08 Fakultät Mathematik und Physik
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Item Open Access Quasiparticle recombination and 2Δ-phonon-trapping in superconducting tunnelling junctions(1976) Eisenmenger, Wolfgang; Lassmann, Kurt; Trumpp, Hans-Joachim; Krauß, RichardThe experimental recombination lifetime τeff of quasiparticles in superconducting films in general exceeds the intrinsic recombination lifetime τR by phonon trapping. On the basis of geometric acoustic propagation and reabsorption of phonons emitted in quasiparticle recombination, τeff is calculated as a function of film thickness d taking into account longitudinal and transverse phonon reabsorption, bulk loss processes and acoustical phonon transmission into the substrate. With increasing thickness d three characteristic ranges are found: range 1 with film thickness d small compared to the phonon reabsorption mean free path Λw, range 2 with d larger than Λw and dominating boundary losses, and range 3, also with d larger than Λw but with dominating bulk losses. For very small d the relation between τeff and τR, the intrinsic recombination lifetime, contains only the limiting angle of total reflection of phonons within the superconducting film. Therefore, τR can be directly obtained by τeff measurements and from the sound velocities of the film-substrate system. Range 2 is characterized by a linear dependence of τeff on d. In this range it is not possible to obtain τR from τeff measurements, however, τeff allows a determination of the phonon boundary transmission. Range 3 shows no thickness dependence of τeff on d in the limit of large d values. In this range a further method for obtaining τR from τeff values is suggested.Item Open Access Continuous high resolution phonon spectroscopy up to 12meV : measurement of the A+ binding energies in silicon(1986) Burger, Wilfried; Lassmann, KurtWe have measured the binding energies of Ga+, Al+, and In+ centers in silicon with energy-resolved phonon-induced electrical conductivity. For Ga+ and Al+ we obtain the value of about 2 meV as earlier found for B+, whereas the binding energy of In+ is 6 meV. Spectral structures attributed to impurity interactions found for higher concentrations of In at energies up to about 12 meV demonstrate that acoustic phonons up to this energy are transmitted from the tunnel junction to the substrate.Item Open Access Experimental results on absolute phonon detection sensitivity of superconducting tunneling junctions(1972) Trumpp, Hans-Joachim; Epperlein, Peter W.; Lassmann, KurtSuperconducting tin tunnelling junctions are used for generating and detecting 300 GHz phonons. The absolute phonon detection sensitivity can be obtained, making possible a comparison of the number of phonons detected to the number of phonons generated. This, together with measurements of the dependence of junction time constant on its thickness, gives an indication that far more phonons are radiated into liquid He than is expected from a simple acoustic model.Item Open Access Reflection of high frequency phonons at free silicon surfaces(1978) Marx, Dieter; Buck, Jochen; Lassmann, Kurt; Eisenmenger, WolfgangIn reflection experiments at free silicon [100]-surfaces we could distinguish between specularly and diffusely reflected transverse phonons propagated along <100>-directions. With increasing phonon frequency the number of diffusely scattered phonons increase relative to that of specularly reflected phonons.Item Open Access Effective quasiparticle recombination times and electronic density of states at the Fermi level in superconducting films(1978) Epperlein, Peter W.; Lassmann, Kurt; Eisenmenger, Wolfgang-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 Phonon spectroscopy of the low energy vibrations of interstitial oxygen in germanium(1993) Gienger, Martin; Glaser, Markus; Lassmann, KurtIn oxygen doped Ge we find by phonon spectroscopy with superconducting tunnelling junctions a series of lines between 0.18 meV and 4.08 meV which can be interpreted as due to low lying states of the interstitial oxygen (Oi) as a rigid rotator around a <111>-axis slightly perturbed by the lattice potential. The sequence of transitions can be fit assuming a binding angle of (106 ± 1)° which is much smaller than the value of (162 ± 1)° for Oi in Si. Line shifts and splittings with uniaxial stress along <100>, <110> and <111> are in qualitative agreement with this interpretation.Item Open Access The influence of the dynamic Jahn-Teller effect on the phonon-scattering mechanism at acceptors in semiconductors with cubic symmetry(1982) Sigmund, Ernst; Lassmann, KurtPhonon scattering experiments of various types in cubic semiconductors doped with deep effective mass acceptors indicate an extra resonance scattering at some meV. It is shown, using Green's function and transformation techniques that these resonances are due to a dynamic Jahn-Teller effect of the 8 acceptor ground state.Item Open Access Intrinsic and experimental quasiparticle recombination times in superconducting films(1977) Eisenmenger, Wolfgang; Lassmann, Kurt; Trumpp, Hans-Joachim; Krauß, RichardExperimental quasiparticle recombination lifetime data for superconducting Al, Sn, and Pb films are compared with calculations based on a ray acoustic model taking account of the film thickness dependence of the reabsorption of recombination phonons. Information on the true or intrinsic quasiparticle recombination lifetime obtained from these and other data is discussed.Item Open Access The distribution of splittings (Ultrasonic investigation of the acceptor ground state of Si(B) ; 2)(1982) Zeile, Heinrich; Lassmann, KurtThe splitting distribution of the acceptor ground state of Si(B) is determined from the frequency dependence of the ultrasonic resonance attenuation and from acoustic paramagnetic resonance. In the purest crystals a residual distribution is found of unknown origin. In crystals containing carbon or oxygen at concentrations above about 10 22 m-3 the distribution is broadened in rough accordance with statistical estimates.