bluuebunny/crossref_metadata_2025 huggingface dataset:
Ejection of neutral and charged particles from CdTe and Cd0.96Mn0.04Te induced by pulsed laser irradiation
Authors: Dubowski J. J. , Bhat P. K. , Williams D. F. , Becla P.
Published: July 2002

The nature and density of the species present in the vapor state during pulsed laser evaporation of CdTe and Cd0.96Mn0.04Te have been studied as a function of laser power P. The thresholds for species ejection were 1 and 1.5 J/cm2, respectively. The generated current due to electrons is greater than that due to ions when P<2 J/cm2, and lower than the ion current when 24.0 J/cm2 the ion current decreases below the electron current intensity. Possible mechanisms which could give rise to this general behavior are discussed.
Modeling of dopant diffusion during rapid thermal annealing
Authors: Fair Richard B.
Published: July 2002

Observations of enhanced dopant diffusion during rapid thermal annealing (RTA) have been made and correlated with the existence of the following phenomena: (1) amorphization of the ion implanted layer; (2) damage-induced dislocation formation; (3) damage annealing; (4) self-interstitial trapping; or (5) dopant solubility enhancement. Thus, modeling the diffusion of As, B, P, and Sb during RTA presents a unique challenge, since point-defect generation, damage annealing, and solid solubility levels are occurring or changing during the short diffusion intervals. The base line modeling environment for studying transient diffusion must include normal, thermally assisted diffusion processes such as electric field effects, concentration-dependent diffusion, clustering or precipitation, dopant misfit strain, etc. In addition, transient phenomena must be introduced. We have handled transient modeling by overlaying the time-dependent effects on steady-state thermally assisted diffusion calculations. Temperature and point-defect transients are calculated by performing calculations over small time intervals in which average parameter values are determined. Calculations and measurements have been performed for As, P, B, and BF2 implants into crystalline and preamorphized Si. Atomic level models are proposed and activation energies have been determined for each substrate–dopant combination.
Chemical reaction and anion trapping at the Yb/GaAs(110) interface
Authors: Nogami J. , Williams M. D. , Kendelewicz T. , Lindau I. , Spicer W. E.
Published: July 2002

Synchrotron radiation photoelectron spectroscopy was used to study the interface between the rare earth metal ytterbium, and the GaAs(110) cleaved surface. From trends in line shape and intensity of the Ga 3d, As 3d, and Yb 4 f core level signals, we have deduced a picture of the formation and the final structure of the interface at room temperature. For metal coverages up to 1 ML, there is a weak chemical interaction between deposited metal and substrate. The coverage range between 1 and 2 ML is marked by strong interdiffusion and reaction, and the formation of an Yb arsenidelike phase at the surface that is stable with further metal deposition. This reacted layer appears to restrict further interdiffusion; the As is trapped at the interface, and additional metal deposition results in the growth of an Yb metal rich overlayer. From the continuous shift of the Ga 3d signal with coverage, and the behavior of the Yb 4 f line shape, the overlayer appears to be an Yb/Ga alloy that becomes more dilute in Ga as Yb is deposited.
Low temperature material reaction at the Ti/Si(111) interface
Authors: Tromp R. M. , Rubloff G. W. , van Loenen E. J.
Published: July 2002

High resolution medium energy ion scattering has been used to study material reactions at the Ti/Si(111) interface at temperatures which are anomalously low (∼250–400 °C) relative to normal silicide growth temperatures (≥600 °C). The depth-dependence of compositional mixing is inconsistent with the simple interfacial silicide formation process established for many metal/silicon systems. The results suggest that mechanisms of material reaction other than interfacial silicide compound formation dominate the interfacial reaction at low temperatures, such as grain boundary diffusion leading to localized silicide formation at grain boundaries.
Direct-laser writing of silicon microstructures: Raman microprobe diagnostics and modeling of the nucleation phase of deposition
Authors: Herman Irving P. , Magnotta Frank , Kotecki David E.
Published: July 2002

Two topics vital to the analysis and applications of direct-laser writing of silicon microstructures are addressed here: optical diagnostics and modeling. The use of real-time and postprocessing Raman microprobe analysis of laser-written doped polysilicon microstructures on CMOS gate arrays is shown to be a useful diagnostic tool. Also, the results of a Monte Carlo simulation of adatom migration and desorption are applied to the study of nucleation effects in direct-laser writing, with specific reference to the deposition of silicon.
Damage and contamination-free GaAs and AlGaAs etching using a novel ultrahigh-vacuum reactive ion beam etching system with etched surface monitoring and cleaning method
Authors: Asakawa K. , Sugata S.
Published: July 2002

I n situ monitoring and suppression of damage and contamination induced by GaAs and AlGaAs reactive-ion-beam-etching (RIBE) have been investigated to establish clean surfaces, required for fabricating III–V compound optoelectronic integrated circuits (OEIC’s). A novel ultrahigh-vacuum RIBE system with etched surface monitors and a surface cleaning gun has been developed for this purpose. Damage suppression with low energy (10–100 eV) RIBE was confirmed with an ideality factor in a Schottky diode. Removal of Cl contamination induced by Cl2 plasma was established with temperature-controlled (200 °C) RIBE or heat treatment (400 °C) after RIBE. Furthermore, it was demonstrated for the first time that both GaAs and AlGaAs native oxide layers could be successfully removed simply with irradiations of H and Cl radical beam released from the novel, compact electron-cyclotron-resonance (ECR) plasma gun.
Crystallization of zirconia films by thermal annealing
Authors: Rujkorakarn R. , Sites J. R.
Published: July 2002

