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Sang-Yun Lee Thesis Defense 6/9/11

Thesis Defense

Sang-Yun Lee

Thursday, June 9, 2011 3:30pm (110 INSCC)

Title: Pulsed Electrically Optically Detected Magnetic Resonance Spectroscopy of Disordered Semiconductors


Electrically and Optically detected magnetic resonance (EDMR and ODMR) spectroscopy allows to investigate the microscopic nature of paramagnetic centers which influence the electrical or optoelectronic properties of semiconductors. Traditionally, EDMR and ODMR have been conducted as adiabatic magnetic field sweep spectroscopies under continuous wave (cw) application of electromagnetic fields. It is shown here that information about the dynamics of spin-dependent processes obtained from cwEDMR and cwODMR is determined by many electronic- and spin-relaxation parameters, which make the interpretation of experimental data quantitatively ambiguous [1]. In contrast, it is shown that transient EDMR and ODMR experiments, so called pulsed (p)EDMR and pODMR are significantly less ambiguous [2-4]. for spin-dependent processes based on intermediate pairs of paramagnetic states, the cwEDMR and cwODMR as well as pEDMR and pODMR dynamics is derived analytically and the application of these results for the interpretation of experimental data is discussed for two examples: (i) The pEDMR study of spin-dependent recombination in silicon rich hydrogenated amorphous silicon nitride (a-SiNx:H) which showed the presence of a variety of mechanisms such as dangling bond recombination through weakly spin-coupled paramagnetic states but also recombination through band tail states which were strongly dipolar or exchange coupled [5]. These processes had previously been observed in hydrogenated amorphous silicon (a-Si:H) [6]. However, while in a-Si:h, these processes took place solely as geminate recombination, they were of non-geminate nature in the a-SiNx:H. (ii) The pODMR study of excitonic recombination in a pi-conjugated polymer, namely, poly[2-methoxy-5-(20-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) [7]. The presence of magnetic resonance induced spin-beat oscillations in the fluorescence intensity was confirmed. Based on the existing polaron-pair recombination model, previously pEDMR-detected beat signals seen here with pODMR in an identical manner [8]. Two types of MEH-PPV, one fully hydrogenated and one partially deuterated were subjected to pODMR [9]. The duuterated materials showed a different beat oscillation dependence of the driving field power patter which was indicative of smaller hyperfine fields in the deuterated material.

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