Phonon Density of States in Germanium at 80 K Measured by Neutron Spectrometry

Abstract

WEAK ABSORPTION TAILS IN AMORPHOUS SEMICONDUCTORStion cross section. In this interpretation the internal electric fields' ' make the glasses more transparent than a crystal with the same concentration of states in the gap. One can roughly visualize the nature of the effect with the following picture. As the percolation theory suggests, ' above the mobility edge, but close to it, the extended states do not exist in the whole volume V, of the sample but only in a part V, (Fig. 5). If we neglect transitions between states located at different sites, the absorption is reduced by a factor V, /V, . ACKNOWLEDGMENTS %'e are grateful to Miss Phys. C~4 93 (1971). These two authors ascribe the weak absorption tails (which they observed at absorption levels very different from each other) to indirect phononassisted transitions.However, the observed temperature dependence cannot be explained by the current theory of such transitions.More than 500 frequencies of phonons with reduced wave vectors evenly distributed over an irreducible section of the first Brillouin zone have been measured in germanium at 80 K with a neutron crystal spectrometer.The phonon density of states was calculated from the data with an improved sampling technique.Comparisons between thermodynamic quantities derived from calorimetric data and from the present spectrum reveal an excellent agreement. A critical-point scheme determined by use of a method originating from Phillips is also presented. The scheme properly satisfies the Morse relations and other topological conditions, and most of the van Hove singularities expected are clearly displayed in the spectrum.

Dispersion‐related theory for heat capacities of semiconductors

“…For Si and Ge, e.g., we have found a rather good agreement (see Fig. 4) between thermodynamic P ( ) n ε values and their counterparts that have been detected in [7] from the theoretical PDOS spectra published in [34,35] (cf. Fig.…”

“…Table 4 in [8]). Further we have shown, by empty squares or circles, comparable sequences of P ( ) n ε values which had been determined in conjunction with the preceding re-digitization [7] of graphical representations of theoretically calculated PDOS spectra functions, P ( ) g ε , for Si [34] and Ge [34,35]. Original Paper whole sequence of the genuine, material-specific PDOS spectra moments, P n ε , starting from the 3 n AElimiting behavior, 12,13], up to an order of 10 n £ .…”

Relevance of Charge-Density Measurements for High-Precision Calculations

“…No high-accuracy neutron diffraction data on the Debye-Waller factor in Ge are available. So it was deduced from the measured phonon dispersion relations (Neliu & Nilsson, 1972). As reported in Dewey et al (1994), it was found to be…”

GeO2 Films with Ge-Nanoclusters in Layered Compositions: Structural Modifications with Laser Pulses

“…In large Ge nanocrystals, the spectral position of the Raman peak is at 301,5 cm -1 , with its blue shift becoming notable at nanocrystal sizes < 6-7 nm. Data on the spectral position of the Raman peaks due to Ge nanocrystals hosted in a GeO2 matrix as calculated from two theoretical models (data of (Nelin & Nilsson, 1972) and data calculated from the model of effective density of folded vibration states ) are shown in Fig. 16.…”

“…Figure 16. The spectral position of the Raman peak due to Ge nanocrystals versus nanocrystal size in GeO2<Ge-NCs> heterolayers: • -data of (Nelin & Nilsson, 1972), ▲ -data calculated by the model of effective density of folded vibration states . Using the Raman spectra in Fig.…”