Electronic transport in amorphous CdAs₂

D.c. conductivity σ and thermopower S measurements have been carried out on a-CdAs₂ as a function of temperature. The a.c. conductivity σ(ω) has also been investigated between 5-500 KHz and at temperatures down to 90 K. Below 320 K conduction is due to holes hopping between localized states in the band tail. At higher temperatures transport in extended states takes over. However, in order to explain a more rapid decrease of the thermopower than that expected for unipolar transport by holes, an electron contribution has to be taken into account. Below about 180 K the a.c. conductivity obeys the law σ(ω) ∞ ω^S with s ≅ 1.1. This indicates that variable-range hopping in localized states at the Fermi level is the dominating process between 90-180 K.