From loop emission to dislocation jamming: Contrasting nanoindentation-induced plasticity in wurtzite ZnO and GaN

Dislocations govern plastic deformation in crystalline solids and also strongly influence the functional performance of semiconductor crystals. Nanoindentation provides a localized and controllable route for introducing dislocations, even in materials that are brittle at the bulk scale, and can generate nontrivial dislocation configurations under appropriate conditions. Here, we examine the dislocation structures generated by nanoindentation in two wurtzite semiconductors, GaN and ZnO, indented on the (0001) 45° off plane. In GaN, dislocations exhibit strong mutual interactions and jamming, leading to an entangled three-dimensional tube-like morphology. In contrast, ZnO predominantly develops a one-dimensional array of dislocation loops. The emission of multiple discrete dislocation loops produces multiple pop-ins in the load-depth curve of ZnO, whereas only a single pop-in occurs in GaN. Dislocations in ZnO extend much deeper into the crystal than those in GaN, indicating less effective local strain accommodation than in GaN, where dislocation entanglement and jamming enhance the back stress. In addition, 1 / 3 < 11 2 ¯ 3 > pyramidal dislocations are activated at relatively small normalized indentation depths in GaN, whereas in ZnO they appear only at larger normalized depths in the simulations and are not retained in post-mortem experimental observations. These results demonstrate that the shared wurtzite structure alone does not determine the indentation-induced dislocation architecture; rather, material-specific lattice resistance, dislocation interactions, and back-stress evolution control the plastic response and the resulting opportunities for dislocation engineering.