CuAu-type ordering in epitaxial CuInS2 films

Ordering of Cu and In atoms in near-stoichiometric ${\mathrm{CuInS}}_{\mathrm{2}}$ epitaxial films grown on Si (111) by molecular beam epitaxy was studied by transmission electron microscopy. Nonchalcopyrite ordering of the metal atoms in ${\mathrm{CuInS}}_{\mathrm{2}}$ is observed, which is identified as CuAu-type ordering. Sharp spots in electron diffraction patterns reveal the ordered Cu and In atom planes alternating along the [001] direction over a long range. High-resolution electron microscopy confirms this ordering. The CuAu-ordered structure coexists with the chalcopyrite ordered structure, in agreement with theoretical prediction.