CARRIER INJECTION INTO SEMICONDUCTING POLYMERS - FOWLER-NORDHEIM FIELD-EMISSION TUNNELING

Carrier injection at the metal/semiconductor interface has been analyzed using diode structures fabricated from semiconducting polymers. The current versus voltage (I-V) curves are field dependent (rather than voltage dependent) suggesting a tunneling mechanism. Using single-carrier devices, either 'hole-only' or 'electron-only', we analyze the I-V curves in terms of Fowler-Nordheim tunneling. The results indicate that these polymer sandwich structures are tunnel diodes. Using this analysis, we find that polyaniline, in its conducting form, is more electronegative than indium/tin oxide (ITO) and provides a smaller barrier to hole injection into poly(2-methoxy-5-(2'-ethyl-hexoxy)-1,4-phenylene-vinylene), MEH-PPV. As a result, bilayer transparent electrodes (ITO/PANI) lead to significant improvement in light-emitting diode performance.