Comparison of the phonon spectra of sup 70 Ge and natural Ge crystals: Effects of isotopic disorder
- Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-7000 Stuttgart 80, Federal Republic of Germany (DE)
- Lawrence Berkeley Laboratory, Berkeley, California 94720 (USA)
- University of California, Berkeley, California 94720 (USA) Lawrence Berkeley Laboratory, Berkeley, California 94720 (USA)
The difference in phonon energies and broadenings between an isotopically enriched crystal of {sup 70}Ge (95.9%) and a germanium crystal of natural isotopic composition was measured with high accuracy in first- and second-order Raman spectra (with laser excitation energies of {ital E}{sub {ital L}}=2.41 eV and {ital E}{sub {ital L}}=2.183 eV, respectively) and compared to coherent-potential-approximation and lowest-order perturbation-theory calculations. The energy of the first-order {ital O}({Gamma}) phonon shifts up by 4.9{plus minus}0.1 cm{sup {minus}1} in the isotopically pure crystal, in good agreement with the calculated value of 4.3{plus minus}0.4 cm{sup {minus}1}. No broadening due to isotopic disorder was observed for optical phonons at the {Gamma} point (full width at half maximum (FWHM) of 0.99{plus minus}0.03 cm{sup {minus}1} at 80 K for both crystals). However, additional broadening at the {ital W} and {ital L} point was found in the second-order Raman spectra (FWHM broadening of 6.5{plus minus}0.5 cm{sup {minus}1} at the {ital L} point). This broadening and the shifts of the acoustic- and optical-phonon peaks in the second-order spectra agree well with calculations of the phonon overtone density of states.
- OSTI ID:
- 5736487
- Journal Information:
- Physical Review, B: Condensed Matter; (USA), Vol. 43:6; ISSN 0163-1829
- Country of Publication:
- United States
- Language:
- English
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