Amorphous oxide semiconductors are promising for their use in thin-film transistor (TFT) devices due to their high carrier mobility and large-area uniformity. However, their commercialization is limited by the negative gate bias stress experienced under continuous light illumination. Here, we report an approach to improve the negative bias illumination stress (NBIS) stability of amorphous oxide semiconductors TFTs by using lanthanide-doped indium oxide semiconductors as the channel layer. The effect of different lanthanide dopants on performances of solution-processed Ln:In 2 O 3 TFTs are investigated. All lanthanides exhibit strong suppression of oxygen vacancy, which shift the V on from −13.5 V of pure In 2 O 3 TFT to −1~1 V of Ln:In 2 O 3 TFTs (except Ce). However, only Pr:In 2 O 3 and Tb:In 2 O 3 TFTs exhibit much better NBIS stability with same Δ V on of −3.0 V, compared to much higher Δ V on of −7.9~−15.6 V for other Ln:In 2 O 3 TFTs. Our comprehensive study reveals that praseodymium and terbium act as a blue light down-conversion medium with low charge transfer transition energy for lowing photosensitivity of oxide semiconductors.
The applications of thin-film transistors (TFTs) based on oxide semiconductors are limited due to instability under negative bias illumination stress (NBIS). Here, we report TFTs based on solution-processed In2O3semiconductors doped with Pr4+or Tb4+, which can effectively improve the NBIS stability. The differences between the Pr4+-doped In2O3(Pr:In2O3) and Tb4+-doped In2O3(Tb:In2O3) are investigated in detail. The undoped In2O3TFTs with different annealing temperatures exhibit poor NBIS stability with serious turn-on voltage shift (ΔVon). After doping with Pr4+/Tb4+, the TFTs show greatly improved NBIS stability. As the annealing temperature increases, the Pr:In2O3TFTs have poorer NBIS stability (ΔVonare −3.2, −4.8, and −4.8 V for annealing temperature of 300, 350, and 400 °C, respectively), while the Tb:In2O3TFTs have better NBIS stability (ΔVonare −3.6, −3.6, and −1.2 V for annealing temperature of 300, 350, and 400 ℃, respectively). Further studies reveal that the improvement of the NBIS stability of the Pr4+/Tb4+:In2O3TFTs is attributed to the absorption of the illuminated light by the Pr/Tb4fn—O2p6to Pr/Tb 4fn+1—O2p5charge transfer (CT) transition and downconversion of the light to nonradiative transition with a relatively short relaxation time compared to the ionization process of the oxygen vacancies. The higher NBIS stability of Tb:In2O3TFTs compared to Pr:In2O3TFTs is ascribed to the smaller ion radius of Tb4+and the lower energy level of Tb 4f7with a isotropic half-full configuration compared to that of Pr 4f1, which would make it easier for the Tb4+to absorb the visible light than the Pr4+.
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