Electronic conduction in Pb-modified amorphous semiconductors Pb20GexSe80-x exhibiting a p-n transition

Abstract

Abstract A.c. conductivity and dielectric relaxation studies of Pb-modified amorphous semiconductors Pb20GexSe80-x, exhibiting a p-n transition at x = 21, are reported as functions of frequency in the range 100Hz-10kHz and as functions of temperature in the range 180–450 K. The a.c. conductivity σa.c(ω) is found to be proportional to ω5. The temperature dependence of σa.c (ω) and of the exponent s for all the compositions examined have been interpreted using the correlated-barrier-hopping model. Analysis of the results reveals that electronic conduction in GeSe3·5 takes place via bipolaron hopping in the whole temperature range of study. The addition of Pb impurities induces new types of defect (C1 1 and Pb2+) which contribute predominantly to single-polaron hopping at higher temperatures. However, the conduction at lower temperatures is of bipolaron type in compositions with or without Pb. Strong temperature and frequency dependences of the loss tangent tan δ at higher temperatures in the compositions containing Pb have been observed. The dielectric constant ε1 and defect density NNp , have minimum values for x = 21. The results have been discussed in the light of the microstructure of these glasses.