Atomic understanding of elastic-plastic deformation and crack evolution for single crystal AlN during nanoscratch

Single crystal aluminum nitride (AlN) as a new generation of ultra-wide band gap semiconductor materials is the preferred substrate material for high power, high RF devices, but single crystal AlN is hard and difficult to process. To obtain high-quality substrate requires comprehensive understanding of the material deformation and removal mechanism. In this paper, the molecular dynamics simulation method is used to scratch the AlN on the (0001) plane. Set up multiple sets of scratch depths to study the elastic-plastic deformation, material removal mechanism and crack evolution of single crystal AlN. The simulation results show that with the increase of scratch depth, the single crystal AlN workpiece undergoes elastic deformation to continuous plastic deformation and then to brittle fracture. The deformation mode in the elastic stage is phase-change, from wurtzite-structure to graphite-like (GL) phase. The plastic deformation of single crystal AlN is achieved by dislocations moving on the basal and pyramidal planes, and horizontally extended stacking faults. There is almost no subsurface damage below the stacking faults. When the scratch depth exceeds 6 nm, the material will undergo brittle fracture, and the fracture surface is the cleavage surface {10-10} of single crystal AlN.