Spin-dependent transport in Si thin-film transistors

Defects and carrier transport processes in silicon based thin-film transistors (TFTs) are investigated by spin-dependent transport (SDT). The resonance signal arising from less than 10⁶ defects in the hydrogenated amorphous silicon (a-Si:H) TFT is detected with a sufficient signal-to-noise ratio. The leakage current mechanism in a-Si:H under high source-drain fields is identified by SDT as electron hopping via defect states located at the interface between undoped a-Si:H and the passivation silicon nitride layer. At temperatures below 100K, spin-dependent hopping of electrons in conduction band tail states is observed. The change of the dominant transport path from extended states conduction to variable range hopping with decreasing temperature is confirmed. SDT measurements on polycrystalline silicon (poly-Si) TFTs having silicon nitride and silicon dioxide as the gate dielectric films reveal differences in the defect structure in these devices. The overall results demonstrate that SDT is a powerful method to probe paramagnetic defects and carrier transport in TFTs.