Planarized ambipolar a-SiGe:H thin-film transistors: Influence of the sequence of fabrication process

•TFTs with SOG as passivation show ambipolar behavior, while SiNx as passivation show unipolar.•Use of SOG or SiNx as passivation apparently may not have influence in the electrical performance.•The device modeling is successfully presented.•Ambipolar phenomena is observed when the device enters to the condition Vds > Vgs.•Transitions of linear to saturation and then to ambipolar phenomena are appreciated.

This work presents the fabrication, characterization and modeling of inverted staggered a-SiGe:H TFTs with planarized gate electrode. Using this structure two different sequences of fabrication are presented, where spin-on glass and silicon nitride are used as passivation layer, respectively. The results show ambipolar and unipolar behavior in the a-SiGe:H TFTs depending on the fabrication sequence. Also, trap density and characteristic energies for the deep localized states in the a-SiGe:H film are obtained. Using these parameters the device modeling is presented.