CONDUCTIVITY OF THIN POLYCRYSTALLINE
OF FeSe2 SYNTHESIZED BY VARIOUS SELENIZATION PROCESSES
T. Abachi1*, J. C. Bernède2, A. Khelil3, N. Hamdadou3
1 Ecole Normale Supérieure E.N.S 16000 Kouba Algérie
Received: 23 February 2008; revised version accepted: 21 October 2008
The thin layers of FeSe2 were synthesized by selenization of a thin layer of iron under selenium pressure. Two methods of selenization were used and led to two types of layers: For the first type (I-FeSe2), after selenization during half an hour at 723 K, the layers were annealed under selenium pressure during two hours at773 K. For the second type (II-FeSe2), the thin layers were directly annealed under selenium pressure during two hours at 773 K. The two types of layers crystallized in the the orthorhombic structure. The size of the grains of the second type (500nm) is larger than that of the first type (100nm). The measurement of the variations of electric conductivity versus of the reciprocal temperature shows that the two film families have different behaviors. For the first type one observes a continuous decrease of conductivity with the reciprocal of the temperature. Conductivity is limited by the grain boundaries, the model of Werner well explains the behavior of this type of structure in high and low temperatures. For the second type of structures have observes two distinct domains of conductivity; for the domain of the high temperatures as conductivity is close to that of the monocrystals and than the grains are “large” one can propose here that conductivity is limited by the crystals. In this case the energy activation measured imposes that one supposes the presence of states traps not very deep due to defects in the forbidden band. As for conductivity at the low temperatures, it is the tunnel effect which controls it.
Keywords: FeSe2 thin films; Selenization; Conductivity; Grain boundary.