Transmission electron microscopy investigation and first-principles calculation of the phase stability in epitaxial CuInS2 and CuGaSe2 films

Ordering of metal atoms in CuInS2 and CuGaSe2 thin films grown by vapor-phase epitaxy on Si (001) and GaAs (001) substrates were studied using transmission electron microscopy and first-principles total energy calculations. Chalcopyrite and CuAu-like orderings of the metal atoms were observed coexisting in CuInS2 films, while only chalcopyrite ordering was found in CuGaSe2 films. First-principles total energy calculations find that the formation enthalpy difference between chalcopyrite and CuAu-like phases of CuInS2 is very small (2 meV/atom), while it is large for CuGaSe2 (9 meV/atom), indicating that the existence of CuAu-like phase in the nominally chalcopyrite semiconductors is controlled by bulk thermodynamics. (C) 1999 American Institute of Physics. [S0003-6951(99)02118-X].