Effect of the density of collision cascades on implantation damage in GaN

Damage accumulation in wurtzite GaN films bombarded with 0.5 MeV Bi₁ and 1 MeV Bi₂ ions (the so-called molecular effect) is studied by Rutherford backscattering/channeling spectrometry. Results show that an increase in the density of collision cascades dramatically enhances the level of implantation-produced lattice disorder in GaN. This effect is attributed to (i) an increase in the defect clustering efficiency with increasing density of ion-beam-generated point defects and/or (ii) to collective nonlinear energy spike processes. Such a strong influence of the density of collision cascades is important to take into account for a correct estimation of implantation-produced lattice disorder in GaN.