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 T-sub from 30 to 180 degrees 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 sigma(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 T-sub between 90 and 120 degrees C exhibit an anomalous T-sub dependence. However, this anomalous T-sub 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 T-sub between 90 and 120 degrees C involves a thermal interconversion between meridional and facial Alq3 isomers. (c) x 2007 American Institute of Physics.