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

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 AlO_xdouble gate dielectric. Exposing the device to 352 nm UV irradiation on caused a positive threshold voltage (V_th) 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 V_thmodification. 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 V_thfor 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.