Raman studies of isotope effects in Si and GaAs

Widulle, F.; Ruf, T.; Göbel, A.; Silier, I.; Schönherr, E.; Cardona, M.; Camacho, J.; Cantarero, A.; Kriegseis, W.; Ozhogin, V. I.

doi:10.1016/s0921-4526(98)01390-8

Cited by 36 publications

(23 citation statements)

References 9 publications

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“…Therefore, phonon frequencies of 28 Si are expected to be larger than those of nat Si, and the phonon density of states is expected to shift toward higher frequencies. A manifestation of this effect is the shift of the peak in the Raman spectrum from 524 cm −1 for nat Si to 525 cm −1 for 28 Si:P, 18 which was also found for the Si samples of this paper. This also might affect the transitions involved in the decay of the 2p 0 state.…”

Section: Resultssupporting

confidence: 76%

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Isotope effect on the lifetime of the 2p0state in phosphorus-doped silicon

et al. 2013

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The low-temperature (∼5 K) phonon-assisted relaxation of the 2p 0 state of phosphorus donors in isotopically pure, monocrystalline 28 Si has been studied in the time domain using a pump-probe technique. The lifetime of the 2p 0 state in 28 Si:P is found to be 235 ps, which is 16% larger than the lifetime of a reference Si:P sample with a natural isotope composition. The interaction of the 2p 0 state with intervalley g-type longitudinal acoustic and f -type transverse acoustic phonons determines its lifetime. This interaction, which depends on the homogeneity of the crystal, becomes weaker in 28 Si because of its more perfect crystal lattice compared to natural Si, and this leads to a longer lifetime. The difference between the linewidths of the 1s(A 1 ) → 2p 0 transition in 28 Si:P and natural Si:P is more than a factor of two. It follows that linewidth broadening due to isotopic composition is an inhomogeneous process.

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Section: Resultssupporting

confidence: 76%

“…3); and the phononic spectra. 18 In this paper, we report on direct lifetime measurements of the 2p 0 state in phosphorus-doped, isotopically enriched 28 Si using a terahertz pump-probe technique on the 1s(A 1 ) → 2p 0 transition. We carried out the same measurements with phosphorus-doped nat Si.…”

Section: Introductionmentioning

confidence: 99%

Isotope effect on the lifetime of the 2p0state in phosphorus-doped silicon

et al. 2013

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“…Similar results have been also found for silicon [11] and gray tin [12]. They contrast rather strikingly with the data obtained by Raman spectroscopy for diamond [13 to 15].…”

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confidence: 82%

“…The Ge crystals used in [3] were grown by a modified Bridgman method using a graphite mold. The 30 Si crystals of [11] were grown from a Ga or In solution (only 1 g of 30 Si, a rather expensive isotope, was available). Very recently, single crystals of 28 Si have been grown by the flowting zone, crucible free method.…”

Section: Procurement Of Stable Isotopesmentioning

confidence: 99%

Isotopic Effects in the Phonon and Electron Dispersion Relations of Crystals

Cardona

2000

phys. stat. sol. (b)

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During the past ten years, the relaxation of international tensions between East and West has resulted in the so‐called “peace dividends”. Among these dividends, solid state physicists have profited from the increasing availability of stable isotopes of many elements at affordable prices. These isotopes originate sometimes in the United States and sometimes in Russia. They can either be purchased or obtained “on loan” on the basis of scientific collaboration. With these isotopes, single crystals with tailor‐made isotopic compositions have been grown. Using these crystals, information on a number of rather basic physical properties has been obtained. We discuss in this review the following properties of such semiconductor crystals: 1. dependence of the lattice parameters on isotopic masses; 2. effect of isotopic disorder on thermal conductivity; 3. anharmonic effects on the phonon frequencies and linewidths and their dependence on isotopic mass; 4. effects of isotopic disorder on phonon frequencies and linewidhts; 5. renormalization of the energy of electronic states through electron–phonon interaction; and 6. self‐diffusion of atoms in crystals. Because of space limitations this discussion will not be exhaustive. We hope, however, to give sufficient references to published work so that the interested reader can easily find the primary literature sources to this rapidly expanding field of solid state physics. (A few multilingual short reviews are listed under [1].)

