Study of the Homology between Silicon and Germanium by Thermal-Neutron Spectrometry

Abstract

Two maxima in the conduction band density of states were located with respect to the bottom of the conduction band by comparing our data for the outermost core d and p electrons for these compounds with transition energies measured by uv absorption, uv ref lectivity, and electron-energyloss experiments. One maximum is located between 0. 8 and l. 4 eV above the bottom of the conduction band depending on the material and the other is located between 3 and 4 eV. This analysis showed that the higher peak was only observed in transitions from the outermost d levels of the cation while the lower peak was observed in transitions from all, of the core levels for which data were available. Both peaks correspond rather closely with the two lowest maxima which have been obtained in published density-of-states calculations for some of these compounds. ACKNOW LEDGMENTSWe wish to thank T. C. Collins for helpful discussions. We also wish to thank B. Terrants of the U. S. Air Force Materials Laboratory for furnishing the GaP and M. Davis of the U. S. Aj.r , Phys. Rev. Letters 25, 659 (19V0).The phonon dispersion relations in silicon and germanium are found to be nearly homo1ogous with small but significant deviations. These results, which have been obtained by thermalneutron spectrometry, are strongly supported by an analysis in which comparison is made with elastic constants, heat capacities, and Haman frequencies for these elements. Previously observed discrepancies between results obtained from shell-model calculations and from heat-capacity measurements are explained. Attempts are made to elucidate the origin of the observed differences between the dimensionless phonon frequencies of group-IVB elements with the diamond-type crystal structure.

Ab initiothermal transport in compound semiconductors

“…The solid black curve corresponds to κ natural using the temperature-altered lattice constant, Experimental data are given by black circles [71]. The pseudopotential used in the LDA/DFPT calculation was Ge.pz-bhs.UPF [34].…”

“…The pseudopotential used in the LDA/DFPT calculation was Ge.pz-bhs.UPF [34]. Experimental data are given by black circles [71]. The pseudopotentials used in the LDA/DFPT calculation were Al.pz-vbc.UPF and P.pz-bhs.UPF [34].…”

Raman scattering of folded acoustic phonons in self-assembled Si/Ge dot superlattices

“…For the FLA phonons higher than 150 cm Ϫ1 , however, there exists a frequency discrepancy between the experimental data and those calculated by the Rytov model. By additional consideration of the nonlinear acoustic phonon dispersion of c-Si, 9 the calculated dispersion curves of the Si/Ge dot SL ͑solid line in the inset of Under nonresonant conditions fulfilled at 647 nm excitation, 3 Raman scattering from folded acoustic phonons can be treated as a coherent sum of scattering within bulklike layers due to the photoelastic effect. 10 The scattered mth-order FLA Raman intensity I m is related to the SiGe alloy layer thickness d 1 as, 9…”

Resolution analyses for Mössbauer diffraction: resolved TDS profiles in silicon

“…The dispersion curves have been mapped by thermal neutron scattering and modeled theoretically (Dolling & Cowley, 1966;Nilsson & Nelin, 1972), so that the momentum dependence of the vibrational spectrum is very well known. In addition, large perfect crystals are readily available, making silicon a convenient sample for evaluating a TDS separation method.…”

“…The TDS contribution can be calculated if the phonon dispersion relations and the volume observed in reciprocal space are known. The TDS contributions for a number of specific types of scans around the reciprocal-lattice point have been calculated (Nilsson, 1957;Cooper & Rouse, 1968;Willis, 1969) with sound velocities averaged over all directions.…”