Lattice location of Ca in GaN using ion channeling

The Ca dopant site in the GaN lattice has been investigated using ion chann eling. Metal organic chemical vapor deposition grown GaN on c-plane sapphir e substrates implanted with Ca-40 at a dose of 1 x 10(15) cm(-2) with posti mplant annealing were studied. Our results indicate that more than 80% of C a are near Ga sites even in as-implanted samples, however, they are displac ed by similar to 0.2 Angstrom from the Ga sites and that the Ca goes to the exact Ga sites after annealing at 1100 degrees C while the annealing did n ot change the apparent fraction of substitutional Ca. We suggest that the d isplaced Ca in the as-implanted sample are electrically compensated due to formation of complex defects with donor-like point defects and that Ca-Ga b ecomes electrically active when these complex defects are broken and the po int defects diffuse away with annealing at 1100 degrees C. (C) 1999 America n Institute of Physics. [S0003-6951(99)05016-0].