Strite S. , Stonert A. , Turos A. , Tan H. H. , Swilliams J. , Jagadish C.
Published: April 2011

GaN semiconductor is characterized by strong bonding and high vapor pressure of nitrogen. The strong bonds limit an efficiency of annealing procedures required for variety of semiconductor technologies, for example, post-implantation annealing, or doping by diffussion. Maximum temperatures employed up to now (at ambient pressure) in GaN annealing have not exceeded about 1100°C. A desired increase of annealing temperatures would cause a decomposition of GaN unless an elevated pressure of N2 is supplied. In this work, we report onapplication of high pressure annealing procedures (temperatures up to 1550°C and pressures up to 16 kbar) which enabled us to study variation of the properties of epitaxial films and bulk crystal of GaN. In particular, we discuss the following results obtained using high pressure annealing: i) structural quality improvement and increase of the thermal strain in as grown epitaxial layers of GaN/A12O3, The annealing at above 1300°C resulted in the decrease of the X-ray rocking curve width from about 700 arc sec. down to 470 arc sec., ii) drastic increase of bandedge (bound exciton) photoluminescence intensity iii) enhancement in removal of implant damage, iv) increase of diffusivity of Zn and Mg atoms (introduced by implantation and/or diffusion from external source). For Zn in epitaxial layers of GaN/A12O3 a diffusion starts at 1200–1250°C, v) enhancement of the blue-photoluminescence intensity in Zn and Mg implanted GaN. The performed experiments give an evidence of the importance of the defect (dislocations) in diffusion of Zn and Mg in the GaN semiconductor.
In-Situ Observation Of Aln Formation During Nitridation Of Sapphire By Ultrahigh Vacuum Transmission Electron Microscopy
Authors: Yeadon M. , Marshall M. T. , Hamdani F. , Pekin S. , Morkoc H. , Gibson J. M.
Published: April 2011

Using a novel ultrahigh vacuum transmission electron microscope (UHV TEM) with insitu molecular beam epitaxy capability we have studied the nitridation of (0001) sapphire upon exposure to ammonia. Atomically flat sapphire surfaces for the experiments were obtained by high temperature annealing. Subsequent exposure to ammonia flow at 950°C led to the successful synthesis of epitaxial AIN; the films were characterized in-situ using TEM. Complimentary ex-situ atomic force microscopy (AFM) was also performed in order to characterize the surface morphology before and after nitridation.

The experiments indicate that AIN grows by a 3D island growth mechanism. Electron diffraction patterns suggest an abrupt AIN/sapphire interface with no evidence of the formation of Al–O–N compounds. The rate limiting step in the nitridation reaction appears to be the diffusion of nitrogen and oxygen species between the free surface of the growing AIN film and the reaction interface. It is inferred from kinetic measurements that diffusion of these species occurs along the boundaries between coalescing AIN islands.
A Technique For Rapid Thick Film Sic Epitaxial Growth
Authors: Khlebnikov I. , Sudarshan T. S. , Madangarli V. , Capano M. A.
Published: April 2011

In this paper we demonstrate the growth of thick SiC epitaxial layers (≥100 μm) of good structural quality at a high growth rate (>100 μm/hr) by controlling the vapor dynamics during conventional physical vapor transport (PVT) process. We propose that our PVT technique be used to ‘repair’ or ‘heal’ commercially available substrates dominated by micropipes, by ‘filling up’ the micropipes through crystal growth inside the micropipe. Extensive experiments performed on thick SiC epitaxial layers grown on Lely substrates indicate that the thick epitaxial layers are of single polytype of high structural quality, with a single peak X-ray rocking curve of less than 12 arcsecs FWHM.
Metallization Of Thin Graphite Layers After Cs Deposition On 4H-Sic(0001) Surfaces
Authors: Nienhaus H. , Elsbergen V. Van
Published: April 2011

The interaction of cesium atoms with graphitized 4H-SiC(0001) surfaces was investigated by use of Auger electron, ultraviolet photoemission and high-resolution electron energy-loss spectroscopy (HREELS) as well as work function measurements with a Kelvin probe. The samples were annealed at temperatures well above 1300 K resulting in a formation of about two graphite layers on top of the SiC substrates. The corresponding low-energy electron diffraction image shows a () pattern. Cs deposition on graphitized SiC occurs in two subsequent stages. First, even small amounts of evaporated Cs lead to a spontaneous decrease in work function by 1.8 eV. The work function stays constant after further evaporation corresponding to an intercalation of Cs into the graphite overlayer. In the second stage Cs atoms are adsorbed on top of the Cs-intercalated compound resulting in a further decrease of work function. The graphite layer is effectively metallized by Cs evaporation. This is confirmed by a Fermi edge which is observed in the photoemission spectra even after the smallest dose applied. Moreover, the excitation of optical Fuchs-Kliewer phonons in SiC by HREELS is significantly quenched by the metallic overlayer and the electron energy-loss spectra exhibit features which are typical for thin homogeneous metal layers on surfaces of heteropolar semiconductors.
Pld Epitaxial Tin And Pt Ohmic Metallizations To P-Type 6H-Sic Using Focused Ion Beam Surface Modification
Authors: Iliadis A. A. , Andronescu S. N. , Edinger K. , Orloff J. H. , Talyansky V. , Vispute R. D. , Sharma R. P. , Venkatesan T. , Wood M. C. , Jones K. A.
Published: April 2011

