Electron drift mobility and electroluminescent efficiency of tris(8-hydroxyquinolinolato) aluminum

The electron drift mobility in films of tris(8-hydroxyquinolinolato) alumin um (Alq) deposited at different rates (0.2, 0.4, and 0.7 nm/s) on silicon h as been determined by the time-of-flight technique. It has been found that the drift mobility of electrons in Alq increased by about two orders of mag nitude as the deposition rate decreased from 0.7 to 0.2 nm/s. Further, the electron drift mobility in all Alq samples increased linearly with the squa re root of the applied electric field. Electroluminescent devices with a st ructure of indium tin oxide/alpha-naphthylphenylbiphenyl amine (NPB, 90 nm) /Alq (90 nm)/Mg:Ag were fabricated at different Alq deposition rates. The d evice efficiency was found to increase with increasing electron mobility in Alq. As the electron is the minority carrier in the present device, an inc rease in electron mobility in Alq would thus lead to an increase in device efficiency. (C) 1999 American Institute of Physics. [S0003- 6951(99)02251-2 ].