Electrical transport mechanisms in a-Se95M5 films (M = Ga, Sb, Bi)

The temperature dependence of direct current (dc) conductivity has been reported in thin films of a-Se₉₅M₅ (where M = Ga, Sb, Bi), in the temperature range 219-375 K, in order to identify the conduction mechanism and to observe the doping effect of different metals on amorphous selenium. It is found that the conduction in high temperature range (314-375 K) is due to thermally activated tunneling of charge carriers in the band tails of localized states; and in the low temperature range (219-314 K) conduction takes place through variable range hopping in the localized states near the Fermi level. Current-voltage (I-V) measurements at high electric fields (the field dependence of dc conductivity) have also been carried out for the samples of present system. The analysis of data shows the existence of space charge limited conduction (SCLC) in these glassy alloys. The density of localized states near the Fermi level is calculated for these alloys using dc conductivity (Mott parameters) and SCLC measurements data. The properties have been found to be highly composition dependent.