STRUCTURES OF GAN(0001)-(2 X 2), -(4 X 4), AND -(5 X 5) SURFACE RECONSTRUCTIONS

Various reconstructions on the GaN(0001) surface are studied by scanning tunneling microscopy (STM). Based on the comparison between the STM observations and first-principles total-energy calculations, we propose an adatom scheme for the basic $2\ifmmode\times\else\texttimes\fi{}2$ and $4\ifmmode\times\else\texttimes\fi{}4$ structures, and others as well. It is revealed that the $5\ifmmode\times\else\texttimes\fi{}5$ phase consists of a linear chain of unevenly displaced Ga adatoms along the $[11\overline{2}0]$ direction due to lattice relaxation.