Efficient dipole-dipole coupling of Mott-Wannier and Frenkel excitons in (Ga,In)N quantum well/polyfluorene semiconductor heterostructures

We investigate interactions between Mott-Wannier (MW) and Frenkel excitons in a family of hybrid structures consisting of thin organic (polyfluorene) films placed in close proximity (systematically adjusted by GaN cap layer thickness) to single inorganic $[(\mathrm{Ga},\mathrm{In})\mathrm{N}∕\mathrm{Ga}\mathrm{N}]$ quantum wells (QWs). Characterization of the QW structures using Rutherford backscattering spectrometry and atomic force microscopy allows direct measurement of the thickness and the morphology of the GaN cap layers. Time-resolved photoluminescence experiments in the $8--75\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ temperature range confirm our earlier demonstration that nonradiative energy transfer can occur between inorganic and organic semiconductors. We assign the transfer mechanism to resonant F\"orster (dipole-dipole) coupling between MW exciton energy donors and Frenkel exciton energy acceptors and at $15\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ we find transfer efficiencies of up to 43%. The dependence of the energy transfer rate on the distance $R$ between the inorganic QW donor dipole and organic film acceptor dipole indicates that a plane-plane interaction, characterized by a $1∕{R}^{2}$ variation, best describes the situation found in our structures.