The effect of hydrogen dilution on hot-wire thin-film transistors

Bottom-gate thin film transistors (TFT) were fabricated with amorphous and microcrystalline silicon active layers deposited by hot-wire (HW) chemical vapor deposition using different levels of hydrogen dilution. As the hydrogen dilution was increased above 80%, the active layer made a transition from amorphous to microcrystalline. This transition resulted in an increase of the TFT off-current and in an increase of the TFT subthreshold slope. The TFT on-current and the TFT mobility remained at levels comparable to those of the a-Si:H HW TFTs. A comparison is made between TFTs with amorphous and microcrystalline silicon active layers prepared both by rf glow discharge and HW. HW TFTs with an active layer consisting of a thin layer deposited with high hydrogen dilution underlying a thicker amorphous silicon layer are also compared to TFTs with an active layer of the same total active layer thickness consisting only of the high hydrogen dilution film.