The development of low resistance ohmic metallizations to p-type 6H-SiC using a novel approach of focused ion beam (FIB) surface-modification and ex-situ epitaxial pulsed laser deposition (PLD) of TiN and Pt without further annealing, is reported. The FIB(Ga) surfacemodification and ex-situ epitaxial TiN and Pt PLD metallizations showed a significant reduction in contact resistance with surface-modification, reaching a minimum contact resistance value of 4.4×10−5 Ohm cm2 for the TiN system at an ion dose of 5.0×1016 ions/cm 2 and energy of 20 KeV. This contact resistance value is one of the lowest values reported to date. The Pt system showed increased contact resistance values as compared with the TiN, and reached minimum values for lower ion doses. The contact resistance values reported here are comparable to or lower than those reported for conventionally deposited and annealed contacts to p-type SiC.
Single Crystal Silicon Carbide On Silicon Using A Supersonic Gas Jet Of Methylsilane
Authors: Ustin S. A. , Long C. , Lauhon L. , Ho W.
Published: April 2011

Cubic SiC films have been grown on Si(001) and Si(111) substrates at temperatures between 600 °C and 900 °C with a single supersonic molecular beam source. Methylsilane (H3SiCH3) was used as the sole precursor with hydrogen and nitrogen as seeding gases. Optical reflectance was used to monitor in situ growth rate and macroscopic roughness. The growth rate of SiC was found to depend strongly on substrate orientation, methylsilane kinetic energy, and growth temperature. Growth rates were 1.5 to 2 times greater on Si(111) than on Si(001). The maximum growth rates achieved were 0.63 μm/hr on Si(111) and 0.375μm/hr on Si(001). Transmission electron diffraction (TED) and x-ray diffraction (XRD) were used for structural characterization. In-plane azimuthal (ø-) scans show that films on Si(001) have the correct 4-fold symmetry and that films on Si(111) have a 6-fold symmetry. The 6-fold symmetry indicates that stacking has occurred in two different sequences and double positioning boundaries have been formed. The minimum rocking curve width for SiC on Si(001) and Si(111) is 1.2°. Fourier Transform Infrared (FTIR) absorption was performed to discern the chemical bonding. Cross Sectional Transmission Electron Microscopy (XTEM) was used to image the SiC/Si interface.
Epitaxial Growth Of High Quality Sic By Sublimation Close Space Technique
Authors: Nishino S. , Yoshida T. , Nishio Y.
Published: April 2011

Semiconducting SiC is expected for power devices and higher breakdown voltage of the device is required. Growth rate of epilayer by conventional CVD is about 3 μ m/h. To make a thick epilayer, more than 10 hours are needed. To minimize the growth time, we propose sublimation epitaxial method by close space technique (CST). In the CST, source ( polycrystalline 3C–SiC plate) and substrate is closely separated by spacer and source material is sublimed and transferred to the substrate in argon. Epitaxial layers with specular surface were obtained on 6H–SiC substrates at a substrate temperature around 2200 °C and growth rate was about 100 μ/h. Nitrogen-bound exciton was observed by PL measurement at 2 K in the epilayer when 3C–SiC plate with high purity was employed as the source material. Crystallinity of the epilayer was characterized by Raman spectroscopy.
A Fast And Efficient Simulation Tool For The Voltage Handling Capability Of High Voltage Devices
Authors: Stefanov E. , Charitat G. , Nolhier N. , Spiesser Ph.
Published: April 2011

The user-oriented simulator POWER2D for studying the voltage handling capability of power semiconductor devices is presented. The simulation is based on the Poisson's equation solution for an arbitrary shaped 1D, 2D, and cylindrical 3D high voltage semiconductor structures. Very fast solution of the potential is obtained for a high level of applied bias, based on incomplete LU decomposition preconditioned biconjugate gradient method, and combined with a multi-damping scheme for the Newton linearization of the non-linear algebraic equations. An original algorithm is developped ensuring a very fast and automatic search of the breakdown via the ionization integrals calculus. The predicting capability of the program is illustrated for different termination techniques showing good agreement with the experiment.
Development Of Diamond Based Power Microelectronics
Authors: Davidson J. L. , Kang W. P. , Gurbuz Y. , Kerns D. V. , Davis L. , Holmes K. , Jiang L. , Pulugurta Venkata , Anurat W. , Howell M.
Published: April 2011

