IMPURITY EFFECTS IN CHALCOGENIDE AMORPHOUS SEMICONDUCTORS BY LOW-TEMPERATURE DIFFUSION OF METAL IONS.

Cu and Cd ions were found to diffuse into a-As//2Se//1Te//2 films below the glass transition temperature. Cu-doped samples exhibited p-type conduction, while Cd-doped samples exhibited n-type conduction, and the conductivity of the sample films doped with these metal ions increased with the impurity content. Activation-type conduction was dominant over a wide temperature range even in heavily-doped samples, and the band-gap shrinkage due to doping with impurities was small compared with the decrease in the activation energy for conduction. The strong impurity effects are thus considered to be caused not by an increase in the portion of hopping conduction through defect states but by a shift in the Fermi level. A model explaining the formation of donor and acceptor centers in Cu-doped and Cd-doped samples is presented.