Mechanical and Machining Properties of InP Wafers: A Combined Study via Theoretical Calculations, Molecular Dynamics...

Single-crystal indium phosphide (InP) wafers, characterized by atomic-scale surface roughness and minimal subsurface damage, are ideal substrates for high-frequency microwave devices, optoelectronic applications (e.g., solar cells and large-scale integrated circuits), and military systems (e.g., guidance, navigation, and satellites). However, challenges arise during ultraprecision machining due to InP's low hardness, brittle-to-ductile transition behavior, and mechanical anisotropy across crystallographic planes, which compromise surface integrity and degrade material performance, epitaxial film quality, and device reliability. This study employs a multiscale approach integrating theoretical calculations, molecular dynamics (MD) simulations, and nanoindentation experiments to systematically explore the deformation mechanisms and damage evolution in InP wafers along the (100), (110), and (111) planes. Theoretical calculations indicate that the (100) plane exhibits moderate anisotropy with periodic symmetry, the (110) plane shows marked anisotropy, and the (111) plane demonstrates quasi-isotropic mechanical behavior. MD simulations reveal subsurface damage depths of 2×, 7×, and 2.5× the indentation depth for the (100), (110), and (111) planes, respectively. The difficulty in obtaining a high-quality, damage-free surface follows this order: (110) > (111) > (100). Additionally, more dislocations are observed in the (100) plane during the indentation process, with very few present in the (111) plane. Upon unloading, dislocations in the (100) plane decrease, while those in the (111) plane increase sharply. Nanoindentation experiments show that the (100) plane along the [01̅0] and [001̅] crystal directions has the lowest fracture toughness (0.31 and 0.374 MPa·m^1/2), with cracks preferentially propagating along the ⟨100⟩ crystal direction family. By inhibiting crack propagation along ⟨100⟩, damage-free machining on the (100) plane is achievable. This work establishes a relationship between crystallographic anisotropy and machining-induced damage in InP wafers, offering theoretical guidance for optimizing ultraprecision machining processes in InP-based device fabrication.