bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of thin-film systems using nonresonant multiphoton ionization
Authors: Pallix J. B. , Becker C. H. , Newman N.
Published: July 2002

Surface analysis by laser ionization (SALI) has been used to probe thin-film chemical compositions. Ar+ sputtering at 5–7 keV is used for ion beam milling together with nonresonant photoionization of sputtered neutrals. Photoions are analyzed by reflection time-of-flight mass spectrometry. SALI depth profiles of UHV deposited Au on GaAs show diffusion of Ga and As in the Au film and dramatic compositional variation at the interface after annealing at 405 °C for 10 min. Mass spectra taken from different depths within a superconducting thin film of nominal composition YBa2Cu3O7 show a variety of impurity compounds even though critical current densities are quite high.
Electronic properties of BaO on W(001)
Authors: Hemstreet L. A. , Chubb S. R. , Pickett W. E.
Published: July 2002

In order to better understand the mechanisms responsible for the lowering of the work function that is observed when surface layers containing barium and oxygen are adsorbed on refractory metals such as tungsten, we have initiated a series of full-potential linearized augmented plane wave electronic structure calculations on well-defined model systems representing the Ba–O/W interface. We report here our initial results for a model in which c(2×2) overlayers of upright BaO molecules have been positioned on both sides of a five-layer W(001) film. Three independent self-consistent calculations were performed involving two different Ba–O separations and two different distances between planes of Ba and surface W atoms. We find that the work function of the clean five-layer tungsten slab (4.65 eV) is lowered by ∼1.8–2 eV by the adsorption of the Ba–O surface layer in this geometry, and that this result is relatively insensitive to the Ba–O separation in the overlayer. The most important factor determining the value of the work function seems to be the position of the barium plane above the W substrate. We find evidence of significant bonding between the d-like surface states of the tungsten substrate and both the Ba d and the oxygen 2p adsorbate levels. As a result, multiple dipoles are formed at the interface and the competition between these polarized charge distributions leads to a net lowering of the work function.
Use of porous plugs in the transition flow range for the calibration of vacuum gauges
Authors: Sharma J. K. N. , Mohan Pardeep
Published: July 2002

The use of a porous plug for admitting gases in the molecular flow range is well known. In this paper, the authors deal with the transition flow region, for which the pressure of gas leaking through the plug is expressible in terms of a polynomial of nth degree in time unlike the simple exponential relation for the molecular flow region. The conductance of the plug in the transition flow range, determined from the time derivative of this polynomial, varies linearly with pressure. The slopes of the conductance versus pressure curves for helium, nitrogen, and argon when multiplied by respective viscosities are found to be constant for a plug, as expected from theory. The flowmeter thus established has been used for the calibration of vacuum gauges using an orifice flow system both in the constant volume and constant pressure modes.
Leak detection on the DIII-D tokamak using helium entrainment techniques
Authors: Brooks N. H. , Baxi C. , Anderson P.
Published: July 2002

The entrainment of helium in a viscous gas flow was utilized to compartmentalize, and then to pinpoint, a leak across the inner skin of the double-walled DIII-D vacuum vessel. Inaccessible from the outside, the leak connected the cooling channels in the wall interspace with the primary vacuum chamber. By entraining helium in the pressurized flow from the single-pass gas circulation system, well-defined portions of the wall were exposed to helium without disassembly of the poorly accessible cooling manifolds. Varying the helium injection point permitted the localization of the leak to a single 30° toroidal sector of the vessel. The exact location of the leak was found from inside the vessel by spraying helium on suspect regions, while sweeping the contents of the cooling channels to the foreline of a Varian Contraflow leak detector with a 0.1 Pa m3/s flow of nitrogen. Flow speed calculations were used to predict the response time to entrained helium of the actual leak detection setup.
Transmission electron microscopy of elastic relaxation effects in Si–Ge strained layer superlattice structures
Authors: Perovic D. D. , Weatherly G. C. , Houghton D. C.
Published: July 2002

A series of Si/GexSi1−x (x≂0.2–0.4) strained layer superlattices have been grown by molecular-beam epitaxy on (100) oriented substrates in order to study elastic relaxation effects. In the bulk of a Si–Ge strained layer system grown on a relatively massive substrate, the elastic misfit strain resulting from unit-cell expansions and contractions is accommodated in the GexSi1−x alloy layers. However, it is known that these stresses can be significantly relaxed near surfaces of the bulk or in thin foils prepared for cross-sectional transmission electron microscopy. It has been found that this stress relaxation introduces a number of electron diffraction effects which are superimposed on structure factor or other contrast effects associated with layered structures. We derive equations describing the relaxation strain field for GexSi1−x alloy layers ≂10 nm in thickness present on relatively massive substrates (>100 nm) based on the solution of a line force acting on an elastic half-space. This predicts a long-range stress relaxation.
Mechanism of band discontinuity control at heterojunction interfaces
Authors: Niles D. W. , Tang Ming , Margaritondo G. , Quaresima C. , Perfetti P.
Published: July 2002

We performed synchrotron radiation photoemission experiments on the lattice matched ZnSe–Ge heterojunction with and without a thin (<3 Å) Al intralayer. The intralayer increases the valence-band discontinuity ΔEv, by 0.2 to 0.3 eV. The increase saturates for an intralayer thickness less than one monolayer, and the Al 2p core emission shows the formation of Al2Se3. These two experimental observations support the idea that Al-induced interfacial dipoles are responsible for the measured ΔEv increase.
Chemical and electrical properties at the annealed Ti/GaAs(110) interface
Authors: McCants C. E. , Kendelewicz T. , Mahowald P. H. , Bertness K. A. , Williams M. D. , Newman N. , Lindau I. , Spicer W. E.
Published: July 2002

