Inorganic semiconductor multiple quantum well structures have been a subject of intense study due to their interesting electronic and optical properties which have many promising applications in optoelectronic device technology.In the past decade

following organic semiconductor research

organic semiconductor multiple quantum well structures have been studied by many research groups.Organic crystals are bonded by relatively weak Van der Waals forces.Therefore

the potential exists for fabrication of high quality heterostructures or multilayer structures without inducing large strains using a variety of organic crystalline materials.In this paper

quantum well structures consisting of alternating layers of organic 4

4’-N

N’-dicarbazole-biphenyl (CBP)/8-hydroxyqunoline aluminum (Alq

3

) have been grown by organic molecular beam deposition.Energy level

structure and optical property of the quantum well are determined by cyclic voltammetry

optical absorption

small angle X-ray diffraction and photoluminescence.Cyclic voltammetry and optical absorption results indicate that the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) levels of CBPare-2.74 and-6.00 eV

and those of Alq

3

are-3.10 and-5.80 eV

respectively.It is clear that the CBP/Alq

3

multilayers possess the energy lineup which can be classified as Type-Ⅰ

where the HOMO of Alq

3

is higher than that of CBPand the LUMO of Alq

3

is lower than that of CBP.The quantum well structure exhibits clear high-order Bragg peaks by small angle X-ray diffraction measurements and this indicates the structure of the quantum well is precisely ordered.The PLexperimental results indicate that the structures of CBP/Alq

3

possessing a Type-Ⅰ energy lineup

exhibit the rapid energy transfer from CBP to Alq

3

and lead to the increase of Alq

3

PLintensity.The PLpeaks of Alq

3

shift to higher energy as the Alq

3

layer thickness is decreased.The origin of the peak emission energy blue shift is discussed with the theoretical and experimental results published in the literatures.