Universität Stuttgart
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Item Open Access A study of the ground state of acceptors in silicon from thermal transport experiments(1981) Goer, Anne M. de; Locatelli, Marcel; Lassmann, KurtThermal conductivity measurements of silicon crystals doped with Bor In have shown the presence of several phonon scattering processes. The resonant effect observed below 1 K is ascribed to the existence of a distribution of splittings N(δ) of the Γ8 ground state of the acceptor, which could be related to the presence of oxygen and carbon impurities. In two cases, the maximum of N(δ) occurs for δ max near 6 GHz, in agreement with previous ultrasonic studies.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 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.Item Open Access Linear Stark and nonlinear Zeeman coupling to the ground state of effective mass acceptors in silicon(1992) Köpf, Andreas; Lassmann, KurtIt is shown by dielectric resonance absorption at 60 GHz that there is a linear coupling of the electric field to the ground state of effective mass acceptors in Si reflecting the lower Td symmetry in the central portion of the ground-state wave function. The coupling increases strongly with increasing binding energy from B to In, i.e., with decreasing Bohr radius of the acceptor. An unexpected nonlinear Zeeman splitting is observed the magnitude of which also increases from B to In. For all acceptors a central fine structure is found which correlates with the homogeneous linewidth.Item Open Access Investigation of the Kapitza anomaly by frequency resolved phonon transport in silicon wafers(1987) Klar, Wolfgang; Lassmann, KurtThe threshold at 85 GHz for anomalously large transmission of phonons into LHe has been investigated with Si-wafers for various surface treatments and coverages by phonon spectroscopy. With this multiple boundary scattering geometry we observe an increased sensitivity to spectral features. Connected with the threshold there is a phase shift of the signal compatible with a loss of the slower diffuse portion of the phonon signal to the covering liquid helium. This phase shift depends nonlinearly on modulation frequency between 5 kHz and 200 kHz (modulation of the generator to sort out the monochromatic phonons) and in a characteristic manner on the surface treatment. The finite phase shift at 5 kHz is indicative of very long lived 85 GHz phonons up into the 100 µs is range inspite of the multiple Si-LHe-interface scattering involved. Minor differences in polishing quality show up clearly in the phase shift at low modulation frequencies.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 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 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.