We present the results of a photoemission study of the annealed Ti/GaAs(110) interface, using soft x-ray (SXPS), x-ray (XPS), and ultraviolet (UPS) photoelectron spectroscopies to monitor the substrate and overlayer core levels and the valence band for Ti thicknesses between 6.7 and 20 monolayers and annealing temperatures between 200 and 425 °C. The SXPS data imply the formation of a stable Ti–As region near the Ti/GaAs interface that increases in width with temperature. Concomitant to this, the binding energy of the Ga changes from its room-temperature position towards elemental Ga. The XPS data suggest the presence of elemental Ga at or near the overlayer surface. The UPS data suggest the possibility of cluster formation on the overlayer surface. In situ current–voltage (I–V) measurements were also made on thick-film systems fabricated using similar methods to those used in the photoemission studies [i.e., cleaving, depositing metal (∼1000 Å), and annealing in UHV]. The movement of Ti–As reaction products into the substrate provides a framework to explain the observed increase upon annealing of the I–V barrier height for Ti/n-GaAs Schottky contacts.
High-Z elements in laser fusion targets
Authors: Gobby P. L. , Moore J. E. , Snow R. C. , Archuleta T. A. , Espinoza B. F. , Gomez V. M. , Barthell B. L.
Published: July 2002

Recent laser fusion experiments conducted by Los Alamos physicists have required the use of high-Z elements in atypical applications. Gold, a commonly used element, has been deposited in low-density smoke form onto plastic and glass spheres. Thorium and uranium have been requested as x-ray backlighter materials, and wires etched to <10 μm have been produced for this purpose. Uranium has also been vapor deposited onto spheres and 7–10 μm fibers with varying degrees of success.
Study of oxygen incorporation in AlGaAs layers grown by molecular-beam epitaxy
Authors: Achtnich T. , Burri G. , Ilegems M.
Published: July 2002

Quantitative measurements of oxygen content in epitaxial AlGaAs layers grown by molecular-beam epitaxy (MBE) are presented and compared with results on liquid phase (LPE) and metalorganic vapor phase epitaxy (MOVPE) layers. The analysis of oxygen concentration profiles measured on GaAs/AlGaAs or GaAs/AlAs multilayers shows that the oxygen incorporation in AlxGa1−xAs layers is arrival rate limited with a sticking coefficient essentially equal to one. The incorporation appears to proceed by a surface exchange reaction via an intermediate O-containing floating boundary layer. This interpretation is consistent with the experimental observations that the oxygen content of the MBE layers is independent of growth temperature between 600 and 700 °C, and that the oxygen level goes through a sharp maximum at the interface between a high Al and low Al content layers due to surface accumulation effects. Oxygen levels are found to be lower by a factor of 2 to 3 in multiquantum well (MQW) compared to random alloy layers of the same average Al content. Lowest 16O levels measured in ternary AlxGa1−xAs layers with 0.3<x<0.4 are around 4×1017 cm−3 for bulk MBE layers, around 1.2×1017 cm−3 for MBE MQW layers, and around (1.4–1.9)×1017 cm−3 for bulk layers grown by LPE and MOVPE.
Chemical modifications of Hg0.1Cd0.9Te surfaces: Analysis with Auger electron spectroscopy
Authors: Tenne R. , Brener R. , Triboulet R.
Published: July 2002

It was previously found that n-type Hg(1−x)CdxTe with 0.7<x<0.9 can have good photoresponse (albeit relatively poor stability) if a series of appropriate surface treatments are used. In order to have a better control on the state of the surface it was desirable to analyze it by Auger electron spectroscopy, during each of the stages of surface preparation. It is shown that photoelectrochemical etching under certain conditions which is followed by KCN treatment leads to a stoichiometric surface which then produces the best photoresponse.
Electron spectroscopic studies of the Dy/Si(111) interface
Authors: Wang Y. X. , Li B. Q. , Xing Y. R. , Hsu C. C.
Published: July 2002

Low-energy electron diffraction (LEED), x-ray photoelectron (XPS), ultraviolet photoelectron (UPS), and Auger electron (AES) surface spectroscopic techniques were used to study the chemical interaction between Dy atoms and Si atoms at the Dy–Si interface at room temperature, as well as Dy silicides formed after annealing at 400 °C for 30 min. Experiment shows that at low coverages [≤4 monolayers (ML)] atom intermixing takes place, causing chemical shifts of Dy 4f and Dy 3d. However, no significant chemical shift of Si 2p has been observed, suggesting a lack of strong chemical bonds of the Dy–Si type. With coverage increasing, a (7×7) LEED pattern from a clean Si(111) surface turns into a (1×1), and finally becomes ambiguous. After annealing for 30 min at 400 °C, the Dy silicides formed with an atomic concentration ratio of Dy to Si of ∼1:2. The binding energies of Dy 4f (Dy Si2), Dy 3d(Dy Si2), and Si 2p(Dy Si2) are 5.5, 1295.2, and 98.65 eV, respectively.
Influence of target microstructure on the propensity for whisker growth in sputter-deposited aluminum alloy films
Authors: Succo L. , Esposito J. , Cleeves Monty , Whitney S. , Lionetti R. E. , Wickersham C. E.
Published: July 2002

