Morphology, interfacial electronic structure, and optical properties of oligothiophenes grown on ZnSe(100) by molecular beam deposition

We report on the growth of two types of oligothiophenes, alpha-sexithiophene and a substituted terthiophene, on c(2x2) reconstructed ZnSe(100) surfaces by molecular beam deposition. The study is aimed at a deeper understanding of the structural and electronic properties of organic/inorganic semiconductor interfaces. The structure and morphology of the organic adlayer from submonolayer up to several monolayer coverage were characterized by atomic force microscopy. The interfacial electronic structure and the optical properties were investigated by photoemission and photoluminescence spectroscopy, respectively. The results reveal that the organic adlayer is bonded by van der Waals forces to the ZnSe(100) c(2x2) surface. The electronic structure and the optical properties of the two materials forming the interface remain unperturbed, indicating that surface passivation, which is found indispensable when using other covalent inorganic semiconductor surfaces such as GaAs as substrates for organic thin films, is not required to allow for an ordered growth of the organic adlayer on ZnSe(100).