Multiscale investigation of mechanical anisotropy and machining-induced damage mechanisms in single-crystal gallium Nitride: Insights from first-principles calculations and molecular dynamics simulations

XN Wen and JY Deng and ZL Bai and JC Geng and H Wei and HB Liu and F Qiu and F Hui, MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING, 199, 109837 (2025).

DOI: 10.1016/j.mssp.2025.109837

As a critical epitaxial substrate material for chip manufacturing, single-crystal gallium nitride (GaN), a thirdgeneration semiconductor, requires a damage-free, atomically smooth surface for its applications. However, the challenges of high machining difficulty and elevated processing costs have consistently hindered the achievement of such atomically smooth surfaces. This study systematically investigates the relationship between mechanical anisotropy and machining performance of GaN by integrating first-principles calculations and molecular dynamics (MD) simulations, with a focus on three primary crystallographic planes (a-, c-, and m-planes) and three indenter types (Berkovich, Spherical, and Vickers indenters). First-principles calculations reveal significant mechanical anisotropy in GaN: Young's modulus and hardness exhibit strong crystallographic orientation dependence, while shear modulus demonstrates quasi-isotropic behaviour. MD simulations of nanoindentation elucidate the dynamic responses of different planes under mechanical loading, including stress distribution, dislocation nucleation/propagation, and atomic displacement vectors. The results show that a- and m-planes exhibit similar stress distribution and dislocation propagation patterns, whereas the c-plane demonstrates a smaller subsurface damage zone and lower dislocation density, indicating its reduced susceptibility to subsurface damage during machining. Temperature, kinetic energy, and potential energy analyses further highlight the influence of indenter type on localized thermal effects, with Spherical indenters exhibiting superior elastic recovery during c-plane processing. Coordination number and phase transformation analyses confirm that the c-plane under Berkovich indentation effectively suppresses defect generation and maintains a shallower damage layer (similar to 70-90 angstrom), underscoring its advantages in ultra-precision machining. These findings provide theoretical insights for optimizing the machining processes of GaN wafers.

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