Mécanismes de conduction en liaison avec les conditions de préparation de couches minces de fluorure de magnésium

The electrical properties of evaporated magnesium fluoride thin films are studied in relation to the conditions of preparation. Results concerning the d.c. and a.c. conduction are given for two series of films. The first series of layers, obtained under “normal” conditions, give the same resistivity as that obtained in previous studies: from 300° to 500°K the conduction is of the Poole-Frenkel type. For the second series of layers obtained under the best conditions of preparation, particularly after refluoration of the powder before sublimation, we have observed an increase of resistivity by a factor of 10². In this case, the conductivity through metal-MgF₂-metal structures is attributed to a “hopping” process for temperatures below 400°K and to the Poole-Frenkel mechanism from 400° to 450°K, whereas above 450°K it presents ionic characteristics. The use of different analysis techniques has allowed an identification of the impurities probably responsible for these conduction mechanisms.