Substrate dependence of Purcell enhancement in ZnO-Ag multilayers

Ag films in Ag-MgO-ZnO thin film multilayers support surface-plasmon-polaritons whose evanescent fields can dramatically affect the ZnO exciton recombination rate. Ultraviolet femtosecond pump-probe spectroscopy and photoluminescence spectroscopy on these multilayers demonstrate that for MgO film thicknesses of 30 nm or less, the ZnO photoluminescence is enhanced, while the recombination rate is dramatically reduced for film thicknesses of 40-60 nm, resulting in quenched photoluminescence. A comparison of heterostructures grown on Si and Al₂O₃ confirms that this phenomenon is substrate independent, though Si substrates do allow for surface plasmon polariton outcoupling through Si waveguide modes.