Band alignment at organic-inorganic semiconductor interfaces: α-NPD and CuPc on InP(110)

Photoemission spectroscopy was used to investigate the heterojunctions between InP(110) and two organic semiconductors, N,N′-diphenyl-N,N′-bis(1-naphthyl)-1-1′biphenyl-4,4″diamine (α-NPD) and copper-phthalocyanine (CuPc). Both interfaces exhibit dipole barriers that demonstrate the breakdown of the vacuum level alignment rule, and suggest a displacement of negative charge form the organic to the inorganic semiconductor. The direction of the charge displacement is consistent with the relative electron affinities and ionization energies of the solids.