Study On The Controllable Fabrication Of ?-FeSi₂ Nanostructures And Its Luminescence Properties

?-FeSi₂ is a new type of semiconductor material with a band gap of 0.81-0.87 eV and a corresponding luminescence wavelength of 1.5?m.Because the fabrication process of?-FeSi₂has good compatibility with the Si-based technology,?-FeSi₂ is very suitable for application in Infrared light-emitting devices for optical communications.Compared with thin-film?-FeSi₂ and heterojunction?-FeSi₂/Si,?-FeSi₂ nanostructures with different shapes(rods,islands,and small spheres)has the potential to exhibit better luminescence properties.The luminescent intensity on the nanometer scale not only depends on the shape and size of the nanostructure,but its crystalline state,phase state and crystal quality are also the main factors that restrict its luminescent performance.However,the conventional fabrication methods are still difficult to achieve precise control of the shape and crystalline phase of the?-FeSi₂ nanostructures.Therefore,accurately controlling the shape and size of?-FeSi₂nanostructures,suppressing the generation of other phases,and improving the crystalline quality of?-FeSi₂ are key issues that need to be solved to achieve high-efficiency photoluminescence of?-FeSi₂ nanostructures at room temperature.Focusing on?-FeSi₂ that can achieve infrared luminescence,a simple magnetron sputtering method is used to deposit FeSi₂ film on amorphous SiO₂,and?-FeSi₂nanostructures are formed by three different heat treatment methods(Thermal Annealing,Rapid Thermal Annealing and H₂ Plasma Treatment).The crystalline phase and surface morphology of the formed?-FeSi₂ nanostructures were characterized by using X-ray Diffractometer(XRD),Scanning Electron Microscope(SEM)and other methods.In this paper,the influence of heat treatment process parameters on the shape and crystalline phase of?-FeSi₂ nanostructures is analyzed and discussed,and its room temperature luminescence characteristics are further studied.The physical mechanism of the formation of?-FeSi₂nanostructures and crystalline phases on the nanometer scale were discussed,and the room temperature luminescence characteristics were further studied.Research indicates:(1)The problem of stoichiometric ratio mismatch in thin films is effectively solved by growing a thin amorphous SiO₂ layer on the Si substrate effectively suppresses the mutual diffusion of Fe element and Si element from the substrate.This approach can avoid the formation of other impurity phases,and form pure phase?-FeSi₂nanostructures.(2)FeSi₂ thin films were fabricated by using magnetron sputtering at different sputtering power(30?150 W)and different sputtering time(1.5?30 min).The morphology,thickness and other characteristics of the deposited FeSi₂ film have a greater impact on the shape and crystal phase of the nanostructure?-FeSi₂ formed by subsequent heat treatment.When the sputtering power is 30?50 W and the sputtering time is 10?30 min,it is more conducive to the formation of?-FeSi₂ Nano-dot structure.(3)The FeSi₂ film was post-processed for different time(10?720 min)by conventional thermal annealing,and it was found that the annealing time and temperature have a greater impact on the formed nanostructures.When the annealing time is 10-30 min,the surface grains will agglomerate and cause local protrusions,but the morphology changes are not obvious;When the annealing time is increased to more than 60 min,the spherical grains on the surface gradually aggregate,and the continuous film aggregates and separates to form small massive islands and further grow to become continuous.The crystallinity of the film after annealing is poor,and other miscellaneous phases are formed.It can be seen that the effect of forming?-FeSi₂ nanostructures by conventional thermal annealing treatment is not very effective.(4)The FeSi₂ films fabricated at different sputtering conditions(Power:30 W,Time:1.5?30 min)are thermally annealed(600?950?)by using rapid thermal annealing.The sputtering time and annealing temperature have a great influence on the nanostructures formed.After rapid thermal annealing of FeSi₂ films with different sputtering times at 950?,the surface grain size increases with the increase of sputtering time,and changes from dots to islands.For FeSi₂ films rapid thermal annealed at different temperatures,a single-phase?-FeSi₂ crystalline phase begins to form at 800?,and when the temperature rises to 850?,small island-like grains are formed on the surface.A single-phase small island?-FeSi₂nanostructures can be formed by rapid thermal annealing,and the PL signal at 1.6?m can be observed at room temperature.(5)The heat release effect of H₂ plasma during the recombination process on the film surface are used to locally heat the film surface to form?-FeSi₂ nanostructures.The FeSi₂film(Sputtering Power:30 W,Time:30 min)was treated with different pressures(0.5?1.5Torr)by the H₂ plasma.The H₂ plasma pressure has a great influence on the size of the formed nanostructures.A spherical?-FeSi₂ nanostructure with different sizes distributions can be formed by H₂ plasma treatment,but its crystallinity is poor,and other impurity phases are generated simultaneously,which is closely related to the H₂ plasma treatment process.Because the high-speed particles in the hydrogen plasma generated by the CCP coupling will etch the surface of the film,resulting in the mismatch of the chemical ratio between Fe-Si and the change of grain height and density,as well as the further reaction between Fe-Si.(6)Pre-deposited an ultra-thin Ag layer,and then prepare nanograins of different shapes and sizes by thermal annealing and H₂ plasma treatment.The ultra-thin Ag layer can promote the faster transformation of amorphous FeSi₂ into?-FeSi and?-FeSi₂ mixed phase.The shape and size of?-FeSi₂nanostructure can be controlled by changing the thickness of the Ag layer.In summary,the?-FeSi₂ nanostructures was fabricated by thermal annealing,rapid thermal annealing,H₂ plasma treatment and pre-deposited ultra-thin Ag layer.The small island?-FeSi₂ nanostructures formed by the rapid thermal annealing exhibits unique PL luminescence at room temperature.This research lays a solid foundation for the preparation of?-FeSi₂ nanostructures with controllable shape and crystal phase,expands the methods and processes for the controllable preparation of?-FeSi₂ nanostructures,and provides experimental support for the development of new optoelectronic devices.