Doping of Al_xGa_(1-x)N alloys

摘要

We have investigated the doping of Al_xGa_(1-x)N alloys on the basis of density-functional-pseudopotential calculations for native point defects and dopant impurities. We have identified two possible 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.