Optical properties of nanocrystalline silicon embedded in SiO2 (original) (raw)
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Luminescence and Raman characterization of molecular and nanocrystalline silicon clusters
Thin Solid Films, 1997
Silicon clusters prepared by low energy cluster beam deposition exhibit visible luminescence similar to that observed in porous silicon. The structure and properties are characterized by different complementary techniques with a special emphasis on Raman spectroscopy. The comparison with silicon clathrates structures is promising. The validity of the confinement model in a size range down to a few ångströms is discussed. q 1997 Elsevier Science S.A.
Characterisation of silicon nanocrystals in silica and correlation with luminescence
Nanocrystalline silicon emits visible light (1.7eV) even though bulk Si has an indirect bandgap in the infra-red region. Si nanocrystals have been produced by ion implantation into an amorphous silica substrate followed by annealing at 1050 degrees Celsius. It was observed that the wavelength and intensity of emission is dependent on the ion implantation dose, annealing time and annealing temperature and is presumably related to the particle distribution. The mechanism for emission in such nanocrystals is as yet only partly understood, although recent results suggest interplay between quantum confinement and interface defect states.
Surface and confinement effects on the optical and structural properties of silicon nanocrystals
Nanocrystals, and Organic and Hybrid Nanomaterials, 2003
In this work we investigate, by first-principles calculations, the structural, electronic and optical properties of: (1) oxygenated silicon-based nanoclusters of different sizes in regime of multiple oxidation at the surface, and (2) hydrogenated Si nanoclusters (H-Si-nc) in their ground and excited state configurations. Structural relaxations have been fully taken into account in all cases through total energy pseudopotential calculations within density functional theory.
Surface and confinement effects on the optical and structural properties of silicon nanocrystals
2003
In this work we investigate, by first-principles calculations, the structural, electronic and optical properties of: (1) oxygenated silicon-based nanoclusters of different sizes in regime of multiple oxidation at the surface, and (2) hydrogenated Si nanoclusters (H-Si-nc) in their ground and excited state configurations. Structural relaxations have been fully taken into account in all cases through total energy pseudopotential calculations within density functional theory. In the first case we have varied systematically the number of Si=O bonds at the cluster surface and found a nonlinear reduction of the energy gap with the Si=O bond number. A saturation limit is reached, which allows us to provide a consistent interpretation of the photoluminescence (PL) redshift observed in oxidized porous silicon samples. Our results help also to explain some very recent findings on the single silicon quantum dot photoluminescence bandwidth. In the second case, after a preliminary study of the clusters stability, the properties of the ground and excited states have been compared varying the cluster dimensions from 1 to 29 Si atoms. Ab-initio calculations of the Stokes shift as a function of the cluster dimension will be presented. A structural model linked to the four level scheme recently invoked to explain the experimental outcomes relative to the observed optical gain in Si-nc embedded in a SiO2 matrix will be also suggested.
Size-dependent optical properties of silicon nanocrystals
Journal of Luminescence, 1999
We have synthesized green and red luminescent silicon nanocrystals in a SiO matrix by RF co-sputtering on a quartz substrate. The transmission coe$cient measurements were used to estimate the nanocrystal size distribution. The size distribution reveals peaks in the range 1.1}2.6 nm with a long tail towards the larger size. As the nanocrystal size reduces photoluminescence spectrum shifts from red to green wavelengths. The measured PL emission energy is in agreement with the corrected LDA calculations. With decreasing nanocrystal size, the phonon Raman spectra exhibit softening accompanied with increasing asymmetrical broadening. The observed line shape is explained by considering phonon con"nement in a spherical nanocrystal. The major contribution to the phonon line shape comes from those nanocrystals that favor resonance interaction with either incoming or outgoing photon.
