15 Fakultätsübergreifend / Sonstige Einrichtung

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/16

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Institute: search.filters.UBSInstitut.1. Physikalisches Institut

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    Influence of defects on the splitting of the acceptor ground state in silicon
    (1984) Ambrosy, Anton; Lassmann, Kurt; Goer, Anne M. de; Salce, Bernard; Zeile, Heinrich
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    Resonance and relaxation attenuation by neutral acceptors in a magnetic field
    (1977) Schad, Hanspeter; Lassmann, Kurt; Zeile, Heinrich
    Fine structure, level splitting, and relaxation times of the acceptor ground state in cubic semiconductors can be deduced from ultrasonic attenuation. By the application of a magnetic field it is possible to vary the coupling strength and the number of acceptors on speaking terms with the ultrasonic wave. Making use of this possibility, we have determined directly effective coupling constants for relaxation attenuation and the temperature dependence of the critical intensity for saturation of the resonant interaction. Results obtained for p-type GaAs and Si are discussed in comparison with analogous results for glasses.
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    Down-conversion of high-frequency acoustic phonons
    (1987) Galkina, Tatjana I.; Blinov, A. Y.; Bonch-Osmolovskii, M. M.; Koblinger, Otto; Lassmann, Kurt; Eisenmenger, Wolfgang
    Measurements of phonon transport in amorphous media can give valuable information on the structural properties of these materials and may be of practical interest for its own concerning the question of thermalization in electronic devices. The existence of two-level systems in a-Si:H as one of these technically important materials has been concluded from measurements of dispersion and attenuation of acoustic surface waves.
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    Shallow traps correlated with deep impurities in silicon as obtained by phonon induced conductance
    (1986) Burger, Wilfried; Lassmann, Kurt; Holm, Claus; Wagner, Peter
    At low temperatures shallow neutral donors and acceptors in silicon can bind an extra carrier to form the so-called D- and A+ centers. With the method of phonon-induced electrical conductivity (PIC) we find the same threshold energies for the detachment of these carriers associated with the shallow impurities P and B, as have been obtained previously by FIR measurements. This shows that the detachment is by a one-phonon process. We find that there is no central cell correction for the binding to the deeper acceptors Al and Ga, whereas for In+ the binding energy is as large as 5,8 meV. We interprete this dependence on acceptor species as another example of the shallow-deep instability of the binding energy with the variation of the central cell potential.
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    Phonon spectroscopy of defects correlated with the diffusion of Zn into Si
    (1994) Staiger, Joachim; Groß, Peter; Lassmann, Kurt; Bracht, Hartmut; Stolwijk, Nicolaas A.
    We analyse by phonon spectroscopy low lying phonon scattering states from defects that are introduced by the diffusion of Zn into thick Si wafers.
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    Polarization profiles of polyvinylidene fluoride films polarized by a focused electron beam
    (1989) Schilling, Doris; Dransfeld, Klaus; Bihler, Eckardt; Holdik, Karl; Eisenmenger, Wolfgang
    The depth profiles of the polarization in films of polyvinylidene fluoride (PVDF) as well as in vinylidene‐fluoride–trifluoroethylene (VDF‐TrFE) copolymer films polarized by a focused electron beam were investigated using the piezoelectrically generated pressure step method. The dominant polarization exhibits a broad maximum inside the film. The position of this maximum depends not only on the energy of the incident electrons but also on the material parameters of the sample. Close to the surface exposed to the electron beam we have in addition observed a small secondary maximum of opposite polarization (amounting to about 1 mC/m2). A qualitative model is presented for the poling of films of PVDF and its copolymers with TrFE by focused electron beam accounting for most of the observed features. The application of electron beams for the poling of ferroelectric films allows the production of piezoelectric bimorphs. By using a well‐focused electron beam also ferroelectric domains of very small lateral dimensions can be created which could become important for ferroelectric data storage.
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    Phonon spectroscopy measurements at amorphous films
    (1994) Mebert, Joachim; Eisenmenger, Wolfgang
    Phonon spectroscopy measurements were used to examine the scattering of high frequency phonons (300 GHz-1 THz) in amorphous materials. The experiments were done with the use of time and frequency resolved measurements of the phonon transmission behaviour through amorphous single films of different thicknesses. The typical film thicknesses were of the order of 10 nm. In contrast to the pure amorphous semiconductors Si and Ge our experiments show inelastic phonon scattering processes in the case of SiO 2 and Si:H. This inelastic phonon scattering also occurs when the pure semiconductors Si and Ge are prepared in an O 2 or H 2 atmosphere, but is missing when the preparation process is done in an N 2 atmosphere. In films of the pure semiconductors a-Si and a-Ge we only found evidence to elastic scattering processes. In further experiments at heated a-Si:H samples we could examine the atomical bonded hydrogen to be the center of the inelastic phonon scattering.