Molecular dynamics simulation of AlN thin films under nanoindentation

A large-scale molecular dynamics (MD) simulation of nanoindentation was performed to study the structural deformation on wurtzite aluminum nitride (B4-AlN). The nanoindentation induced B4-B1 phase-transition, amorphization and dislocation glide in AlN (0001) thin films were found. It shows that the B4-B1 phase-transition path includes two processes: an anti-parallel vertical movement of N and Al atoms along the [0001] axis, followed by horizontal rearrangements of the two types of atoms. Indentation force-depth (P-h) curve shows minor and major pop-in events. Detailed analysis of the results shows that the first three minor load drops in the P-h curve are related to the nucleation of amorphous structure, whereas the subsequent major load drop is related to the dislocation nucleation and expansion. The dislocations in AlN thin film involve perfect dislocations and Shockley partial dislocations, the latter is associated with the formation of intrinsic stacking faults (SFs) type I₂ during the expansion of dislocation loops.