An arithmetical view of point defects in chalcopyrite CuxGaySez grown by molecular beam epitaxy

Cu_xGa_ySe_z{x/y>1} films were grown on [001]-oriented GaAs substrates. Crystallographic structure and lattice parameters were examined using X-ray diffraction. All films had the chalcopyrite-type structure. The a lattice parameter was observed to decrease slightly with increasing molecularity while the c parameter contracted. The points defects probable in a chalcopyrite-type ^I A_x ^IIIB_y ^VIC_z {x:y:x=≠ 1:1:2} crystal of valence stoichiometry are discussed under several simplifying constraints. A combination of two species of point defect is determined to be the minimum requirement to preserve valence stoichiometry; possible combinations of the defect species were then estimated arithmetically. The occupancy of the sublattices was evaluated using the diffraction intensity ratio of the 004 to the 008 reflection.