Molecular Dynamics Simulation Study Of The Directional Induced Growth Of GaN Twin Structure

Gallium nitride is the most representative new material in the third generation semiconductors,and its devices have superior performance such as high frequency,high power,high voltage resistance,high temperature resistance,irradiation resistance.It is the core material for the development of independent innovation,transformation and upgrading of strategic industries,such as new generation mobile communication,national defense industry and new energy.At present,the third-generation semiconductor industry has become one of the focuses of the world’s scientific and technological competition.It is the highest demand in the market to prepare the high quality GaN crystals,and the most common methods for preparing GaN crystals are metal organic chemical vapor deposition,hydride vapor-phase epitaxy,and ammonothermal growth,but none of them can avoid the various defects during the preparation process.The main reasons for these defects are the lattice mismatch between the substrate and the epitaxial layer and the large differences of thermal expansion coefficient.Among them,twin defects have a great influence on the crystal quality,and its presence has a great impact on the optoelectronic performance of GaNbased devices.Due to the limitations of current experiments,it is challenging and difficult to study the structure of nano-twinned GaN through experimental observation.Therefore,the simulation method of molecular dynamics simulations was used to study the nanotwinned GaN.Firstly,the diversity of twin crystal structures in GaN crystal was investigated,and categorized the twin crystal structure in GaN according to the stacking method of zincblende and wurtzite structures,it was shown that the energy difference between the two structures is small,which leads to the competitive growth of these two structures,then described the evolution of nano-twinned GaN.Secondly,the solidliquid model of nano-twinned GaN and liquid GaN were constructed,multiple temperatures were set up to induce the directional growth of liquid GaN by nanotwinned GaN,the structure of the twins is stable during the induced growth and the growth rate is strongly influenced by the temperature,zincblende is prone to stacking faults on the(111)crystal plane,and calculated stacking fault energy of zincblende,it indicates that this structure is very unstable on the(111)crystal plane.Finally,a special dislocation(dislocation loop)was found in the process of nano-twinned GaN induced directional crystallization,which is obtained from the reaction of other dislocation lines,and proposed several parameters to analyze length of dislocation loop and shape of dislocation loop,a mechanical analysis of the system with and without dislocation loop was carried out,which showed that the system with dislocation loop would be subjected to more stress than the system without dislocation loop.In order to avoid twin defects,it is necessary to look at the nature of twin defects and investigate the mechanism of its formation,which not only provides an effective reference value for experiments,but also provides a lot of insights for more scholars to understand the study of nano-twinned GaN structures.