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Résumé:

We study the inter-well excitonic coupling in a series of In0.17Ga0.83N/GaN Double QWs (DQWs) with varying central barrier width. We observe the switching between indirect IX (inter-well) and direct DX (intra-well) excitons, for thin barriers (2 nm or less), depending on the exciton density. This density is controlled, in cw-PL, by the pumping laser power density (LPD). Above a certain threshold, we observe a sudden change of the PL blue-shift, when switching from IXs (large slope) to DXs (weak slope). In time-resolved PL, the exciton density evolves as the PL intensity decays with time, and the switching occurs from DXs to IXs, after a certain characteristic time. The decay time of IXs is of the order of hundreds of s, whereas the decay time of DXs is shorter by three orders of magnitude. The switching thresholds in both cw- and TR-PL present clear exponential dependences upon the width of the central barrier, which demonstrates the role of carrier tunneling in the overall switching processes. The described effects were studied at T10K but we found that IXs persist up to T=300K pointing out the importance of large exciton biding energy in nitride QWs.