A comparative investigation of the damage build-up in GaN and Si during rare earth ion implantation

The medium range implantation of rare earth ions at room temperature in GaN layers leads to the formation of point defect clusters, basal and prismatic stacking faults from the lowest fluence. When a threshold fluence of about 3 × 1015 at/cm2 is reached, a highly disordered ‘nanocrystalline layer' (NL) is observed to form at the surface. This layer is made of a mixture of misoriented nanocrystallites and voids. Beyond this NL, I1, I2 and E basal stacking faults (BSFs) have been identified, as well as in GaN implanted at lower fluences than the threshold. Prismatic stacking faults (PSFs) with Drum atomic configuration connect the I1 BSFs. A similar investigation of the damage in Eu implanted Si shows a completely different behaviour; in this case, from the relatively low fluence 1 × 1014 at/cm2, amorphization starts in patches at the projected range and extends very rapidly towards the surface and the bulk, to form a uniform amorphous layer already at 2 × 1014 at/cm2