Energy barriers from ferromagnetic contacts to semiconducting polymers

The authors present built-in potential, current-voltage (I-V), and electroluminescence-voltage (EL-V) measurements of as deposited and plasma oxidized ferromagnetic metal/polymer/Ca light-emitting diode structures. They specifically considered Co, Fe, Ni, and a Ni:Fe alloy in contact with poly[2-methoxy,5-(2(')-ethyl-hexyloxy)-1,4-phenylene vinylene] and poly (9,9-dioctylfluorene). Built-in potential measurements showed that the oxidized films had hole Schottky barriers corresponding closely to the pristine metal work function, whereas the as deposited films had barriers 0.65-0.95 eV larger. Plasma oxidation improved hole injection, consistent with the reduced energy barriers, as demonstrated by I-V and EL-V measurements. These results enable design of spin based organic electronic devices. (c) 2007 American Institute of Physics.