Thin films of zirconium dioxide were produced by ion-beam sputter deposition onto fused silica substrates. The deposition process involved a Kaufman-type ion source with ion energy of 1100 eV, beam current density 1.5 mA/cm2, and argon to oxygen ratio of 40:60. Raman scattering was used to monitor crystallization. When the zirconia film was thermally annealed in air, it first crystallized into a mixed tetragonal and monoclinic phase at 450 °C. Further heating beyond 900 °C showed a transformation to a cubic phase. The crystalline transformations decreased the film refractive index from 2.2 to 2.0, significantly increased both the optical absorption and scattering, and lowered the optical band gap from 3.8 to 3.2 eV.
Effects of process parameters on low frequency modulation on sputtered disks for longitudinal recording
Authors: Hill F. A. , Reineck S. , Roell K.
Published: July 2002

In-line magnetron sputtering systems with nonrotational substrate fixturing are attractive as a way to produce magnetic media (e.g., hard disks) in large quantities. However, magnetic materials sputtered in in-line sputtering systems seem to have an inherent magnetic anisotropy correlated to the direction of substrate travel, resulting in a low frequency modulation of the readback signal when typical magnetron sputtering parameters (e.g., Ar pressure, sputtering rate) are used. Experiments have been carried out to determine the effects of such parameters as argon pressure, static sputtering rate, magnetic field, film thickness, substrate temperature, and others on this low frequency modulation. Results of experiments performed on magnetic films consisting of 80% Co–20% Ni alloy over a Cr underlayer indicate that low frequency modulation can be suppressed to an acceptably low level mainly through the proper optimization of pressure and rate.
Optical properties of nonstoichiometric zinc oxide films deposited by bias sputtering
Authors: Brett M. J. , Parsons R. R.
Published: July 2002

Thin films of composition ZnOx, with 0.7<x<1, have been deposited by modified planar magnetron sputtering using an rf discharge at the substrate to control film stoichiometry. A decrease in resistivity from 0.02 to 0.002 Ω cm and an associated transition from an absorbing to transparent appearance was observed as the oxygen content of the films was increased. For all films, the optical constants n and k in the wavelength range 0.4–2.5 μm were deduced and the reflectivity was measured between 2.5 and 20 μm wavelength. The optical properties of transparent and absorbing films were modeled by a dielectric function incorporating the Drude theory of free electrons, the Lorentz theory of lattice absorption, and a Maxwell–Garnett description of zinc inclusions.
Deposition of a-Si,Sn:H alloy films by reactive magnetron sputtering from separate Si and Sn targets
Authors: Parsons G. N. , Cook J. W. , Lucovsky G. , Lin S. Y. , Mantini M. J.
Published: July 2002

We have deposited thin film a-Si,Sn:H alloy films in a dual magnetron sputtering system, and have studied the chemical bonding of the constituent atoms by infrared (IR) absorption spectroscopy, Auger electron spectroscopy (AES), and x-ray photoelectron spectroscopy (XPS). We have also measured the band-edge optical absorption, the photoconductivity, and the temperature dependence of the dark conductivity. We find that the variation of the optical band gap, the dark conductivity and the photoconductivity are essentially the same in these films as in films produced by the glow discharge decomposition of silane (SiH4) and either SnCl4 or Sn(CH3)4. For Sn concentration as high as 26 at. %, we cannot detect SnH vibrations by IR. We find that the optical gap decreases monotonically with increasing Sn concentration, but that the dark conductivity does not display a conduction mechanism with an activation energy close to one-half of the optical gap. Instead, both the dark and photoconductivities display a transition to a hopping conduction mechanism at a Sn concentration between about 1 and 2 at. % (this corresponds to an optical gap just below 1.7 eV). We propose a model for this transition in which the Sn is incorporated in nontetrahedral bonding geometries.
Molecular beam epitaxial growth and characterization of HgCdTe, HgZnTe, and HgMnTe on GaAs(100)
Authors: Faurie J. P. , Reno J. , Sivananthan S. , Sou I. K. , Chu X. , Boukerche M. , Wijewarnasuriya P. S.
Published: July 2002

We present here the growth and the characterization of n- and p-type layers of HgCdTe, HgZnTe, and HgMnTe grown on GaAs(100) substrates by molecular beam epitaxy. These films are grown on a CdTe or CdZnTe buffer layer previously deposited on the GaAs(100) substrates. The buffer layers have the (100) or (111) orientation depending on the GaAs preheating treatment. For all three semiconducting alloys in situ electron defraction experiments and Hall characterization attest to the excellent quality of the epilayers. n-type and p-type layers have been obtained for all three alloys by controlling the crystal stoichiometry deviation. p-type layers for HgCdTe and HgZnTe films exhibit extremely high hole mobilities. We have also presented results using indium as a n-type dopant during growth. These results confirm that GaAs is emerging as the candidate for replacement of CdTe in HgCdTe epitaxial growth and also that HgZnTe is a potential candidate to replace HgCdTe.
Stimulated emission from Cd1−xMnxTe–CdTe heterostructures and Cd1−xMnxTe–Cd1−yMnyTe multiple quantum well structures
Authors: Bicknell R. N. , Giles-Taylor N. C. , Schetzina J. F. , Anderson N. G. , Laidig W. D.
Published: July 2002

