Array Density Effect On The Optical And Photoelectric Properties Of Silicon Nanowire Arrays Via Metal-Assisted Chemical Etching

Compared with bulk silicon(Si),silicon nanowire(SiNW)arrays have the advantages of excellent light-trapping performance and short carrier collection distance,which make it easier to fabricate high-performance Si-based photodetectors.In particular,SiNW arrays fabricated by metal-assisted chemical etching(MACE)have been applied in the solar cell industry due to their simple,efficient and low-cost fabrication.The optical/photoelectric properties are closely related to the structural parameters of SiNW arrays.However,the research on the relationship between the density of SiNW arrays fabricated by MACE and their optical/photoelectric properties is still insufficient.Related research is expected to optimize the fabrication of SiNW arrays and improve the performance of Si-based optoelectronic devices.In this thesis,the density of SiNW arrays was controlled in MACE and the effects of the SiNW array density on their optical and photoelectric properties were systematically studied.The following progress was achieved:1.Controlling of the density of SiNW arrays:The reaction time of Si wafers in seed solution was controlled in MACE process,which adjusts the size and density of Ag particles.It is found that the transverse size distribution of SiNWs that fabricated with different reaction time in the seed solution is consistent.Thus,the density of SiNWs can be reflected by calculating coverage ratio of SiNWs on the surface of the Si wafer.Large coverage ratio indicates high density of SiNWs.After reacting in the etching solution,SiNW arrays with different densities were fabricated.As the reaction time increases from 10 s to 240 s in the seed solution,the coverage area of SiNWs on the surface of Si wafers gradually decreased from 34.5%to 7.5%,indicating that the density of SiNW arrays can be effectively controlled by controlling the reaction time of Si wafers in the seed solution.The above results provide a research model for studying the influence of SiNW array density on the optical and photoelectric properties.2.Effect of SiNW array density on the optical property:The absorbance spectra of SiNW arrays with different densities were characterized to establish the structure-activity relationship between the density and the optical property of SiNW arrays.Although all SiNW arrays exhibited light-trapping effect,there were differences in the absorption of samples with different densities.With the extension of the reaction time in the seed solution,the light absorption of SiNW arrays first gradually increased and then gradually decreased.Among them,the SiNW arrays with a seed reaction time of 90 s have the best light absorption performance,and the light absorption efficiency generally exceeds 98%in the wavelength range of 300-1000 nm.In addition,from the statistical data,the absorption efficiency of the SiNW arrays with the reaction time of 90 s in the seed solution was relatively stable.The above results show that SiNW arrays with the reaction time of 90 s in the seed solution are most suitable for applications that require high light absorption.3.Effect of SiNW array density on the photoelectric property:By fabricating PEDOT.PSS/SiNWs heterojunction photodetectors,the relationship between the density of SiNW arrays and their photoelectric property was established.It is found that PEDOT:PSS can be conformally wrapped on the surface of SiNW arrays.The device performance will mainly reflect the photoelectric property of SiNW arrays.The statistical results showed that the SiNW arrays with the reaction time of 90 s and 150 s in the seed solution have the best photoelectric performance.When the reaction time in seed solution is too short,the SiNW array density and thus the specific surface area will be large,which resulted in serious surface recombination.When the reaction time in seed solution is too long,the SiNW array density will break and lodging.Therefore,the photoelectric property for samples with too short or too long reaction time in the seed solution is poorer than those for samples with the optimal fabrication conditions.This research provides an effective reference for optimizing the fabrication conditions of SiNW arrays for high-performance optoelectronic devices.