We have studied different surface treatments for the back side of the channel of bottom gate a-Si:H TFTs. Two sets of different (i) channel layer thicknesses, and (ii) gate dielectric silicon nitride compositions were studied. The back channel Si-surfaces were either (i) exposed to products from an N2O plasma, or (ii) plasma oxidized. Comparisons of these back channel passivation methods indicated that relative to oxidized surfaces, the plasma N2O process, which created an oxynitride surface layer, (i) reduced the threshold voltage, (ii) decreased the sub-threshold slope (defined as V/decade of current increase) of the I-V characteristic, and (iii) increased the transconductance, or equivalently, the effective channel mobility.
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This work is supported by NREL and ONR.
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He, S.S., Stephens, D.J. & Lucovsky, G. Back-Channel Surface Modifications for a-Si:H Thin Film Transistors, TFTs, by Exposure to Plasma Excited N2O. MRS Online Proceedings Library 318, 489–494 (1993). https://doi.org/10.1557/PROC-318-489