Diamond based power device structures such as resistor, capacitor, Schottky diode, p-n diode, thyristor, and field emitters are being investigated. Diamond resistors similar to standard thick film components in form and dimension were fabricated of polycrystalline diamond film. Using PECVD (plasma-enhanced chemical vapor deposition) processing to achieve diamond dielectric layers, high power, high energy density capacitors have been built. Despite grain boundaries and defects of polycrystalline diamond film, electronic devices such as field-effecttransistors and Schottky diodes have been developed. We have fabricated micro-patterned microtip arrays with this versatile new diamond technology as electron emitters. This paper will review diamond technology and results of this work.
A Study of the CdS/CuIn(Ga)Se2 Interface in Thin Film Solar Cells
Authors: Ramanathan Kannan , Wiesner Holm , Asher Sally , Niles David , Webb John , Keane James , Noufi Rommel
Published: April 2011

In this paper we describe our research efforts directed towards the understanding of the CdS/CuInGaSe2junctions and, specifically, the interaction of the chemical bath with the CuInGaSe2 (CIGS). We find that Cd and S diffuse into the absorber during the CdS growth. Heating the absorbers in Cd partial baths resuled in a significant improvement in the ZnO/CIGS device properties. Photoluminescence measurements indicate that the effect of Cd is very similar to that of CBD CdS.
Very high hole concentrations in C-doped InGaAs using new sources with APOMVPE
Authors: Tandon A. , Cohen R. M.
Published: April 2011

New sources have been used to grow the first carbon doped, highly p-type InxGa1-xAs (0.2>x>0.7) epilayers on InP substrates by atmospheric pressure organometallic vapor phase epitaxy (APOMVPE). Excellent morphology was obtained simultaneously with high hole concentrations at growth temperatures near 450 °C. High hole concentrations of 1.6×1019 – 8.7×1019 cm−3 (the highest reported to date for APOMVPE), and the corresponding room temperature hole mobilities of 65 – 25 cm2/s, respectively, have been obtained from Hall measurements. X-ray diffraction is consistent with excellent crystal quality. Annealing at temperatures of T=400–500 °C in the presence of either nitrogen or hydrogen was found to change the carrier concentration by only 0–15%. However, after annealing at T=650 °C, irreversible changes occurred in the InGaAs. After a high temperature anneal, reversible order of magnitude changes in the hole concentration was obtained upon further annealing at low temperatures, depending upon the ambient. These results conclusively show that hydrogen does not passivate C acceptor ions in InGaAs. Since changes in the carrier concentration become substantial and reversible only after high temperature annealing, the results strongly suggest that a structural change occurred in the crystal at high temperatures. We consider it likely that this structural change is the precipitation of carbon out of a supersaturated solid solution, and that hydrogen atoms associated with these precipitates act as donors which compensate the hole concentration.
Optical Characterization of Ultrathin Silicon Substrates
Authors: Globus T. , Jones S. H. , Digges T.
Published: April 2011

In this paper we present results for the absorption coefficient and refractive index spectra of p-and n-type silicon membranes doped with phosphorous or boron at different levels. These results cover the wide energy range from 0.5 eV up to 2.5 eV, thus including effects of subgap defect and impurity absorption, and the range of possible transitions to higher conduction band minima. The results have been obtained by utilizing both a conventional transmission and reflection measurement technique at small values of transmittance, and a recently developed optical interference spectroscopy characterization technique. The results in the visible and near infrared regions from the two techniques have been compared, and the range of transmission where the conventional technique is applicable have been determined. The preliminary analysis of these data indicate that a new information regarding the Si electronic band structure can be extracted.
Plasma Deposition and Interface Control in Low Temperature Processing of Thin Film Solar Cells
Authors: Jagannathan B. , Anderson W. A.
Published: April 2011

Plasma deposition of thin silicon films with a variable microstructure and controlled interface formation techniques are being developed for thin film silicon/polycrystalline silicon solar cells. Low hydrogen content amorphous (a-Si) or microcrystalline silicon (μ c-Si) films were obtained by controlling the H2 dilution of 2% SiH4/He in a microwave ECR discharge. The films were characterized for structural and electro-optic properties. Junction creation for solar cells was investigated by depositing single or multilayers of the film silicon onto crystalline silicon (c-Si). Effort to improve carrier transport and photovoltaic (PV) properties was pursued through interface modifications effected by varying the microstructure of the layer in contact with the substrate. Cells with 7% conversion efficiency (No A/R) were obtained for an a-Si/c-Si heterojunction configuration. Improved carrier transport and PV properties (9% ef ficient) were achieved by inserting a thin μ c-Si layer in the above structure.
Nanocrystalline Silicon/Amorphous Silicon Dioxide Superlattices
Authors: Fauchet Philippe M. , Tsybeskov Leonid , Zacharias Margit , Hirschman Karl
Published: April 2011