We report the first observation of stimulated emission from Cd1−xMnxTe–CdTe and Cd1−xMnxTe–Cd1−yMnyTe multiple quantum well structures. The active superlattice (SL) regions of these new laser structures consist of either 25 CdTe or 25 Cd1−yMnyTe quantum wells alternating with 24 Cd1−xMnxTe barriers. The emission from the Cd1−xMnxTe–CdTe lasers occurs at 763–766 nm when optically pumped at T=25 K. The Cd1−xMnxTe–Cd1−yMnyTe lasers emit coherent, visible red radiation (665–670 nm) when optically pumped at T=15 K at a peak power density of 2.00×104 W/cm2. Stimulated emission from double-layer Cd1−xMnxTe–CdTe heterostructures has also been observed.
Effects of ion implantation on deep electron traps in Hg0.7Cd0.3Te
Authors: Cotton V. A. , Wilson J. A.
Published: July 2002

Ion implantation is commonly used to create n+ on p junctions for photovoltaic detectors in HgCdTe. This process is known to create a high level of donors due to lattice damage. This work reports results of a deep level transient spectroscopy (DLTS) study of traps in n-type Hg0.7Cd0.3Te also associated with the implant induced lattice damage. A new trapping center is found at Ec−0.19 eV which is distinctly due to implant damage. The electron trapping characteristics of this level are unusual, showing a small capture cross section of σn=5×10−21 cm2 and a large barrier potential to electron capture. This indicates a weak electron trap and implies a strong hole trapping nature. As yet, these data do not account for shortened lifetimes seen in n+ on p diodes formed by ion implantation.
Effect of alloy disorder on deep levels in Hg1−xCdxTe
Authors: Myles Charles W. , Ford William C.
Published: July 2002

The effects of alloy disorder on deep levels in Hg1−xCdxTe are investigated, using the embedded cluster method and the theory of deep levels. For the present application, only the effects of the nearest-neighbor disorder on deep levels produced by substitutional impurities on the anion (Te) site of this material are considered. However, the approach used can be generalized to account for such disorder effects in the second- and higher-neighbor environments of an impurity and can thus be extended to impurities on the cation (Cd/Hg) site in Hg1−xCdxTe. Results are presented for the composition dependences of the component lines, the center, and the width of the alloy broadened spectrum of a deep level occurring at ‘‘midgap’’ for x=0.25.
The effect of inert gas plasma exposure on the surface structure of hydrogenated amorphous silicon (a-Si:H)
Authors: Collins R. W. , Tuckerman C. J.
Published: July 2002

I n situ ellipsometry experiments have been used to study the modification of hydrogenated amorphous silicon (a-Si:H) surfaces exposed to He and Ar plasmas at room temperature in an asymmetric capacitively coupled radio-frequency (rf) glow discharge reactor. Such a system provides an informative way of studying the microstructural changes caused by ion bombardment at two different accelerating potentials. A photon energy of 3.5 eV is used as a probe in the ellipsometry experiment in order to maximize sensitivity to changes in the volume density of Si–Si bonds near the sample surface. As expected, significant differences are observed between the effects of exposure at the anode and the cathode owing to the greater potential difference between the cathode and the plasma. When the a-Si:H is exposed to a 0.3 W/cm2 He plasma at the cathode (∼–30 V dc bias), a surface layer with a low density of Si–Si bonds is formed, reaching a thickness of ∼35 Å after 30 min. For a fixed time interval and plasma power, the thickness of the low density layer caused by the He plasma is about 2–3 times greater than that caused by Ar. The surface layer is readily consumed by oxidation and its properties are attributed to the presence of microvoids ≲50 Å in size. For samples exposed to a 0.3 W/cm2 He plasma at the anode (grounded), no significant damage is detected. In this case the effect of the plasma is to remove a very thin oxide overlayer. Thus, ellipsometry experiments are effective in determining plasma operating conditions which result in improved surfaces while minimizing roughness layers and damage.
Plasma luminescence generated in laser evaporation of dielectrics
Authors: Sankur H. , Nelson J. G. , Pritt A. T. , Gunning W. J.
Published: July 2002

Emission from the plasma generated when a pulsed CO2 laser is used to evaporate dielectric materials is analyzed in the 200–900 nm region by means of an optical multichannel analyzer. Atomic spectra consisting of excited neutral and singly, doubly, and triply ionized species were observed from laser irradiation of Al2O3, SiO2, ZnO, PbF2, TiO2, and HfO2. Emission from the B–X transition of AlO was observed under vacuum conditions becoming more intense in the presence of added gases. Assuming local thermal equilibrium, plasma temperatures were calculated using the emission intensities of several selected atomic species. Possible effects of the observed phenomena on the properties of thin films deposited by laser-assisted deposition are discussed.
Majority-carrier mobility in p-type Hg1−xCdxTe
Authors: Meyer J. R. , Bartoli F. J. , Hoffman C. A.
Published: July 2002

We report a detailed experimental and theoretical investigation of mechanisms limiting the majority-carrier mobility in p-type Hg1−xCdxTe. For the first time, transport measurements have been performed on samples with well-characterized compensation densities. Mobilities calculated assuming an alloy scattering energy parameter within present theoretical bounds (ΔEh≤0.3 eV) are found to be at least a factor of 3 higher than the data at intermediate temperatures (T≊30 K). While alloy scattering may be somewhat stronger than is currently believed, a better fit to the data is obtained if one assumes that the low-temperature scattering is dominated by strain fields resulting from neutral point defects.
Controlled substitutional doping of CdTe thin films grown by photoassisted molecular-beam epitaxy
Authors: Bicknell R. N. , Giles N. C. , Schetzina J. F. , Hitzman C.
Published: July 2002

