'973' program [2012CB619301, 2011CB925600]; '863' program [201144034111, 2014AA032608]; National Natural Science Foundation of China [61106008, 60827004, 90921002]; Natural Science Foundations of Fujian Province [2010 J01343, 2012 J01024]; fundamental research funds for the central universities [2011121042]According to first principles calculations, the solubility of Mg as a substitute for Ga or Al in AlxGa1- xN bulk is limited by large, positive formation enthalpies. In contrast to the bulk case, the formation enthalpies become negative on AIxGa(1 - x)N surface. In addition, the N-rich growth atmosphere can also be favorable to Mg incorporation on the surface by changing the chemical potentials. On the basis of these special features, we proposed a modified surface engineering technique that applies periodical interruptions under an ultimate V/III ratio condition (extremely N-rich), to enhance Mg effective incorporation. By optimizing the interruption conditions (2 nm interruption interval with 2 s interruption time), the enhancement ratio can be up to about 5 in the Al0.99Ga0.01N epilayer
