Orientation-dependent deformation and subsurface damage mechanisms of sulfur-doped InP wafers under indentation loading

Sulfur-doped indium phosphide (InP) is an important III–V compound semiconductor used in high-speed optoelectronic and photonic devices. Its brittle and anisotropic response makes it susceptible to orientation-dependent deformation, cracking and subsurface damage during precision machining. Molecular dynamics simulations, nanoindentation experiments, focused ion beam (FIB) cross-sectioning and cross-sectional transmission electron microscopy (XTEM) were combined to investigate indentation-induced deformation and damage in sulfur-doped InP wafers with (100), (110) and (111) orientations. Crystallographic orientation strongly affected plasticity initiation, defect evolution and crack propagation. The (100) plane showed early plastic activation, extensive multi-slip activity, dense interconnected dislocation networks and the greatest measured longitudinal crack penetration of 19.50 μm. The (110) plane exhibited more localised deformation and the shallowest penetration depth of 14.03 μm, although interacting transverse cracks produced pronounced surface spalling. The (111) plane showed delayed defect nucleation, the highest hardness and the greatest elastic recovery (24.82%), but developed long radial cracks and a penetration depth of 15.27 μm, together with deeper defect propagation and localised lattice rotation. HRTEM and diffraction analyses further revealed orientation-dependent lattice distortion and localised structural disorder near cracks. When considered together with the pop-in response, dislocation structures, strain localisation and crack morphology, maximum resolved shear stress analysis provided a qualitative crystallographic interpretation of the measured damage-depth ranking of (100) > (111) > (110). These findings show that each orientation has a distinct combination of surface and subsurface damage and provide a mechanistic basis for orientation-aware damage control during precision machining.