Sputtering target microstructure can significantly affect the reliability of integrated circuit metallizations through the growth of aluminum single-crystal whiskers during sputter deposition at substrate temperatures in excess of 400 °C. Whisker densities in the film ranged from over 1500 to 133 cm−2 as the aluminum–silicon–copper alloy target microstructure was varied from a low to a high concentration of second-phase precipitates. The mechanism by which the micro- structure of the sputtering target influences the propensity for whisker growth in the deposited film is proposed to be the emission of silicon–silicon and aluminum–copper dimers by the target. These dimers nucleate second-phase precipitates in the growing film which reduces grain boundary mobility and suppresses film stress relief by hillocking. The film stress is consequently relieved by the rapid growth of the aluminum single-crystal whiskers.
Interface formation by atom and cluster deposition: Novel electronic and structural properties
Authors: Aldao C. M. , Waddill G. D. , Vitomirov I. M. , Weaver J. H.
Published: July 2002

High-resolution synchrotron radiation photoemission has been used to examine changes induced at semiconductor interfaces related to sample temperature and whether atoms or metal clusters are deposited. Atom deposition at 300 and 60 K for Au/n-InP(110) and Co/n-GaAs(110) results in substrate disruption, different rates of Fermi-level movement, but the same final Fermi-level pinning positions. A novel method has been developed for the deposition of preformed clusters onto atomically clean surfaces. Such deposition produces minimal substrate disruption for Au/InP and no disruption for Co/GaAs but the apparent unrelaxation of the surface in the vicinity of the cluster. Cluster deposition also leads to unique pinning positions of 0.42 and 0.32 eV below the conduction-band minimum, respectively, that do not change as the amount of metal changes from 0.05 to 30 Å. These positions are far from the charge neutrality point expected for metal induced gap states, even though up to ∼85% of the surface has a fully metallic jacket. Likewise, they do not appear to be related to known defects. We postulate that they reflect states derived from unrelaxed surface states, modified by the presence of the metal overlayer.
Gas/surface reactions in the chemical vapor deposition of tungsten using WF6/SiH4 mixtures
Authors: Yu Ming L. , Eldridge Benjamin N.
Published: July 2002

We have studied the surface reactions of WF6/SiH4 mixtures on Si(100) that are relevant to the chemical vapor deposition of tungsten using x-ray photoemission and molecular-beam reactive scattering. The overall reaction is found to be 3SiH4+2WF6→2W+3SiF4+6H2 with very little production of HF. The reaction proceeds by repeating the cycle of tungsten deposition by the reaction of WF6 with silicon, and the deposition of silicon by the reaction of SiH4 with the fluorinated tungsten surface.
Remote plasma enhanced chemical vapor deposition of silicon nitride on III–V semiconductors: X-ray photoelectron spectroscopy studies of the interface
Authors: Sodhi Rana N. S. , Lau W. M. , Ingrey S. I. J.
Published: July 2002

A remote plasma enhanced chemical vapor deposition reactor has been constructed which can be directly attached to a high spectral resolution x-ray photoelectron spectroscopy (XPS) system, thereby allowing the application of thin dielectric films and subsequent study of the interface by XPS without the need to resort to sputter-profile techniques. This apparatus has been used to study the deposition of silicon nitride (≤5 nm thick) on various n- and p-type surfaces of InP and GaAs. The effect of the remote plasma alone has also been investigated. The studies focus on the chemical structure of the near surface region and the surface Fermi-level (FL) position of the substrate using XPS. It was seen that thin, uniform films of silicon nitride could be obtained with ≤1% oxygen content. The spectra of the underlying substrate were seen to be very similar to that of the clean surface, thereby indicating a sharp and clean interface region. There were no ‘‘(III–V)–N’’ bonds apparent, as was the case with the interaction of the substrate with the excited nitrogen alone. In all cases, both the formation of nitrides and the deposition of silicon nitride were seen to change the surface FL. The results for InP are compared to previous work on oxidized and sputtered surfaces.
Fermi-level pinning at the interfaces of Sb, Sn, and Ge on GaAs(110) surfaces
Authors: Cao Renyu , Miyano K. , Lindau I. , Spicer W. E.
Published: July 2002

The interfaces of Sb, Sn, and Ge on GaAs(110) prepared at room temperature (RT) and 80 K low temperature (LT) have been studied using photoelectron spectroscopy. It is found that all the overlayers grow in a Stranski–Krastanov mode at RT, and the same growth mode holds at LT too. In contrast to many metals on GaAs(110) studied before, lack of temperature dependence of the Fermi-level pinning behavior has been observed. Two distinct pinning positions are found (0.75 and 0.5 eV above the valence-band maximum for n- and p-type GaAs, respectively) at RT and LT. Defects are responsible for those pinnings. Additional change in the Fermi-level position at the Sn/GaAs interface is related to the metallization of Sn overlayer.
TiN formed by ion beam nitriding of TiSi2
Authors: Hörnström S. E. , Moy D. , Charai A. , Harper J. M. E. , Robertsson A. , Gong S. F.
Published: July 2002

A low-energy nitrogen ion beam has been used to transform part of a TiSi2 layer on Si to TiN. This process, in conjunction with a self-aligned TiSi2 process, forms a self-aligned TiN barrier layer. The nitriding was performed using a broad beam Kaufman ion source operated in N2 at 300-eV beam energy. Various substrate temperatures and N2 ion doses were evaluated. Auger electron spectroscopy, cross-sectional transmission electron microscopy, and etching in HF were used to characterize the samples. The results show that the nitrided surface layer grows in thickness with substrate temperature and exposure time to the ion beam, and that an equilibrium thickness can be reached. A comparison with films produced by conventional annealing in NH3 shows that superior film properties can be achieved by ion beam nitriding at temperatures below 500 °C.
The influence of Sb doping on the growth and electronic properties of GaAs(100) and AlGaAs(100)
Authors: Jamison K. D. , Chen H. C. , Bensaoula A. , Lim W. , Trombetta L. , Ignatiev A.
Published: July 2002

