The local structure of As[sbnd]Se[sbnd]S chalcogenide glasses studied by neutron diffraction and Raman scattering

Abstract

The local structures of amorphous As40Se60, As40Se30S30, As33.3Se33.3S33.4 chalcogenide glass semiconductors have been studied by neutron diffraction and Raman scattering methods. The neutron diffraction data-sets were modeled by Reverse Monte Carlo (RMC) simulation technique. Several first and second neighbour distances, coordination numbers and bond-angle distributions have been calculated. It is established that the first neighbour atomic distances are overlapping at three characteristic distances, namely the SS and SeS are centered at 2.2(5)Å, while the AsS and SeSe are centered at 2.35Å, the AsAs and AsSe are centered at 2.4(5)Å. The average coordination numbers in As40Se60 (ZAs=3.03; ZSe=2.02) and As40Se30S30 (ZAs=3; ZSe=2.07; ZS=2) compositions were determined and found to be consistent with, “8-N” rule. The slight deviations from this rule is discovered in case of As33.3Se33.3S33.4 (ZAs=3.07; ZSe=2.09; ZS=1.95) composition. The main role in the formation of medium range order belongs to SeSe bonds. It has been identified that the replacement of Se with S atoms causes a slight change in coordination numbers. The similarity of θSeAsSe and θAsSeAs bond angle distributions suggest that S atoms have a similar role in the structure formation as Se atoms. The RMC models highlighted a glassy network built-up from AsSe3 trigonal bipyramids, in all binary and ternary samples.