Effects of isomeric transformation on characteristics of Alq3 amorphous layers prepared by vacuum deposition at various substrate temperatures

Abstract

Organic tris(8-hydroxyquinoline)aluminum (Alq3) amorphous layers are prepared by vacuum deposition at various substrate temperatures Tsub from 30 to 180 °C. The surface morphology and electrical characteristics of these as-deposited layers are studied by atomic force microscopy and current-density versus electric-field (J-E) curves. The temperature dependence of the dark electrical conductivity σ(T) determined from J-E curves is also examined. These experimental results reveal that the surface and electrical properties of Alq3 amorphous layers deposited at Tsub between 90 and 120 °C exhibit an anomalous Tsub dependence. However, this anomalous Tsub dependence is not observed from infrared absorption measurements, and therefore is not the result of chemical degradation. The observed behavior is explained in terms of the property that the vacuum deposition of Alq3 with Tsub between 90 and 120 °C involves a thermal interconversion between meridional and facial Alq3 isomers.