Isotopic disorder-effects on the phonons in germanium

Phonon Engineering in Isotopically Disordered Silicon Nanowires

“…Moreover, we also observed that upon heating, phonons in 28 Si x 30 Si 1−x nanowires behave remarkably differently from those in 29 Si nanowires suggesting a reduced thermal conductivity induced by mass disorder. Using Raman nanothermometry, we found that the thermal conductivity of isotopically mixed 28 Si x 30 Si 1−x nanowires is ∼30% lower than that of isotopically pure 29 Si nanowires in agreement with theoretical predictions. KEYWORDS: Nanowires, stable isotopes, phonons, thermal conductivity, Raman spectroscopy, atom probe tomography I sotope engineering in semiconductors, which refers to controlling the content of each stable isotope within a lattice, has been a powerful paradigm to investigate and manipulate some of the important physical properties of semiconductors and exploit them in innovative device structures.…”

“…With this perspective, we report on phonon engineering in metalcatalyzed silicon nanowires with tailor-made isotopic compositions grown using isotopically enriched silane precursors 28 SiH 4 , 29 SiH 4 , and 30 SiH 4 with purity better than 99.9%. More specifically, isotopically mixed nanowires 28 Si x 30 Si 1−x with a composition close to the highest mass disorder (x ∼ 0.5) were investigated. The effect of mass disorder on the phonon behavior was elucidated and compared to that in isotopically pure 29 Si nanowires having a similar reduced mass.…”

“…We found that the disorder-induced enhancement in phonon scattering in isotopically mixed nanowires is unexpectedly much more significant than in bulk crystals of close isotopic compositions. This effect is explained by a nonuniform distribution of 28 Si and 30 Si isotopes in the grown isotopically mixed nanowires with local compositions ranging from x = ∼0.25 to 0.70. Moreover, we also observed that upon heating, phonons in 28 Si x 30 Si 1−x nanowires behave remarkably differently from those in 29 Si nanowires suggesting a reduced thermal conductivity induced by mass disorder.…”

“…4 The nuclear spin is another significant difference between stable isotopes. For instance, natural silicon (Si) has three stable isotopes: 28 Si, 29 Si, and 30 Si with isotopic abundances of 92.23, 4.67, and 3.10%, respectively. Among these three isotopes, only 29 Si has a nuclear spin of 1/2, whereas 28 Si and 30 Si are nuclear spin-free.…”

Isotopically Controlled Semiconductors

“…Using a spring-and-ball analog, we recall that the phonon frequency is proportional to 1/ M (M = isotope mass). A direct verification of this dependence has been made by Fuchs et al (1) in Raman spectroscopy experiments with four of the five stable isotopes of germanium. Approximately 80% of all the elements have two or more stable isotopes, including the common semiconductors silicon ( 28 Si, 29 Si, 30 Si), germanium ( 70 Ge, 72 Ge, 73 Ge, 74 Ge, 76 Ge), gallium arsenide ( 69 Ga, 71 Ga, 75 As) and diamond ( 12 C, 13 C).…”