FREQUENCY-DEPENDENT HOPPING CONDUCTIVITY IN A-SI1-YTAY - H-THIN-FILMS

Samples of a-Si1-yTay:K prepared by rf co-sputtering with y ranging fr om 0 to 0.018 have been studied in sandwich configuration between room temperature and 20 K using de and ac techniques. A sample with y = 0. 009 shows variable range hopping in the de and, as expected, the ac re duced conductivity scales well with reduced frequency. Values for the localisation length alpha(-1) obtained from the ac data and from the d c low and high electric field dependencies are in good agreement. Samp les with smaller y values, although they scale well, give unphysical l ocalisation lengths. We account for this data provisionally in terms o f the movement of the Fermi level from mid-gap into states associated with Ta impurities.