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  • Articles: DFG German National Licenses  (44)
  • Electronic Resource  (44)
  • 1
    Electronic Resource
    Electronic Resource
    Investigation on the quantum well structure of a GaAs/Al0.3Ga0.7As superlattice grown on a misoriented substrate (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 3795-3797 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We analyzed the Raman spectra and x-ray diffraction of two GaAs/Al0.3Ga0.7As superlattices grown by molecular-beam epitaxy on a 4 ° misoriented (001) GaAs substrate and an exactly (001)-oriented GaAs substrate respectively. From the frequency shifts of the longitudinal-optical- (LO) confined phonons in the Raman spectra and the variation in linewidths of both the LO-confined phonons and the satellite peaks in x-ray diffraction, we found that the 4 ° misorientation of the GaAs substrate from (001) toward [110] direction improves the interface quality of the superlattices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346283
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  • 2
    Electronic Resource
    Electronic Resource
    An experimental study of the influence of oxygen on silicide formation with tungsten deposited from tungsten hexafluoride (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 213-219 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tungsten disilicide (WSi2) was formed by annealing tungsten films deposited by low-pressure chemical vapor deposition on 〈100〉-silicon substrates. The influence of oxygen on the silicidation rate was studied. Si wafers with different oxygen content in the form of Czochralski, float-zone, and epitaxial wafers were used. Oxygen was also ion implanted into either the silicon substrate or the as-deposited tungsten film. The Rutherford backscattering technique was used to follow the progress of the silicidation. The silicidation rate was found to be dependent on the oxygen content of the Si substrates. The rate was lowest for Czochralski substrates and highest for float-zone substrates. Secondary ion mass spectroscopy was used to study the oxygen and fluorine profiles in the films prior to and after silicidation. Growth of WSi2 was found to be retarded concurrently with a pile-up of fluorine at the tungsten side of the W/WSi2 interface and a gettering of oxygen from the annealing atmosphere at the interface. Growth of WSi2 was then transferred to the tungsten surface. Oxygen implantation into silicon and tungsten, respectively, reduced the rate of silicide formation. Oxygen implantation into tungsten altered the distribution of fluorine and suppressed WSi2 growth at the tungsten surface. The observations led to a conceptual model, which ascribes the retardation in the growth of the inner WSi2 to a"poisoning'' effect caused by the increase of oxygen and fluorine levels at the interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347753
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  • 3
    Electronic Resource
    Electronic Resource
    Formation of C54 TiSi2: Effects of niobium additions on the apparent activation energy (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6409-6415 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The formation of C54 TiSi2 using Ti–Nb alloys deposited on polycrystalline Si substrates was studied by means of in situ x-ray diffraction and resistance measurements during temperature ramping. Alloys with Nb contents ranging from 0 to 13.6 at. % were used. The formation temperature of C54 TiSi2 was reduced in the presence of Nb. However, the addition of Nb in Ti did not cause fundamental changes in the evolution of resistance versus temperature. This latter observation suggests that the mechanism for the formation of C54 TiSi2 remained the same in spite of the enhancement effect. For alloys with up to 8 at. % of Nb, the C49 TiSi2 phase formed first, as with pure Ti. When annealing the alloy with 13.6 at. % Nb, neither C49 TiSi2 nor C54 were found in the usual temperature ranges, instead, C40 (Nb,Ti)Si2 was observed. This phase transformed to C54 (Nb,Ti)Si2 above 950 °C. The apparent activation energy associated with the formation of C54 TiSi2 was obtained by annealing the samples at four different ramp rates from 3 to 27 K/s; it decreased continuously from 3.8 to 2.5 eV with increasing Nb content from 0 to 8 at. %. The apparent activation energy for the formation of C40 (Nb,Ti)Si2 was found to be 2.6 eV. The possible physical meaning, or lack thereof, of the high activation energies derived from experimental measurements is extensively discussed. A qualitative model is proposed whereby nucleation would be rate controlling in pure TiSi2, and interface motion in samples with 8 at. % Nb. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1413952
