  Inorganic semiconductor materials are integral to various modern
technologies, yet their brittleness and limited deformability/processability
pose a significant challenge in the development of flexible, wearable, and
miniaturized electronics. The recent discovery of room-temperature plasticity
in a few inorganic semiconductors offers a promising pathway to address this
challenge, but the deformation mechanisms of these materials remain unclear.
Here, we investigate the deformation of InSe, a two-dimensional (2D) van der
Waals (vdW) semiconductor with substantial plasticity. By developing a
machine-learned deep potential, we perform atomistic simulations that capture
the deformation features of hexagonal InSe upon out-of-plane compression.
Surprisingly, we discover that InSe plastifies through a so-far unrecognized
martensitic phase transformation; that is, the layered hexagonal structure is
converted to a tetragonal lattice with specific orientation relationship. This
observation is corroborated by high-resolution experimental observations and
theory. It suggests a change of paradigm, where the design of new
plastically-deformable inorganic semiconductors should focus on compositions
and structures that favor phase transformations rather than traditional
dislocation slip.