Isoelectronic doping using antimony has been shown to reduce traps and improve material properties during epitaxial growth of Si doped GaAs(100) and AlGaAs(100). In this study, the effect of the antimony dopant on the optimal growth temperature is examined with the aim of producing high-quality heterostructures at lower temperatures. High-quality films of GaAs and AlGaAs have been grown by molecular-beam epitaxy at the normal growth temperatures of 610 and 700 °C, respectively, and 50–100 °C below this temperature using varying small amounts of Sb as a dopant. Electrical properties of the films were then examined using Hall mobility measurements and deep-level transient spectroscopy. Isoelectronic Sb doping of GaAs and AlGaAs allows the growth temperature for these materials to be reduced by up to 80 °C with trap densities and Hall mobilities at least comparable or better than those for films grown at optimal temperatures. It should therefore be possible to grow GaAs and AlGaAs heterostructures at one temperature without sacrificing the electrical properties of the individual materials.
Methodology for electron stimulated desorption ion angular distributions of negative ions
Authors: Joyce Stephen A. , Johnson Allen L. , Madey Theodore E.
Published: July 2002

The electron stimulated desorption angular distributions technique has been extended to measure the angular distributions of negative ions desorbing from surfaces. The apparatus is a modification of an existing display-type detector. Time-of-flight methods have been employed to separate the negative ions from the large background of electrons, and to permit mass-resolved measurements of both positive and negative ions. General trends in negative ion desorption from a series of fluorinated molecules (PF3 , NF3 , and hexafluoroacetone) adsorbed on Ru(0001) are presented. In these systems, negative ions arise primarily from molecularly intact adsorbates while positive ions can arise from both intact and dissociated species with similar probability.
A study of Pd–Ta on Si(100) using Auger electron spectroscopy, Rutherford backscattering spectrometry, and variable energy positron annihilation
Authors: van der Kolk G. J. , Kuiper A. E. T. , Duchateau J. P. W. B. , Willemsen M. , Nielsen Bent , Lynn K. G.
Published: July 2002

The applicability of PdxTa1−x as a diffusion barrier on Si has been investigated. For this purpose PdxTa1−x films of 200-nm thickness (x ranges from 0 to 1) were deposited on Si(100), and the reaction between overlayer and substrate was studied as a function of temperature. Interaction was found to occur at temperatures increasing with the Ta content. The as-deposited PdxTa1−x films with 0.2≤x≤0.6 were found to be amorphous. The amorphous phase had a higher reaction temperature than the crystalline one, causing a discontinuous step in the reaction temperature. Rutherford backscattering spectrometry spectra revealed that for the Pd-rich compositions, first a stoichiometric Pd2Si layer formed underneath a pure Ta layer. At higher temperatures TaSi2 formed at the surface. For Ta-rich compositions Pd2Si formed first as well; however, the reaction temperature was so high that Pd2Si grains formed in a Si matrix. The defect density of the Ta layer, which remained after outdiffusion of Pd, was investigated using variable energy positron annihilation. The defect concentration is very high, as deduced from the trapped positron fraction. A model is presented that describes the composition dependence of the reaction temperature.
Novel band-tuning effects in Hg-based quantum structures by external electric or magnetic fields
Authors: Yang Z. , Schetzina J. F. , Furdyna J. K.
Published: July 2002

Novel band-gap tuning effects by external electric or magnetic fields in Hg-based quantum wells and superlattices are studied theoretically. It is found that in Hg-based quantum wells the band gap can be dramatically changed by applying an electric field perpendicular to the well interfaces. In Hg-based diluted magnetic semiconductor superlattices, the optical cutoff wavelength can also be substantially tuned by a magnetic field at 77 K. Possible device applications of these new band-gap tuning effects include high-speed optic modulators, nonlinear optic devices at wavelengths of 4 to 15 μm, and cutoff wavelength tunable infrared or far-infrared detectors.
A study of the structure and electrical properties of CdxHg1−xTe grown by metalorganic vapor phase epitaxy (interdiffused multilayer process)
Authors: Irvine S. J. C. , Gough J. S. , Giess J. , Gibbs M. J. , Royle A. , Taylor C. A. , Brown G. T. , Keir A. M. , Mullin J. B.
Published: July 2002

Epitaxial layers of CdxHg1−xTe (CMT) have been grown by the interdiffused multilayer process (IMP) at 350 °C. The electrical properties are fixed by the equilibrium conditions of the interdiffused structure and subsequent cooling of the layer in a Hg ambient. Indiffusion of Hg during cooldown can be prevented by the growth of a 1000-Å-thick cap layer of CdTe. X-ray double-crystal rocking curves for the 400 reflections have been measured to find whether IMP introduces any residual structure or strain into the CMT. For CMT grown onto CdTe/GaAs, a postgrowth anneal of 30 min or longer reduces rocking curve widths to below 100 arc s, with a best value of 55 arc s. The best value on CdTe substrates was 72 arc s. Depth profiling of x-ray peak widths for CMT/CdTe/GaAs structures has shown that the CMT/CdTe interface improves the crystalline quality of the epilayer. One contribution to peak width broadening has been identified as pyramidlike morphological defects. Epitaxial layers have been grown onto GaAs substrates with regions >1 cm2 free of pyramids.
Properties of HgCdTe films and Hg-based quantum well structures grown by photoassisted molecular-beam epitaxy
Authors: Myers T. H. , Yanka R. W. , Harris K. A. , Reisinger A. R. , Han J. , Hwang S. , Yang Z. , Giles N. C. , Cook J. W. , Schetzina J. F. , Green R. W. , McDevitt S.
Published: July 2002

