X-ray photoelectron spectroscopy studies of n-type bismuth-modified amorphous thin films of Ge20Se80 and As2Se3

The charged state of bismuth atoms in n-type bismuth-modified amorphous thin films of Ge20Se80 and As2Se3 has been studied by x-ray photoelectron spectroscopy. On the basis of the observed chemical shift, it is concluded that the Bi atoms in the modified films are positively charged. The charged Bi atoms perturb the equilibrium between positively and negatively charged defect centers, thereby causing a shift of the Fermi level towards the conduction band. The observed enhanced electrical conductivity and the conductivity conversion from p to n type in the modified films is the result of such a Fermi level shift.