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

• The β-tin phase of GaP was isolated beneath the indenter tip during the simulation. • Pile-ups were observed in the simulation having a preferential direction to grow. • Pop-ins from experimental data were divided into short and long pop-ins. • Loading rate influences hardness and the contact pressures of the longer pop–ins. • Pile-ups were observed in the indents in the absence of cracks. 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 0.4 Å/ps into a GaP substrate. Post-processes used coordination number analysis, hydrostatic pressure, and structural identification algorithms. Experiments used a Berkovich indenter with 5 mN and 10 mN 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.