Microscopic Structure Evolution Of GaN During The Solidification Processes

The gallium nitride(GaN) on behalf of the third generation of semiconductor material with the advantages such as wide band gap, high breakdown field strength, high saturated electron drift velocity and high luminous efficiency etc., has been widely used in modern microelectronics and optoelectronic fields.This paper studies the microscopic structure during the solidification processes of liquid Ga N at different cooling rates and pressures using the molecular dynamics simulation method, combined with the radial distribution function, the bond angle distribution function and the Voronoi polyhedron index methods. At the same time, the evolution of the cluster and the structure are shown by the visualization technology.First, the liquid GaN was rapidly solidified at the cooling rate of 1×1013K/s. The structure of the system was amorphous, with some crystal clusters in the system. And the system was solidified at about 2773 K to 2973 K.(4 0 0 0) polyhedra accounted for about 90% of all the polyhedra in the system, when the temperature was down to 200 K. The basic unit of crystal cluster is a kind of six-ring which is formed by several(4 0 0 0) polyhedra through the analysis of the formation and evolution of clusters by the visualization technology. At 2500 K, the relatively stable crystal clusters were generated in the system.Secondly, the solidification processesses at different cooling rates such as 1×1011K/s、1×1012K/s、1×1013K/s and 1×1014K/s were simulated. The amorphous structures were formed at the cooling rates over 1×1013K/s. The crystal structures were formed at the cooling rates under 1×1012K/s. At the cooling rate of 1×1011K/s, the multi-crystal structure was formed ultimately. Lower the rate is, the short-range and medium-range order increase.Then, the solidification processes were simulated under different pressures. After discussing the simulation results, the conclusions were as follows: At the cooling rate of 1×1012K/s, the amorphous structure was formed when the pressure was 50 GPa. When the pressure is 1GPa、5GPa、10GPa、20GPa and 40 GPa, there are polycrystal structures in the systems. As the pressure increases, the short-range order increases before the pressure increases to 5GPa. With the pressure increases, the spacing between atoms in the system decreases, and the distribution is more uniform and compact. 20 GPa pressure condition is more conducive to the formation of more crystal structures with large volume.