This project investigates photonic structures with novel functions fabricated by interfacing sol-gel films with crystalline silicon surfaces. Preliminary results using erbium-doped films show that this combination yields high emission levels for band-gap radiation from the silicon has disclosed an unexpected property of photonic materials. This is significant for surmounting obstacles to emission posed by the indirect band gap nature of crystalline Si, where free carriers usually recombine non-radiative generating heat rather than photons.
The proposed research aims to elucidate the physical mechanism responsible for the enhanced emission and to determine structures for producing optimal quantum efficiencies. It will build on evidence that the emission of band-gap photons is promoted by non-uniform elastic strains in the silicon near the interface adjacent to a sol-gel film containing non-uniform stresses. The theoretical framework posits that carrier localization within such strain fields enhances radiative recombination in silicon by increasing electron-hole interactions.
The experimental approach is to use test structures processed on Si and sili¬con-on-insulator (SOI) material for improved optical and electronic isolation and resolution. Experimental techniques for studying relevant aspects of the materials and photonics science are specifically: excitation-matrix photoluminescence, lifetime measurements, emission depth profiling, strain measurement by X-ray diffraction and micro-Raman spectroscopy, infrared spectroscopy, MOS capacitor analysis, and electrical transport. Sol-gel film study encompasses its formulation chemistry and cation doping with species both optically active and not.
The goal of this research is to characterize the optically active region in the silicon, indicated to lie adjacent to the interface with the sol-gel film, and quantifying internal and external emission quantum efficiencies. Relating film composition and mechanics to optical modifications of the adjacent silicon will also be fully explored.