Analysis of gallium phosphide nanoindentation with the aid of molecular dynamics simulations

Gallium phosphide (GaP) is a hard-brittle semiconductor with desirable properties for near-infrared (NIR) and mid-wavelength infrared (MWIR) optics. Despite this, its industrial use remains limited to LEDs. One way to broaden GaP’s applications is by better understanding its plastic deformation behaviour, crucial for improving machining of GaP lenses. In this context, this paper aims at exploring GaP phase transformations during nanoindentation thorugh Molecular Dynamics (MD) simulations and experiments. Using an available force field, a simulation was performed with a 3.5 nm radius repulsive sphere as an indenter moving at 0.4Å/ps into a GaP substrate. Post-processes used coordination number analysis, hydrostatic pressure, and structural identification algorithms. Experiments used a Berkovich indenter with 5mN and 10mN maximum loads, alongside Atomic Force Microscopy (AFM) measurements. Results from simulation shown pile-up formation, pop-in events, dislocations, and the β-tin structure formation (metallization). Experimentally, 10 nm pile-ups were observed, confirming plastic deformation, and hardness varied with loading rate. The simulation findings aligned with experimental data, particularly in estimating hardness values (9.6 GPa and 12.5 GPa respectively). These results shown GaP plasticity and metallization, validating the chosen force field for studying GaP nanoindentation, and potentially for simulating its cutting mechanisms, which should include metallization.