ELFT HÍRADÓ

[Varga Imre <varga AT neumann.phy.bme.hu>]

                                     MEGHIVO

                  a BME Fizikai Intezet, Elmeleti Fizika Tanszek
                                  szeminariumara:

                                 Gerhard Weiser
                    FB Physik, Philipps-Universitaet Marburg

          "Non-radiative energy transfer to radiative centres (Er3+)
                               in a-Si(1-x)C(x):H"

        Helye: BME Fizikai Intezet,
               Elmeleti Fizika Tanszek
               Budafoki ut 8.
               F-epulet, III. lepcsohaz, magasfoldszint
               szeminariumi szoba

        Ideje: 2005. marcius 11. pentek, 10:15.

        Abstract: Rare earth ions emit light by intra- f-shell transitions
        at wavelengths which are fairly independent of the host lattice.
        Of particular interest is the emission of Er3+ at 1.5 micron
        preferred by fiber communication systems. Er ions thus may link
        Si-based electronics to optical communication but despite much
        effort intensity emitted from Er in c-Si is small due to a limited
        solubility of Er and has vanished at room temperature. More Er can
        be solved in amorphous semiconductors and samples of amorphous Si
        prepared by magnetron assisted plasma deposition showed strongly
        increased efficiency and thermal stability of the Er-emission.
        These samples have a large density (1018cm-3) of bonding defects,
        and it was suggested that electrons recombining at these defects
        transfer their energy in an Auger process to Er3+ ions. Implicitly
        it was presumed that Er creates these defects, linking defect
        recombination and energy transfer efficiently. Samples prepared by
        plasma decomposition of silane (SiH4) have much less defects and
        with the improved electronic quality the efficiency of
        electrically pumped diodes increased by about 2 orders of
        magnitude. Spectroscopic data obtained for both types of samples
        are inconsistent with the Auger model and lead to a Frster
        transfer, i.e. dipolar interaction, as the most likely mechanism
        for an energy transfer.

        The talk will present experimental data which led to a model of
        competing relaxation and thermalization processes in an amorphous
        material. It will also show the physics behind the excitation of
        rare earth ions in an amorphous host, emphasizing the difference
        to crystalline hosts.


        Minden erdeklodot szivesen latunk.


                                                        Varga Imre