bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Low Intensity Laser Enhancement of Oxygen Chemisorption on GaAs Using O2 and N2O
Authors: Bertness K. A. , McCants C. E. , Chiang T. T. , Mahowald P. H. , Wahi A. K. , Kendelewicz T. , Lindau I. , Spicer W. E.
Published: March 2011

The sticking coefficient for molecular oxygen on GaAs(110) up to about one-halft monolayer coverage can be enhanced by two or three orders of magnitude when the semiconductor surface is illuminated by an argon ion laser with intensities of 5 W/cm2 or less. Previous work has shown that this effect is nonthermal and roughly independent of wavelength for above-bandgap radiation, implying that photogenerated electrons and/or holes are responsible in some way. In this paper we present recent work which shows that transfer of energy from the GaAs to oxygen molecules physisorbed on the surface causes the breakup of the oxygen and so enhances the reaction. This conclusion comes from comparison of our photoemission results for O2 and N2O exposures made under the same conditions, N2O being chosen since only 1.7 eV is needed to remove the oxygen atom as opposed to the 5.1eV required to break an O-O bond. Nitrous oxide, in contrast to O2, shows only slight photoenhancement and has a much lower activation energy for the dissociative sticking coefficient, demonstrating that removal of the dissociation of O2 as a reaction step also removes the major part of the activation energy barrier to oxygen chemisorption. Since N20 and photoenhanced O2 have similar kinetics, we conclude that the breakup of O2 is the reaction step accelerated by illumination. Another clue to the nature of the photoenhancement comes from our finding that both n- and p-type GaAs display similar O2 laser enhancement ratios. An estimate of the carrier concentrations at the surface predicts that electrons and holes are present in equal amounts at the surfaces of both doping types, however, so this result does not distinguish between single-carrier and recombination-related enhancement mechanisms.
UV Laser Processing of Semiconductor Devices
Authors: Sigmon T. W.
Published: March 2011

The use of a pulsed UV excimer laser based process for the incorporation of dopant impurities into Si is described. The process can result in high concentration shallow box like profiles suitable for submicron VLSI device fabrication. The process consists of exposure of the clean silicon surface to a doping gas (B2H6, AsH3, PH3) then driving the adsorbed monolayers of dopant into the Si by a melt-regrowth process initiated by a pulsed XeCl excimer laser. Modeling of the process allows prediction of the resulting doping profiles and electrical properties of the doped layers. Excellent crystal quality of the doped layers is found even without a postdoping anneal. Also, recent results indicate that post doping annealing may not be needed for improvement of the electrical characteristics of the doped layers provided certain conditions are met. Detailed descriptions of the process, results, modeling and device fabrication are presented.
GaAs Circuit Restructuring by Multi-Level Laser-Direct-Written Tungsten Process
Authors: Black Jerry G. , Doran Scott P. , Rothschild Mordechai , Sedlacek Jan H.C. , Ehrlich Daniel J.
Published: March 2011

Laser-direct-writing processes are employed to fabricate a GaAs digital integrated circuit. The lithography-free techniques deposit and etch conductors and resistors, and remove insulating layers, thus enabling multilevel interconnections. These combined directwrite processes provide the flexibility of clip-lead prototyping on a micrometer scale.
Holographic Photoetching of High-Quality Diffraction Gratings in P-GaAs for Distributed Feedback Lasers
Authors: Matz Richard
Published: March 2011

Quarter micrometer period diffraction gratings having depth-to-spacing ratios around 0.5 have been photochemically etched in p-GaAs using direct holographic illumination with 257 nm UV light. The results suggest the interaction of the incident light with the etched grating. The etch process is represented with the aid of a potential-pH diagram calculated from literature data.
In-situ Rapid Isiheial Pocessing of Thin Epitaxial Dieleciric Films on Silicon and Compound Semi Semiconductors
Authors: Singh R. , Radpour F. , Narayan J. , Joshi S. P. , Rahati M. , Anandakugan S. , Kahng S. K.
Published: March 2011

Abstracr

We have developed a new rapid isothermal processing technique for the deposition of epitaxial dielectric films (II–VIa fluorides and their mixtures) on silicon and ccmpound semiconductors. In this process, epitaxial dielectric films are deposited in an e-beam system at room teqperature and subsequently subjected to in-situ rapid isothermal annealing by using incoherent light sources incorporated in the e-beam system. Epitaxial dielectric films of CaF2 and CaxS1−xF2 have been deposited on Si, GaAs and InP. In this paper, prelimilifty results of electrical and structural characteristics of. epitaxial dielectric films on Si and cupourd semiconductors are presented.
Quantification of Hydrogen and Determination of the Binding State in a-Si:H:D by Thermal Desorption Spectroscopy
Authors: Yabumoto Norikuni , Muramatsu Yasuji , Oshima Masaharu
Published: March 2011

Thermal desorption spectroscopy (TDS) is used to quantify the amount of hydrogen in hydrogenated amorphous silicon(a-Si:H) as well as to determine the binding state. It is possible to measure the quantity and binding state of hydrogen in 100–8000Å thick a-Si:H films. Hydrogen is incorporated in the 100Å thick film at a rate of about three times greater than that in the over 1000Å thick film. Hydrogen in all films is bonded to silicon with three kinds of binding states at 2.8, 3.1 and 3.3eV. a-Si:H:D is prepared from SiH4/D2 plasma in order to clarify the origin of hydrogen in the films which are usually deposited from SiH4 and diluted H2 gas. TDS spectra of H2, HD and D2 show that there is more hydrogen from SiH4 in the film in each of the binding states, than from the diluent H2.
Chemical Vapor Deposition of Gold
Authors: Larson Carl E. , Baum Thomas H. , Jackson Robert L.
Published: March 2011

