| This work has focused on the fabrication, manipulation, and characterization of crystalline silicon at nanoscale dimensions for electrical and optical applications. Nanocrystalline silicon can be fabricated in two basic ways, self assembly of silicon atoms or erosion of larger crystals.; Self assembly has been explored with the technique of thermal crystallization of thin amorphous silicon (a-Si) layers. Using a well characterized sputter deposition process, a-Si layers as thin as 3 nm, sandwiched between barrier layers of silicon dioxide, were crystallized with a combination of rapid thermal processing and furnace annealing. This process creates high density continuous layers of silicon nanocrystals with size distribution controlled by the original a-Si thickness. This process is compatible with silicon microelectronic processing and can be used as charge storage elements in semiconductor memories. Of particular interest in this study was the effect of surface topography on crystallization dynamics and the potential for introducing lateral in-plane order to this structure. As part of this research, a new technique for preparing ultrathin suspended membranes for transmission electron microscopy (TEM) was developed and used for material characterization.; Electrochemical etching of single crystal and multicrystalline silicon to form porous silicon (PSi) with nanoscale features was also investigated. With this process, crystalline silicon is exposed to a solution containing hydrofluoric acid in a specially designed etching cell. When an electric current is passed through the cell, the resulting chemical reaction forms pores in the silicon surface that propagate into the substrate, leaving an interconnected nanoscale network of crystalline silicon. Using this process, thin broadband antireflective films were developed for silicon solar cell applications and superior performance to existing antireflective coatings was demonstrated.; Although no commercial products have yet incorporated nanocrystalline silicon as a design element, this work focused on realistic applications of this material that could be implemented with existing technology. |
