We calculate the ground and excited electron and hole levels in spherical Si nanocrystals (quantum dots) embedded within SiO 2 in a multiband effective mass approximation. The obtained energies of electron and hole are used to estimate the Auger Recombination (AR) lifetime in Si Nanocrystals (NCs). The excited electron, excited hole and biexciton AR types are considered. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.

Ultra-thin nanocrystalline silicon films with varying thickness from 5 to 30nm were grown on quartz by low pressure chemical vapor deposition (LPCVD) of Si. Observations on cross-sectional transmission electron microscopy (TEM) specimens revealed that the films had a columnar growth, i.e. the third dimension of the nanocrystals, perpendicular to the Si/SiO 2 interface, was approximately equal to the film thickness, while the lateral size of nanocrystals was defined during the initial stage of growth and was not very much affected bythe film thickness. The observed columnar growth gives the possibility to obtain two-dimensional nanocrystal arrays on quartz with well defined size in the z-direction. Plane view images showed that the lateral distribution of nanocrystal size presents a well-defined maximum in all the films. The mean lateral size of the nanocrystals did not change very much with the film thickness, being in the range of 11-13 nm. The number of grains with size larger than the mean one tended to increase with the thickness of the film. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.

In this work, the morphology, structure, surface chemical composition, and optical properties of very thin (10-70 nm) anodic silicon films grown on a silicon substrate by electrochemical dissolution of bulk crystalline silicon in the transition regime between the porous formation and electropolishing were investigated in detail. Anodization was performed by using short single pulses of anodization current in low and high hydrofluoric acid (HF) concentration electrolytes. A systematic comparison was made between films grown at low and high HF concentration electrolytes. The morphology and structure of the films were investigated by combining atomic force microscopy and transmission electron microscopy (TEM), while x-ray and ultraviolet photoelectron spectroscopies were used to investigate the chemical composition of the films. Photoluminescence was used to investigate the optical properties. It was found that films that formed at low HF concentrations were much thinner than films that formed at high HF concentrations due to surface dissolution of the films during anodization. High resolution TEM images revealed an amorphouslike structure (porous) in all of the films in which discrete Si nanocrystals (NCs) were identified. NC size was, on the average, larger in films fabricated in low HF concentration electrolytes and these films were not luminescent. On the other hand, films fabricated in high HF concentration electrolytes were thicker and contained smaller NCs. A silicon oxide layer covered the internal surface of all films, this oxide being much thinner in films grown at high HF concentrations. This last effect was attributed to self-limiting oxidation of the very small NCs constituting these films. © 2008 American Institute of Physics.