Effects of Cu alloying on the structural and electronic properties in amorphousCux(As0.4S0.6)1−

Abstract

The composition dependence of the atomic structure and bonding properties in amorphous Cu x ͑As 0.4 S 0.6 ͒ 1−x ͑x = 0.0, 0.024, and 0.11͒ is investigated by means of ab initio molecular-dynamics simulations. Our results show that Cu atoms introduced tend to bind with S atoms with a well defined bond length. The pair distribution functions obtained reveal that As-As correlation is influenced appreciably by the addition of Cu atoms, whereas changes in S-S correlation are relatively small. It is found that the unoccupied electronic states near the bottom of the conduction band have a nonbonding character and have large amplitudes of their wave functions around the As atoms that are coordinated with two S atoms as well as around Cu atoms. We suggest that these electronic states will play an important role in the suppression of photodarkening in Cu-doped arsenic chalcogenides.