High polysilicon TFT field effect mobility reached thanks to slight phosphorus content in the active layer

The paper deals with the effect of slightly phosphorus atoms introduced during deposition of polysilicon films. Polysilicon films are used as an active layer in thin film transistors (TFTs) fabricated on glass substrates at a maximum temperature of 600 °C.Three phosphorus atoms contents, determined by the value of the phosphine to silane ratio: Γ (3.7 × 10− 7, 8 × 10− 7, 26 × 10− 6), are used to optimize the active layer quality. The in-situ doped layers induce a better stability of the electrical characteristics, a higher mobility and lower value of the threshold voltage for the slightly doped active layers [M. Zaghdoudi, M.M. Abdelkrim, M. Fathallah, T. Mohammed-Brahim and F. Le-Bihan Control of the weak phosphorus doping in polysilicon, Materials Science and Forum, Vols. 480–481 (2005) pp.305.]. The present work shows that the effect of slightly phosphorus content improves the quality of oxide/polysilicon interface and decreases the defects density. Degradation of electrical properties is shown to originate from the creation of defect at the channel-interface oxide and in the grain boundaries. The effect of temperature change on the electrical properties was studied and the behaviour was also analyzed.