Photoluminescence enhancement of ZnO via coupling with surface plasmons on Al thin films

Abstract

We present that the ultra-violet emission of ZnO can be enhanced, as much as six-times its integral intensity, using an Al thin interlayer film between the Si substrate and ZnO thin film and a postfabrication laser annealing process. The laser annealing is a cold process that preserves the chemical state and integrity of the underlying aluminum layer, while it is essential for the improvement of the ZnO performance as a light emitter and leads to enhanced emission in the visible and in the ultraviolet spectral ranges. In all cases, the metal interlayer enhances the intensity of the emitted light, either through coupling of the surface plasmon that is excited at the Al/ZnO interface, in the case of light-emitting ZnO in the ultraviolet region, or by the increased back reflection from the Al layer, in the case of the visible emission. In order to evaluate the process and develop a solid understanding of the relevant physical phenomena, we investigated the effects of various metals as interlayers (Al, Ag, and Au), the metal interlayer thickness, and the incorporation of a dielectric spacer layer between Al and ZnO. Based on these experiments, Al emerged as the undisputable best choice of metal interlayers because of its compatibility with the laser annealing process, as well as due to its high optical reflectivity at 380 and 248 nm, which leads to the effective coupling with surface plasmons at the Al/ZnO interfaces at 380 nm and the secondary annealing of ZnO by the backreflected 248 nm laser beam. Published by AIP Publishing. [http://dx

Enhancement and tailoring of photoluminescence by the use of metallic nanostructures

“…The same result, the reduction of the needed fluence, was also observed when a Si substrate was covered with an aluminium thin film (Chapter 7), before ZnO film deposition and ELA, that approximately double the substrate reflectivity at 248 nm [354]. This can also be the reason of the lower of the fluence needed for achieving pure NBE emitting 30 nm thick ZnO film.…”

“…The above drives the research of alternative annealing routes, including microwave [353] and optical annealing process. In the case of optical annealing processes, ELA has presented the most interesting results [38,39,41,44,45,354]. C. Tsakonas et al [43] have presented the superiority of ELA, for the fabrication of high-intensity UV emitting ZnO, due to the nature of ELA, as it is an ultrafast approach that allows precise delivery of energy to the constituents and is compatible with large area processing.…”

“…Finally, the coupling of the PL emission of ZnO nanostructures (NSs) with either Surface Plasmon Resonance (SPR) [47,354,[382][383][384][385] or Localized Surface Plasmon Resonance (LSPR) [386][387][388][389] with the fabrication of metal thin films or NPs in the vicinity of the ZnO have been extensively studied due to the enhancement in the PL intensity that can be achieved.…”

“…and a broad Visible (VIS) peak spanning from 450 to 750 nm, associated with DLE from intrinsic and extrinsic defects [9,184,396,397]. Additionally, several studies have shown that the PL emission of ZnO can be tailored with an ELA post-fabrication treatment [354]. Selection of appropriate ELA conditions can lead to ZnO exhibit a PL emission spectrum with a specific NBE/DLE emission intensity ratio [43].…”

Enhanced UV Emission from ZnO on Silver Nanoparticle Arrays by the Surface Plasmon Resonance Effect

“…However, the low UV light emission efficiency blocks its commercial application. Hence, different metals (Ag [11][12][13][14][15][16][17][18], Au [12,15,19,20], Al [21][22][23][24], Cu [25], Ti [26,27], Ni [27], Pt [28]) with different shapes (gratings, sphere, cylinder, triangular prism, tetragonal prism, bowtie) have been applied to enhance the near band-edge UV emission of ZnO. Among them, Ag NPs with a sphere shape composited by hydrothermal method were most widely used due to relatively easy fabrication and effective light emission enhancement.…”