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  • 4
    Electronic Resource
    Electronic Resource
    Raman spectroscopy of nanocrystalline GaN synthesized by arc plasma (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 4562-4567 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on a Raman study of nanocrystalline GaN with the wurtzite structure synthesized by arc plasma method. Resonant Raman scattering is observed using 514.5 nm (2.41 eV) laser excitation, which is near the band gap of the "yellow band" (2.2–2.3 eV). Under such near-resonant excitation, new Raman bands unexpected in an ideal wurtzite GaN crystal were found. The transverse optical modes of A1 (531 cm−1) and E1 (560 cm−1), and the nonpolar modes of E2 [567 cm−1 (high) and 143 cm−1 (low)] normally observed in bulk crystals, were recorded and were observed to be resonantly enhanced. Two new bands (680 and 344 cm−1) were assigned to the inactive optical phonon modes B1 (high) and B1 (low), respectively. A broadband centered at 710 cm−1 was attributed to surface modes of the nanocrystals, providing good agreement with the calculated result based on Fröhlich theory. As a result of this study, Raman scattering of GaN nanocrystals has been characterized. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1452762
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  • 5
    Electronic Resource
    Electronic Resource
    Differences between interfacial and surface molybdenum in the formation of TiSi2 (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 1641-1646 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Backscattering and diffraction results are presented for the effects of an interfacial or a surface Mo layer on the formation of Ti-silicides during solid-state interaction between Ti films and Si substrates. It is shown that the interfacial and surface Mo are fundamentally different in their involvement in the Ti-silicide formation. The interfacial Mo induces the formation of C40 (Mo,Ti)Si2 at the interface adjacent to the Si substrate already after annealing at 550 °C, in agreement with our previous results. Hence, the desired C54 TiSi2 can grow directly on top of the C40 (Mo,Ti)Si2 at relatively low temperatures as a result of the template effect. The surface Mo is, however, found in a metal-rich silicide presumably (Mo,Ti)5Si3 at 550–600 °C, which eventually converts to (Mo,Ti)Si2 upon annealing at higher temperatures. Underneath this metal-rich silicide lies a fully developed C49 TiSi2 layer. Consequently, the formation of C54 TiSi2 in the presence of surface Mo follows the usual path of the C49–C54 phase transition. This important difference in the participation of Mo in the silicide formation spreads doubts about the validity of using interfacial Mo versus surface Mo to study the dominant mechanism(s) responsible for the enhanced formation of C54 TiSi2. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1333736
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  • 6
    Electronic Resource
    Electronic Resource
    Hydrogen in undoped and heavily in situ phosphorus doped silicon films deposited using disilane and phosphine (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1970-1973 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The kinetics of hydrogen incorporation in amorphous silicon films were studied. The layers were deposited by low pressure chemical vapor deposition using disilane (Si2H6) and phosphine (PH3). The hydrogen concentration, determined by nuclear resonant reaction analysis, increased with decreasing substrate temperature. In accordance with the reported reduction of hydrogen adsorption in the presence of surface phosphorus, the addition of phosphine to disilane was observed to reduce the hydrogen film concentration. The results are discussed in terms of hydrogen adsorption/ desorption kinetics. The activation energy for hydrogen desorption in an undoped film was 1.8±0.2 eV, in good agreement with previously reported values obtained by surface analysis and desorption studies. When phosphine was added, an increase in activation energy was observed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370995
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  • 7
    Electronic Resource
    Electronic Resource
