  Zn in GaN forms an efficient radiative center and acts as a deep acceptor
which can make the crystal insulating. Four different Zn-related centers have
been by now identified, leading to light emission in the range between 1.8 eV
and 2.9 eV. We present a first-principles investigation total energy and
electronic structure calculations for Ga-substitutional and hetero-antisite
N-substitutional Zn in wurtzite GaN, using ultrasoft pseudopotentials and a
conjugate-gradient total energy minimization method. Our results permit the
identification of the blue-light emission center as the substitutional
acceptor, while contrary to a common belief the Zn_N heteroantisite has a very
high formation energy and donor behavior, which seems to exclude it as the
origin of the other centers.
