Damage buildup and removal in Ca-ion-implanted GaN

Ca has been considered as a promising shallow acceptor in GaN and was chosen as a dopant for ion implantation with energy of 180 keV at room temperature. The as-implanted GaN films were characterized by Rutherford backscattering channeling, Raman spectroscopy, high-resolution X-ray:diffraction, and compared with an unimplanted film as well as implanted samples subsequently annealed at 1150 degrees C for 15 s. The quantitative dependence of the damage buildup and its removal on the implantation dose has been determined. Lattice expansion that depends on dose and substrate temperature has been found. An initial amorphous component arises at a dose of 8 x 10(14) cm(-2) Implantation with higher doses causes unrecoverable damage that deteriorates the electrical properties. The possibilities to realize effective p-type doping by ion implantation are discussed.