Cascade mechanism and mechanical property of the dislocation loop formation in GaN twin crystal-induced crystallization

Single-crystal gallium nitride (GaN) is considered as the key to future high-performance light emitters and power devices. Nevertheless, a mixed phase with micro twins often exists in GaN films. The formation of twin strongly affects the electronic properties of GaN-based devices. Based on the molecular dynamics (MD) simulation, we built a perfect nano-twinned cubic GaN (NT-cGaN) and created a solid-liquid (S/L) model in order to study the growth characteristics of the NT-cGaN at different isothermal temperatures. We observed an interesting dislocation loop (DL) in some systems. Our work not only reveals the formation process of DLs and its effect on mechanical properties, but also proposes some parameters to describe the length and shape of DLs. The results indicated that a perfect DL is coalesced by other dislocation lines after some dislocation reactions. A system with a DL is more stable than a system with a dislocation network (DN), and the length and shape of the DLs are closely relative to the isothermal time and temperatures. Moreover, increasing the isothermal time and temperatures can relieve the DL. In general, understanding nucleation and coalescence of dislocations is crucial in decreasing the dislocation density in a GaN crystal.