Universität Stuttgart
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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 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 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 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 Phonon scattering at acceptors with gamma8 ground states in semiconductors(1980) Sigmund, Ernst; Lassmann, KurtThe ground state of acceptors in cubic semiconductors is fourfold degenerate and the interaction with the lattice vibrations leads to the possibility of a Jahn-Teller effect, causing a dynamical splitting of the electronic levels. However, due to the extended nature of the wave function of the defect, random internal fields may have dominant influence to destroy the J.T. effect. Such an influence should be smaller for deeper acceptors, where the wavefunctions are more concentrated.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.Item 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 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 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 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.