Enhancement of photoluminescence from zinc oxide by aluminum nanoparticle surface plasmon

Abstract

During the past few decades, surface plasmons (SPs) have become a research hotspot. The SPs are the collective oscillations of free electrons at the interface between metal and dielectric surrounding. Localized surface plasmon resonance (LSPR) for metal nanoparticles (NPs) has a wide application in the light emission enhancement by the selective photon absorption and by increasing local electromagnetic field. Nowadays, many achievements of SP-enhanced-emissions are applied to light emitting diodes. With the advantages of the direct wide band gap (3.37 eV) and large exciton binding energy (60 meV), zinc oxide (ZnO), which is considered as a potential material, has a wide range of applications, especially in ultraviolet (UV) optoelectronic devices. However, the low photoluminescence efficiency of ZnO limits the commercial applications of ZnO-devices. The relevant research shows that the selection of different metal NPs, such as platinum (Pt), aluminum (Al), argentum (Ag), aurum (Au), is one of the approaches to improving the UV emission from ZnO. In this study, two-dimensional arrays of Al NPs are used to improve the LSPR photoluminescence efficiency from ZnO grown by the atomic layer deposition (ALD). The two-dimensional arrays of Al NPs are fabricated on the surfaces of p-type Gallium nitride (GaN) substrates by colloid lithography. With the air-liquid interface self-assembly, the monolayer masks for colloid lithography are obtained on the substrates of p-type GaN. Then, after a 50-nm Al layer is deposited by thermal evaporation, the Al NPs’ arrays are gained by being dipped into toluene and extra sonication to remove the masks. Finally, 15 nm Al<sub>2</sub>O<sub>3</sub> and 200 nm ZnO films are deposited in sequence by ALD at a temperature of 125 ℃. The extinction spectra of Al NPs’ arrays are acquired by an ultraviolet-visible spectrophotometer. The results of the extinction spectra suggest that the radiative recombination rate is increased by the resonance coupling between the localized surface plasmons (LSP) of the Al NPs arrays and the excitons of the ZnO. A 1.91-fold enhancement of photoluminescence integral intensity in band-edge emission is measured because of the Al NP arrays coupled with ZnO. The result means that the LSP of the Al NPs’ arrays can increase the UV-emission of the ZnO. Therefore, this cost-effective and facile approach can be used in high-performance optoelectronic devices.