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A7.04 - Synthesis Characterization and Simulation of Silicon Nanocrystal Structures 
Date/Time:
April 24, 2014   9:30am - 9:45am
 
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Si 
 
 
 
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Silicon nano-crystals are a novel material that have many potential applications as a tunable high band gap layer in thin film solar cells, a gain medium suitable for silicon based opto-electronics and light emission, and very recently as a thin film electronic ink. The quantum confinement of carriers in silicon nanocrystals are well known to exhibit light emission and enhanced photo-luminescence. We develop here a novel method to generate silicon nanocrystals, and relate experimental measurements to simulations. In our procedure, we grow super-lattices of a-Si:H and silicon oxide (SiO2) by plasma enhanced chemical vapor deposition (PECVD), with individual layer thicknesses varying between 5 and 20 nm. We have developed a novel step-wise annealing procedure, where these films were annealed to in temperature steps to 1100 C, that results in crystallization of silicon nano-crystals within an amorphous silicon matrix. X-Ray diffraction peaks confirms nano-crystallite formation through the appearance of diffraction peaks. Raman measurements indicate a crystalline volume fraction exceeding 50%. Transmission electron microscopy (TEM) demonstrate the appearance of silicon nano-crystals that are 5-15 nm in size. Photo-luminescence exhibits peaks between 700-800 nm associated with the nanocrystal formation. We will describe the nano-crystal dimension and photo-luminescence as a function of the superlattice layer thickness, and annealing conditions, to understand the crystallization process. To understand the morphology of these nano-crystals we have performed classical molecular dynamics simulations that generate nano crystals of varying sizes by an annealing procedure. The simulated nanocrystals have many structural similarities to the experimentally synthesized. We will discuss the interfaces between the nano-crystals with the amorphous matrix, both theoretically and experimentally.
 


 
 
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