Study On The Phase Change Mechanism And Optical Properties Adjustment Of Chalcogenide Phase Change Material Induced By Picosecond Laser Irradiation

With the coming of artificial intelligence and big data,high-efficiency computing and high-density data storage are urgently needed.Brain-like computing and multi-level storage are most effective methods so far based on the multi-level optical properties of storage material.As one of typical and widely applicable storage materials,chalcogenide phase change material(GST)shows great potential in these emerging storage and computing application fields.Therefore,how to improve the multi-level optical properties of GST is the important research problem.This research mainly focus on the microstructure and multi-level optical properties of the phase change material from the viewpoint of material design and laser irradiation strategy as follow:1.Typical element doping technology can adjust the properties but also leads to elemental segregation,which therefore is not suitable for high-speed?high-frequency data storage.In this study,stable CuO nano-structure is embeded in chalcogenide phase change material,which changes the micro-structure while persist the unique properties of this material.(CuO-GeTe)and(CuO-GeTe)/(GeTe)composite film are prepared by a "deposition-annealing" method proposed in this study.Experiment and simulation results show that the Cu doping promotes the formation of GeTe local ordered structure.CuO nano-structure formed after the annealing treatment.Then,(CuO-GeTe)/(GeTe)film is prepared by depositing a-GeTe film on CuO-GeTe film.CuO nano-structure embeds into GeTe film and leads to structure gradient benefitting to formation of more intermediate state.7-level reflectance states can be obtained by changing pulse number as input energy unchanged.2.A novel "two-step" laser irradiation strategy of which the first step induces incompleted crystallization and the second step adjusts the micro-structure is proposed.Effect of laser center distance,input energy and two-pulse duration time on micro-structure and optical reflectance are investigated.Results indicates that wider reflectance range can be obtained by changing the input energy and center distance of the second-step laser irradiation.Because a great number of crystal-amorphous interface and local ordered structure are introduced into the a-GST after the first-step laser irradiation leading the phase change mechanism change from single nucleationdominated to nucleation dominated and interface growth dominated mixed mechanism.Basing on the effect of these two mechanism,much more micro-structure and optical states can be obtained,and 10-level optical reflectance states are obtained here.