We report the successful substitutional doping of CdTe films grown by a new technique: photoassisted molecular-beam epitaxy. This new growth technique gives rise to dramatic changes in the electrical properties of as-grown epilayers, as determined by variable-temperature Hall-effect measurements. In particular, highly conducting n-type and p-type CdTe films have been grown using indium and antimony as n-type and p-type dopants, respectively. Double-crystal x-ray diffraction rocking curve data indicate that the doped epilayers are of high structural quality. Using the photoassisted molecular-beam epitaxy technique, double-layer thin-film CdTe p–n junction diodes have been successfully fabricated for the first time. The application of this new film growth technique to control the electrical properties of another II–VI material has also been demonstrated by the successful n-type doping of CdMnTe epilayers with indium.
Sources of surface contamination affecting electrical characteristics of semiconductors
Authors: Slusser G. J. , MacDowell L.
Published: July 2002

Surface cleanliness has become an extremely critical concern in the manufacture of semiconductor products. The parts per 109 levels of contaminants in a chemical cleaning solution can drastically affect electrical parameters. Using a buried surface layer technique in conjunction with secondary ion mass spectrometry, it is shown that contaminants that are present at low levels in solution can concentrate on the surface of wafers. When the contaminant is boron, inversion layer problems can occur, while aluminum contamination can affect threshold voltage readings on dual dielectric films. Stainless-steel contamination is deadly for leakage concerns. The sources of these and other contaminants must be located and monitored closely.
Schottky barriers and band lineups at interfaces
Authors: Kane Evan O.
Published: July 2002

The principle concepts underlying our understanding of Schottky barriers for well-characterized interfaces are reviewed. The Tersoff ‘‘neutral point’’ picture based on metal-induced gap states seems promising but does not explain submonolayer results. The Tersoff band lineup model for semiconductors is tested by a Si–Ge heterojunction calculation. The difference between Si and Ge potentials is small enough to allow the junction potential to be decomposed into contributions from individual Ge planes in a Si matrix. Planes away from the junction lead to an ‘‘intrinsic’’ offset while those near the junction give a much smaller ‘‘junction sensitive’’ offset, justifying Tersoff’s assumption of an intrinsic process. A small change in the Schottky offset is strongly screened by a dielectric constant of order 10 as predicted by Tersoff. The offset is shown to be best understood using the principle of strict charge neutrality, emphasizing the irrelevance of interface dipoles as causing the offset. The offset is caused by the need to line up the hybrid energies (or neutral points) plus a correction of order 0.14 eV which compensates for the difference in bond strength between silicon and germanium.
Formation of silicides in the Ti, Ti(Ox)/Si(111), and Ti/SiO2/Si(111) systems
Authors: Hsu C. C. , Wang You-Xiang , Yin Shi-Duan , Li Bao-Qi , Ji Ming-Ron , Wu Jian-Xin
Published: July 2002

Reactions at Ti/Si and Ti/SiO2/Si interfaces under the conditions of steady-state thermal annealing and cw Ar+ laser annealing have been studied using a variety of techniques including Auger electron spectroscopy (AES), x-ray photoemission spectroscopy (XPS), Rutherford backscattering, and x-ray diffraction. Ti thin films on silicon have been transformed to Ti5Si3, TiSi, and TiSi2 after steady-state annealing at 500–600 °C, and only TiSi2 can be observed after annealing above 650 °C. In the case of the Ti/SiO2/Si system a Ti5Si3 thin film with a TiO overlayer has been formed in the temperature range 750–1000 °C. The growth of the Ti–Si2 layer on silicon and the Ti5Si3 layer on SiO2 shows a diffusion-limited behavior, i.e., x∝t1/2. Continuous-wave Ar+ laser scanned annealing can induce the solid-phase reaction of Ti/Si at a power density less than 2.7 kW/cm2, but a liquid-phase reaction at a power density of about 3.8 kW/cm2. A mixture of TiSi2 and pure Si was observed after the liquid-phase reaction. Ti(Ox) on atomically clean Si(111) and on Si(111) with native oxide has been studied using ultraviolet photoemission spectroscopy, XPS, and AES. The sequential deposition of Ti(Ox) at room temperature on clean Si(111) showed that the interface is unreacted. However, with moderate annealing (300 °C), the intermixing of Ti and Si atoms has been observed. Ti(Ox) on a clean Si(111) surface produces oxygen chemisorption of the Si(111) surface, but Ti(Ox) on Si(111) with native oxide produces the Ti oxides—TiO and TiO2.
An investigation of the chemistry of the dielectric/FeCoTb interface by x-ray photoelectron spectroscopy and Auger electron spectroscopy
Authors: Stickle W. F. , Coulman D.
Published: July 2002

The interfacial chemistry of magneto-optic structures of sputter deposited SiO, SiO2, Si3N4/FeCoTb/SiO, SiO2, and Si3N4 was studied in detail by x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). XPS and AES depth profiles have revealed a substantial amount of redox chemistry at the dielectric/rare-earth transition metal interfaces. The chemical reactions occur preferentially with the terbium as revealed in the XPS portion of the study by the formation of terbium oxide and terbium silicide. In the case of Si3N4 evidence of TbNx has also been observed. ‘‘As deposited’’ and annealed samples of the magneto-optic structures are compared and contrasted. It is concluded that Si3N4 is a superior dielectric for magneto-optic media.
Oxygen effect on secondary ion emission of impurities in GaAs
Authors: Tanaka T. , Homma Y. , Okamoto H.
Published: July 2002

