We present a photoemission study of the electronic properties of an interface between the organic semiconductor; 3, 4, 9,10 perylenetetracarboxylic dianhydride (PTCDA) and n-type GaAs(100). We examine the evolution of the interface electron distribution as a function of PTCDA overlayer thickness. The highest occupied molecular orbital level of PTCDA is measured at 0.7±0.1 eV below the GaAs valence band maximum. The PTCDA ionization potential is measured at 6.4±0.15 eV. The discrepancy between the band alignment deduced from photoemission and transport measurement suggests that interface states or polarization effects play a role in determining the transport properties of the organic-inorganic heterojunction diodes.

A study of the formation of an interface between the archetype organic semiconductor, 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA), and GaAs(100) is presented. We examine the growth of thin (few monolayers) and thick (up to 3000 Å) organic layers are examined at room and low temperature, and conclude that bonding across the PTCDA/GaAs interface is stronger than the PTCDA van der Waals intermolecular bond. Although the molecular stacking distance of 3.21 Å is clearly seen in x-ray diffraction, the films are polycrystalline, and no interface molecular ordering is detected. The interface electronic structure and the energy band lineup are studied with photoelectron spectroscopy. The highest occupied molecular orbital in PTCDA is found at 0.7 eV below the top of the GaAs valence band, in agreement with a vacuum level alignment a this interface.