Stoichiometry and surface reconstruction of epitaxial CuInSe2(112) films

CuInSe2(112) films were grown on GaAs(111)A substrates by molecular beam epitaxy. The resulting surface stoichiometry was deduced by consideration of results from various surface analytic techniques. The obtainable Cu/In stoichiometry range in XPS was 0.4–1.2, where 1.2 marks the onset of Cu2 − xSe phase segregation at the surface and 0.4 corresponds to the copper-depleted surface with ordered defect compound (ODC) composition. For the stoichiometric CuInSe2(112) surface, a c(4 × 2) reconstruction of the zinc blende surface periodicity is observed in the LEED pattern, with three rotational domains present on the flat GaAs(111) substrate. With the use of stepped (111) substrates, domain formation could be suppressed. By comparison of the LEED data and concentration depth profiles from angle-resolved XPS, two types of surface reconstructions could be distinguished. According to surface energy calculations in the literature, these correspond to surfaces stabilized by either CuIn or 2VCu defects. The surface of copper-poor CuIn3Se5 shows no reconstruction of the zinc blende order.