Chemical vapor deposition of gold from dimethyl-2,4-pentandionato gold (III) and two fluorinated derivatives is reported. At substrate temperatures of 200–300°C, high purity gold films were obtained on SiO2 and Si substrates. Films with resistivities down to 1.3 times that of bulk gold were obtained at deposition temperatures of ∼200°C, where films with very small grain size could be deposited.
Photon and Ion Beam-Induced Chemistry of Palladium Acetate Films
Authors: Gross M. E. , Brown W. L. , Linnros J. , Harriott L. R. , Cummings K. D. , Funsten H. O.
Published: March 2011

Electrically conducting palladium features have been produced by laser and ion beam irradiation of thin palladium acetate films. The photothermal reaction induced by scanned continuous wave Ar+ laser irradiation leads to metal lines that may exhibit periodic structure. This results from repeated propagation of “explosive” reaction fronts generated by coupling of the heat from the absorbed laser radiation with the heat of the decomposition reaction of the film. In contrast, 2 MeV He+ ion irradiation produces smooth metallic-looking features that contain up to 20% of the original carbon and 5% of the original oxygen content of the film. Films irradiated with 2 MeV Ne+ ions contain slightly lower amounts of carbon and oxygen residues, but fully exposed thick films (0.90 μm) appear black rather than metallic silver. In addition to having significantly higher purity, the laser-written features have lower resistivities than the ion beam-irradiated features. Infrared spectroscopy of the ion beam-irradiated films as a function of dose indicates a progressive loss in intensity of the characteristics acetate (COO-) vibrations. This occurs at doses lower than those associated with major C and O loss from the films. Partially ion-exposed films continue to decompose to metallic-looking material over a period of weeks after irradiation. Metallic palladium particles apparently catalyze this process.
Material Considerations in the Microfabrication of Grating Microstructures for use in a Laser-Powered Linear Accelerator
Authors: Warren John B.
Published: March 2011

Collaborative work between Brookhaven and Los Alamos National Laboratories is developing a new type of linear accelerator that uses a high-power, picosecond pulse CO2 laser to irradiate a specialized form of grating with a pitch of 10.6 microns. The electromagnetic field that results can be used to accelerate electrons at field gradients of several GeV/m with potential efficiencies much better than current accelerators. The grating must be conductive to minimize resistive losses, be able to withstand high fields without damage, and requires dimensional tolerances in the sub-micron range. These requirements focus attention on grating material selection, microfabrication methods, and metrological methods used for quality control. At present, several types of gratings have been manufactured by reactive ion etching of fused silica in CHF 3/Ar or etching silicon with KOH/H 2O or ethylenediamine-pyrocatechol solutions. Metrological analysis of the gratings has begun with a Tracor Northern 5700 digital image analyzer.
Localization and Electron-Electron Interaction Effects in Platinum Silicide Thin Wires
Authors: Ishida S. , Murase K. , Shimamoto Y. , Ishibashi K. , Gamo K. , Namba S. , Uematsu S.
Published: March 2011

The low-temperature magnetoresistance of PtSi thin wires of varying width, prepared with different mask elements (Cu and Ni) in the reactive ion beam etching, has been studied, to determine the width dependence of the physical parameters in the weak localization. A drastic decrease of the magnetic impurity scattering time τs and that of the superconducting transition temperature Tc have been found for the wires prepared by Ni mask with narrowing width, which suggests that the phase coherence of diffusing electrons responsible for the weak localization and the superconductivity are strongly affected by the presence of a small amount of Ni impurities recoil implanted into the surface region of the sidewalls of wires.
Hot Jet Etching through Stencil Masks
Authors: Geis M. W. , Pang S. W. , Efremow N. N.
Published: March 2011

This article contains a description of hot jet etching through stencil masks. The dry etching technique does not damage the stencil mask, but anisotropically etches GaAs at rates as high as 10 μm min−1. Resolution less than 50 nm has been demonstrated. At present the etched surfaces are rough, but improvement of the etching technique may result in smooth surfaces.
193-NM Excimer Laser-Assisted Etching of Polysilicon
Authors: Armacost K. D. , Babu S. V. , Nguyen S. V. , Rembetski J. F.
Published: March 2011

193-nm excimer laser-assisted etching of polysilicon was studied in vacuum and in the presence of Ar, CF3 Br, CF2 Cl2, and NF3. In inert atmospheres (vacuum, Ar) exposure to the laser led to jagged profiles at high fluences (>350 mJ/(cm2-pulse)) resulting from surface temperature gradients. At lower fluences, a resolidified Si-SiO2 lump was formed by thermal and surface tension gradients induced by laser heating. In the presence of 193-nm radiation, CF3Br showed some propensity to etch polysilicon, while CF2Cl2 did not show any appreciable etching.

