Ultrafast Broadband Optical Nonlinearity And Dynamics Of Indium Selenium Nanocomposite Films

Indium Selenide(InSe)nano film is a typical ?-? group two-dimensional semiconductor film material.Because of its high carrier mobility,adjustable band structure and outstanding photoelectric properties,InSe has attracted widespread attention in different scientific fields such as photocatalysis,solar cells,thin film transistors and photovoltaic devices thus becoming a research hotspot in the fields of microelectronics and photoelectric materials.However,due to the inherent defects of amorphous InSe nano film,there are still many difficulties in preparing photoelectronic devices made from single crystal InSe nano film of high quality,high performance and strong stability.Therefore,composite structure design of amorphous InSe nano film and polycrystalline InSe nano film can effectively reduce the internal defects of the crystal as well as enhance the interaction between its electronic energy states and strong coulomb.Showing a series of excellent photophysical properties,they have been widely concerned by researchers.For example,through the interband charges transfer between type II heterojunction structure,metal-doped non-equilibrium carrier injection and the reduction of the polycrystal internal defect mode InSe nonlinear optical properties of nanometer thin film and the carrier dynamics process can be enhanced and regulated.This has great application potential in the fields of broadband,ultrafast microelectronics and nonlinear photonic devices.In view of this,we successfully manufactured amorphous InSe nano film on a sapphire substrate by magnetron sputtering,and revealed the influence of carrier transport properties on its nonlinear optical properties.Afterwards,through the construction of II heterojunction structure,and the production of polycrystalline phase transition by using in-situ annealing heat treatment technology,the internalcarrier-photon interaction and defect states are obtained.Also,the opticalphysical parameters such as nonlinear absorption coefficient,refractive index and carrier relaxation life are determined.It is of great significance for the enhancement,regulation and application of nonlinear optical properties of amorphous InSe nano film.The research work carried out mainly includes the following aspects:(1)By using transient absorption spectroscopy detection method,the two-photon induced carrier dynamics of amorphous InSe/WSe₂heterojunction film excited by 650 nm pump light were systematically studied.The experiment captured the ultrafast free carrier absorption signal(<1 ps)generated by the interband charge transfer.When the peak intensity of the pump light is 114.9 GW/cm²,the amorphous InSe/WSe₂heterojunction film has a reverse saturation absorption(RSA)response covering the entire detection light band(790 nm-1080 nm).At the same time,due to the cooling of electron-phonon scattering in the conduction band and the relaxation of electron radiation,a two-channel carrier relaxation process was produced.According to the experimental results,the double-e exponential function fitting was established to obtain the carrier relaxation lifetime of the amorphous InSe/WSe₂heterojunction film.(2)The optical properties and nonlinear optical properties of amorphous metal doped InSe nano film(Ag:InSe,Al:InSe and Cu:InSe)have been systematically studied by UV-NIR spectrophotometer and femtosecond Z-scan experiments.The experimental results show that the band structure can be regulated by different metal doping and different metal doping concentration,resulting in the change of band gap width(1.52 e V-2.61 e V).Meanwhile,the doping level was formed in the band by the way of non-equilibrium carrier injection,which regulated the absorption and refraction behavior of free carriers,and opened up a new carrier relaxation channel.The experiment quantitatively analyzed the nonlinear optical parameters of three types of amorphous metal-doped InSe nano films,and distinguished different nonlinear optical response mechanisms.(3)The effects of annealing temperatures at 400?,500?,600?and 700?on the nonlinear optical properties and carrier dynamics of polycrystalline InSe nano films were investigated by using femtosecond Z-scan experiment and transient absorption spectroscopy.The results showed that the reduced defective state of the polycrystalline InSe nano film after high temperature annealing and recrystallization directly enhanced the trapped electron effect,resulting in an increase in the nonlinear absorption coefficient from 320 cm/GW to 684 cm/GW.The nonlinear refractive index increased from-1.43×10^-2cm²/GW to-3.16×10^-2cm²/GW.When the annealing temperature is 600?,the carrier relaxation life of the polycrystalline InSe nanofilms is extended to 4.71 ns.The results of this study show how interband charge transfer,intraband non-equilibrium carrier injection and defect reduction affect the nonlinear optical properties and carrier dynamics of amorphous and polycrystalline InSe nano films.It is of significance to the study of the photophysical mechanism of composite structure amorphous and polycrystalline InSe nano films.The experimentally detected optical information,such as nonlinear absorption coefficient,refractive index and carrier relaxation lifetime provides a necessary reference for the development of next-generation nonlinear photonic devices.