Electron Spin Resonance Observation of Gate-induced Charge Carriers in Organic Field-effect Devices Fabricated on Silicon Substrates

Electron spin resonance (ESR) measurements have been performed on metal–insulator–semiconductor (MIS) diode structures of regioregular poly(3-hexylthiophene), RR-P3HT, fabricated on silicon substrates with SiO 2 layers as gate insulators. The conductivity of substrates was chosen so that it does not significantly lower the quality factor of the ESR cavity. Clear ESR signals due to field-induced polarons have been observed at g -values of around 2.002, consistent with those observed in the MIS devices of RR-P3HT fabricated on Al 2 O 3 gate insulators. Carrier spins tend to saturate above the charge concentration of about 0.3%, suggesting the conversion of polarons with spin 1/2 to spinless bipolarons for higher carrier concentrations. The angular dependence of ESR signals exhibits distinct anisotropy, reflecting the fact that the surface of SiO 2 is flatter than that of Al 2 O 3 . These results demonstrate that ESR can be performed on organic field-effect devices fabricated on silicon substrates.