Universität Stuttgart
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Item Open Access 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-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 Resonance and relaxation attenuation by neutral acceptors in a magnetic field(1977) Schad, Hanspeter; Lassmann, Kurt; Zeile, HeinrichFine 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.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 Ultrasonic spectroscopy of the acceptor ground state in cubic semiconductors(1980) Lassmann, Kurt; Zeile, HeinrichIn the following we will discuss ultrasonic measurements on p-type semiconductors reflecting spontaneous and defect sensitive modifications of the acceptor ground state.Item Open Access Shallow traps correlated with deep impurities in silicon as obtained by phonon induced conductance(1986) Burger, Wilfried; Lassmann, Kurt; Holm, Claus; Wagner, PeterAt 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.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 Anisotropy of phonon emission from hot electrons in germanium(1976) Reupert, Wolfram; Lassmann, Kurt; Groot, Peter deWe have measured quantitatively the anisotropy of the electron-acoustical phonon scattering in n-germanium in five directions of the (lTO) plane utilizing tunneling junctions for calibrated detection of the phonon radiation emitted from a small avalanche breakdown region in the germanium surface. For comparison and evaluation of phonon focusing a constantan heater and a tunneling junction were also used as phonon sources. A similar experiment has been reported by A. Zylbersztejn, but he could only compare the ratio of the amplitudes of longitudinal and transverse phonon pulses in a given crystal direction to the calculation.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 molecule