Study Of Luminescence Properties Of Microstructure Silicon-based ZnO Composite Films

Zinc oxide（ZnO）is a wide band gap semiconductor material with fluorescence emission covering the UV and visible range.Silicon is the main raw material for semiconductor devices.Investigation of silicon-based ZnO materials is of great significance for the development and application of optoelectronic devices.How to design the structure of silicon-based ZnO composites and optimize the experimental parameters to enhance the fluorescence emission efficiency and explore the fluorescence emission mechanism in the visible region is a key scientific problem to realize the application of ZnO blue emission devices.In this paper,porous silicon（PS）structures are prepared on p-type silicon by electrochemical anodic oxidation method under different etching current densities,etching times and etching solution systems.The morphologies of porous silicon are characterized.Ag nanoparticles are prepared on PS substrates with suitable pore size by magnetron sputtering.PS/Ag/ZnO composite films are obtained by pretreatment and deposition of ZnO under vacuum and high temperature conditions.The optical emission mechanism of the PS/Ag/ZnO composite films is investigated by combining theoretical COMSOL simulations and fluorescence results.By introducing Al₂O₃ interlayer into the structure of PS/Al₂O₃/ZnO films,the fluorescence characteristics of the films with different structures are analyzed.Finally,the fluorescence enhancement mechanism in the visible region is investigated.The main research work in this paper is as follows:（1）PS structures are prepared by etching p-type silicon using electrochemical anodic oxidation.The effect of etching conditions on the pore size and microstructure morphologies of PS are compared and analyzed by varying the etching current density,etching time and solution system.It is found that a longer etching time（above 60 min）causes the collapse of PS surface structure and the destruction of the ordered pore structures.In addition,there is a critical value of etching current,when the etching current increases,the etching mode is changed from vertical to horizontal.The pore size gradually becomes large.Compared to the ethanol system,PS prepared in a mixed solution system of DMF and hydrofluoric acid has a uniform and ordered pore structure.（2）Ag nanoparticles are prepared on the above preferred PS substrate using magnetron sputtering method,and then Ag nanosphere structures are obtained by agglomeration treatment under vacuum and high temperature environment,and finally ZnO films are deposited to prepare PS/Ag/ZnO composite film structures.The effect of sputtering time of Ag nanoparticles on the fluorescence properties of the composite film structures is investigated.The results show that the introduction of Ag nanoparticles enhances the UV and visible region light emission of the PS/Ag/ZnO composite films,and the ratio of visible to UV intensity reaches 3.9 at 5 s Ag deposition time.The theoretical COMSOL simulation results further confirm that the strong local field effect generated by the dimerization of Ag nanoparticles under P polarization makes the PS/Ag/ZnO composite film structure produce more excitons and thus enhance the photoemission efficiency.（3）PS/Al₂O₃/ZnO and PS/Ag/Al₂O₃/ZnO composite films are fabricated by continuing to introduce an Al₂O₃ interlayer into the above silicon-based ZnO composite film structure system.The modulation effect of Al₂O₃ interlayer thickness on the band edge and inter-band emission is compared and analyzed in the two composite film systems.The experimental results show that the luminescence intensity in the visible region of PS/Al₂O₃/ZnO increases with the thickness of Al₂O₃,and the ratio of visible to UV intensity is 6.875 when the Al₂O₃deposition time is 10 min,while the luminescence intensity in the visible region of the PS/Ag/Al₂O₃/ZnO composite film structure decreases with the introduction of Al₂O₃.We conclude that the Al₂O₃ spacer barrier introduced between ZnO,Ag and PS can effectively modulate the carrier concentration at the interface,allowing electron-hole recombination within each functional layer and thus modulation of the fluorescence emission in the visible region.