Crystal Orientation Dependence of Gallium Nitride Wear

We explore how crystallographic order and orientation affect the tribological (friction and wear) performance of gallium nitride (GaN), through experiments and theory. Friction and wear were measured in every direction on the c-plane of GaN through rotary wear experiment. This revealed a strong crystallographic orientation dependence of the sliding properties of GaN; a 60° periodicity of wear rate and friction coefficient was observed. The origin of this periodicity is rooted in the symmetry presented in wurtzite hexagonal lattice structure of III-nitrides. The lowest wear rate was found as 0.6 × 10 −7 mm 3 /Nm with <1 1̄ 1 ¯ 00>, while the wear rate associated with <1 2̄ 2 ¯ 10> had the highest wear rate of 1.4 × 10 −7 mm 3 /Nm. On the contrary, higher friction coefficient can be observed along <1 1̄ 1 ¯ 00> while lower friction coefficient always appeared along <1 2̄ 2 ¯ 10>. We developed a simple molecular statics approach to understand energy barriers associated with sliding and material removal; this calculated change of free energy associated with sliding revealed that there were smaller energy barriers sliding along <1 2̄ 2 ¯ 10> as compared to the <1 1̄ 1 ¯ 00> direction.