Etch experiments were also performed in the presence of NF3 Maximum etch rates of 0.6 A/pulse were obtained for pressures greater than 500 torr and fluences exceeding 200 mJ/(cm2-pulse). An adsorptive etch mechanism is proposed, where NF3 molecules diffuse to the surface, adsorb and then react after absorbing laser radiation. Etching of micron profiles in polysilicon was also examined.
Anisotropic and Selective Reactive Ion Etching of SiC in CHF3 and Oxygen Plasma
Authors: Pan W-S. , Steckl A. J.
Published: March 2011

The use of CHF3 plus oxygen plasma to achieve selective and anisotropic patterning of SiC thin films in the reactive ion etching (RIE) mode is reported. Experiments were performed using various levels of oxygen percentage (from zero to 90%), pressure (from 20 to 300 mTorr) and power (from 100W to 350W). Anisotropic etching of SiC with a vertical-to-lateral etch ratio in excess of 8:1 was measured for a CHF3 + 75%02 mixture at 20mT pressure and 200W RF power. Under these conditions, the SiC etch rate was measured to be 400 A/min and the selectivity over Si was approximately 2.2:1. The effect of the cathode DC potential and emission intensity of various species in the plasma on the SiC and Si etch rates is considered.
Reactive Ion Etching of AI(Cu) Alloys
Authors: Hu C.-K. , Small M. B. , Schadt M.
Published: March 2011

Reactive ion etching of Al( ≤ 4 wt.% Cu) and AI(Cu)/W films is described. Using single layer resist, 1 μm lines are demonstrated over 0.3 μm topography in the bilayer films and 0.5 um lines in the single layer layer films over planar surfaces. For Al alloys with Cu concentration in the ranges 2–4 wt.% it is found that clean etching is strongly dependent on deposition condition. A model is proposed to explain this.
Reactive Ion Etching of Multi-Layer Resist
Authors: ng H. Y. , Klaus D. P. , Polcari M. R. , molzen W. W.
Published: March 2011

Multi-layer resist has been utilized commonly in optical and E-beam lithography for its ability to resolve submicron feastures over topography. In addition, the use of a low-Z(atomic number) material as the intermediate layer reduces the proximity effect. This paper describes the development of etching process used to pattern a tri-level resist based on polyimide, an inorganic intermediate layer, and positive resist as top image layer. A highaspect-ratio image can be anisotropically transfered from the inorganic intermediate layer into the polyimide planarizing layer by oxygen RIE. Directionality, profile control, and backsputtering residue are the primary considerations during the pattern transfer etching. The influence of pressure, power and self-bias voltage on the etching process are described. The residue is caused by sputtering of the electrode material and the etch barrier material. Backsputtering residue from electrode can be prevented by covering all exposed conducting surfaces with an organic dielectric material, in this case an ardel plate. Etch residue contributed by the intermediate layer is quantified according to its pattern density and the influence of the pressure. Sidewall profiles and their relationship to planarizing layer thickness are also discussed.
Post Oxidation Anneal and Re-Oxidation Effects in 5 nm SiO2 Films
Authors: Dori L. , Arienzo M. , Sun Y. C. , Nguyen T. N. , Wetzel J.
Published: March 2011

Ultrathin silicon dioxide films, 5 nm thick, were grown in a double-walled furnace at 850°C in dry O2. A consistent improvement in the electrical properties is observed following the oxidation either with a Post-Oxidation Anneal (POA) at 1000°C in N2 or with the same POA followed by a short re-oxidation (Re-Ox) step in which 1 nm of additional oxide was grown. We attribute these results to the redistribution of hydrogen and water related groups as well as to a change in the concentration of sub-oxide charge states at the Si-SiO2 interface. A further improvement observed after the short re-oxidation step had been attributed to the filling of the oxygen vacancies produced during the POA. High resolution Transmission Electron Microscopy cross-sectional observations of the Si-iSO2 interface have evidenced an increase in the interface roughness after the thermal treatment at high temperature. These results are in agreement with recent XPS data.
A Process for 0.5 Micron CMOS Gate Definition
Authors: Stanasolovich D. , Katz S. , Schnur S. , Danner D. , Wang L. K.
Published: March 2011

A RIE process has been developed for the etching of 0.5 μm CMOS Polysilicon gates defined using both E-Beam direct writing and sub-micron optical lithography. Profile control and selectivity were enhanced by using a two-step pattern transfer process wherein the Photoresist mask was used to define a thin Silicon Nitride layer which was subsequently used to define the underlying Polysilicon gate electrode. High etch selectivity to both the Silicon Nitride mask and the thin gate oxide was achieved using a Cl2 plasma chemistry after a BCl3 initiation step. The effect of BCl3 initiation on the poly profile and the effect of loading on profile and selectivity will be presented.
The Effect of Window Edge Stress on Dopant Diffusion in Silicon
Authors: Huang C. K. , Kook T. , Jaccodine R. J.
Published: March 2011

An experimental study of dopant diffusion at Si3N4 and SiO2 film edge is reported. The results show that an alternation of enhanced and retarded diffusion of both As and Sb at the Si3N4/SiO2 film edge was observed after 1100°C heat treatment in N2. The observed effect has been correlated to the alternation of tensile and compressive stress field at the film edge for the first time. Additionally, the different shape of junction profile of As and Sb seems to be a result of impurity misfit strain effect. From this experiment, it is obvious that the interaction of film edge stress fields will make the control of dopant profile more difficult for smaller window width. Hence the film edge effect should be taken into account especially for the fabrication of submicron devices.
Boron Diffusion in Polycrystalline Silicon
Authors: Ghannam Moustafa Y. , Dutton Robert W. , Novak Steven W.
Published: March 2011

The diffusion of boron in ion implanted LPCVD polycrystalline silicon is shown to be dominated by grain boundary diffusion at low and moderate concentrations. The diffusion coefficient is 2 to 3 orders of magnitude larger than its value in crystalline silicon. In preannealed polysilicon, the boron diffusion coefficient is found to be 30% smaller than in polysilicon annealed after implantation. This reflects the effect of the grain size in the diffusion coefficient since preannealed polysilicon has larger grains and smaller density of grain boundaries per unit area.
Confinement and Fluorescence of Aromatic Molecules in Microporous Amorphous Superlattices
Authors: Roxlo C. B. , Mitra P. , Deckman H. W. , Abeles B. , Wong P. P.
Published: March 2011

