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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 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 Phonon scattering due to deep acceptors in semiconductors(1976) Combarieu, Andre de; Lassmann, KurtWe have measured the magnetothermal conductivity in GaAs(Mn) and Si(In) for temperatures between 1.4 K and 90 K at magnetic fields up to 8 T. In both cases the dopants are deep acceptors with binding energy much larger (110 meV and 165 meV respectively) than given by the effective mass theory (~ 35 meV). There is a double interest in such systems: First, an excited level 3 meV (4.2 meV) above the acceptor ground state has been concluded from ultrasonic measurements. Such an excited state might be connected with a Jahn-Teller effect of these deeper acceptors and should be seen by resonant phonon scattering in thermal conductivity. Second, an anomalous behavior of the magnetothermal conductivity has been found for shallowacceptors in Ge (but not in Si) making comparison with systems with different g-factors desirable. The g-factors of acceptors in GaAs are roughly three times, the g-factor of Si(In) about 0.6 times that of Si(B).Item Open Access Ultrasonic attenuation due to the neutral acceptor indium in silicon(1976) Schad, Hanspeter; Lassmann, Kurt-