Thin layers made of densely packed silicon nanocrystals sandwiched between amorphous silicon dioxide layers have been manufactured and characterized. An amorphous silicon/amorphous silicon dioxide superlattice is first grown by CVD or RF sputtering. The a-Si layers are recrystallized in a two-step procedure (nucleation + growth) to form layers of nearly identical nanocrystals whose diameter is given by the initial a-Si layer thickness. The recrystallization is monitored using a variety of techniques, including TEM, X-Ray, Raman, and luminescence spectroscopies. When the a-Si layer thickness decreases (from 25 nm to 2.5 nm) or the a-SiO2 layer thickness increases (from 1.5 nm to 6 nm), the recrystallization temperature increases dramatically compared to that of a single a-Si film. The removal of the a-Si tissue present between the nanocrystals, the passivation of the nanocrystals, and their doping are discussed.
Si Surface Preparation with Si Beam Irradiation on the Growth of III-V on Si
Authors: Kawanami H. , Baskar K. , Sakata I. , Sekigawa T.
Published: April 2011

The preliminary results of the effects of the Si beam irradiation for the Si surface preparation on the growth of GaAs on Si by MBE are reported. The effects are combined with thermal cyclic anneal (TCA). A slight improvement in the crystalline quality is observed on the photoluminescence spectra of the films grown with Si irradiation. In our experimental conditions, Si irradiation during the Si surface preparation has not indicated large effects on the FWHM of XRD. It is also indicated that initial substrate surface treatment affects the quality of thicker film through TCA treatment. Higher substrate temperature during Si beam irradiation is expected to indicate positive Si beam irradiation effects.
Electroluminescent Devices Based On Polycrystalline Silicon Films For Large-Area Applications
Authors: Koshida N. , Takizawa E. , Mizuno H. , Arai S. , Koyama H. , Sameshima T.
Published: April 2011

It is shown that porous polycrystalline Si (PPS) diodes operate as light-emitting diodes (LEDs) with efficiencies comparable to conventional porous silicon (PS) diodes fabricated on singlecrystalline substrates. Judging from the electroluminescence (EL) characteristics such as emission spectra, diode current dependence of EL intensity, and its temperature dependence, the common EL mechanism seems to exist in PPS and PS diodes. Observed similarity in the photoluminescence (PL) properties between PPS and PS is consistent with this hypothesis. The capability of a poly-Si thin film transistor as a driver of PPS-LED is also demonstrated.
A Led Based on Porous Polycrystalline Silicon
Authors: Huang W. N. , Tong K. Y. , Chan P. W.
Published: April 2011

Previous studies on electroluminescence in porous silicon were based on crystalline wafers. In this paper, we shall report the characteristics of a LED based on porous effects in a cast polycrystalline silicon substrate. A layer of porous region was first formed on a cast polycrystalline silicon substrate by anodization, followed by the deposition of a semitransparent Au layer. Under forward bias, the LED emits stable yellowish white light (with the presence of bright spots) for currents above 20 mA/cm2. From the electroluminescence spectra measured, we suggest that the emission is due to the recombination of electron-hole pairs in a microplasma region. We propose a model where the microplasma is present in the depletion region of the heterojunction formed between the bulk polysilicon and the surface porous polysilicon. The defects and grain boundaries in a polycrystalline material facilitate the formation of such microplasma. The heterojunction model will also be used to explain the current characteristics of the LED. The effect on the LED characteristics due to indium coating on the porous substrate prior to Au deposition was studied, and the results agree with the heterojunction model. Our work shows that cast polycrystalline silicon substrates have potential for LED fabrication in cheap and large area applications.
Electroluminescence study of Si-Si1-xGex/Si1-yCy-Si p-i-n diode structures
Authors: B. Joelsson Kenneth , Ni Wei-Xin , Du Chun-Xia , V. Hansson Göran
Published: April 2011

The electroluminescence from p-i-n diode structures with Si1-yCy/Si1-xGex layers in the depletion region has been studied. Emission attributed to an overlap of the wavefunction associated with electrons confined in the Si1-yCy layer and the wavefunction associated with holes confined in the Si1-xGe, layer has been observed. For low injection currents, emission due to recombination occurring in the Si1-xGex layer is more dominant. For structures with higher C concentration, the interface related emission can persist up to higher temperatures.
Lattice Sites and Stability of Implanted Er in FZ and CZ Si
Authors: Wahl U. , Correia J. G. , Langouche G. , Vantomme A. , collaboration Isolde
Published: April 2011

We report on the lattice location of 167Er in Si measured by conversion electron emission channeling. In both FZ and CZ Si, a high fraction of Er (>65%) occupies near-tetrahedral interstitial (T) sites directly following 60 keV room temperature implantation at doses of 6× 1012 cm−2 For higher doses, the as-implanted near-T fractions of Er visible by emission channeling are smaller, due to the beginning of amorphization. Following the recovery of implantation damage at 600°C, more than 70% of Er is found on near-T sites in both FZ and CZ Si. In FZ Si, Er exhibits a remarkable thermal stability and only prolonged annealing for several hours reduces the near-T fraction. On the other hand, annealing of CZ Si at 900°C for more than 10 minutes results in the majority of Er probes in sites of very low symmetry or disordered surroundings.
Photoluminescent Silicon in Nanoporous Aluminium Oxide
Authors: Heilmann Andreas , Jutzi Peter , Klipp Andreas , Kreibig Uwe , Neuendorf Rolf , Sawitowski Thomas , Schmid Günter
Published: April 2011