To investigate quantitatively the effect of oxygen on the ion yields in secondary ion mass spectrometry (SIMS) analysis of impurities in GaAs, oxygen-implanted GaAs crystals were prepared. Oxygen-induced ion yield enhancement was demonstrated by the SIMS analysis of these oxygen-implanted GaAs crystals. B, Cr, Cu, and Mn in these crystals were found to have impurity ion yields 50 times larger than those without oxygen under Ar+ bombardment. The ion yield enhancement of impurities by oxygen has been interpreted by treating ion yields as a function of oxygen fraction, i.e., probability of occupying the adjacent site to the impurities by oxygen atoms. For oxygen fractions, the local thermodynamic equilibrium calculations were carried out to obtain T parameters which enable the impurity ion yields to be estimated only by ionization potentials if the oxygen fraction is given.
Oxidation of amorphous Ni–Nb films: Surface spectroscopy studies
Authors: Christensen T. M.
Published: July 2002

Sputter deposited amorphous Ni–Nb alloy films have been proposed as thin-film metallization layers for high-temperature (>300 °C) compound semiconductor applications. We have used x-ray photoelectron spectroscopy (XPS) to investigate the oxidation behavior of 1-μm-thick, sputter deposited, amorphous Ni60 Nb40 films exposed to oxygen or room air at temperatures in the range 30–500 °C for times of 5 min to 45 h. The initial stages of oxidation were examined in situ at oxygen partial pressures below 1×10−6 Torr. At all temperatures, Nb2 O5 formed on the surface; this remained the dominant corrosion product for specimens oxidized in air for 45 h at temperatures up to 200 °C. Angle-resolved XPS measurements indicated that a thin (5–10 Å) NiO layer formed on the surface of the Nb2 O5 after long exposures at these temperatures. Specimens oxidized at temperatures above 240 °C, however, quickly developed a thick (>100 Å), crystalline NiO layer on top of the Nb2O5.
Nonmonotonic evolution and thermodynamic trends at metal/(Hg,Cd)Te interfaces: Yb/Hg0.78Cd0.22Te
Authors: Peterman D. J. , Raisanen A. , Chang S. , Philip P. , Wall A. , Franciosi A.
Published: July 2002

The microscopic interaction of cleaved Hg0.78Cd0.22Te surfaces with the highly reactive rare earth Yb was studied by use of photoemission spectroscopy and synchrotron radiation. We compare the results of this study with our previous investigation of Sm/(Hg,Cd)Te interface formation. Yb and Sm are similar in their initial stage of interface formation: rapid attenuation and near loss of the Hg emission is followed by its dramatic recovery. However, differences in valency between Sm and Yb develop during metal deposition and subsequently lead to differences in interface morphology. Calculated heats of solution are shown to correlate with the different behaviors observed during rare earth/(Hg,Cd)Te interface formation.
Metal–Si bonding in Cu/Si(111)‘‘5×5’’ using angle-resolved ultraviolet photoemission spectroscopy and band structure calculations
Authors: Chambliss D. D. , Rhodin T. N. , Kasowski R. V.
Published: July 2002

Photoemission spectra from reacted submonolayer deposits of noble metals on Si both reflect the surface atomic configuration and measure metal–Si bonding behavior. We have studied the ‘‘5×5’’ structure of annealed Cu on Si(111) with angle-resolved ultraviolet photoemission spectroscopy, varying polarization and photon energy (14–25 eV) to examine the symmetries and atomic origins of observed features. Experimental results are compared in detail with ab initio computations of band structure for model structures using the pseudofunction method. The results indicate that most Cu atoms reside at highly symmetric sites, and bonds between coplanar atoms dominate the Cu d structure. The energy levels suggest a model with threefold rather than sixfold Cu–Si coordination. The Cu d states appear to obey dispersion determined by an expanded overlayer rather than by the substrate lattice.
Metal-induced gap states at the Ag and Au/GaAs interfaces
Authors: Stiles K. , Kahn A. , Kilday D. , Margaritondo G.
Published: July 2002

The initial formation of several metal–GaAs(110) interfaces has recently been reexamined by evaporating the metal on the semiconductor surface cooled to 70–100 K. Overlayer homogeneity and metal-induced unrelaxation are increased at low temperature (LT), whereas clustering, interdiffusion, and chemical reactions are substantially inhibited. Ag and Au interfaces with n- and p-GaAs were studied with soft x-ray and ultraviolet photoemission spectroscopies (SXPS, UPS) and low-energy electron diffraction. Both interfaces displayed the very asymmetric LT pinning of the Fermi level (EF) reported earlier: (1) fast EF movement at ultralow coverage (<0.1 Å) on p-GaAs and slow EF movement up to ∼2 Å on n-GaAs and (2) transition around 2 Å with a sharp drop of EF on n-GaAs toward its high-coverage position and concomitant but small shift of EF on p-GaAs. SXPS and UPS measurements of the LT Ag 4d and Au 5d valence bands show a sharp increase in the full width at half-maximum from values characteristic of isolated atoms or small clusters to values characteristic of metallic layers at precisely the same coverage. These results therefore point out a correlation between high-coverage (>2 Å) pinning and appearance of metallic character in the overlayer.
Al surface mobility on Si(111) during initial stages of ionized cluster beam deposition
Authors: Levenson L. L. , Asano M. , Tanaka T. , Usui H. , Yamada I. , Takagi T.
Published: July 2002