We have investigated molecular confinement in materials with nanometer sized pores, fabricated from amorphous superlattices of a-Si:H/a-SiOx:H, using 1,10-bis(1-pyrenyl)decane as a fluorescent probe. In large (46 Å) pores, the emission and excitation spectra and their time dependence are similar to microcrystalline material, showing the presence of molecules aggregated in the ground state. This dimer emission decreases sharply as the pore size is decreased, showing that the minimum size for aggregate formation is about 20 Å.
High Field Microscopy Studies of Gallium Arsenide-Metal Interface
Authors: Patel Chand
Published: March 2011

The Field Emission Microscope has been extensively used in the study of metal and semiconductor surfaces. The process of Field Emission is, itself, of great interest and a considerable amount of both theoretical and experimental work has been carried out in this field. The Field Emission Microscope also yields useful information of a more practical nature, such as the nature of bulk and surface impurity, diffusion, chemisorption and surface potential barriers. It is essential that the surface to be studieg can be prepared in the form of a high curvature tip, with a radius of 10−5cm and can be cleaned sufficiently well for a symmetrical reproducible pattern to be observed.

Field Emission technique has been applied to study the behaviour of thin overlayers of gold on GaAs. Using Fowler-Nordheim plots, change in the work function φ, is examined for temperatures, T=77K and T=300K. φ changes slightly for low doses of gold and significantly for larger ones {φ=4.3 − 3.7 eV}. Desorption of gold is also examined and the results indicate two different adsorbed states in Au-overlayers formed at room temperature. Finally, a brief description of sample preparation is also included.
The Effect of Implant and Rapid Thermal Annealing Temperatures on Ion Beam Mixing of Titanium Silicide
Authors: Mattiussi G. A. , Whitton J. L. , Naem A. A. , Ho V. Q.
Published: March 2011

Ion beam mixing has been used to form layers of titanium disilicide on Si wafers. Doses of Ge+ up to 1×1016 ions/cm2 were implanted at 140 keV through 51 nm of sputtered Ti. The substrate was held at different temperatures; 150°C, 300°C and 400°C. In addition, some samples were processed without temperature control. Two rapid thermal annealing cycles were used, 800°C for 10 s and 650°C for 50 s in an N2 ambient to form stoichiometric TiSi2. As-implanted samples showed an increase in the number of mixed Ti and Si atoms with higher implant temperature and larger dose. In addition, a thin layer with a Ti/Si ratio of 1:1 as seen in some samples indicating possible TiSi phase formation. Lower implant temperatures, higher doses and higher anneal temperatures all produced greater TiSi2 thicknesses. Ion beam mixing yields thicker. silicide layers than those formed without mixing. The silicide interface smoothness was improved by ion beam mixing although some residual implant damage was observed after annealing. The implanted Ge+ accumulated below the silicide/Si interface and in the surface Ti oxide layer.
The Stability of Ion Projection Lithography Masks
Authors: Randall J. N. , Bellavance D. , Sivasankar R.
Published: March 2011

Ion projection lithography (IPL) has demonstrated the ability to replicate high resolution patterns with very short exposure times. Computer modeling of masks used in a hypothetical IPL system Is accomplished to estimate mask distortion during fabrication and exposure. Radiation cooling is shown to play an important role in temperature control. Two different methods of mask temperature control are examined. Results suggest a high degree of pattern stability can be expected from this type of mask.
Maskless Patterning of Mo and Si by Focused Ion Beam Implantation
Authors: Gamo Kenji , Yonehara Katsuyuki , Nagatomo Shohei , Namba Susumu
Published: March 2011

Maskless patterning of Mo and Si was done by implanting 50 keV focused Ga+ ion beam and by plasma etching using CF4 gas. The implantation is done to modify the chemical properties of the sample surface. It was found that Mo films became etch-resistant for the plasma etching after implantation at a dose higher than 4×1015 /cm2. Si crystals showed a positive tone pattern due to a radiation enhanced etching at a dose lower than 5x1016/cm2. At higher doses, the etching rate decreased and above 8 x 1016/cm2, no etching was observed in the implanted region. Patterns with a thickness of a several hundred nanometers were formed by the present maskless patterning technique.
Fabrication of Encapsulated Indium Films for Melting Experiments
Authors: Scofield John H. , Epworth R. W. , Tennant D. M.
Published: March 2011

We describe the fabrication of submicron, multiprobe thin indium film conductors for electrical measurments above their melting transition. Problems unique to handling liquid films were overcome by using tri-level Si3N4/In/W structures. Tungsten (W) leads made good electrical contact to, yet did not alloy With the liquid indium (In). A silicon-nitride (Si3N4 ) encapsulating layer deposited over the In/W devices prevented the indium from forming islands when liquid. Indium wires were fabricated using e-beam lithography and liftoff. Low temperature reactive sputtering technique was used to deposit the Si3N4 without melting the indium. The technique could be easily adapted to use with other low melting point materials.
Submicron Pattern Delineation Using a Pulsed Electron-Beam in Soft Vacuum
Authors: Krishnaswamy Jayaraxn , Li Lumin , Collins G. J. , Hiraoka H.
Published: March 2011

