N. Franco

Amorphization of GaN by ion implantation

Abstract The ion-beam-induced amorphization of GaN was studied by using 180 keV Ar+ and Ca+ implantation at −150°C and room temperature, respectively. The structure of the GaN films before and after implantation was characterized by Rutherford backscattering/channeling and X-ray diffraction. Lattice expansion due to ion implantation was found, and excessive lattice expansion results in local collapse of the GaN lattice into amorphous clusters. Accumulation of these amorphous zones should be the mechanism of amorphization. The critical energy deposited into nuclear processes is determined to be 90 eV/atom, or 8×10 21 keV / cm 3 , above which amorphization and below which dynamical crystallization dominates. This high value indicates that GaN is extremely resistant to amorphization compared to other semiconductors.

Enhanced dynamic annealing and optical activation of Eu implanted a-plane GaN

The implantation damage build-up and optical activation of a-plane and c-plane GaN epitaxial films were compared upon 300 keV Eu implantation at room temperature. The implantation defects cause an expansion of the lattice normal to the surface, i.e. along the a-direction in a-plane and along the c-direction in c-plane GaN. The defect profile is bimodal with a pronounced surface damage peak and a second damage peak deeper in the bulk of the samples in both cases. For both surface orientations, the bulk damage saturates for high fluences. Interestingly, the saturation level for a-plane GaN is nearly three times lower than that for c-plane material suggesting very efficient dynamic annealing and strong resistance to radiation. a-plane GaN also shows superior damage recovery during post-implant annealing compared to c-plane GaN. For the lowest fluence, damage in a-plane GaN was fully removed and strong Eu-related red luminescence is observed. Although some residual damage remained after annealing for higher fluences as well as in all c-plane samples, optical activation was achieved in all samples revealing the red emission lines due to the ^5Do -> ^7F_2transition in the Eu_3+ ion. The presented results demonstrate a great promise for the use of ion beam processing for a-plane GaN based electronic devices as well as for the development of radiation tolerant electronics.