Poster abstract

The effect of aluminium and indium on the formation energies and acceptor levels of magnesium and carbon dopants in GaN have been calculated using a density functional approach. Single aluminium and indium atoms are incorporated into the lattice at a minimal distance from the acceptor species. The formation energies are obtained as a function of the Fermi level position. In the absence of aluminium or indium, magnesium in a charge neutral state is found to have a formation energy of 1.1 eV whereas carbon has a formation energy of 2.6 eV. In the presence of indium, the magnesium formation energy rises to 1.6 eV whereas the addition of aluminium has no effect. For carbon, the presence of aluminium and indium increases the formation energy by 0.4 and 0.3 eV respectively. Furthermore, the calculations predict that the magnesium acceptor level becomes more shallow by the addition of aluminium (from 0.14 to 0.01 eV above the valence band maximum) but is made deeper by indium (from 0.14 to 0.27 eV above the valence band maximum). The carbon acceptor level is found to remain approximately unchanged with aluminium and indium doping. These results are compared to experimental data and the effect of various approximations in the calculations is discussed.