Direct evidence and atomic-scale mechanisms of reduced dislocation mobility in ZnS under illumination

Photo-plasticity in semiconductors, wherein their mechanical properties such as strength, hardness, toughness, and ductility are influenced by light, has been reported for several decades. Although such phenomena have drawn significant attention to the manufacturability of deformable semiconductor devices, their underlying mechanisms are not well understood due to the lack of direct evidence. Here we provide experimental observation and atomic insights into the reduced mobility of dislocations in zinc sulfide (ZnS), as a model material, under light. Using photo-nanoindentation and transmission electron microscopy, we observe that dislocations glide shorter distances under light than in darkness, and there are no apparent deformation twins in both conditions. By atomic-scale simulations, we demonstrate that the decreased dislocation mobility is attributed to the increased Peierls stress and enhanced stress fields around dislocation cores due to photoexcitation. This study improves the understanding of photo-plastic effects in inorganic semiconductors, offering opportunities for modulating their mechanical and related functional properties using light.