ELECTRICAL AND OPTICAL STUDIES IN SOME BI DOPED AMORPHOUS-CHALCOGENIDE THIN-FILMS

A study of the electrical and optical properties of amorphous Ge20M75B i5 (M = S, Se or Te) thin films has been carried out. For Ge20Te75Bi5, the values of the pre-exponential factor sigma(o) (sigma = sigma(o) e xp - DELTAE/kT) are smaller and the thermal activation energy DELTAE i s less than half the optical gap. A disturbance in the balance of C1- and C+ charged centers shifting the Fermi level from mid-gap is propos ed. For Ge20S75Bi5 and Ge20Se75Bi5, incorporation of 5 at.% Bi seems t o have no drastic effect on the electronic structure as the Fermi leve l is still pinned at mid-pp.