Thermal decomposition of a metastable silane in nanoporous alumina leads to the formation of luminescent silicon nanostructures. While varying the pore size of the transparent membranes the luminescence can be shifted from 504 nm up to 537 nm by building up a sheet-like structure of siloxene on the inner pore surface.
Electronic Structures of Halogenated Polysilanes
Authors: Motoyama Hideshi , Takeda Kyozaburo , Shiraishi Kenji
Published: April 2011

The electronic structures of halogenated polysilanes (PSi), whose side chains are replaced by halogen (X) atoms, have been theoretically investigated based on the firstprinciples calculations. It was found that non-bonding (n) electrons localizing at the X atom produce an important orbital mixing with the u valence electrons delocalized in the direction of the PSi skeleton (a-n mixing). This a-n mixing splits the top of the valence bands, and creates unoccupied states in the band gap. This valence-band-splitting effectively narrows the band gap to the visible range, and the unoccupied state in the band gap has the potential to be an electron acceptor. Moreover, we also investigated several replacement patterns as well as the kind of replaced halogen species (X=F, Cl, Br, I). The dispersion and energy position of the unoccupied state(s) can be artificially tuned by these chemical modifications. Thus, halogenation can change PSi into optelectronic polymers with visible photoluminescence.
Active Silicon Integrated Optical Circuits
Authors: Bestwick Tim D.
Published: April 2011

Active Silicon integrated Optical Circuits (ASOC™) is a technology based on single-mode rib waveguides formed on silicon-on-insulator that is being used to manufacture commercial integrated optics components. Silicon waveguides have excellent properties for many applications in the 1.3 and 1.55 micron telecommunications bands including relatively low loss. An important aspect of ASOC™ technology is the development of a set of waveguide-based elements that can be assembled into practical integrated optics devices. The fundamental waveguide elements include bends, couplers and fiber-waveguide interfaces, and additional elements include doped structures and waveguide gratings. Discrete lasers and photodetectors are also incorporated into ASOC™ technology to form hybrid devices. The technology is being used to manufacture devices for applications in telecomunications and optical sensing, the first major product being a two-wavelength single-fiber bi-directional optical transceiver.
Generating an Intracellular Diffusion Map by Two-Photon Fluorescence Correlation Spectroscopy
Authors: So P. T. C. , Duggar K. , Berland K. M. , Gratton E.
Published: April 2011

A new technique for determining cellular viscosity has been developed based on two-photon excitation and fluorescence correlation spectroscopy. We have applied this method to map intracellular diffusion coefficient of small molecules at selected cytoplasmic locations of mouse fibroblast cells. The cytoplasmic diffusion rate is one tenth of that in an aqueous environment.
Structure and Forces in Transfection Related Surfactant Systems
Authors: Campbell Samuel E. , Park Chad K. , Lasic Dan D. , Israelachvili Jacob N.
Published: April 2011

Experiments have been performed on the cationic bilayer and liposome-forming surfactant DODAB, a successful DNA transfection agent. The surface forces apparatus (SFA) was utilized to measure the long-range colloidal and short-range adhesion forces between Langmuir-Blodgett bilayers exposing DODAB in the outer monolayers. Forces were measured in aqueous solutions of varying salt concentrations between 1 and 10 mM, with and without single-stranded DNA added to the solution. These represent the first measurements of the forces between surfactant/DNA assemblies. At low salt concentrations without DNA, the interbilayer forces are repulsive due to their electrostatic interaction, in agreement with DLVO theory. In contrast, in the presence of DNA which adsorbs to the bilayer surfaces, the forces between the bilayers changed to an enhanced and longer ranged repulsive steric-electrostatic interaction. At shorter range. the DNA can be excluded from the gap leading to an enhanced adhesion at contact accompanied by lipid rearrangement.
On Motion of Adhering Vesicles
Authors: Durand I. , Misbah C.
Published: April 2011

We study theoretically phospholipid vesicle locomotion caused by adhesion. The problem is solved numerically, and an analytical solution is obtained in a perturbative scheme. The analytical result reproduces the numerical one. We provide an expression for the drift velocity as a function of relevant parameters when only local dissipation is present. We briefly discuss the transition from sliding to rolling when hydrodynamics are included. We mention situations where the vesicle may itself establish an adhesion gradient. We propose some simple experimental protocols.
Reptation of Microtubules in F-Actin Networks : Effects of Filament Stiffness and Network Topology on Reptation Dynamics
Authors: Shah Jagesh V. , Flanagan Lisa A. , Bahk David , Janmey Paul A.
Published: April 2011

