Doping of AlxGa1−xN alloys

We have investigated the doping of AlxGa1-xN alloys on the basis of density–functional–pseudopotential calculations for native point defects and dopant impurities. We have identified two possible causes for the experimentally observed decrease in n-type conductivity for x>0.4: (1) in the case of doping with oxygen, a DX transition that converts the shallow donor into a deep level; and (2) compensation by cation vacancies. For p-type doping, the reduction in doping efficiency with increasing x is attributed to (1) compensation by nitrogen vacancies; and (2) an increase in the Mg acceptor ionization energy. We also investigated a number of alternative acceptor impurities; none, however, exhibit overall characteristics superior to those of Mg. Only beryllium emerged as a possible candidate, though it may be hampered by compensation due to Be interstitial donors.