Comparison of the phonon spectra of sup 70 Ge and natural Ge crystals: Effects of isotopic disorder

Journal Article · Fri Feb 15 04:00:00 EST 1991 · Physical Review, B: Condensed Matter; (USA)

DOI:https://doi.org/10.1103/PhysRevB.43.4835· OSTI ID:5736487

Fuchs, H D; Grein, C H; Thomsen, C; Cardona, M ^[1]; Hansen, W L ^[2]; Haller, E E; Itoh, K ^[3]

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1. Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-7000 Stuttgart 80, Federal Republic of Germany (DE)
2. Lawrence Berkeley Laboratory, Berkeley, California 94720 (USA)
3. 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), Journal Name: Physical Review, B: Condensed Matter; (USA) Vol. 43:6; ISSN 0163-1829; ISSN PRBMD
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360104* -- Metals & Alloys-- Physical Properties
CRYSTALS
ELEMENTS
GERMANIUM
ISOTOPE EFFECTS
METALS
OPTICAL PROPERTIES
PERTURBATION THEORY
PHONONS
PHYSICAL PROPERTIES
QUASI PARTICLES
RAMAN SPECTRA
SPECTRA