We describe herein an electron-beam, proximity lithograghic process which operates in soft vacuum (50 mT< p <1 Torr) using highly directed electron emission from a cold cathode. The electron-beam operates with large areas(<10 cm2) and with large total currents (Ipeak< 100A). Using this soft vacuum beam we could replicate feature sizes of ∼0.5 μm on∼3 μm thick PMMA, with a resist layer to stencil mask spacing of 25 to 30 μm. While resist exposed in a helium background showed vertical wall profiles (developed thickness ∼3 ¼m), resists exposed in air showed sloped walls (∼ 60°). Resist behavior also appears to be dependent on the number of pulses used for exposure ranging from simple exposure ( 1 to 5 pulses) to self-development ( >25 pulses).
Characterization of Epitaxial Films by Grazing-Incidence X-Ray Diffraction
Authors: Segmüller Armin
Published: March 2011

Grazing-incidence x-ray diffraction, a surface-sensitive technique, has been used to obtain structural details parallel to the interface of an epitaxial system, such as lattice parameters, strain, crystallite size and orientation, on films with thicknesses ranging down to a few mono-atomic layers. Tungsten grows epitaxially on the (1102) plane of sapphire, with the orientation W (001) ∥ Al2O3 (1102) and W [110] ∥ Al2O, [1120]. Sufficient diffraction intensity for characterization could be obtained from ∼30A-thick W films. Layers of GaAs can be grown epitaxially on the basal plane of sapphire with the orientation GaAs(111) ∥ Al2O3(00.1) and GaAs [110] ∥ Al2O3[1120]. Niobium films grow on GaAs (001) and (111) substrates with a (001) plane parallel to the interface, whereas molybdenum films prefer to grow with a (111) plane on both substrates. The best orientation, i. e. the smallest mosaic spread, of the film is obtained when the substrate plane has the same symmetry as the preferred film growth plane. In all these cases with relatively large misfit, the strain observed parallel to the interface is only a small fraction of the theoretical misfit strain, indicating the relief of the misfit strain within the first few atomic layers.
Nexafs Studies of Unsaturated Carboxylic Acids and Alcohols Adsorbed on the Si(111)(7×7) Surface
Authors: Outka D. A. , Stöhr J. , Madix R. J. , Rotermund H. H. , Hermsmeier B. , Solomon J.
Published: March 2011

The adsorption of formic acid (HCOOH), acrylic acid (CH2= CHCO2H), propiolic acid (HC=CCO2H), and the corresponding alcohols on the Si(111)(7×7) surface have been investigated by NEXAFS. In each case, well-defined dipole transitions to σ* and π* molecular orbital s were observed above the C and 0 K-edges and used to probe the orientation and chemistry of these molecules on this silicon surface. Monolayer coverages of these molecules on silicon, bond strongly to the silicon surface via the carboxylic acid or alcohol group. In contrast, the C-C double and triple bonds of these molecules do not react initially with the silicon surface. Upon heating, however, the C-C double and triple bonds which are held in proximity to the surface by the carboxylic acid or alcohol group, are lost either by polymerization on the surface or reaction with the silicon substrate. These results illustrate the capabilities of NEXAFS to investigate molecular orientations on surfaces and the electronic structure of polyatomic adsorbates.
Mixed-Cation Optical Thin Films from Tailored Composition Targets
Authors: Denatale J. F. , Harker A. B.
Published: March 2011

Amorphous optical thin films of mixed oxides have been fabricated whose composition and optical index of refraction have been varied in a controlled manner as a function of film thickness using a single ion beam source with tailored composition targets. The microstructure, transformation behavior, and stress in the films are being studied for the systems Al2O3-TiO2, TiO2-SiO2, and ZrO2-SiO2. The technique has been found to be a convenient means of producing gradient index optical structures.
High Temperature Implantation of Single Crystal Beta Silicon Carbide Thin Films
Authors: Edmond J. A. , Withrow S. P. , Wadlin W. , Davis R. F.
Published: March 2011

Ions of aluminum, gallium and nitrogen were implanted into (100) oriented β-SiC thin films at temperatures of 623K, 823K and 1023K. Rutherford backscattering/ion channeling analyses revealed that implantation of any one of the ionic species at 623K resulted in only slight crystal lattice damage. In comparison, implantation conducted using the same dosimetry and energy at room temperature resulted in extensive lattice damage; in the case of gallium, amorphization occurred. The backscattered yield from samples implanted at 1023K was nearly that of a virgin aligned spectra. This in situ annealing effect did not, however, result in the complete electrical activation of implanted species. In order to increase the percent of electrical activation, samples were annealed at 1473K for 1800s following implantation. Differential capacitance-voltage, spreading resistance and sheet resistance measurements were made in order to electrically characterize these layers. These measurements indicated the activation of p-type and n-type species in samples implanted with aluminum or gallium and nitrogen, respectively. The authors have previously reported p-type formation in β-SiC implanted with aluminum at room temperature following a 2073K - 300s anneal. By heating to 1023K during implantation and annealing at 1473K after implantation, improved structural and electrical properties have been achieved.
Theoretical Investigation of Twist Boundaries in Germanium
Authors: Payne M. C. , Bristowe P. D. , Joannopoulos J. D.
Published: March 2011

Results of the first completely ab-initio investigation of the microscopic structure of a grain boundary in a semiconductor are presented. Using the molecular dynamics simulated annealing method for performing total energy calculations within the LDA and pseudopotential approximations, the σ=5(001) twist boundary in germanium is studied. A low energy structure is identified which exhibits a rigid body translation and a small contraction at the boundary.
a-Si:H Films Prepared by Ecr Plasma Enhanced CVD
Authors: Yamamoto H. , Hine S. , Yamakawa S. , Tubouchi N. , Miyamura M.
Published: March 2011

