Quantitative photon-probe evaluation of trap-containing channel/dielectric interface in organic field effect transistors

We report on photo-excited trap-charge-collection spectroscopy as a direct probe of the traps in organic field-effect transistors (OFETs). Monochromatic photon beams transmitted through the working channels of 5 V operating pentacene-OFETs with 60 nm thick Al2O3 dielectrics liberate interface charges trapped at the matched energy level while the oxide surfaces were prepared with various self-assembled monolayers (SAMs). The density of states (DOS) of traps is directly mapped as a function of the photon energy by tracking the change in the threshold voltage. While conventional electrical stability measurements qualitatively support our trap DOS spectroscopy results, our direct measurement technique provides a powerful tool for quantitative analysis of the nature and density of interfacial traps in field-effect transistor devices.