A molecular dynamics study on indentation response of single crystalline wurtzite GaN

A series of molecular dynamics simulations are carried out to investigate the plastic deformation in wurtzite GaN. Besides the formation of an amorphous zone under the contact region, plastic slips nucleated on the m plane (10-10), c plane (0001), r plane (10-12), and s plane (10-11) are observed in the indentation. Combined with a close analysis of critical stress that induces a specific slip on different crystalline planes, the defect evolution is discussed in detail. Slip systems of [10-1-1](10-12) and 1/3[2-1-1-3](10-11) on the pyramidal planes are not supposed to nucleate easily since higher stress is required to activate them. However, a significant decrease in the shear stress that induces a pyramidal slip could be expected if the slip evolves gradually following a two-step procedure. The gradual slips on both the r plane (10-12) and s plane (10-11) are observed in our indentation simulation; the mechanism is studied by the calculation of generalized stacking fault energy.