| β-FeSi2 is a new type of semiconductor material with a band gap of 0.81-0.87 eV and a corresponding luminescence wavelength of 1.5μm.Because the fabrication process ofβ-FeSi2has good compatibility with the Si-based technology,β-FeSi2 is very suitable for application in Infrared light-emitting devices for optical communications.Compared with thin-filmβ-FeSi2 and heterojunctionβ-FeSi2/Si,β-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 theβ-FeSi2 nanostructures.Therefore,accurately controlling the shape and size ofβ-FeSi2nanostructures,suppressing the generation of other phases,and improving the crystalline quality ofβ-FeSi2 are key issues that need to be solved to achieve high-efficiency photoluminescence ofβ-FeSi2 nanostructures at room temperature.Focusing onβ-FeSi2 that can achieve infrared luminescence,a simple magnetron sputtering method is used to deposit FeSi2 film on amorphous SiO2,andβ-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 formedβ-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 ofβ-FeSi2 nanostructures is analyzed and discussed,and its room temperature luminescence characteristics are further studied.The physical mechanism of the formation ofβ-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 phaseβ-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 nanostructureβ-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 ofβ-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 formingβ-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-phaseβ-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 islandβ-FeSi2nanostructures can be formed by rapid thermal annealing,and the PL signal at 1.6μm 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 formβ-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 sphericalβ-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 intoε-FeSi andβ-FeSi2 mixed phase.The shape and size ofβ-FeSi2nanostructure can be controlled by changing the thickness of the Ag layer.In summary,theβ-FeSi2 nanostructures was fabricated by thermal annealing,rapid thermal annealing,H2 plasma treatment and pre-deposited ultra-thin Ag layer.The small islandβ-FeSi2 nanostructures formed by the rapid thermal annealing exhibits unique PL luminescence at room temperature.This research lays a solid foundation for the preparation ofβ-FeSi2 nanostructures with controllable shape and crystal phase,expands the methods and processes for the controllable preparation ofβ-FeSi2 nanostructures,and provides experimental support for the development of new optoelectronic devices. |
