Diode Devices Based on Amorphous Selenium Films

Abstract

Different M1/a-Se/M2 sandwich structures have been studied with M1, M2 = Al, Au, Cr, SnO2. Rectifying contacts have only been obtained when an aluminium underlayer was used. It is shown that the aluminium/aluminium oxide layer should be in contact with the amorphous selenium (a-Se) film, since there is no rectifying effect when an insulating poly(N-vinyl carbazole) films is introduced between the aluminium and the selenium. A forming process, either electrical or thermal, is needed to obtain the rectifying effect. a-Se/Al samples before and after thermal forming process, i.e. annealing at 325 K for 1 h, have been studied by XPS depth profile. It is shown that a complex aluminium oxide thin films is present at the interface. There is not only alumina but also aluminium hydroxyl in this layer. Moreover it is shown that after formation there is interdiffusion between Se and Al. At the interface, the selenium plot follows that of the oxygen present at the interface. The OH radicals and/or some oxygen present at the interface can passivate dangling bonds present in the amorphous selenium. Therefore it is assumed that the interaction between the selenium and the aluminium oxides modify the properties of the Al/a-Se contact in such a way that rectifying contacts are obtained.