Study On Rapid Solidification Process Of Liquid GaAs Nanoparticles

Gallium arsenide?GaAs?materials have high electron mobility and photoelectric conversion efficiency,and are widely used in optoelectronic devices and microelectronic devices.Nanomaterials are at the forefront of today's materials science research,and GaAs nanoparticles are one of the most valuable nano-semiconductors.Due to the microstructure of the material determines its macroscopic properties,the study of the microstructure of GaAs nanoparticles is particularly critical.However,the evolution process of material microstructure is difficult to be captured in experiments but can be traced by theoretical simulation.Theoretical research can make people have a deeper understanding of scientific experiments,and has certain guiding significance for the production and application of GaAs nanoparticles.In this paper,the rapid solidification process of ideal sphalerite structure GaAs nanoparticles at the heating rate of 1×10¹¹ K/s and its relaxtion process,the rapid heating process of GaAs nanoparticles with disordered structure at the heating rate of 1×10¹³ K/s and its relaxtion process,the solidification process of liquid GaAs nanoparticles at different cooling rates have been simulated using molecular dynamics simulation.The Radial distribution function,average atomic potential energy,coordination number analysis,angular distribution,dihedral angle distribution and visualization are used for microstructure analysis.The results are as follows.?1?When the temperature is higher than 520 K,since the saturated vapor pressure of As is much larger than that of Ga,As can be easily separated from the system in forms of As vapor while Ga is stable,which separates a part of As atoms from GaAs nanoparticles.Due to the surface effect,GaAs nanoparticles can achieve solid-liquid phase change by obtaining less energy from the outside than GaAs crystals.?2?The melting point of ideal sphalerite structure GaAs nanoparticles is 1100 K.Due to the different potential energies of the atoms at different positions of the particles,the amount of energy provided by the external regions for melting is different,and the GaAs nanoparticles exhibit a staged and regional melting phenomenon.During the melting process,the polarization distortion of the partial sphalerite structure of GaAs nanoparticles leads to the formation of wurtzite structure in the system,and the surface profile changes rapidly toward the spherical shape.?3?The liquid-solid phase transition temperature Tc of the liquid GaAs nanoparticles is 970 K,which is lower than that of the GaAs crystal of 1460 K.When the temperature is higher than T_c,the system is in a liquid random spherical structure.When the temperature is lower than T_c,Ga and As atoms rapidly nucleate and crystallize,forming a six-ring honeycomb structure with the outermost surface as a defect,and the secondary outer surface is two-dimensional close-packed structure with defects filled by Ga,As with CN=4,5,6 and its neighboring atoms,and eventually get higher structural densities.?4?As the temperature drops from 970K to 920K,the crystallization of liquid GaAs nanoparticles is not obvious when the cooling rate R is greater than or equal to 2×10¹00 K/s.However,it is obvious when cooling rate R is less than 2×10¹00 K/s.At 200 K,atoms with coordination number of 3 or 4 are mainly distributed on the surface of the particles,forming a defective six-ring honeycomb structure.Further analysis shows that the six-ring structure is the?111?surface of the defective sphalerite structure.The higher the cooling rate,the higher the order degree of the system after crystallization,the more the number of atoms with coordination number of 3 or 4,the more the number of six rings on the surface,the less the number of atoms with coordination number of 3,the more the GaAs nanoparticles tend to be spherical.