Fabrication and characterization of rare earth-doped silicon nanocrystals and rare earth-doped silicon dioxide nanostructures

Abstract

The intrinsic indirect bandgap of Si limits the applicability of Si as an optoelectronic device due to the lack of efficient light emission. Several strategies exist to overcome the inefficient photoluminescence (PL) of Si, including the formation of nanophase Si in a quantum confined size regime and the integration of luminescent rare-earth ions with SiO 2 layers on Si. Until this point it has not been possible to study the properties of discrete silicon nanoclusters which have been doped with a luminescent rare earth center. Studies of Er 3+ in Si with nanoscale dimensions has been restricted to Er 3+ and Si nanostructures co-deposited as thin films. This research represents the first reported synthesis of discrete Er 3+ -doped Si nanocrystals. Erbium-doped Si nanoparticles are prepared by the co-pyrolysis of disilane and an Er 3+ precursor in a He carrier gas with collection of the aerosol in an ethylene glycol bubbler. Analysis of the reaction products indicates that the Er 3+ -doped Si nanoparticles aggregate, and that the size distributions of those aggregates can be controlled by varying the length of the oven used for pyrolysis. The Er 3+ -doped Si nanocrystals are composed of crystalline Si. Er 3+ -doped Si nanoparticles show characteristic 1.54 ?m PL ascribed to Er 3+ . The excitation mechanism for the Er 3+ PL is thought to arise through carrier-mediated energy transfer from electron-hole pair recombination in the Si lattice. A hybrid approach to the formation of luminescent Si involves a technique, called spark processing. Spark processing uses the high energy arc from a Tesla coil to ablate and oxidize a Si surface that has been coated with a layer of a rare earth salt. Studies of spark processing using Eu 3+ salt layers on Si suggest that the rare earth ions are incorporated in the growing SiO 2 layer. Spark processing can also be applied to the formation of luminescent Er 3+ -doped spark processed SiO 2 layers on Si. The luminescent intensity of the Er 3+ PL is controlled to some extent through the initial concentration of Er 3+ ions before spark processing. High resolution photoluminescence measurements indicate that the Er 3+ is in fact trapped in the SiO 2 layer and does not form a separate oxide phase.