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“…In GaAs, the LO Raman peak is broadened by isotopic disorder. This broadening was found to be 0.12 cm 21 at low temperature from measurements of isotopically pure samples [15]. The isotopic disorder contribution has been subtracted from our experimental GaAs linewidth.…”

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Anomalous LO Phonon Lifetime in AlAs

et al. 2002

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The temperature dependence of the frequencies and linewidths of the Raman-active longitudinal optical (LO) phonons in GaAs and AlAs have been measured. The low-temperature lifetime of the LO phonon in AlAs is found to be 9.7 ps, very close to the corresponding GaAs value of 9.5 ps. This contradicts early theoretical predictions. The agreement between theory and experiment can be restored when the accidental degeneracy between the AlAs LO phonon frequency and a feature in the two-phonon density of states is taken into account. DOI: 10.1103/PhysRevLett.88.215502 PACS numbers: 63.20.Kr, 78.30.Fs The lifetime of the Raman-active longitudinal optical (LO) phonon in III-V semiconductor compounds is of critical importance for the coupled dynamics of carriers and phonons in these materials. Accordingly, an intense effort has been devoted to the study of this quantity for the past 20 years [1]. The recent availability of ab initio predictions of phonon lifetimes [2-5] represents a significant breakthrough, since they pinpoint the relevant LO phonon decay channels that may open the door for the engineering of phonon lifetimes.In spite of the technological relevance of the Al-Ga-As system, the lifetime t of LO phonons in AlAs has not been reported thus far. From time-domain measurements on an Al 0.3 Ga 0.7 As alloy sample, Tsen and Morkoç find t 7 6 1 ps (at 10 K) for both the GaAs-like and AlAs-like LO vibrations [6]. These results are quite puzzling since, as pointed out by Kash and Tsang [1], the phonon dispersion curves for GaAs and AlAs (which determine their possible LO decay channels) are quite different. A comparison of these curves for several semiconductors suggests that t AlAs should be significantly longer than t GaAs . The first ab initio estimates of phonon lifetimes added to the puzzle [3], since they predict t AlAs 12.7 ps . t GaAs 9.2 ps, in agreement with Kash and Tsang's qualitative argument. The reliability of the theoretical prediction was underscored by the good agreement with the existing experimental data for GaAs [7][8][9][10][11].The above discrepancies between theory and experiment could be dismissed by arguing that the GaAs-like and AlAs-like LO vibrations in AlGaAs alloys are not equivalent to the LO phonons in binary GaAs and AlAs crystals, so that a direct comparison is not legitimate. In this Letter, however, we report Raman measurements of the LO phonon frequencies and lifetimes in GaAs and AlAs. Our results show that the low-temperature lifetimes of LO phonons in GaAs and AlAs are indeed very similar. But we also find that these experimental results do not imply a failure of the ab initio method. Instead, they arise from a breakdown -in the case of AlAs -of the standard formalism used to compare theory with experiment. This breakdown is caused by the accidental degeneracy between the frequency of the AlAs LO phonon and a Van Hove singularity in the two-phonon density of states. Such degeneracies have been proposed in the past -most notably in the case of the transverse-optic phonon in ...

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Raman studies of isotope effects in Si and GaAs

Cited by 36 publications

References 9 publications

Isotope effect on the lifetime of the 2p0state in phosphorus-doped silicon

Isotope effect on the lifetime of the 2p0state in phosphorus-doped silicon

Isotopic Effects in the Phonon and Electron Dispersion Relations of Crystals

Anomalous LO Phonon Lifetime in AlAs

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