Microstructures Evolution Of Liquid GaAs During Rapid Solidification

GaAs is one of the most widely used synthetic semiconductor materials,because of its high electron mobility and photoelectric conversion efficiency,is widely used in optoelectronic devices and microelectronic devices.The theoretical study of GaAs is mainly focused on the calculation of the first principle and the simulation of molecular dynamics(MD)methods.However,the evolution of GaAs microstructures during rapid solidification has not been reported.In this study,MD simulation was performed for liquid GaAs at the cooling rate 1×1010 K/s.The pair distribution function,the total energy per atom,the bond angle distribution function,the dihedral angle distribution and visualization method were used to analyze the variations of microstructure during the solidification process.Rresults show that the onset temperature of crystallization of GaAs liquid is 1460 K.The random network is the essential structural feature of liquid.The rapidly cooled crystallization is Zinc-blende based polycrystalline structure,with the grain boundary in a eutectic twin structure is a layer of wurtzite structure.At temperature below 520 K,part of As atoms segregate into simple cubic structure As8.A simulation study was performed for the effects of different cooling rates on microstructure during solidification of liquid GaAs by means of molecular dynamics method.Through the pair distribution function,the total energy per atom,the average coordination number,the bond angle distribution function and visualization method were used to analyze the variations of microstructure during the solidification process.results show that part of the As atoms converged and formed ?-As(simple cubic structure As8),when the cooling rate is 1×1010 K/s and 2×1010 K/s,the Ga enrichment area are mainly composed of zinc-blende and wurtzite crystal structure;when the cooling rate is higher than 5×1010 K/s,the Ga enrichment area are mainly formed of amorphous structure to give priority to the structure of Ga-As-Ga and Ga-Ga-Ga ternary ring.The crystallization process under different pressures and cooling rates of liquid GaAs are simulated by molecular dynamics method.The main conclusion are as follows: when the cooling rate is 1×1012 K/s,as the pressure is 0 GPa,1 GPa,5 GPa,10 GPa,15 GPa,20 GPa,25 GPa and 30 GPa during the solidification process,it is found that the pressure has little influence on the micro-structural evolution and formed of amorphous structure at 200 K.when the cooling rate is 1×1010 K/s,the application of pressure on the structure of the system had a tremendous impact.As the pressure increases from 0 GPa to 10 GPa,the system changes from crystalline to amorphous.When the pressure is in 0 GPa to 4 GPa,the system mainly forms tetrahedral crystal structure and the structure are dominated by CN4.As the pressure increases,the crystal content decreases,and the structure number of As8 and Ga4 increases.When the pressure is form 5 GPa to 10 GPa,the structure are dominated by CN5 and CN6,As the pressure increases,the structures number of As8 increases while the Ga4 decreases.