Universität Stuttgart
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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 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 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 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 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, KurtThe 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.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 Down-conversion of high-frequency acoustic phonons(1987) Galkina, Tatjana I.; Blinov, A. Y.; Bonch-Osmolovskii, M. M.; Koblinger, Otto; Lassmann, Kurt; Eisenmenger, WolfgangMeasurements 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.Item 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, KurtBy 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.Item Open Access Frequency dependence of the specular and diffuse phonon scattering from silicon surfaces(1985) Burger, S.; Lassmann, Kurt; Eisenmenger, WolfgangPhonon 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.Item 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, WolfgangWe 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.