Atomistic simulation of damage production by atomic and molecular ion irradiation in GaN

We have studied defect production during single atomic and molecular ion irradiation having an energy of 50 eV/amu in GaN by molecular dynamics simulations. Enhanced defect recombination is found in GaN, in accordance with experimental data. Instantaneous damage shows non-linearity with different molecular projectile and increasing molecular mass. Number of instantaneous defects produced by the PF4 molecule close to target surface is four times higher than that for PF2 molecule and three times higher than that calculated as a sum of the damage produced by one P and four F ion irradiation (P+4×F). We explain this non-linearity by energy spike due to molecular effects. On the contrary, final damage created by PF4 and PF2 shows a linear pattern when the sample cools down. Total numbers of defects produced by Ag and PF4 having similar atomic masses are comparable. However, defect-depth distributions produced by these species are quite different, also indicating molecular effect.