Universität Stuttgart
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Item Open Access Phono-conduction spectroscopy of shallow states in semiconductors(1990) Lassmann, Kurt; Gienger, Martin; Groß, PeterPhonoconduction spectroscopy of shallow states in semiconductors by help of superconduction Al-junctions as phonon sources with high spectral resolution is a sensitive new technique with phonon frequencies well up in the Debye range. The large k-vector of the phonons involved opens new possibilities for the investigation of electron dynamics and states in semiconductors.Item Open Access Linear stark coupling to the ground state of effective mass acceptors(1989) Köpf, Andreas; Ambrosy, Anton; Lassmann, KurtIt is shown by dielectric resonance absorption at 24 GHz and by ultrasonic resonance spectroscopy between 5 and 10 GHz that linear coupling of the electric field to the ground state of effective mass acceptors in Si exists and has a distinct chemical shift from B to In.Item Open Access One-phonon ionization of neutral donors in germanium(1989) Gienger, Martin; Groß, Peter; Lassmann, KurtHere we show by phonon spectroscopy with superconducting tunnelling junctions that one-phonon excitations from the ground state to the conduction band (CB) are measurable as phonon induced conductivity (PIC) changes in the special case of donors in Ge. For the conductivity thresholds we find somewhat smaller binding energies than evaluated from optical measurements whereas for the 1s-singlet to 1s-triplet ground state splitting as seen by elastic phonon scattering we obtain the optical values.Item Open Access Investigation of A+-states in Si and Ge by phonon-induced conduction under uniaxial stress(1993) Groß, Peter; Lassmann, KurtBy the analysis of the stress dependence of phonon induced conductivity (PIC) with superconducting Al-tunneling junctions as phonon generators we have now found strong evidence for a split ground state in the cases Si:Ga+, Si:Al+ and Ge:Zn+.Item Open Access Phonon spectroscopy of low energy vibrations of interstitial oxygen in germanium(1993) Lassmann, Kurt; Gienger, Martin; Glaser, MarkusWe can summarize our results as follows: Whereas the band of lowest lying mechanical states of interstitial oxygen in Si can be approximated by a two-dimensional oscillator perturbed by a central potential, the corresponding states in Ge can be well understood by a bindered rotator with a large central potential opposing a bending oscillation and with a sixfold modulation of the rotation due to the influence of the 6 neighbours to the Ge-O-Ge moleculeItem Open Access Depopulation effects in the phonoconduction response of A+ -states in silicon and germanium(1990) Groß, Peter; Gienger, Martin; Lassmann, KurtWe show here that deviations from these assumptions are effective in the experiment and responsible in particular for the observed illumination dependence of the phonoconduction signal. The phonon spectrum of an Al - STJ at bias V = eU > 2ΔAl consists of a continuum with a sharp threshold at Ώm = V - 2ΔAl. In the differentiated spectrum Ώm becomes the most prominent bias-tunable feature, namely the quasimonochromatic line of phonon spectroscopy used for the approximate analysis of sharp phonon scattering resonances such as the OI line of Fig. 1a (which shows inversion of the center due to strong scattering).Item Open Access Resonant phonon scattering by calcium colloids in electron irradiated calcium fluoride(1993) Wurster, Clemens; Lassmann, Kurt; Eisenmenger, WolfgangHere we report on such an investigation of Ca-colloids produced by e- -irradiation in CaF2. We find a good correlation of the observed phonon scattering (and its variation with thermal treatment) with a resonance peak in the optical Mie scattering.