The thermally driven motions of fluorescently labeled microtubules embedded in a network of filamentous actin polymers are analysed as the diffusion of a rod-like polymer within a virtual tube formed by the surrounding semiflexible actin filaments. The apparent diffusion constant parallel to the tube scales with the inverse of the microtubule length and the magnitude is consistant with diffusion through a medium with a viscosity of approximately 10 centipoise. Introduction of crosslinks between the actin filaments does not alter the diffusion of the microtubules in the actin network.
Quantal Motor Action in Muscle Contraction
Authors: Pollack G. H. , Blyakhman F. , Shklyar T. , Tourovskaia A. , Tameyasu T. , Yang P.
Published: April 2011

It is becoming clear that quantal behavior is a central feature of contractile systems. Steplike behavior has been demonstrated in the kinesin - microtubule system and in the myosin - actin filament system-both on molecular scale. We show here that step-like features appear also in the single intact sarcomere. We studied single sarcomeres of single bumblebee myofibrils. Motorimposed ramp length changes on activated myofibrils resulted in sarcomere-length changes that were stepwise. Computer analysis of the stepwise shortening patterns revealed a step-size distribution containing multiple peaks. The peaks were separated by 2.7 nm per half-sarcomere which is the linear actin-subunit spacing. Thus, translation steps are an integer multiple of the actin-subunit spacing. This result parallels the one observed in the kinesin-tubulin spacing where step size is a multiple of the tubulin-subunit spacing. In the muscle system, however, the steps are preserved on a macroscopic scale, implying high synchrony. The quantal steps are easily explained by a model in which the actin filament propels itself over stationary cross-bridges: if actin binds to the cross-bridges between steps, then the observed quantal result is inevitable.
Fermi-Level Effect on Group III Atom Interdiffusion in III-V Compounds: Bandgap Heterogeneity and Low Silicon-Doping
Authors: Chen C.-H. , Gösele U. , Tan T. Y.
Published: April 2011

Heavy n-doping enhanced disordering of GaAs based III-V semiconductor superlattice or quantum well layers, as well as the diffusion of Si in GaAs have been previously explained by the Fermi-level effect model with the triply-negatively-charged group III lattice vacancies identified to be the responsible point defect species. These vacancies have a thermal equilibrium concentration proportional to the cubic power of the electron concentration n, leading to the same dependence of the layer disordering rate. In this paper, in addition, we take into account also the electric field effect produced by the material bandgap heterogeneity and/or hetero-junctions. In heavily n-doped or long time annealing cases, this effect is negligible. At low n-doping levels and for short annealing times, the layer disordering rate can be enhanced or reduced by this effect. Available experimental results of low Si-doped and very short-time annealed samples have been satisfactorily fitted using the Fermi-level effect model.
Defect Reactions Induced by Reactive Ion Etching
Authors: Zhao Song , Kimerling Lionel C.
Published: April 2011

Reactive ion etching (RIE) causes substrate surface contamination, substrate damage, and induces defect reactions to produce carrier traps at depths into μm range. We have developed a model describing the indiffusion of interstitials and the subsequent reactions in the defect reaction region to predict the defect depth profiles. We formulate the reaction kinetics as a series of 1-D coupled interstitial diffusion-reaction partial differential equations (PDEs) with a moving boundary. The predicted defect depth profiles are consistent with those measured in the photoluminescence (PL) experiments. We conclude that the defect depth profiles are determined by interstitial diffusion coefficient (Di), etch rate (υE), etch time (tE), defect reaction rate (K), and background dopant and impurity concentrations ([C], [B] and [O]) in the Si substrate. The μm range defect depth profiles can be explained as: (i) fast diffuser Si self-interstitial (Sii) indiffusion to a μm depth range of (Di/K)1/2 limited by [C] and [B]; (ii) the generation of carbon and boron interstitials (Ci and Bi) through the Watkins replacement reactions, and (iii) the formation of Ci- and Bi-related defect pairs through diffusion limited pairing reactions. Ci and Bi indiffusion are limited by υE and extremely shallow (Di/υE) during a typical RIE process with υE≈1000Å/min and tE≈10min. The indiffusion of vacancies (V), contamination from the etching plasma and enhanced diffusion effects are also considered in the model.
Chemical Kinetics Models for Semiconductor Processing
Authors: Coltrin Michael E. , Meeks Ellen , Grcar Joseph F. , Houf William G. , Kee Robert J. , Randall Creighton J.
Published: April 2011

Chemical reactions in the gas-phase and on surfaces are important in the deposition and etching of materials for microelectronic applications. A general software framework for describing homogeneous and heterogeneous reaction kinetics utilizing the Chemkin suite of codes is presented. Experimental, theoretical and modeling approaches to developing chemical reaction mechanisms are discussed. A number of TCAD application modules for simulating the chemically reacting flow in deposition and etching reactors have been developed and are also described.
Modeling of Grain Structure Evolution and its Impact on the Reliability of Al(Cu) Thin Film Interconnects
Authors: Riege S. P. , Andleigh V. , Thompson C. V. , Frost H. J.
Published: April 2011