Hydrogenated amorphous silicon (a-Si:H) films prepared by electron cyclotron resonance plasma enhanced CVD (ECR PECVD) were investigated electrically and optically. The electrical and optical properties of a-Si:H were strongly dependent on magnet coil current, microwave power, and substrate temperature. A high deposition rate of a-Si:H up to 150 nm/min was realized by this technology. The photoconductive characteristics prepared at 300°C are comparable to those obtained by glow discharge PECVD (GD PECVD).
Elastic Properties of Superlattices
Authors: Grimsditch M.
Published: March 2011

A calculation of the effective elastic moduli of a super-lattice, in terms of the elastic moduli of its constituents, is presented. Contrary to what has been found in many real systems, these calculations show that in the long wavelength limit the effective elastic moduli are independent of the modulation wavelength. A discussion of the experimental results on Nb/Cu, Mo/Ni and Au/Cr shows that the elastic anomalies can be understood on the basis of concomitant changes in lattice spacings.
Effect of Si Implantation and Rapid Thermal Annealing on GaAs/AlGaAs Superlattice Disordering.
Authors: Flood J. D. , Bahir G. , Merz J. L. , Kobayashi J. , Fukunaga T. , Ishida K. , Nakashima H.
Published: March 2011

The enhanced disordering of GaAs/AlGaAs superlattices by diffusion of Zn or Si has been reported by many authors. In the case of Si diffusion, the Si can be introduced during epitaxial growth, by implantation, or by diffusion from a sputtered Si mask. In this paper ion implantation is investigated, and the effect of rapid thermal annealing (RTA), used to minimize Si diffusion while eliminating the implant damage, is compared with furnace annealing (FA). Using low temperature photoluminescence (PL) and SIMS, it is found that no disordering of a GaAs/Al0.5Ga0.5As superlattice takes place for a 2 sec anneal at 900°C, and very minimal partial disordering is observed (reproducibly) for a 10 sec anneal at 970°C. This is in sharp contrast with the FA case (850°C for 30 min), for which significant disordering occurs. The PL spectra show luminescence from both GaAs and GaAs/Al0.5Ga0.5As layers in the case of high-temperature RTA suggesting that recrystallization has occurred without disorder, whereas strong emission is observed after FA which corresponds to a disordered layer of average-composition GaAs/Al0.15Ga0.25As In both cases, PL indicates that annealing of the implant damage has occurred. Thus, damage can be eliminated either with or without disordering the superlattice by using FA or RTA, respectively. This is important for 2-D electron gas structures, for which no broadening of the hetero-interface is desired.
Electron Transport Through Epitaxial Metal/Semiconductor Heterostructures
Authors: Levi A. F. J. , Tung R. T. , Batstone J. L. , Gibson J. M. , Anzlowar M. , Chantre A.
Published: March 2011

Abrupt, epitaxial silicide/silicon heterostructures may be grown so that, for the first time, the physics of electron transport across near perfect, single crystal, metal/semiconductor interfaces may be probed experimentally. Transport measurements through type-A and -B oriented NiSi2 layers on Si(111) substrates have revealed Schottky barrier heights differing by 140 meV. In this paper we present results of experiments designed to explore the possible role of bulk and interface defects in determining the potential barrier at these near ideal epitaxial metal-semiconductor contacts. We have found little evidence for the presence of defects and the Schottky barrier is insensitive to details of the microscopic interfacial perfection. By contrast we find that both the electrical quality and magnitude of the barrier occurring at the NiSi2 /Si(100) heterojunction are dependent upon details of the microscopic interfacial perfection.
The Composition Dependence of the Interdiffusivity in Artificial Amorphous Si/Ge Multilayers
Authors: Prokes S. M. , Spaepen F.
Published: March 2011

The interdirfusivity in artificial amorphous Si/Ge multilayers is found to be strongly dependent on the average composition of the films. The interdirfusivity of films with different average composition was determined from the decay of the first X-ray satellite. The nonlinear diffusion resulting from the composition dependence was observed by the evolution of the higher-order satellites.
Properties of MoO3 Thin Film Polymorphs
Authors: McCARRON E. M. , Carcia P. F.
Published: March 2011

Thin film polymorphs of molybdenum trioxide have been synthesized by RF sputtering. Films deposited on thermally floating substrates are polycrystalline and exhibit preferred orientation. Depending upon the oxygen partial pressure maintained during sputtering, the films can be made to crystallize in either the thermodynamically stable orthorhombic a MoO3 form (unique 2D-layered structure) or the metastable monoclinic /3 MoO3 phase (3D ReO3-related structure). Metastable β films can be converted thermally to the a phase and the transformation appears topotactic. Films deposited on cooled substrates are amorphous. A correlation between the particular phase formed and adatom mobility is noted.
Dopant Diffusion in TiSi2
Authors: d'Heurle F. M. , Michel A. E. , LeGoues F. K. , Scilla G. , Wetzel J. T. , Gas P.
Published: March 2011

Dopant elements, B and Ga, P, As and Sb, and Ge as well, have been implanted into thick (350–400 nm) layers of TiSi2 prepared by Ti-Si reaction. Both B and Sb appear to be immobile, this behavior is thought to result from very small solid solubilities, rather than from very small diffusion coefficients. The other elements display about the same behavior, with detectable grain boundary diffusion at temperatures as low as 600°C, and lattice diffusion becoming considerable at 750°C, so that with the cooperation of both phenomena almost complete homogenisation of these relatively thick layers occurs in 30 minutes at 800°C. Germanium is used in lieu of a Si radioactive tracer because it can be analyzed by Secondary Ion Mass Spectroscopy. Its behavior is thought to imply that there is little equilibrium adsorption of the dopant elements at the Si/TiSi2 interface. The comparable values of the diffusion coefficients for the mobile elements confirm the anticipation that the dopants move as substitutional atoms on the Si sublattice. Results obtained with some samples implanted with both dopant and Ti indicate that in these silicon-saturated suicide layers the diffusion process is not significantly affected by small changes in stoichiometry.
X-Ray-Optical Multilayer Structures Studied Using High Resolution Electron Microscopy.
Authors: Stearns Mary Beth , Petford-Long Amanda K. , Chang C.-H. , Stearns D. G. , Ceglio N. M. , Havryluk A. M.
Published: March 2011