Illumination of the substrate during growth by molecular-beam epitaxy (MBE), known as photoassisted molecular-beam epitaxy, has been investigated for (111)B, (211)B, and (100) oriented growth of HgCdTe on CdZnTe. The results of this investigation indicate that photoassisted MBE of HgCdTe results in significant improvements in structural perfection. HgCdTe epilayers with average double-crystal x-ray diffraction full widths at half-maximum of <30 arc s can be obtained for all three orientations. Dislocation line densities as low as 5×104 cm−2 have been observed. The structurally perfect HgCdTe epilayers also exhibit outstanding electrical properties after n-type annealing. Hg-based multilayer structures have also been grown by photoassisted MBE at North Carolina State University. HgCdTe–CdTe superlattices grown by this technique are comparable in structural quality to III–V superlattices. Hg-based double-heterojunction structures, suitable for fabrication of injection lasers, have also been grown. These latter structures exhibit bright IR photoluminescence.
Oxygen reactive ion etching mechanisms of organic and organosilicon polymers
Authors: Jurgensen Charles W. , Rammelsberg Anne
Published: July 2002

The oxygen reactive ion etching characteristics of a silyl novolac polymer and an organic novolac polymer were investigated as a function of pressure, self-bias voltage, power density, radio frequency (rf) frequency, and other system variables. For each etching condition, sheath thickness measurements were used as a diagnostic to estimate the flux and average bombardment energy of ions and the energetic neutral products of charge transfer collisions. The estimated flux allows the observed etching rate to be converted into a yield per bombarding particle. The trends for the etching rate as a function of pressure and other system variables were found to reflect a single trend for the yield as a function of the average bombardment energy. The yield of the organic novolac is proportional to the bombardment energy and is equal to 12 carbon atoms per 100 eV. The silicon atom yield of the organosilicon novolac is equal to the sputtering yield of SiO2 as predicted by the steady-state model of organosilicon polymer etching. The selectivity in bilayer lithographic schemes (the ratio of the organic to organosilicon etching rates) increases as the bombardment energy decreases because the SiO2 sputtering yield is negligible for bombardment energies less than 50 eV.
Atomic force microscopy of layered compounds
Authors: Miller R. G. , Bryant P. J.
Published: July 2002

Physical properties of lamellar solid surfaces have been investigated by means of atomic force microscopy (AFM) with nanometer resolution. The effects of contact forces from 10−7 N to 10−5 N have been studied. The role of frictional forces was noted. Surface modifications caused by a probe exerting up to 10−5 N on muscovite and selenite samples were observed. The materials included in this study were muscovite, selenite, graphite, and molybdenite; a unique set, offering a wide range of material properties. These lamellar materials were chosen to explore the applicability of the AFM technique for investigations of surface forces.
Improved structural quality of molecular-beam epitaxy HgCdTe films
Authors: Koestner R. J. , Liu H.-Y. , Schaake H. F. , Hanlon T. R.
Published: July 2002

The structural defects in molecular-beam epitaxy (MBE) grown HgCdTe(112)Te, (001)-0° and -5° layers are examined with chemical etching, x-ray diffraction, Nomarski microscopy, and cross-sectional transmission electron microscopy. Photoassisted MBE grown HgCdTe(001)-0° films exhibit a low dislocation density (1–2×105 cm−2) over a wider range of growth conditions than comparable HgCdTe(001)-0° layers grown by conventional MBE. HgCdTe(112)Te epilayers grown by conventional MBE reproducibly show very low dislocation (3–5×104 cm−2) and twin fault (2×103 cm−2) densities; in addition, the twin faults along this growth direction do not lead to highly defective surface hillocks under appropriate growth conditions. Finally, HgCdTe(001)-5° films do not show the growth front roughness or x-value variation generally present in HgCdTe(001)-0° layers.
1/f noise characterization of n+–p and n–i–p Hg1−xCdxTe detectors
Authors: van der Ziel A. , Fang P. , He L. , Wu X. L. , van Rheenen A. D. , Handel P. H.
Published: July 2002

1/f noise in n+–p and n–i–p Hg1−xCdxTe photodiodes is discussed. The n+–p diodes have coherent-state 1/f noise or umklapp 1/f noise. The n–i–p diodes have much lower values for the Hooge parameter αH and their noise is probably due to generation–recombination-type (trapping) 1/f noise.
Competitive reactions of fluorine and oxygen with W, WSi2, and Si surfaces in reactive ion etching using CF4/O2
Authors: Oehrlein Gottlieb S. , Lindstöm J. Lennart
Published: July 2002

