In this letter, we report on accurate comparative measurements of Raman scattering from bulk crystalline Si and from hydrogenated amorphous Si thin films before and after their pulse laser annealing, performed for the purpose of Si crystalline grain formation. Being accompanied by the respective optical transmittance/reflectance measurements, these data allowed us to estimate the integrated Raman scattering cross section ratios of crystalline and microcrystalline Si to hydrogenated amorphous Si and to compare the results with those known from the literature. For crystalline Si, the obtained ratio is equal to 0.75, while for microcrystalline Si, it is equal to at least 2. Our results are found to contradict the proposed earlier exponential decay dependence of the integrated Raman scattering cross section ratio of microcrystalline to amorphous Si on the crystalline grain size. The physical reasons, which support our findings, are discussed.

Spectra and transients of the photoluminescence (PL) of undoped and Er-doped size-controlled nanocrystalline $\mathrm{Si}∕\mathrm{Si}{\mathrm{O}}_2$ multilayered structures with mean nanocrystal size of $1.5–4.5\mathrm{nm}$ have been comparatively investigated. The Er-doped structures exhibit a strong Er-related PL band at $0.81\mathrm{eV}$ , while the efficiency of the intrinsic PL band of Si nanocrystals at $1.2–1.7\mathrm{eV}$ decreases by several orders of magnitude in comparison with the undoped structures. At low temperature the PL spectra of the Er-doped structures show several dips separated by the energy of Si TO-phonon and bound to the transition energies between the second and third excited states to the ground state of ${\mathrm{Er}}^{3+}$ . The Er-related PL is characterized by lifetimes of around $3–5\mathrm{ms}$ , a weak temperature quenching, and a high efficiency, which is comparable or even stronger than that of the intrinsic PL in the corresponding undoped samples. This efficient sensitizing of the Er-related luminescence is explained by the structural properties of the samples, which favor a strong coupling between the excitons confined in Si nanocrystals and upper excited states of the ${\mathrm{Er}}^{3+}$ ions in the $\mathrm{Si}{\mathrm{O}}_2$ matrix.

Superlattices of Si₃N₄ and Si-rich silicon nitride thin layers with varying thickness were prepared by plasma enhanced chemical vapor deposition. After high temperature annealing, Si nanocrystals were formed in the former Si-rich nitride layers. The control of the Si quantum dots size via the SiN_x layer thickness was confirmed by transmission electron microscopy. The size of the nanocrystals was well in agreement with the former thickness of the respective Si-rich silicon nitride layers. In addition X-ray diffraction evidenced that the Si quantum dots are crystalline whereas the Si₃N₄ matrix remains amorphous even after annealing at 1200 °C. Despite the proven Si nanocrystals formation with controlled sizes, the photoluminescence was 2 orders of magnitude weaker than for Si nanocrystals in SiO₂ matrix. Also, a systematic peak shift was not found. The SiN_x/Si₃N₄ superlattices showed photoluminescence peak positions in the range of 540–660 nm (2.3–1.9 eV), thus quite similar to the bulk Si₃N₄ film having peak position at 577 nm (2.15 eV). These rather weak shifts and scattering around the position observed for stoichiometric Si₃N₄ are not in agreement with quantum confinement theory. Therefore theoretical calculations coupled with the experimental results of different barrier thicknesses were performed. As a result the commonly observed photoluminescence red shift, which was previously often attributed to quantum-confinement effect for silicon nanocrystals, was well described by the interference effect of Si₃N₄ surrounding matrix luminescence.