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PhD Defence

par Hervé Henry - publié le , mis à jour le

Monday september 25th at 3pm in amphi Drahi-X

PhD defence
Spin-dependent recombination on localized states of paramagnetic centers in ternary III-V dilute nitrides.


Spin-dependent recombination (SDR) in nonmagnetic semiconductors is a quantum correlation effect that occurs when spin-polarized carriers undergo Shockley-Read-Hall recombination through a paramagnetic defect. While the majority of SDR-related studies focus on a few well-characterized centers, e.g. NV centers in diamond, SDR effects of record magnitude have been observed in the dilute GaAs1-xNx nitride where evidence suggests that the SDR active defect is a Ga2+ interstitial. In this thesis, two main experimental studies were carried out. First, using polarization-resolved photoluminescence (PRPL) combined with Roosbroeck-Shockley analysis, a means of determining the nitrogen content of the alloy is detailed and compared favorably to a more widely accepted technique based on Raman spectroscopy. PRPL is also used in a detailed study of the dependence of SDR excitation power, conduction electron spin polarization and Hanle half-width for a GaAs0.978N0.022. alloy. The standard set of coupled rate equations used in the literature to model these power dependencies are shown to fail, although better agreement is obtained by adding band-to-band Auger recombination which becomes predominant at the excitation powers the highest. It is necessary to refine this model. Second, the deep center trapping energy associated with the Ga2+ interstitial defect is reported for the first time. Using a novel polarized photo-current transient spectroscopy (pol-PICTS) technique that reveals the spin-dependent nature of the electron trapping process, the trapping state responsible for the SDR in dilute nitrides is found at approximately 0.27 eV below the edge of the conduction band. Observation of hole emission from the same trap reveals that it lies 0.79 eV above the edge of the valence band, giving a gap of 1.06 eV in very good agreement with the average value of 1.11 eV obtained by the Roosbroeck-Shockey analysis of the PRPL spectra.