Optimization of n nc-Si:H and a-SiNx:H layers for their application in nc-Si:H TFT |
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Authors: | Tamila Anutgan Mustafa AnutganIsmail Atilgan Bayram Katircioglu |
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Affiliation: | a Department of Physics, Karabuk University, 78050 Karabuk, Turkey b Department of Physics, Middle East Technical University, 06531 Ankara, Turkey |
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Abstract: | The n-type doped silicon thin films were deposited by plasma enhanced chemical vapor deposition (PECVD) technique at high and low H2 dilutions. High H2 dilution resulted in n+ nanocrystalline silicon films (n+ nc-Si:H) with the lower resistivity (ρ ∼0.7 Ω cm) compared to that of doped amorphous silicon films (∼900 Ω cm) grown at low H2 dilution. The change of the lateral ρ of n+ nc-Si:H films was measured by reducing the film thickness via gradual reactive ion etching. The ρ values rise below a critical film thickness, indicating the presence of the disordered and less conductive incubation layer. The 45 nm thick n+ nc-Si:H films were deposited in the nc-Si:H thin film transistor (TFT) at different RF powers, and the optimum RF power for the lowest resistivity (∼92 Ω cm) and incubation layer was determined. On the other hand, several deposition parameters of PECVD grown amorphous silicon nitride (a-SiNx:H) thin films were changed to optimize low leakage current through the TFT gate dielectric. Increase in NH3/SiH4 gas flow ratio was found to improve the insulating property and to change the optical/structural characteristics of a-SiNx:H film. Having lowest leakage currents, two a-SiNx:H films with NH3/SiH4 ratios of ∼19 and ∼28 were used as a gate dielectric in nc-Si:H TFTs. The TFT deposited with the NH3/SiH4∼19 ratio showed higher device performance than the TFT containing a-SiNx:H with the NH3/SiH4∼28 ratio. This was correlated with the N−H/Si−H bond concentration ratio optimized for the TFT application. |
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Keywords: | n+ Nanocrystalline silicon Thin film transistor RF power Amorphous silicon nitride NH3/SiH4 gas flow ratio |
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