We have extended a 2D simulation of grain growth to treat the effects of precipitates on the evolution of interconnect grain structures during post-patterning processing. It is known from experiments that different annealing histories result in different precipitate sizes and locations. Precipitates capture and effectively pin grain boundaries and inhibit grain growth and evolution toward bamboo structures. We find that even a small volume fraction of precipitates prevent an interconnect strip from reaching the fully bamboo structure by retarding grain growth and lowering the average grain size. At a late stage of evolution, cluster regions are pinned by precipitates on both sides, preventing further transformation to the by far more reliable bamboo structure. The results from grain growth simulations have been used with our electromigration simulator MTT/EmSim to investigate the dependence of interconnect reliability on linewidth and precipitate distribution. We find that in lines with precipitates the bamboo structure is not reached during post-pattern annealing even if the line width is smaller than the average grain diameter. Furthermore, it is found that while Cu in solid solution improves interconnect reliability, Al2Cu precipitates can inhibit post-patterning grain structure evolution to more reliable bamboo or near-bamboo structures so much that similar lines made of pure Al would be more reliable. Linked grain structure evolution and electromigration simulations allow process optimization for maximum interconnect reliability.
Simulation Study of IBE Process for III-V Compounds in Mesa and Trenches
Authors: Houlet L. , Rhallabi A. , Turban G.
Published: April 2011

The Ion Beam Etching (IBE) model is developed assuming the analogy between the evolution of hydrodynamic surfaces and that of vacuum-solid interfaces. The main physical phenomenon in the IBE is the ion sputtering where the transfer of ion energy to the surface allows to eject the surface atoms. The local etching rate is thus proportional to the energetic flux and to the sputtering yield. Mask erosion and shadowing are taken into account in the model. The angular dependence of the sputtering yield permits to underscore the faceting and trenching phenomena which respectively represent the formation of the facets in mask comers and the overetching in the trench sides. Besides, the effect of mask erosion on pattern transfer of both trench and mesa structures is studied. In comparison with the experimental profile, the simulated etching profile of the mesa, based on the IBE model, shows a good agreement.
Effects of Compositional Segregation and Short Channel on Threshold Voltage of nMOSFET
Authors: Lee Julie Y. H. , Lee Tom C. H. , Embry Mike , Evans Keenan , Koch Dan , Tucker Robert
Published: April 2011

This study calculates the threshold voltage (VT) roll-off behavior caused by short channel effect (SCE) as a result of scaling and the reverse short-channel effect (RSCE) due to B segregation around source and drain junctions by using the 2D device simulator - SILVACO™-ATLAS. The simulation results are comparable with the experimental data. It suggests that the drift diffusion physics can predict SCE and RSCE very well to sub-0.25μ Si n-MOSFET devices. The modeling results indicate the VT roll off at shorter channel length for devices with higher substrate doping concentration. VT increases if the local p-dopant segregation exists around the source and drain junction. It is observed that RSCE is more significant for devices with lower substrate doping concentration and shorter channel length.
Computationally Efficient Model for 2D Ion Implantation Simulation
Authors: Temkin Misha , Chakarov Ivan
Published: April 2011

A computationally efficient method for ion implantation simulation is presented. The method allows two-dimensional ion implantation profiles in arbitrary shaped structures to be calculated and is valid for both amorphous and crystalline materials. It uses an extension of the one-dimensional dual Pearson approximation into the second dimension.
Atomic Dynamics During Silicon Oxidation and the Nature of Defects at the Si-SiO2 Interface
Authors: Pantelides S. T. , Ramamoorthy M.
Published: April 2011

Oxidation of thin-film Si, oxygen precipitation in bulk crystalline Si, and the formation of buried oxide layers (as in the SIMOX process for SOI) have been studied extensively for decades but the underlying atomic scale processes have remained elusive. Furthermore, common features of these phenomena have not been generally appreciated, in part because the kinetics are substantially different in the different cases. In this paper we review recent theoretical research based on atomic-scale first-principles calculations that provides a unified description of the three phenomena. In particular, we account for both the normal and enhanced mode of oxygen diffusion that leads to the formation of oxygen clusters known as thermal donors and their subsequent annealing and evolution into SiO2-like precipitates. It is proposed that a novel family of interface defects that are akin to thermal donors, composed of “frustrated” Si-O bonds, are a natural by-product of thin-film oxidation. An explicit mechanism for the emission of Si interstitials, which occurs during both oxidation and oxygen precipitation, is obtained. It is shown that emission of Si interstitials eliminates the frustrated-bond defects, thus explaining the high quality of the resulting interfaces. It is proposed that frustrated-bond defects are responsible for much of the behavior observed at the Si-SiO2 interface that cannot be accounted by dangling bonds and for the amphoteric traps that occur in high concentrations in SOI material.
Cohesive Energies of Be and Mg Chalcogenides
Authors: Porcu M. , Satta G. , Casula F. , Mula G.
Published: April 2011

