Structure and charge transport of amorphous Cu-doped Ta2 O5: An ab initio study

In this paper, we present ab initio computer models of Cu-doped amorphous Ta2O5, a promising candidate for conducting bridge random access memory memory devices, and study the structural, electronic, charge transport, and vibrational properties based on plane-wave density-functional methods. We offer an atomistic picture of the process of phase segregation/separation between Cu and Ta2O5 subnetworks. Electronic calculations show that the models are conducting with extended Kohn-Sham orbitals around the Fermi level. In addition to that, we also characterize the electronic transport using the Kubo-Greenwood formula modified suitably to calculate the space-projected conductivity (SPC) [K. Prasai, K. N. Subedi, K. Ferris, P. Biswas, and D. A. Drabold, Phys. Stat. Solidi Rapid Res. Lett. 12, 1800238 (2018)1862-625410.1002/pssr.201800238]. Our SPC calculations show that Cu clusters and undercoordinated Ta adjoining the Cu are the conduction-active parts of the network. We also report information about the dependence of the electrical conductivity on the connectivity of the Cu submatrix. Vibrational calculations for one of the models has been undertaken with an emphasis on localization and animation of representative modes.