The technique of high resolution electron microscopy has been used to examine the structure of several multilayer systems (MLS) on an atomic scale. Mo/Si multilayers, in use in a number of x-ray optical element applications, and Mo/Si multilayers, of interest because of their magnetic properties, have been imaged in cross-section. Layer thicknesses, flatness and smoothness have been analysed: the layer width can vary by up to 0.6nm from the average value, and the layer flatness depends on the quality of the substrate surface for amorphous MLS, and on the details of the crystalline growth for the crystalline materials. The degree of crystallinity and the crystal orientation within the layers have also been investigated. In both cases, the high-Z layers are predominantly crystalline and the Si layers appear amorphous. Amorphous interfacial regions are visible between the Mo and Si layers, and crystalline cobalt suicide interfacial regions between the Co and Si layers. Using the structural measurements obtained from the HREM results, theoretical x-ray reflectivity behaviour has been calculated. It fits the experimental data very well.
Growth of Epitaxial CoSi2/Si Multilayers
Authors: Runt B. D. , Lewis N. , Schotalter L. J. , Hall E. L. , Turner L. G.
Published: March 2011

Epitaxial CoSi2/Si multilayers have been grown on Si(111) substrates with up to four bilayers of suicide and Si. To our knowledge, these are the first reported epitaxial metal-semiconductor multilayer structures. The growth of these heterostructures is complicated by pinhole formation in the suicide layers and by nonuniform growth of Si over the suicide films, but these problems can be controlled through nse of proper growth techniques. CoSi2 pinhole formation has been significantly reduced by utilizing a novel solid phase epitaxy technique in which room-temperature-deposited Co/Si bilayers are annealed to 600–650δC to form the suicide layers. Islanding in the Si layers is minimized by depositing a thin (<100Å) Si layer at room temperature with subsequent high temperature growth of the remainder of the Si. Cross-sectional transmission electron microscopy studies demonstrate that these growth procedures dramatically improve the continuity and quality of the CoSi. and Si multilayers.
Interfacial Reactions in Titanium - Silicon Multilayers
Authors: Holloway Karen , Sinclair Robert
Published: March 2011

We have used cross-section and through-foil TEM, RBS, and x-ray diffraction to investigate reactions upon rapid thermal annealing of sputtered Ti-Si multilayers of various compositions and bilayer spacings. This study addresses the behavior of the Ti-Si interface at low annealing temperatures (T< 600δC) to determine the extent to which interdiffusion occurs prior to suicide formation, and to detect the formation of the first suicide at an early stage. Whereas most previous work studied a single Ti-Si interface, we have used multilayer films because a reaction occurs at many interfaces, allowing detection of a phase even if it is formed to a very limited extent.

The silicon layers in the as-deposited films are amorphous; the titanium layers are polycrystalline hep. The compositions of the samples are 40 at.% Ti, 60 at.% Si and 60 at.% Ti, 40 aL% Si, and the bilayer periodicity is about 10 nm. After a 30 second anneal at 455°C, significant interdiffusion occurs and we observed the formation of an amorphous Ti-Si alloy by interfacial reaction. The metastable disilicide, C49 TiSi2, nucleated along with a small amount of TiSi in the sample with higher silicon content (60%) upon annealing at 550°C for 10 seconds, but the amorphous alloy remained as the only product of reaction in the 40 at. % Si sample. Cross-section TEM of a sample fabricated at 60°C suggests that interdiffusion had begun during deposition of the films.
A High Schottky Barrier Contact of Metallic Amorphous Si-P on P-Type Si
Authors: Ogino T. , Sakaue M. , Amemiya Y.
Published: March 2011

A high Schottky barrier contact is formed when amorphous Si-P solid solution film and p-type Si are brought into contact. Amorphous Si-P films were deposited by thermal decomposition of a Si2H6-PH3 mixture at 500°C. It was found that conductivity increases rapidly when PH3/Si2H6, is increased from 0.2 to 2. When PH3/i2H6 = 2, conductivity is 0.15 S/cm, and the dominant conduction mechanism is variable-range hopping. Barrier height of amorphous Si-P/p-type Si Schottky contact is estimated to be 0.8 – 0.85 V. This value exceeds the barrier height formed by any normal metal.
In-Situ Ellipsometry Study of Amorphous Silicon Interfaces
Authors: Antoine A. M. , Drevillon B. , Godet C.
Published: March 2011

A systematic comparison of the growth of plasma deposited amorphous silicon a-Si:H on chromium and glass substrates using real-time ellipsometry is presented. In order to compare the optical properties of the substrates before and after a-Si:H deposition, the amorphous films are removed by H-etching. Although the early stage of the growth of a-Si:H on chromium substrates is compatible with a nucleation mechanism, chromium suicides are probably produced at the film substrate interface. A faster chemical reaction between a-Si:H and the glass substrate is observed.
Ge and Gesl Heteroepitaxy on Si(100) by MBE
Authors: Houghton D. C. , Baribeau J.-M. , Maigne P. , Jackman T. E. , Bassignana I. C. , Tan C. C. , Holt R.
Published: March 2011