We have calculated the cohesive energies, bulk moduli and equilibrium volumes of Be and Mg oxides, sulphides and selenides, in both zincblende and rocksalt structures. The calculations have been performed with the Discrete-Variational-Method (DVM), a real space first-principle local-density-functional approach. Comparisons with the experiment and with other first-principles approaches show that the electronic and structural properties of solids can be computed with DVM at least as accurately as with the usual plane-wave pseudopotential methods. This result is especially interesting in view of the fact that an order N implementation of DVM, based on the W. Yang's divide and conquer method, has been recently developed.
Quantum Monte Carlo Simulations of Disordered Magnetic and Superconducting Materials
Authors: Scalettar R. T. , Denteneer P. J. H. , Huscroft C. , Mcmahan A. , Pollock R. , Randeria M. , Trivedi N. , Ulmke M. , Zimanyt G. T.
Published: April 2011

Over the last decade, Quantum Monte Carlo (QMC) calculations for tight binding Hamiltonians like the Hubbard and Anderson lattice models have made the transition from addressing abstract issues concerning the effects of electron-electron correlations on magnetic and metal-insulator transitions, to concrete contact with experiment. This paper presents results of applications of “determinant” QMC to systems with disorder such as the conductivity of thin metallic films, the behavior of the magnetic susceptibility in doped semiconductors, and Zn doped cuprate superconductors. Finally, preliminary attempts to model the Kondo volume collapse in rare earth materials are discussed.
Reliable Estimates of Quasi-Particle Energies and Exci-Tonic Effects in Clusters Through Discrete-Variational-Method Total Energy Calculations
Authors: Cappellini Giancarlo , Casula Francesco , Bechstedt Friedhelm
Published: April 2011

Self-energy corrections to the DFT-LDA HOMO-LUMO gap for clusters have been calculated through an efficient method based on ΔSCF theory. Total energies for the clusters are obtained via discrete variational method (DVM). Good results in comparison with experiments and available theoretical data for the sodium tetramer Na4 and C60 have been obtained. The localization properties of DVM basis-functions play a fundamental role in obtaining the above results with a strongly reduced computational effort in comparison with ab-initio schemes. For the two systems under study an estimate of the first excitonic transition energy is also given.
Environment-Dependent Tight-Binding Model for Molybdenum
Authors: Haas H. , Wang C. Z. , Fähnle M. , Elsässer C. , Ho K. M.
Published: April 2011

A transferable orthogonal tight-binding model for molybdenum is developed which goes beyond the traditional two-center approximation. The elements of the Hamiltonian matrix as well as the repulsive potential are allowed to depend on the environment. Several bulk, atomic defect and surface properties are calculated and compared with ab-initio data and experimental results to check the accuracy of the model.
The Environment-Dependent Interatomic Potential Applied To Silicon Disordered Structures And Phase Transitions
Authors: Bazant Martin Z. , Kaxiras Efthimios , Justo J. F.
Published: April 2011

The recently developed Environment-Dependent Interatomic Potential (EDIP) holds the promise of a new degree of transferability in describing bulk phases and defects of elemental covalent solids with a simple theoretically motivated functional form. Here we explore to what extent the environment-dependence of the model can extrapolate successes of the fitted version for Si for bulk defects to disordered phases, which involve local configurations very different from those used in fitting. We find that EDIP-Si provides an improved description of the metallic bonding bond angles of the liquid and is the first empirical potential to predict a quench directly from the liquid to the amorphous phase. The resulting amorphous structure is in closer agreement with ab initio and experimental results than with any artificial prepration method. We also show that melting of the bulk crystal and premelting of the (100)2×1 surface are reasonably well described by EDIP-Si in spite of its not being fit to any such properties.
Transferable Tight-Binding Approach Of Si-H Interactions
Authors: Kim Eunja , Lee Seung Mi , Lee Young Hee
Published: April 2011

We construct transferable tight-binding parameters of silicon-hydrogen interactions, reproducing the electronic energy levels and vibrational frequencies of the silane(SiH4) molecule accurately. The potential function was rescaled with the exponential factor in order to ensure that the potential energy is smooth at an appropriate cut-off distance, which is very important in molecular-dynamics simulations. The parameters have been applied to other molecules and various surfaces such as hydrogenated Si(100) surfaces, for example, monohydride, dihydride, and (3×1) phase.
Tight-binding Electron-ion Dynamics: A Method for treating nonadiabatic processes and Interactions with Electromagnetic Radiation
Authors: Graves J. S. , Allen R. E.
Published: April 2011

A method is introduced for simulations of the coupled dynamics of electrons and ions in a molecule or material. It is applicable to general nonadiabatic processes, including interactions with an arbitrarily intense radiation field. The field is included in the electronic Hamiltonian through a time-dependent Peierls substitution. The time-dependent Schrödinger equation is solved with an algorithm that preserves orthogonality, and the atomic forces are obtained from a generalized Ehrenfest theorem. Calculations for GaAs and Si demonstrate that the method is reliable and quantitative.