EXCITON CONFINEMENT IN ORGANIC MULTIPLE-QUANTUM-WELL STRUCTURES

High-quality organic multiple quantum well (MQW) structures based on t ris(8-hydroxyquinoline) aluminium (Alq(3)) and 2-(4-biphenylyl)-5-(4-t ert-butyl-phenyl) (PBD) have been prepared by use of a multisource-typ e high-vacuum organic molecular beam deposition system. Small-angle x- ray diffraction measurements indicate that the MQW structures have a v ery uniform layered structure throughout the entire stack. Both optica l absorption and photoluminescence (PL) measurements reveal the eviden ce for exciton confinement in the Alq(3)/PBD MQW structures. The thick ness-dependent blue shift of the PL peak observed upon decreasing the well width is attributed to the change of exciton energy as a result o f quantum confinement. Theoretical calculations have been performed an d the results agree with the experimental results. Light-emitting diod es (LEDs) based on the Alq(3)/PBD MQW structure with greater efficienc y, a narrower electroluminescence spectrum and less of a blue shift th an the single heterostructure LEDs have also been fabricated.