    On the formation of inhomogeneities in epitaxial CoSi2 layers grown from the interaction of Co/Ti bilayers with Si 〈100〉 substrates (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 762-768 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The redistribution of titanium during the formation of epitaxial CoSi2, grown from the reaction of Co(20 nm)/Ti(10 nm) bilayers with Si 〈100〉, has been investigated. Annealing of Co/Ti/Si structures, at temperatures between 850 and 1050 °C, is shown to be associated with the growth of an inhomogeneous CoSi2 layer having Ti-rich surface layer(s) on top. The formation of inhomogeneities in the CoSi2 layer is conclusively attributed to the presence of Ti-rich surface layer(s). It is shown that smooth and morphologically stable CoSi2 layers can be grown by removing these surface layers followed by a high-temperature treatment in nitrogen atmosphere. We propose that the underlying mechanism for the inhomogeneity formation within the CoSi2 layer is a nucleation-controlled process, induced by an anticipated reaction between the CoSi2 layer and Ti-rich phases near the surface. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362884
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  • 8
    Electronic Resource
    Electronic Resource
    Electrical and mechanical characterization of chemical vapor deposition of tungsten on sputter-deposited TiN layers (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 7313-7322 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tungsten (W) films are deposited from tungsten hexafluoride on sputter-deposited TiN adhesion layers in a cold-wall chemical vapor deposition reactor. The film resistivity of the W films is found to be thickness dependent. It decreases monotonically with increasing film thickness. Typical resistivity values of 40-nm-thick W films are about 19.3–23.4 μΩ cm, depending on the structure of the underlying TiN layer used. The resistivity of a 980-nm-thick W film is 9.8 μΩ cm. Oxygen and fluorine impurities, as well as structural difference in the W films are found to be the major causes for the resistivity variations. Lowering impurity level and/or increasing W crystallite size can decrease film resistivity. The stress of all the W films is found to be tensile, independent of the structure of the TiN layers. However, the absolute value of the stress is intimately associated with the structure of the TiN layers. The stress values can differ by a factor of more than 2 for the 40-nm-thick W films deposited on the different underlying TiN layers. The amplitude of stress also monotonically decreases with increasing film thickness. Consequently, the difference in stress induced by the difference in the underlying TiN layers gradually disappears as the film thickness increases. A strong correlation between the stress and the film texture is found. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360379
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  • 9
    Electronic Resource
    Electronic Resource
    Enhanced thermal stability of C49 TiSi2 in the presence of aluminum (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 312-314 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The introduction of a thin layer of Al at the interface between Ti films and Si substrates enhances the formation of C49 TiSi2 and retards the transition from C49 to C54. An Al interlayer, 0.64 nm thick, reduces the time required to form C49 TiSi2 isothermally at 500 °C from 14 to 7 min. The C49–C54 transformation temperature is increased from 767 to 853 °C, when heating the samples at a constant ramp rate of 3 K/s. Most of the Al is found toward the interface between a Ti-rich silicide at the surface and TiSi2, rather than at the interface between TiSi2 and the Si substrate. The grain size of the C49 TiSi2 formed in the presence of Al is about five times smaller than that formed on a control sample with pure Ti, indicating that the increased density of grain boundaries in C49 TiSi2 in the presence of Al does not help the C49–C54 transformation. Therefore, the improved thermal stability of C49 TiSi2 is likely to be caused by other factors such as a reduced electron/atom ratio when replacing Si with Al in the disilicide. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121853
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  • 10
    Electronic Resource
    Electronic Resource
    Photoluminescence microscopy of epitaxial GaAs on Si (1987)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 599-601 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report microscopic photoluminescence images and corresponding spectra of epitaxial GaAs on Si substrates, prepared by molecular beam epitaxy. High magnification (3000×) images directly reveal dislocations present in the epilayer. Several substrate orientations are investigated including nominal (001) tilted 4° toward 〈110〉. The GaAs samples include structures grown with and without superlattice buffer layers. Some samples were annealed at several temperatures from 650 to 850 °C. The dislocation density versus depth is studied by varying the optical probe wavelength and by studying samples that had been beveled and etched. In addition, the images and spectra are studied over a wide temperature range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.98359
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