Al thin films were deposited from an ionized cluster beam onto Si(111) through a 50×1000-μm slot in a stainless-steel mask. The films were deposited under UHV conditions. The substrate temperatures were held at 50, 200, and 400 °C. The acceleration voltage applied to the beam was either 0 or 3 kV. Auger electron line scans across the Al strips were used to determine the distance Al atoms diffused along the surface under the mask in a direction normal to the slot. It was found that for a 0-kV beam (no ionization), Al atoms diffused 17 μm at 50 °C, 28 μm at 200 °C, and 12 μm at 400 °C. With a 3-kV beam, Al diffused 13 μm at 50 °C, 12 μm at 200 °C, and 12 μm at 400 °C. The film structures, as seen by scanning electron microscopy micrographs and by reflection medium-energy electron diffraction were similar for 50 and 200 °C substrates at 0 and 3 kV. However, for 400 °C substrates the film structures were significantly different for 0- and 3-kV beams. The Si(111) substrates were cut 4° off axis. Oriented platelets were formed by 3-kV beams on 200 and 400 °C substrates. The long axes of these platelets followed the direction of ledges, i.e., the [112] direction, probably because of anisotropic surface diffusion.
An electrohydrodynamic formalism for ion and droplet formation in stressed conducting fluids
Authors: Miskovsky N. M. , Chung M. , Cutler P. H. , Feuchtwang T. E. , Kazes E.
Published: July 2002

An electrohydrodynamic surface capillary wave theory is developed for ion and droplet formation in electrically stressed conducting viscous fluids. This theory can be used to describe properties of electrohydrodynamic sources such as the liquid metal ion sources. Using the mathematical models of Chung et al., and Grossman and Muller, we have obtained the first-order corrections of the Navier–Stokes equation for a three-dimensional axially symmetric fluid. Formal solutions are developed for the eigenmodes describing the deformation of the surface as a function of applied electric field with both radial and longitudinal components. It is argued that the spatial variation of the complex mode amplitudes yield both the size and directional distribution of the emitted particles. The real part of the eigenfrequency associated with the excited eigenmode is related to the temporal behavior of instabilities on the fluid surface. From this one obtains the growth and decay rates of the time-dependent ion and droplet emission. Finally, by applying the dynamical Laplace–Young stress condition, the critical fields necessary for the onset of instability of the fluid surface are obtained.
Oxidation at the polyimide/Cu interface
Authors: Chambers S. A. , Chakravorty K. K.
Published: July 2002

We have used x-ray photoelectron spectroscopy in a normal emission configuration to investigate the chemistry of formation of the buried polyimide on Cu interface. We find that oxidation of the Cu surface begins within an hour of the curing process, and that Cu atoms in contact with the polyimide overlayer are completely oxidized to CuO after being stored in air for several days. This conclusion is in stark contrast with that drawn for the inverse system, Cu on polyimide, which has been shown to be essentially unreactive in vacuum over a time scale of several hours. We suggest that the key difference between the two systems is a very slow corrosion reaction perhaps involving trace amounts of chloride ion, water trapped in the polyimide overlayer, and the Cu surface. In contrast, the same experiment involving a Au substrate shows no evidence of reaction over a time frame of weeks.
Quantitative analysis of adsorbed layers by Auger electron spectroscopy
Authors: Millo O. , Many A. , Goldstein Y.
Published: July 2002

A mathematical analysis is presented which enables a simple quantitative characterization of adsorbed layers on a homogeneous substrate. Two main cases are considered: submonolayer coverage by one kind of species (atoms or molecules) and coverage by two different species adsorbed one on top of the other. In both cases, a single Auger spectrum is sufficient to provide the information needed to determine the coverage. The analysis is applied to the case of simultaneous hydrocarbon and oxygen adsorption on polycrystalline silver. The coverage so determined agrees very well with that derived from measurements of adsorption as a function of exposure.
Variation of Hg incorporation in molecular-beam epitaxially grown HgCdTe structures due to growth front roughness and misoriented substrates: Role of kink sites
Authors: Singh Jasprit , Arias Jose
Published: July 2002

Theoretical and experimental results are presented to shed light on the atomistic nature of Hg incorporation during HgCdTe growth. The extremely large difference in the bond strengths of the Cd–Te and Hg–Te forces the choice of growth conditions where Hg incorporation is extremely small and controlled essentially by two key factors: (i) Te2 overpressure and (ii) kink site density at the growing surface. While the role of Te2 overpressure was explored earlier, the role of the second factor will be the subject of this paper. The kink site density is in general time dependent during growth; it can also be varied by choosing different growth directions. Consequently, the Hg incorporation rate, which is closely tied to surface kink site density, is altered. These issues and their importance on HgCdTe alloys and HgCdTe–CdTe heterostructures are explored.
Unique band bending at the Sb/InP(110) interface
Authors: Kendelewicz T. , Cao R. , Miyano K. , Lindau I. , Spicer W. E.
Published: July 2002

