Interfacial Polarization of Thin Alq, Gaq, and Erq Films on GaN(0001)

This report presents results of research on electronic structure of three interfaces composed of organic layers of Alq, Gaq, or Erq deposited on GaN semiconductor. The formation of the interfaces and their characterization have been performed in situ under ultrahigh vacuum conditions. Thin layers have been vapor-deposited onto p-type GaN(0001) surfaces. Ultraviolet photoelectron spectroscopy (UPS) assisted by X-ray photoelectron spectroscopy (XPS) has been employed to construct the band energy diagrams of the substrate and interfaces. The highest occupied molecular orbitals (HOMOs) are found to be at 1.2, 1.7, and 2.2 eV for Alq, Gaq, and Erq layers, respectively. Alq layer does not change the position of the vacuum level of the substrate, in contrast to the other layers, which lower it by 0.8 eV (Gaq) and 1.3 eV (Erq). Interface dipoles at the phase boundaries are found to be -0.2, -0.9, -1.2 eV, respectively, for Alq, Gaq, Erq layers on GaN(0001) surfaces.