Optoelectronic properties of nanocrystalline silicon composites.

摘要

The interest in silicon at the nano-scale level has gained great impetus since the discovery in the last decade of its photoluminescence properties at room temperature; this characteristic has opened up the possibility of creating microelectronics with optical integrated capabilities and has been the main motivation for new research in photonics and optoelectronics applications. To date, the most cost effective technique used to make silicon nanoparticles is the electroetching of silicon wafers in HF electrolytes solutions; this method generates hydrogen-passivated particles by the electrochemical dispersion of bulk silicon. The ultrasonic fracturing of porous silicon structures produces a colloidal suspension of particles in a large variety of organic solvents that can be readily used as photoluminescent tags and to create new optical materials. Silicon nanoparticles can be also produced by sputtering Si-SiO 2, a technique that can render films with distributions of silicon crystallite sizes. This thesis presents the results of an optoelectronic study of nanocrystalline silicon produced by chemical electroetching of silicon wafers and RF-co sputtering of Si-SiO2. Herein are presented the experimental contributions of this work: the development of two novel materials: silica gel monoliths and microfilms doped with porous silicon nanoclusters that have showed blue shifted photoluminescence emission with intensities over five times higher than the original intensity from the native material used for the sol-gel preparation; the enhancement of the photoluminescence of porous silicon substrates by silica gel spin coating. Finally, through a charge transport study of nanocrystalline silicon in Si-SiO2 a relationship between the photoluminescence with the silicon crystallites sizes and concentrations is demonstrated and analyzed along with the diffusion length.