The band bending and the overlayer growth at the Sb/InP(110) interface has been studied with soft x-ray photoemission spectroscopy. In agreement with previous works, our data indicate that 1 monolayer (ML) of Sb is growing in a laminar zig–zag fashion on the unrelaxed substrate. This is consistent with models previously applied to the Sb/GaAs interfaces. We, however, observe some puzzling behaviors unique to the Sb/InP(110) interface. First, we find that for this model system with simple morphology the core level shifts, routinely taken as a measure of the band bending, are different for In 4d and P 2p. This perhaps could indicate a presence of another component but also could indicate some problems in using photoemission in application to the quantitative band bending studies. Despite pronounced quantitative differences, we assumed that the core level movement is dominated by the band bending and find for both core levels a reversal of shift on n-InP indicating reversal of the band bending from a maximum at ∼0.5 ML to a small value of 0.15±0.1 eV (0.1 or 0.2 eV depending on the core level monitored) for few monolayers of Sb. These data are consistent with previous results using Raman spectroscopy and electrical diode measurements which find Ohmic contacts for thick Sb overlayers on InP(110). Also consistent with these works, we find large band bending on p-InP(110).
Structural and electrical characterization of InAs grown on GaAs substrates by molecular-beam epitaxy
Authors: Sheldon P. , Al-Jassim M. M. , Jones K. M. , Goral J. P. , Yacobi B. G.
Published: July 2002

Epitaxial InAs:Sn is grown on semi-insulating GaAs substrates by molecular-beam epitaxy. The large lattice mismatch between these materials (∼7.1%) generates a high density of threading dislocations which propagate into the epitaxial film. Both plan-view and cross-sectional transmission electron microscopy techniques are used to investigate the generation and propagation of these dislocations. For films that exceed the critical thickness, the threading dislocation density is inversely proportional to the epilayer thickness. Epitaxial layers incorporating growth interrupts have lower overall defect densities, yet maintain defect reduction profiles similar to those observed in layers grown without the growth interrupt. Room-temperature mobilities for InAs:Sn epitaxial layers varied from 11 200 to 22 100 cm2/V s for epilayer thicknesses of 0.4 to 4.4 μm, respectively. The thickness dependence on the mobility is attributed to a multiplicity of factors including surface scattering, interfacial strain, surface accumulation, and the high interfacial dislocation density.
Development of an ultrahigh vacuum, i
n v
a
c
u
o wafer transfer facility integrated processing
Authors: Rudder R. A. , Hendry R. C. , Markunas R. J.
Published: July 2002

An ultrahigh vacuum, in vacuo wafer transfer system has been completed for development of integrated wafer processing. Design decisions which determined the structural layout and the interior design of the vacuum transfer vessel are elucidated in this paper. Among the criteria considered were (i) the areal floor space occupied by the transfer device, (ii) the average travel distance per transfer, and (iii) an awareness that mechanical function must be incorporated without leading to wafer particulate contamination. Of these criteria, the first two influenced the structural arrangement of the transfer system while the last criterion influenced the interior design. Elementary calculations are presented for a simple rotary and linear transfer tube design. These calculations show that, for integration of more than four nodes, the linear transfer design occupies less floor space than a rotary design would occupy. Calculations show that the rotary design does offer a shorter average transfer distance. However, trafficking of the process steps will produce comparable average travel distances per transfer between the rotary and linear designs. To reduce wafer particulate contamination, the interior design included face-down susceptors in all deposition chambers, vertical wafer storage, isolation valves off line from the linear transfer, and concealed gear trains. The vacuum transfer vessel currently interconnects a chemical vapor deposition unit, a surface analytical unit, a substrate modification chamber, a molecular-beam epitaxy chamber, and a vertical load lock. Vacuum performance curves for samples entering the transfer vessel from air show that water desorption from the sample carrier and wafer must be enhanced during sample entry into the transfer system; else, water desorption can inadvertently occur during subsequent processing steps.
Selectivity loss during tungsten chemical vapor deposition: The role of tungsten pentafluoride
Authors: Creighton J. R.
Published: July 2002

Our previous studies found evidence for a selectivity loss mechanism that is initiated by desorption of tungsten subfluorides formed by the reaction of WF6 with metallic tungsten surfaces. When a hot (≂600 °C) tungsten surface is exposed to WF6, a nonvolatile subfluoride, apparently WF4 , will accumulate on a nearby SiO2 surface held at ≂30 °C. Disproportionation of this tungsten subfluoride upon heating above 350 °C produces a reactive state of tungsten that induces rapid selectivity loss when exposed to chemical vapor deposition conditions. The net effect of this tungsten subfluoride desorption–disproportionation mechanism is the transport of tungsten from a tungsten surface to the silicon dioxide surface. Isolation of a higher tungsten subfluoride, apparently WF5, has been accomplished by cooling the SiO2 surface to ≂−45 °C under otherwise similar experimental conditions. Preliminary Auger spectroscopic results yield a stochiometry of F/W=4.9±0.5 for this subfluoride, and temperature programmed desorption results are consistent with the behavior of tungsten pentafluoride. Upon heating WF5 multilayers, most of the compound desorbs, but some reaction and disproportionation occurs leaving a reduced state of tungsten on the SiO2 surface. It seems likely that tungsten pentafluoride is the key volatile species in a tungsten transport mechanism that can initiate selectivity loss.
Molecular-beam epitaxial growth and x-ray characterization of (Zn,Cd)Te/CdTe strained layer superlattices
Authors: Golding T. D. , Qadri S. B. , Dinan J. H.
Published: July 2002