We have studied CF4/O2 based plasma and reactive ion etching of dc magnetron-sputtered tungsten, chemical vapor deposited tungsten silicide and single-crystal silicon. Etch rates and optical emission intensities of atomic fluorine and oxygen in the gas phase were determined as a function of gas composition. Etched surfaces were characterized using in situ x-ray photoelectron spectroscopy (XPS) and low-energy ion scattering spectrometry. All three materials exhibit an etch rate maximum as a function of oxygen addition. For silicon (7% O2) and WSi2 (10% O2) it occurs for a smaller percentage of added oxygen than the optical emission maximum of atomic fluorine (15% O2), whereas for W films (35% O2) it occurs at a greater percentage of added oxygen. In postplasma XPS analysis it is shown that for all materials the etch rate decrease coincides with the onset of significant oxidation. From the analysis of the degree of fluorination of the top surface, the oxygen/fluorine ratio of the reaction layer, and the oxygen percentage of the etch rate maximum relative to the fluorine emission maximum, we conclude that the etching of Si and WSi2 is limited by a reduction of fluorine adsorption because of competitive oxygen adsorption. For tungsten, which shows a very low degree of fluorination of the top surface, both the drop in etch rate and the formation of tungsten oxide can be explained by a reduced arrival rate of fluorine atoms to the tungsten surface when etching in oxygen-rich gas mixtures.
Properties of ion beam deposited Pb1−xLax(ZryTiz)1−x/4O3
Authors: Boyer L. L. , Wu A. Y. , Metzger G. W. , McNeil J. R.
Published: July 2002

We have recently investigated ion beam sputtering and ion assisted deposition of Pb1−xLax(ZryTiz)1−x/4O3 (PLZT). Ion beam sputtered PLZT films display strong second-harmonic generation. Good quality material has been deposited on substrates of Si, Si with a buffer layer of SiO2 , and fused silica. The surface morphology of ion beam sputtered PLZT is of very high quality.
Substrate temperature effect on the optical properties of radio-frequency sputtered CuInSe2 thin films
Authors: Santamaria J. , Martil I. , Iborra E. , Gonzalez Diaz G. , Sanchez Quesada F.
Published: July 2002

The influence of growth temperature on the optical properties of CuInSe2 thin films producing sputtering targets of different compositions is presented. CuInSe2 films exhibited direct allowed transitions with values ranging between 0.9 and 1 eV depending on substrate temperature. Additional direct forbidden transitions, ranging between 1 and 1.22 eV, are also observed. A clear correlation is observed between crystallinity and optical gap. On the other hand, film composition, in the range analyzed, did not show influence over optical properties.
Microstructure and properties of dual ion beam sputtered tungsten film
Authors: Kao A. S. , Hwang C. , Novotny V. J. , Deline V. R. , Gorman G. L.
Published: July 2002

The relationship between microstructure and properties of dual ion beam sputtered tungsten film is investigated. Film properties, such as electrical resistivity and residual stress, are found to be dependent significantly on the Ar+ sputtering energy from the deposition source and also on the flux density and energy of the assisting beam. Resistivity increases with increasing Ar+ sputtering energy, and decreases with increasing assisting flux and energy. Residual stress increases with increasing Ar+ sputtering energy and decreasing flux of assisting beam. With high Ar+ sputtering energy, such as 1200 eV, a flux of energetic particles including sputtered atoms and reflected argon is directed toward film surface resulting in the atomic peening and sputter etching of growing film, which is a characteristic result of directional sputtering using ion beam. Microstructural analysis shows that this process causes the formation of finer grains, denser microdefects, sharp strain contours, and metastable β-phase tungsten, which correlate consistently with the observed high stress and resistivity. Bombarding the growing film with low-energy assisting Ar+ flux reduces both stress and resistivity by mobilizing the sputtered atoms on film surface. It is shown that the presence of assisting flux reduces the density of microdefect and strain contours within the grain, and stabilizes the bcc α-phase tungsten without altering the overall microstructure of the tungsten film.
Computer-controlled, three-electron-gun, multisubstrate evaporator for the preparation of multilayer thin films
Authors: Wang X. K. , Yang H. Q. , Sheng K. C. , Davis B. , Chang R. P. H. , Ketterson J. B.
Published: July 2002

We have developed a novel multisource electron-beam evaporator to prepare high-quality multicomponent, multilayer thin films. The essential parts of the evaporator consist of three electron guns, a shutter turntable, and a multisubstrate turntable; the latter can be loaded with up to 20 substrates. A very attractive feature of the system is the implementation of computer control over the movement of the stepping motors. The two turntables are driven by separate stepping motors with optical encoders, and are used to: (i) position a selected substrate over a specified electron gun, and (ii) gate the flux for a desired time. With a suitable programming of the movement of the stepping motors, up to 20 different thin films, with individually tailored layers deposited sequentially from the three sources, can be prepared in a single run. The deposition rate and the sublayer thickness of the three constituents of a multilayer film are individually monitored by three film deposition controllers which communicate directly to the computer and the electron-gun power supply. Predictable and reproducible deposition of thin films is accomplished by accurate, digital control of the deposition process. High-quality films of YBaCuO have been prepared with this system.
Observation of double heterostructures for laser diodes using scanning tunneling microscopy and current imaging tunneling spectroscopy in air
Authors: Tanimoto M. , Nakano Y.
Published: July 2002

The cleaved surfaces of the double heterostructures (n-InP/InGaAsP/p-InP) for laser diodes have been directly observed in air using scanning tunneling microscopy (STM) and current imaging tunneling spectroscopy (CITS). CITS measurements enable us to observe each layer of the double heterostructures. Since local current voltage characteristics depend on the tunneling voltage which determines the tip–sample separation, we can obtain different current voltage characteristics for each layer by selecting a proper tunneling voltage. Each layer of the double heterostructure is identified by the difference in the tunneling current. In order to investigate the lateral distribution of Zn at the n-InP/InGaAsP interface, we have used STM measurements and a stain-etching method whose etching rate is sensitive to the existence of p-type impurity. STM images of the stain-etched cleaved surfaces show hollows straggled along the n-InP/InGaAsP interface. This result reveals that the impurity pileup is localized along the interface, which can not be observed by secondary ion mass spectroscopy (SIMS) analysis.
Observation of multiquantum well structure in air using a scanning tunneling microscope
Authors: Tanaka Ichiro , Kato Takashi , Ohkouchi Shunsuke , Osaka Fukunobu
Published: July 2002

