Frank-Turnbull dopant migration may enhance heteroatom diffusivity: Evidence from alkali-doped Cu(In,Ga)Se2

Dopant atoms captured by vacancies are known to obstruct vacancy-mediated atomic diffusion. Yet, there are cases where the opposite behavior has been reported. Here, Na doping in Cu(In,Ga)Se-2 is shown to enhance or impede the interdiffusion of In and Ga, depending on the relative concentration of Na and Cu. The experimental study suggests that doping a host material may enhance heteroatom diffusivities if (i) dopant migration occurs through the Frank-Turnbull mechanism and (ii) there is overlap between the (cationic/anionic) migration sublattices of dopant and heteroatom. Under such conditions a migration catalysis may occur at sufficiently low dopant concentrations, despite the decreased absolute concentration of point defects responsible for heteroatom diffusion. Herein, a mechanism of doping-assisted catalytic migration is presented.