Journal of Nanophotonics, 2009
Recent developments in the field of silicon nanostructures, particularly those properties and phenomena that are related to the photoluminescence (PL) from silicon nanostructures, have attracted much attention lately. A major source of controversy and disagreement among researchers is the underlying mechanism behind the PL. Two classes of models, i.e., the quantum confinement model that assigns the PL to quantum size effects in the nanocrystalline silicon core of the nanostructures and the surface chemistry model that assign the PL to surface phenomena at the interface between the crystalline core and the host matrix that wrap the nanostructures, are the most notable ones. In recent years, alternative structures to porous silicon, which allow synthesizing high quality silicon nanostructures with better control of their dimensionality, shape and size distribution, have emerged. In particular, fabrication techniques of silicon nanocrystals embedded in silicon-dioxide (SiO 2) matrices have reached a level where consistent investigation of surface and quantum size phenomena can be performed. Recent experimental results and theories suggest that none of the above models alone can explain the entire spectrum of optical phenomena in silicon nanostructures. Instead, a refined model that takes into account the mutual role of quantum confinement and surface chemistry in shaping the optical properties of these nanostructures should be considered.
Towards spectroscopy of a few silicon nanocrystals embedded in silica
Physica E: Low-dimensional Systems and Nanostructures, 2009
This work aims at optical isolation of a few silicon nanocrystals (Si-NCs) embedded in silica. We rely on realization of a SiO single layer followed by annealing under vacuum to generate Si-NCs. We first report on optimization of luminescence of single Si-NC layer in SiO 2 thin film. An optimum of photoluminescence signal was found for annealing at 1050 1C for 95 min. Then, in order to optically isolate single Si-NCs, lithographic processes such as creation of aluminum masks have been employed. We discuss the challenges and the chances of measuring a photoluminescence signal from few Si-NCs.
Journal of Surface Investigation. X-ray, Synchrotron and Neutron Techniques, 2012
The photoluminescence (PL) spectra and kinetics of amorphous and crystalline silicon nanoclus ters are investigated. The given nanoclusters are formed by thermal annealing of thin suboxide silicon films with different volume fractions of silicon. It is demonstrated that the PL intensity and lifetime of the ensem bles of silicon nanocrystals have a steplike dependence on the silicon volume fraction in the film. The influ ence of the percolation effect on the photoluminescence properties of the structures under study is discussed.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999
ABSTRACT Si nanoclusters are formed in a SiO2 matrix by ion implantation and annealing, and a possible mechanism for the light emission from Si implanted SiO2 layers is reported. We have measured dose (concentration of excess Si atoms), annealing time and excitation energy dependence of the photoluminescence. After annealing, a photoluminescence band around 1.7 eV has been observed. The peak energy of the photoluminescence is found to be independent of annealing time and excitation energy, while the intensity of the luminescence increases as the annealing time and excitation energy increase. Moreover, we found that the peak energy of the luminescence is strongly affected by dose of implanted Si ions especially in the high dose range. These results indicate that the emission of photon is not simply due to direct electron–hole recombination inside Si nanoclusters, but is related to defects probably at the interface between Si nanoclusters and SiO2, for which the energy state is affected by Si cluster–cluster interaction. It seems that Si nanoclusters react via a thin oxide interface and the local concentrations of Si nanoclusters plays an important role in the peak energy of the photoluminescence.
Microelectronics Journal, 2003
Nanocrystalline silicon thin films doped with erbium were produced by reactive magnetron RF sputtering. Their structural and chemical properties were studied by X-ray diffractometry at grazing incidence, micro-Raman, spectroscopic ellipsometry and Rutherford Backscattering Spectroscopy, respectively. Films with different crystalline fraction and crystallite size were deposited. Since the luminescence efficiency of Er-doped nc-Si films is strongly influenced by the microstructure and impurity content (i.e. H, O, Er), the photoluminescence characteristics are discussed in terms of the microstructure. The novelty of these films, if compared to usually investigated structures with the nanocrystals embedded in SiO2, is their relative high conductivity, which makes them attractive for device applications.