Reconstruction and Stability of Al_xGa_(1-x)N (0001) and (000) Surfaces with Different Al Compositions: A Density Functional Study

摘要

By means of the plane wave pseudo-potential method based on density functional theory, a thorough investigation was carried out into the equilibrium structures and stability of species-covered (0001) and (000) surfaces of AlxGa1-xN (x = 0, 0.5, 1) crystals with different Al compositions. As revealed by the calculation results, the coordination number of surface atoms, the uniformity of the surface electron distribution and the surface bond strength are crucial influencing factors in the surface stability. It is discovered that the surface structure of AlxGa1-xN (0001) with the same Al component is stable under NH2 and NH3 coverage, whereas the stability is less than satisfactory under N and NH coverage due to the N-N bond formed by surface reconstructions. For the AlxGa1-xN (0001) surfaces with different Al composition, the stability of the relaxed or reconstructed surface with the same covering specie improves with the surface Al composition on the increase, whereas the stability of H-covered AlxGa1-xN (000) surfaces deteriorates as the surface Al composition is on the increase.