Tuning the influence of metal nanoparticles on ZnO photoluminescence by atomic-layer-deposited dielectric spacer

There is increasing interest in tuning the optical and optoelectronic properties of semiconductor nanostructures using metal nanoparticles in their applications in light-emitting and detection devices. In this work we study the effect of a dielectric Al₂O₃ gap layer (i.e., spacer) on the interaction of ZnO nanowires with metal nanoparticles. The Al₂O₃ spacer thickness is varied in the range of 1-25 nm using atomic layer deposition (ALD) in order to tune the interaction. It is found that ∼5 nm is an optimum spacer thickness common for most metals, although the enhancement ratio of the near-bandedge emission differs among the metals. Consistent results are obtained from both photoluminescence (PL) and cathodoluminescence (CL) spectroscopies, with the latter being applied to the optical properties of individual semiconductor/metal nanoheterostructures. The interaction is primarily proposed to be related to coupling of ZnO excitons with local surface plasmons of metals, although other mechanisms should not be ruled out.