We investigated GaInAs/InP and AlAs/GaAs multiquantum well (MQW) structures in air using a scanning tunneling microscope (STM). We obtained clear corrugated images of MQWs with nanometer resolution. These corrugations come not from a topological difference but from the difference between the tunneling conductance of the well layers to the tip and that of the barrier layers to the tip. Also the STM images are affected by various factors such as contamination and humidity in the air. We observed degradation of the STM images which might be due to the surface oxidation accelerated by the tunneling current. The degradation rate of the AlAs/GaAs MQWs was much larger than that of the GaInAs/InP MQWs. This phenomenon is interesting from the viewpoint of nanometer scale processing.
A simple ultrahigh vacuum surface magneto-optic Kerr effect setup for the study of surface magnetic anisotropy
Authors: Qian J.-P. , Wang G.-C.
Published: July 2002

We describe a unique in situ rotatable electromagnet which utilizes only one set of coils. The magnetic field produced by the electromagnet can be aligned either parallel or perpendicular to the plane of a sample.These two magnetized fields allow one to study the surface magnetic anisotropy of ultrathin ferromagnetic films through the measurement of surface hysteresis loops.
Temperature-dependent formation of interface states and Schottky barriers at metal/molecular-beam epitaxy GaAs(100) junctions
Authors: Chang S. , Shaw J. L. , Viturro R. E. , Brillson L. J. , Kirchner P. D. , Woodall J. M.
Published: July 2002

We report temperature-dependent cathodoluminescence spectroscopy (CLS) and internal photoemission spectroscopy (IPS) studies of metal/molecular-beam epitaxy GaAs(100) interfaces. For Au, Cu, and Al deposited at 90 K on clean, ordered GaAs(100) surfaces under ultrahigh vacuum conditions, we observe low intensity, metal-induced optical transitions centered at 0.85 eV. Upon room temperature (RT) annealing, this emission feature increases in intensity, corresponding to an increased density of midgap states. For Al, an additional excitation-energy-dependent emission is evident at 1.2 eV due to states even more localized near the interface. RT IPS measurements for metals deposited on GaAs at 90 K give well-defined Schottky barriers. We obtain stable and reproducible Schottky barrier heights of 1.05 and 0.93 eV for Au/GaAs and Cu/GaAs, respectively. For Al/GaAs, we obtain a Schottky barrier height as low as 0.3 eV with significant, time-dependent variations up to 0.41 eV. After 400 °C annealing, the Schottky barrier height increases to 0.57 eV. These results demonstrate that the barrier height and the formation of metal-induced states are temperature dependent. The correlation between CLS and IPS results indicates that the barrier height depends on the presence of metal-induced interface states and their metal-specific interface reactions. The values of the Schottky barrier height determined here are in close agreement with those obtained from our earlier soft x-ray photoemission studies. Our CLS and IPS results emphasize the detailed role of interface states coupled with chemical interactions for Schottky barrier formation at metal/GaAs interfaces.
Yields, sensitivities, and natural line shapes of Auger lines. I. Ag, Si, Al, Mg, and Cu
Authors: Weisz S. Z. , Resto O. , Goldstein Y. , Many A.
Published: July 2002

With the commonly available analyzer resolution in Auger electron spectroscopy (AES) measurements, the Auger line shapes can be greatly distorted and large errors can be incurred in the measured signal intensities. In view of this, a universal relation was previously derived whereby the experimentally measured line intensities can easily be corrected so as to yield, to a good approximation, the intensities that would have been measured were the resolution infinitely good. In this paper we present high-resolution measurements of the natural line shapes of several Auger lines. Based on the intrinsic linewidths derived from these measurements, we demonstrate the validity of our correction procedure by measuring Auger sensitivities with different resolutions. Whereas the as-measured sensitivity for each element studied varies appreciably as the resolution is changed, the corrected sensitivity remains constant, in most cases to within 10%–20%, independently of resolution. The corrected sensitivities provide good estimates for the true sensitivities, and a compilation of their values is given in tabular form. It is these sensitivities that any theoretical calculations of Auger yields should be compared with. We show here that using the as-measured sensitivities for such a comparison can be grossly misleading, by as much as a factor of 100. Also, the quantitative determination of atomic concentrations becomes more accurate when the measured signal intensities are corrected and the analysis is based on the corrected sensitivities.
Characterization of a large linear ion source
Authors: Ryan T. , Chamberlain P. , Brown I. , Celliers J.
Published: July 2002

Key areas of ion source process development are discussed with emphasis on their application to new or existing sputtering systems utilizing large linear ion sources. In order to minimize film contamination and achieve static deposition thickness uniformity, the development required characterization of the ion source lateral and longitudinal beam divergence as well as beam alignment and stability. Mechanical adjustments to the source grid gap, grid aperture offset and grid outline were employed to optimize the beam characteristics. Additionally, ion source operating conditions were optimized in order to improve beam divergence and stability.
Recombination velocity of the Ga0.5In0.5P/GaAs interface
Authors: Ahrenkiel R. K. , Olson J. M. , Dunlavy D. J. , Keyes B. M. , Kibbler A. E.
Published: July 2002

