Study On The Enhanced UV Emission From ZnO By The Surface Plasmon Resonance Effect Of Metal Nanoparticle Arrays

The potential application of ZnO in the ultraviolet light emitting diodes,lasers and detectors has attracted the attention of a large number of researchers,as its wide band gap（3.37 e V）,high exciton binding energy（60 me V）,and excellent thermal and chemical stability.However,the ultraviolet photoluminescence intensity of ZnO-based devices has been limited as its variety of natural defects,which severely restricts the development of ZnO in the field of ultraviolet optoelectronic.With the development of surface plasma optics,enhancing the photoluminescence of semiconductors by the localized surface plasma resonance effect（LSPR）of metals has become an effective way to realize the stable and efficient ultraviolet optoelectronic devices.The localized surface plasmon resonance wavelength of metal nanoparticles is not only dependent on the metal and the refractive index of the medium,but also closely related to the morphology and size of the nanostructure.In this paper,the effects of Ag and Al metal nanoparticles with different diameters and spacing,and different device structures on the UV photoluminescence of ZnO were studied by combining theory with experiment.The main results are summarized as follows:1.The local electromagnetic field and scattering cross section spectrum of Ag and Al nanoparticles with different diameters and spacing were numerically simulated by FDTD-Solution.It is proved that the local electromagnetic field around the metal nanoparticles is significantly enhanced,and the size of the particles will affect the location of the scattering peak wavelength.Besides,the surface plasmon resonance wavelength of metal nanoparticles varies regularly with the diameter and spacing of the particles.By increasing the diameter of metal nanoarrays,the surface plasmon resonance wavelength makes a red shift under the same space condition.Besides,the surface plasmon resonance wavelength makes a blue shift under the same diameter condition with increased diameter of metal nanoarrays.This is applicable to both Ag and Al metals,so it’s a universal rule.2.Silver nanoparticle（NP）arrays were fabricated by magnetron sputtering method with anodic aluminum oxide（AAO）templates to study the enhanced UV light emission from ZnO by the surface plasmon resonance effect.By introducing Ag NP arrays with the diameter of 40 nm and space of 100 nm,the photoluminescence intensity of ZnO was2-fold enhanced.The lower decay lifetime of ZnO with Ag NP arrays showed by the time-resolved PL measurement indicates the Ag NP arrays may improve spontaneous emission rate of ZnO,which enhances the coupling between the SPs in Ag NP arrays and the excitons in ZnO.The energy band was analyzed to further explain the improvement of the UV-light emission.3.Based on the theoretical simulation of the relationship between surface plasmonic resonance wavelength and the size of Al nanoparticles,Al nanoparticles with different sizes were prepared by AAO template.The UV luminescence intensity of ZnO was enhanced by2.4 times with Al nanoparticle arrays.According to the time-resolved PL measurement,the decay lifetime of ZnO with Ag NP arrays decreased by 0.09 ns,which proved that the enhanced UV luminescence intensity of ZnO could be attributed to the surface plasmonic resonance effect of Al nanoparticles.In this process,there may also be the electron transfer from metal Fermi level to LSPR level and then to ZnO conduction band.4.The ZnO/Al₂O₃/Al NPs and Al NPs/Al₂O₃/ZnO structure were peformed to study the enhanced ultraviolet photoluminescence intensity of ZnO under different structure.Compare with the Al NPs/Al₂O₃/ZnO device,ZnO/Al₂O₃/Al NPs device has higher UV emission intensity,which is 5.3-fold larger than the ZnO without Al NPs.