Raman and x-ray scattering from ultrafine semiconductor particles

Abstract

We prepared ultrafine germanium particles by gas-evaporation techniques. The particle composition was studied by Raman and x-ray scattering. We take an analytical model to explain the Raman profile: the particle is composed of a single-crystalline core and a coating amorphous shell. In this single-crystalline part, the phonon mode is completely localized, and as a result the red shift and the broadening of the Raman signal are induced. We introduce a localization factor to describe the size effect. According to this model we determined the mean diameter of a crystalline particle. The result is compared with that from x-ray diffraction. Our results indicate that the coating amorphous shell thickness is nearly constant, although the crystalline particle size varies by the evaporation-gas pressure. Furthermore, we found that the Raman profile changes by the wavelength of the exciting laser.

Optical Properties of Nanocrystalline GaN Films Prepared by Annealing Amorphous GaN in Ammonia

“…In addition, the broadening behavior of the first-order modes in the Raman spectrum of the nc-GaN film is also in line with the spatial correction or phonon confinement model, which suggests that the phonons in nanometric-sized systems can be confined in space by crystallite boundaries or surface disorders. [24][25][26][27] Consequently, this confinement causes an uncertainty in the relaxation of the phonon momentum selection rule q = 0, which results in not only the Raman-allowed modesÕ broadening but also new modes appearing that correspond to q = 0. In this study, two extra distinguished Raman featuresÕ shifts at 257 cm -1 and 423 cm -1 are also observed in the spectrum, which are not allowed by the C 4 6m space group in first-order Raman scattering at the zone center.…”

Sputter Epitaxial Growth of Flat Germanium Film with Low Threading-Dislocation Density on Silicon (001)

“…A sharp and symmetric Raman shift at ∼301 cm −1 corresponding to crystalline Ge, without the shoulder at lower wavenumbers, indicates that the nanocrystalline phase was absent. 23,24 In the films with d ≤ 50 nm, a phonon peak at 520 cm…”

Raman scattering of nanoporous semiconductors

“…A smaller shift is expected owing to the position of the optical phonon in c-Ge at the lower wavenumber of about 300 cm 1 , but the main reason could be the smaller dispersion of the optical phonons as compared with Si, 65 -67 as was observed by neutron scattering for Ge. 64 Kanata et al 68 investigated gas-evaporated Ge particles with sizes of 10-60 nm, as determined by Raman and XRD measurements. Good agreement was obtained by applying the CM-I model and assuming spheres with a single-crystalline core and an amorphous shell.…”