Double heterostructures have been grown with the structure Ga0.5In0.5P/GaAs/Ga0.5In0.5P by metalorganic chemical vapor deposition (MOCVD). These GaAs active layers were grown to thicknesses between 1 and 4 μm in this series of devices. The n-GaAs active layers ranged from undoped (2–5×1014 cm−3) to doped layers in the range 1×1017–5×1017 cm−3. Time resolved photoluminescence (PL) was used to extract the minority carrier lifetimes. The latter can be shown to be a function of bulk lifetime and the interface recombination velocity (S). The GaInP/GaAs (undoped) devices produced a PL lifetimes of 14 μs for a 1 μ active layer thickness. Most of the data for undoped GaAs were fit with S<2 cm/s. The doped devices were fit with values of S less than 200 cm/s. These ultralow recombination velocities should be useful for devices ranging from solar cells to diode lasers.
Fracto-emission during the interfacial failure of a metal–oxide-semiconductor system: Au–SiO2–Si
Authors: Doering D. L. , Dickinson J. T. , Langford S. C. , Xiong-Skiba P.
Published: July 2002

Two fracto-emission components (electron and photon emission) produced by the adhesive failure of gold films peeled in vacuum from oxidized silicon were measured for different oxide thicknesses. The Au adhesive strength was found to decrease with increasing oxide thickness, whereas the fracto-emission intensities and durations increased significantly with oxide thickness. We interpret these results in terms of interfacial charge created during the formation of the metal–oxide-semiconductor (MOS) structure, leading to charge separation during fracture and to subsequent charge transport within the MOS structure.
Electron trapping characterization by Auger electron spectroscopy in silicon oxynitride thin film
Authors: de Castro A. J. , Fernandez M. , Sacedon J. L.
Published: July 2002

The study of the kinetics of Auger peak shifts with low doses of electron injection (ΔQ≤10−3 C cm−2) in silicon oxynitrides thin films is presented. The nature of these shifts is clearly related with the trapping charge phenomena in the film. The parameters associated with the different traps involved are quantitatively established. Two methods of data acquisition have been developed. The former uses several energy channels in the derivative Auger spectrum (dN/dE) in order to determine each point of the kinetic curve. This method has allowed to measure capture cross sections σ≤5×10−18 cm2. The second method uses only one energy channel for each point in the curve, and reduces the acquisition time up to a factor of 50, measuring faster cross sections σ≤8×10−17 cm2. The numerical values of σ agree satisfactorily with those obtained by conventional C–V injection measurements, as well as the trap densities obtained at 1 kV of primary energy. The discrepancy for the values of N obtained at higher primary energies is explained in terms of thermalization processes into the oxide. Finally, the possibilities and limitations of both methods are discussed.
Macroscopic modeling of oxygen plasmas
Authors: Misium George R.
Published: July 2002

This paper describes a macroscopic model of parallel-plate, radio frequency (rf), oxygen plasma discharges. The model predicts fundamental plasma characteristics as a function of controllable parameters such as pressure, power, and electrode spacing. The simulation results given by the model are in good agreement with the measured plasma characteristics. The experimental reactor has been designed to minimize the self-bias of the powered electrode, hence the discharge is effectively symmetric. The model has been applied to the development of etch processes for dry-develop lithography applications. In particular, simulations of ion flow and energy have provided insight in the behavior of etch rates as a function of controllable parameters. A particular simulation result is that the power imparted to the electrodes by the ions is substantially less than the power delivered by the rf generator, which is in agreement with previously reported experimental results.
Broad beam extraction from a new sputtering-type ion source using an electric mirror
Authors: Matsuoka Morito , Ono Ken’ichi
Published: July 2002

A new sputtering-type metal-ion source for ion beam deposition was developed by using an electric mirror. Ion beams with an area of 80 cm2 were extracted from this source. The ion energy was controlled over a range from 50 to 500 eV. Ions with 200 eV energy were extracted with an average current density of more than 1 mA/cm2. The fraction of ions in the extracted metal reached about 30%. The fraction of metal ions in the total extracted ions, including Ar+ and metal ions, exceeded 10%. These fractions of metal ions monotonically increased with sputtering power. Both Al+ and Fe+ ions were extracted from this apparatus and deposited on the substrate.
Methyl radical etching of compound semiconductors with a secondary afterglow reactor
Authors: Spencer John E. , Schimert Thomas R. , Dinan J. H. , Endres Darrel , Hayes Todd R.
Published: July 2002

While halogen-based dry etching processes are well established for silicon devices, many compound semiconductors have insufficiently volatile halides for successful conventional dry etch processing. These elements, found in groups II B, III A, IV A, V A, and VI A of the Periodic Table, do form volatile organometallic compounds. A secondary afterglow reactor, in which atomic fluorine produced in a microwave discharge is reacted with methane downstream of the discharge, has been used to etch HgCdTe, CdTe, InP, InSb, and GaAs at temperature-dependent rates between 100 Å and 1000 Å/min. This etching is purely chemical and without ion bombardment, and it shows crystallographic orientation dependence on the etch rate. The activation energies for etching in a methyl/atomic hydrogen ambient range from 2.3 and 7.2 kcal/mol. CdTe(111)B etched faster, smoother, and with a higher activation energy than CdTe(100), which produced a surface with submicron texturing. Specular surfaces were observed with CdTe, InP, InSb, and GaAs, although the HgCdTe etched with significant roughness.