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.