Defects in chalcogenide glasses II. The effect of metallic impurities on the transport properties of a-As2Se3

Abstract

Abstract Hole transit times and d.c. resistivities have been measured for films of amorphous As2Se3 doped with Li, Na, K, Mn, Fe, Ni, Cu, Zn, Ga, In and Tl prepared by co-evaporation onto aluminium substrates held approximately at the glass transition temperature of the undoped material. The field and temperature dependences of the electrical parameters were studied. The hole transit time increases or decreases by as much as two orders of magnitude, depending on dopant and concentration. The d.c. resistivity shows similar behaviour but is not always correlated to the transit time. It is suggested that (1) Mn, Fe, Ni (1017-1018 atoms per cm3) and Cu (> 1019 atoms per cm3) introduce hole traps extending from an intrinsic trapping level located at ∼0 . 6eV above the transport states to the middle of the semi-conductor gap, (2) Ga, In and Zn (1018-1020 atoms per cm3) and high concentrations of alkali metals and Tl (1019-1020 atoms per cm3) lead to additional (neutral) states ∼0 . l eV above the intrinsic tran...