Structural and photoluminescence studies of erbium implanted nanocrystalline silicon thin films

Hydrogenated amorphous and nanocrystalline silicon thin films deposited by Hot Wire (HW) and Radio-Frequency Plasma-Enhanced (RF) Chemical Vapor Deposition were Er-bium-implanted. Their pre-implantation structural properties and post-implantation optical properties were studied and cor-related. After one-hour annealing at 150ºC in nitrogen atmos-phere only amorphous films showed photoluminescence (PL) activity at 1.54 μm, measured at 5 K. After further annealing at 300oC for one hour, all the samples exhibited a sharp PL peak positioned at 1.54 m, with a FWHM of ~5 nm. Amorphous films deposited by HW originated a stronger PL peak than corresponding films deposited by RF, while in na-nocrystalline films PL emission was much stronger in sam-ples deposited by RF than by HW. There was no noticeable difference in Er3+ PL activity be-tween films implanted with 1x1014 atoms/cm2 and 5x1015 at-oms/cm2 Er doses.FCT for a post-doctorate grant (SFRH/BPD/14919/2004

Visible and infrared photoluminescence from erbium-doped silicon nanocrystals produced by rf sputtering

Erbium-doped low-dimensional Si films with different microstructures were deposited by reactive magnetron sputtering on glass substrates by varying the hydrogen flow rate during deposition. Amorphous, micro- and nanocrystalline samples, consisting of Si nanocrystalls embedded in silicon-based matrices with different structures, were achieved with optical properties in the visible and IR depending on nanocrystalline fraction and matrix structure and chemical composition. Structural characterization was performed by X-ray diffraction in the grazing incidence geometry and Raman spectroscopy. The chemical composition was studied using RBS/ERD techniques. Spectroscopic ellipsometry was combined with the previous techniques to further re-solve the film microstructure and composition. In particular, the distribution along the film thickness of the volume fractions of nanocrystalline/amorphous silicon and SiOx phases has been obtained. In this contribution we discuss visible and infrared photoluminescence as a function of sample microstructure and of the oxygen/ hydrogen concentration ratio present in the matrix.FCT (POCTI/CTM/39395)INTAS Project #03-51-648

Location of the Energy Levels of the Rare-Earth Ion in BaF2 and CdF2

The location of the energy levels of rare-earth (RE) elements in the energy band diagram of BaF2 and CdF2 crystals is determined. The role of RE3+ and RE2+ ions in the capture of charge carriers, luminescence, and the formation of radiation defects is evaluated. It is shown that the substantial difference in the luminescence properties of BaF2:RE and CdF2:RE is associated with the location of the excited energy levels in the band diagram of the crystals

Optically modulated magnetic resonance of erbium implanted silicon

Er implanted Si is an important candidate for quantum and photonic applications, but the Er centres involved are poorly understood, which has hindered development of these applications. Here we present the first measurement of the crystal field splitting of the 4I13/2 manifold of Er implanted Si, using a technique we call optically modulated magnetic resonance (OMMR). Crystal field analysis allows us to determine that this splitting originates from a photoluminescence (PL) active O coordinated Er centre with orthorhombic symmetry, which is highly localised with, and magically coupled to, an electron paramagnetic resonance (ERP) active O coordinated Er centre with monoclinic symmetry. The orthorhombic centre has a g-factor in agreement with previous Zeeman measurements, and is associated with a previously unreported acceptor state at ~ Ev+425 cm-1, showing that Er in Si is amphoteric, and not a pure donor, as previously thought. The OMMR mechanism involves transitions from this acceptor state to the 4I13/2 manifold, followed by relaxation to the Zeeman ground state