Browsing by Author "Lassmann, Kurt"

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Open Access
Anisotropy of phonon emission from hot electrons in germanium
(1976) Reupert, Wolfram; Lassmann, Kurt; Groot, Peter de
We 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.
Open Access
Continuous high resolution phonon spectroscopy up to 12meV : measurement of the A+ binding energies in silicon
(1986) Burger, Wilfried; Lassmann, Kurt
We 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.
Open Access
Dependence of the phonoionization of A+-states in Si on uniaxial pressure
(1987) Groß, Peter; Gienger, Martin; Lassmann, Kurt
By the new technique of phonon induced conductance we have investigated the dependence on pressure of the phonoionization response of shallow A+-states in Si with superconducting Al-junctions as monochromatic phonon generators. In the case of B+ and Al+ we obtain a much more complicated behaviour than previously found for B+ with FIR-photoconductivity which may be connected with differences in coupling for short wavelength phonons. In the case of in+ on the other hand a shift to lower energies is observed for uniaxial pressure in [100]-direction whereas for pressure in [111]-direction only the signal intensity varies but not the position of the threshold.
Open Access
Depopulation effects in the phonoconduction response of A+ -states in silicon and germanium
(1990) Groß, Peter; Gienger, Martin; Lassmann, Kurt
We 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).
Open Access
The distribution of splittings (Ultrasonic investigation of the acceptor ground state of Si(B) ; 2)
(1982) Zeile, Heinrich; Lassmann, Kurt
The 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.
Open Access
Down-conversion of high-frequency acoustic phonons
(1987) Galkina, Tatjana I.; Blinov, A. Y.; Bonch-Osmolovskii, M. M.; Koblinger, Otto; Lassmann, Kurt; Eisenmenger, Wolfgang
Measurements of phonon transport in amorphous media can give valuable information on the structural properties of these materials and may be of practical interest for its own concerning the question of thermalization in electronic devices. The existence of two-level systems in a-Si:H as one of these technically important materials has been concluded from measurements of dispersion and attenuation of acoustic surface waves.
Open Access
Effect of laser annealing on specular and diffuse scattering of 285 GHz phonons at polished silicon surfaces
(1986) Mok, Erich; Burger, Susanne; Döttinger, Siegfried; Lassmann, Kurt; Eisenmenger, Wolfgang
We have investigated the time resolved backscattering of high frequency phonons (greater-or-equal, slanted 285 GHz) at laser annealed silicon surfaces at low temperatures. It is found that the scattering off the free surface becomes predominantly specular up to frequencies well above 285 GHz and that the anomalous transmission into liquid helium (Kapitza effect) is strongly reduced.
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
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Open Access
Emission of high frequency relaxation phonons by superconducting aluminium tunneling junctions
(1972) Welte, Michael; Lassmann, Kurt; Eisenmenger, Wolfgang
Up to now the emission of relaxation phonons of energy E > 2 Δ by tin tunnelling junctions could not be observed by reason of the strong reabsorption of such phonons in the generator junction. We now report experiments in which the emission of relaxation phonons of energy E > 2 Δ by aluminium tunnelling junctions is observed. The conditions necessary for the emission of high frequency relaxation phonons are discussed.
Open Access
Energy resolved measurements of the phonon ionization of D and A+ centers in silicon with superconducting Al tunnel junctions
(1984) Burger, Wilfried; Lassmann, Kurt
By means of phonon spectroscopy with superconducting-Al tunnel junctions as tunable phonon generators we show that the threshold energy of the phonon-induced conductivity for Si: B+ and Si: P- agrees well with far-infrared data, proving that the ionization is mainly a one-phonon process. This ionization mechanism allows a sensitive detection of very-high-frequency phonons.
Open Access
Experimental results on absolute phonon detection sensitivity of superconducting tunneling junctions
(1972) Trumpp, Hans-Joachim; Epperlein, Peter W.; Lassmann, Kurt
Superconducting 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.
Open Access
Frequency dependence of the specular and diffuse phonon scattering from silicon surfaces
(1985) Burger, S.; Lassmann, Kurt; Eisenmenger, Wolfgang
Phonon backscattering experiments with polished silicon surfaces show that there is no Kapitza anomaly at frequencies corresponding to the aluminum junction detector threshold (sim80 GHz), whereas at higher frequencies the anomalous transmission into liquid helium or solid nitrogen increases (reduced backscattering by the coverage), closely related to the increase of the diffuse scattering at the uncovered surface.
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
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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, Kurt
Phonon 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.
Open Access
Intrinsic and experimental quasiparticle recombination times in superconducting films
(1977) Eisenmenger, Wolfgang; Lassmann, Kurt; Trumpp, Hans-Joachim; Krauß, Richard
Experimental 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.
Open Access
Investigation of A+-states in Si and Ge by phonon-induced conduction under uniaxial stress
(1993) Groß, Peter; Lassmann, Kurt
By 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+.
Open Access
Investigation of the Kapitza anomaly by frequency resolved phonon transport in silicon wafers
(1987) Klar, Wolfgang; Lassmann, Kurt
The 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.
Open Access
Linear Stark and nonlinear Zeeman coupling to the ground state of effective mass acceptors in silicon
(1992) Köpf, Andreas; Lassmann, Kurt
It 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.
Open Access
Linear stark coupling to the ground state of effective mass acceptors
(1989) Köpf, Andreas; Ambrosy, Anton; Lassmann, Kurt
It 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.
Open Access
The longitudinal and transverse relaxation rates of the strain-split two-level system (Ultrasonic investigation of the acceptor ground state of Si(B) ; 1)
(1982) Zeile, Heinrich; Harten, Ulrich; Lassmann, Kurt
The spin-lattice relaxation of the two-level system of the strain-split acceptor ground state of Si(B) is determined from the temperature dependence of the ultrasonic relaxation attenuation, around 10 K. It is found that Raman relaxation alone does not fit the results but that, in addition, an Arrhenius-type of relaxation, possibly due to a Jahn-Teller effect, is involved. The transverse relaxation is obtained from intensity-dependent and hole-burning measurements of the resonant attenuation. At small acceptor concentrations it is determined by spin-lattice relaxation alone; for higher concentrations an additional temperature-independent interaction term is found much smaller than expected for elastic dipole or exchange interaction.