(Zn,Cd)Te/CdTe strained layer superlattices have been grown by molecular-beam epitaxy on CdTe(100), InSb(100), and GaAs(100) substrates and substrate/buffer layer combinations. Superlattice period thicknesses ranged from 90 to 330 Å; total superlattice thickness was 0.8 or 1.6 μm. The ratio in thickness between the (Zn,Cd)Te and CdTe layers was tailored to allow the in-plane lattice parameter of a freestanding superlattice to match that of Hg0.8Cd0.2Te. A high degree of structural quality is indicated by the existence of multiple satellite peaks in the x-ray diffraction spectra from these structures. Structural quality is found to depend on the substrate used.
Positive-ion emission from the fracture of fused silica
Authors: Langford S. C. , Dickinson J. T. , Jensen L. C. , Pederson L. R.
Published: July 2002

Positive-ion emission was observed during and after the fracture of fused silica using time-of-flight techniques and quadrupole mass spectroscopy. Emissions attributed to Si+, SiO+, and Si2O+ were observed during the fracture event itself. An emission mechanism for the silicon-containing ions is proposed involving the mechanical scission of at least three of the bonds joining a silica tetrahedron to the rest of the silica network. The production of silicon-containing ions suggests the activity of nonequilibrium processes which may contribute significantly to the fracture energy of fused silica. A long-lived emission was attributed to the electron stimulated desorption of O+.
Interfacial bonding in W/C and W/B4C multilayers
Authors: Jankowski A. F. , Schrawyer L. R. , Wall M. A. , Craig W. W. , Morales R. I. , Makowiecki D. M.
Published: July 2002

The nature of carbon bonding in W/C and W/B4C multilayer structures is investigated by Auger electron spectroscopy (AES). The interfacial roughness in these x-ray mirrors directly affects their use as efficient optical elements. A significant contribution to interfacial roughness is the possible presence of second phases, WC in particular for the W/C and W/B4C combinations. AES depth profiling of the multilayer interfaces is used as a direct method to probe for the existence of WC.
Floating potential measurements in the near field of an ion cyclotron resonance heating antenna
Authors: Caughman J. B. O. , Ruzic D. N. , Hoffman D. J.
Published: July 2002

Large variations in the plasma potential can lead to large sheath potentials at the surface of the Faraday shield of an ion cyclotron resonance heating (ICRH) antenna. This sheath can accelerate ions to energies where sputtering is significant, resulting in impurity generation. The time-varying floating potential is being measured in the near field of an ICRH antenna by using the Radio Frequency Test Facility (RFTF) at Oak Ridge National Laboratory. The antenna used is a resonant loop antenna that has a two-tier Faraday shield with a layer of graphite on the outer tier. The electron cyclotron heated plasma in RFTF is produced by a 10.6-GHz klystron. The magnetic field at the antenna is ∼2 kG, with a plasma density of ∼1010 cm−3 with an electron temperature of ∼6 eV. Ionization by rf power from the antenna produces a local plasma of ∼1011 with an electron temperature of 12 to 20 eV. The rf floating potential is measured by using a capacitively coupled probe that is scanned in front of the antenna, parallel to the current strap. A stationary Langmuir probe is used to measure the time-averaged floating potential. Measurements indicate that the potential scales with the antenna current and increases with plasma density to values of up to 300 V peak-to-peak. The rf component of the floating potential seems to follow the near field pattern of the antenna, indicating that these fields may be responsible for the potential formation.
Atomic structure in SiO2 thin films deposited by remote plasma-enhanced chemical vapor deposition
Authors: Lucovsky G. , Fitch J. T. , Tsu D. V. , Kim S. S.
Published: July 2002

We have studied selected structure-dependent properties of thin films of SiO2 prepared by remote plasma-enhanced chemical vapor deposition (remote PECVD) and thermal oxidation of crystalline silicon, and have identified process-dependent differences in their local atomic structures. We have determined the frequency ν and linewidth Δν of the Si–O bond-stretching infrared-active vibration near 1075 cm−1, and have found that all relatively thick oxide films, t>1000 Å, prepared by either of these two techniques display the same linear relationship between Δν and ν. This behavior has been interpreted in terms of a central force model that gives the average bond angle 2θ at the oxygen atom sites, and attributes the linewidth to a distribution of vibration modes associated with a ±30° spread in 2θ. We have determined that (i) in remote PECVD films deposited at temperatures (Ts ) between 200 and 350 °C, 2θ varies between 140° and 144°; (ii) in thermal oxides grown over a temperature range (Tox ) between 800 and 1150 °C, 2θ varies from about 147° to 150°; and (iii) in thick oxide films, independent of the preparation method, Δθ/θ is equal to 0.21±0.01. We have compared other oxide properties as well: (a) the optical index of refraction n at 632.8 nm, (b) the intrinsic stress σi, and (c) the etch rate in buffered HF (6:1). In addition, we discuss the electronic properties of remote PECVD and thermally grown SiO2 films in metal–oxide–semiconductor (MOS) structures, where we have observed that the same device quality MOS properties can be obtained in structures employing both types of oxide films. Finally, we compare stress and strain in the remote PECVD and thermal oxides in the immediate vicinity of the Si/SiO2 interface, and the bulk of the oxide films, and correlate the differences we observe with fundamental differences in the two thin-film formation processes.
Monte Carlo simulation of thin-film deposition in a rectangular groove
Authors: Cooke M. J. , Harris G.
Published: July 2002

The deposition of a thin film in a rectangular groove has been simulated by a Monte Carlo method, taking into account collisions in the gas phase, desorption, and surface mobility. The model shows that conformal coating is best achieved by a low sticking coefficient.