Surface segregation and interface stability of AlNÕGaN, GaNÕInN, and AlNÕInN ˆ0001‰ epitaxial systems

Surface segregation in wide band-gap nitride alloys was studied using ab initio calculations. In agreement with recent experiments we find that AlxGa12xN $0001% surfaces prefer Ga termination, and GaxIn12xN and AlxIn12xN $0001% prefer In termination. The segregation energy is found to depend critically on the type of surface reconstruction. For cation-terminated reconstructions on both the ~0001! and (0001̄) surfaces the segregation energies are similar and an order of magnitude larger than in the arsenides or Si/Ge systems. The largest segregation energy of about 3.6 eV is found for the AlN/InN surface. In contrast, segregation effects for the N-adatom 232 reconstruction on the ~0001! surfaces are strongly suppressed. At AlN/GaN and GaN/InN interfaces the segregation effects are very weak and should not affect their morphology. Our results suggest the choice of optimal conditions of growth that lead to sharp interfaces and longer lifetimes of carriers in III-nitride heterosystems.