Competitive Growth Mechanism Of Different Types Of Crystals During GaN Crystallization

Gallium nitride(GaN)is ?—? semiconductor material with wide band gap compound.It has many advantages,such as high thermal conductivity,stable chemical property and strong anti-radiation ability.It is expected to be widely used in microwave power devices,blue light-emitting devices and 5G communication devices.In this paper,the competitive growth of wurtzite and zinc-blende structure in GaN system during rapid cooling process was studied by molecular dynamics simulation(MD).Firstly,the influence of different cooling rates and pressures on the crystallization ability of the system was explored.Secondly,the growth of wurtzite structure and zinc-blende structure under different cooling rates and pressures was explored.Finally,the mutual transformation between different crystal structures was analyzed,and the transformation path between different structures was explored.At different cooling rates(1×10¹¹K/s,1×10¹²K/s and 1×10¹³K/s),the simulation results were analyzed by radial distribution function(RDF),average atomic energy and Voronoi cluster index.The study found that under cooling rates of 1×10¹¹K/s and 1×10¹²K/s,a crystal structure dominated by <4 0 0 0> polyhedrons was formed in the GaN system;An amorphous structure was formed at a cooling rate of 10¹³K/s.The lower the cooling rate,the better the growth of zinc-blende structure,and the larger its proportion in the system;the structure of wurtzite also has similar changes,but the proportion of zinc-blende structure is higher than that of wurtzite structure at lower cooling rate.An amorphous structure was formed in the system at the 1×10¹³K/s cooling rate,and the proportion of wurtzite and zinc-blende structure is relatively small.Under the conditions of different pressures(0Gp,5Gp,10 Gp,30Gp),the simulation results were analyzed through radial distribution function,average atomic energy and visual analysis technology.It was found that the system was formed crystal structure when the pressure was 0Gp,5Gp,10 Gp and 30 Gp.As the pressure increases,the crystal structure in the system first increased and then decreased,and reached the maximum at 5Gp.When the pressure was higher than 5Gp,the crystal structure continued decrease,the order degree of the GaN system also decreases.With the continuous increase of pressure,the proportion of zinc-blende structure in the system and the largest zinc-blende structure both increased first and then decreased,and reached the maximum value at 7Gp,the structure of zinc-blende in the system increases with the pressure increased and become more tightly and orderly;Both the proportion of wurtzite structure in the system and the largest wurtzite structure continue to decrease with the increase of pressure.Under the action of pressure,the wurtzite structure is also tighter and more orderly.In order to study the mutual transformation between different crystal structures and the path of structural transformation,we used visualization technology to analyze the simulation results.The study found that during the rapid cooling process,the phase transition path of the microstructure in the GaN system was not unique.The wurtzite structure and zinc-blende structure can be transformed into each other,and the lower the cooling rate,the more obvious the phase transition between the two structures.In the process of mutual transformation between wurtzite structure and zinc-blende structure,the first and second neighbor atoms temporarily exist as structural transition atoms.The phase transition between the two crystal structures needs to satisfy the system temperature higher than 2000 K.The phase transition of the two different crystal structures was realized by the periodic slip of the crystal lattice,and the length of the slip is ?3?/3.Since the covalent bond density between the crystal faces of the crystal lattice is different,the slip direction can also be [1 0 0],[1 1 0] and other directions of the XOY plane with a lower covalent bond density,influenced by the crystal structure type distribution and other reasons.