Study On The Crystallization Mechanism Of Ge-Sb-Te Superlattice Induced By Pulsed Laser

With the advent of the information age,the capacity and speed of the information storing device is being challenged by the explosion of data and the rapid development of computer technology.Phase change memory?PCM?based on phase-change materials is considered to be an effective solution to meet this need.As a member of the phase-change materials with excellent performance,the Ge-Sb-Te superlattice material?GST-SL?not only improves the speed and power consumption of the PCM,but also has special properties such as topological insulation.Although lots of research on the structure and properties of GST-SL materials was done,there is no unified theory about the phase-transition mechanism of GST-SL.Therefore,a method combined with the experiment and simulation is applied in this paper.Firstly,optimization and properties of GST-SL films were studied by method of laser irradiation.Nextly,the temperature field and kinetics of crystallization were studied by the finite element method and molecular dynamics.Finally,the ultrafast phase-transition mechanism of GST-SL was discussed based on the experiments and simulation results.Firstly,the crystallization of amorphous GST-SL film was induced by picosecond pulsed laser.The GST-SL film with a sublayer thickness of 4 nm was found to have the best crystallization quality and own a lower threshold value than GST according to the optical morphology.In addition,TEM results show that GST-SL has finer crystalline grain than GST when irradiated by picosecond laser pulse,and the structure of GST-SL is more thermally stable.The XRD results showed that the crystallization threshold of GST-SL was 57%lower than that of GST under the nanosecond laser pulse.While the Raman tests showed GeTe₄ structure may be the reason for the better performance of GST-SL.The spectral test results show that the performance of crystalline GST-SL is better than GST.By performing the finite element simulation on the phase-change film irradiated by nanosecond laser irradiation,the curves of Temperature-Time about different laser fluences was obtained.And the temperatures required for crystallization of GST-SL and GST were found to be 700 K and 1200 K,respectively.According to the molecular dynamics simulation about heating process,GST-SL was found to be more stable than the GST structure,and the structure of GST-SL showed an obvious change at 1400 K.It was found that all the three GST-SL models showed the phenomenon that Sb atoms jumped into the Te-Te layer in the amorphization simulations,and the Kooi-mix model exhibited the best stability.In the crystallization simulation at 700 K,both the Kooi-mix and Petrov-mix models enable returned to the initial structure in a few picoseconds,while the crystallization time of the GST model was above 150picoseconds.The stable layer structure of GST-SL is considered to be the reason for the improvement of phase-transition performance,and the behavior of Sb atom jumping into Te-Te layer should be the key to reveal the mechanism of GST-SL.In this paper,the crystallization characteristics of GST-SL are explored by experiments and simulations.The superiority of GST-SL films on the crystallization properties was clarified,and the Sb atom jumping behavior was found in the GST-SL atomic model.This results have guiding significance for exploring the mechanism of phase-change materials and optimization of PCM.