Origin of channel/dielectric interfacial trap states modification by ultraviolet irradiation on organic thin-film transistors

Abstract

The authors report on the origin of channel/dielectric interfacial states modified by ultraviolet (UV) irradiation on pentacene thin-film transistors (TFTs) with poly-4-vinylphenol and AlOx double gate dielectric. Exposing the device to 352 nm UV irradiation on caused a positive threshold voltage (Vth) shift, and then photo-excited charge-collection spectroscopy (PECCS) was applied to the device to clarify the changes of the interfacial density of states (DOS) as the origin of Vth modification. From the PECCS measurement, it could be probed that there was a drastic decrease in DOS for deep traps at ∼1.31 and ∼1.38 eV above the highest occupied molecular orbital level of pentacene. Consequently, we can conclude that the positive shift of Vth for pentacene-TFT by UV irradiation results from the elimination of deep hole traps, which could be introduced by the interfacial dipoles at the channel/dielectric interface.