Study of High-Quality GaN Growth and Fracture Mechanisms: Insights from Molecular Dynamics

Most materials exhibit polymorphism; i.e., their crystallization capacity and behavior are different in different crystal structures. Thus, understanding the material microstructure, particularly the growth behavior of the crystal nucleus, is essential for generating high-performance gallium nitride (GaN) devices. In this study, the inhomogeneity of spontaneous nucleation in the pure liquid system and the growth patterns of GaN crystal nuclei with different structures were studied by a molecular dynamics method. The formation mechanisms of voids and lamellar structures which also appeared in the experimental preparation were analyzed. The lamellar structure formation was largely attributed to the diversity of the nucleus in the early crystallization stage. Introducing crystal nuclei to reduce the structural complexity is beneficial in improving the crystal quality. The morphology and growth rate of the zinc blende and wurtzite crystal nuclei were in great difference. Compared with defects, the dislocation of the pure liquid system was in continuous increase, while the dislocation of the crystal core system was in three states: rapid increase, slow decrease, and dynamic equilibrium. In the mechanical processing, unlike the fracture mechanism of a pure liquid system dominated by voids, continuous grain boundaries or the dislocation entanglement surface were the main reasons for the fracture of the crystal nuclei system. This study further investigated GaN spontaneous nucleation, growth patterns of the crystal nuclei, defect evolution, and the fracture mechanisms on the atomic scale, contributing to the preparation and mechanical processing of high-quality GaN.