We have grown a series of Ge and graded Si1-xGex epilayers on (100)Si substrates by MBE under different conditions. The quality of the layers has been characterized by cross-sectional TEM, Rutherford backscattering/ channeling and x-ray diffraction. This work addresses the optimization of growth temperature, (300–700°C) an evaluation of compositional grading, the effect of the incorporation of strained layer superlattice dislocation filters and post growth anneal cycles. Particular attention has been paid to grading GexSi1-x, x = 0 to 1 and the growth morphology of intermediate alloy epilayers.
Temperature Dependent and Time Resolved Optical Studies of Single Quantum Wells Produced by Interrupted Growth MBE
Authors: Elman B. S. , Koteles Emil S. , Jagannath C. , Chen Y. J. , Charbonneau S. , Thewalt M. L. W.
Published: March 2011

Multiple peaks, recently observed in the low temperature photoluminescence (PL) spectra of GaAs/AlGaAs single quantum wells fabricated by momentarily interrupting the molecular beam epitaxial growth between adjacent but different semiconductor layers, have been interpreted as originating within smooth regions in the quantum well layer differing in width by exactly one monolayer. We have observed similar structure in similarly grown samples but find that low temperature PL can be misleading. However, higher temperature PL or PL excitation spectroscopy do provide unambiguous evidence for the model of interface smoothing due to growth interruption. Further, time-resolved spectra yield decay times of the individual peaks which are consistent with this idea.
Direct Observation of Valence-Band Mixing in GaAs/GaPAs Strained-Layer Superlattices
Authors: Jones E. D. , Biefeld R. M. , Fritz I. J. , Gourley P. L. , Osbourn G. C. , Schirber J. E. , Heiman D. , Foner S.
Published: March 2011

Low-temperature magneto-luminescence studies are used to examine the in-plane valence-band dispersion in GaAs/GaPAs strained-layer-superlattice structures. The results provide a direct observation of valence-band mixing effects in strained-layer systems.

Theoretical and experimental studies of the effect of valence-band mixing upon the magneto-transport properties and magneto-luminescence data for GaAs/AlGaAs latticed-matched superlattices have been recently reported.[1–] Due to the presence of the 2D-quantum well, the valence-band degeneracy between the light-hole and heavy-hole bands at is removed. These studies show, however, that the lowest energy valence-band mass is still strongly dependent upon due to valence-band mixing. On the other hand, because of the large biaxial compression in strained-layer-super lattices (SLS), valence-band mixing effects should be minimal.[8–9] Recent magneto-transport measurements[10] on p-type InGaAs/GaAs SLS structures have provided information regarding nonparabolic valence-bands in these structures.
Evaluation of AlGaAs/GaAs Heterointerface by Shubnikov-de Haas Oscillation Measurements
Authors: Kasai Kazumi , Tanaka H. , Itoh H. , Oh-Hori T. , Takikawa M. , Komeno J.
Published: March 2011

The measurement of Shubnikov-de Haas(SdH) oscillation is proposed as a new technique for evaluating the quality of a heterointerface. The first excited state of 2-dimensional electron energy levels is determined for several samples using the measurements of SdH oscillation. Lower values of the first excited state energy are found for the samples with a low mobility. The low value can be approximately explained in terms of graded interface model.
Magnetic Transitions in Fe/Cr Superlattices
Authors: Sellers Charles H. , Shiroishi Yoshihiro , Hilliard John E. , Ketterson John B.
Published: March 2011

Several series of multilayered Fe/Cr films have been studied, each with a fixed thickness of Fe and several thicknesses of Cr. The coer-civity and in plane anisotropy field were found to increase abruptly for larger Cr thicknesses. The origin of this change in behavior may involve a paramagnetic/antiferromagnetic transition in the Cr.
Characterization of Al and Al-Cr-Al Thin Films
Authors: De Lima O. F. , Lepetre Y. , Brodsky M. B.
Published: March 2011

TEM, X-ray diffraction, and electrical resistivity measurements were used to study the microstructure and the growth of AI-Cr-AI film sandwiches, where the individual Al layers were 300 Å thick and the Cr thickness was varied between 0–10 atomic layers. The base vacuum was around 1.0 × 10−10 torr, substrate temperatures varied between 100–350 °C, and evaporation rates were 3Å/s for Al and ∼0.1 – 0.2 Å/s for Cr. All Al films had a strong (111) texture and showed a non-percolative island structure at 350 °C. The films became connected at lower substrate temperatures, reaching perfect continuity at 100°C. However, electrical conductivity is achieved also for the films deposited at 350 °C when one or more atomic layers of Cr are sandwiched between the Al layers. Results for the superconducting critical temperature and resistivity are discussed in terms of Cr diffusion into Al and the film size effect.
Optical Properties of RF-Sputtered a-SiGe:H:O Alloys
Authors: Pereira J. M. T. , Banerjee P. K. , Mitra S. S.
Published: March 2011

Amorphous thin films of SixGe1-x:O (x = 0.70) were prepared by RF-sputtering at several substrate temperatures. The structural properties of these films were studied by IR spectroscopy and revealed features characteristic of hydrogen and/or oxygen bonded to silicon. The optical constants (n,k) were determined from reflection and transmission measurements at near-normal incidence for photon energies in the range of 1 eV and 2.6 eV. The optical gap was derived from the Taue plot and correlated with the composition of the samples. The increase of hydrogen and/or oxygen decreases the value of the refractive index and increases the optical gap.