Carrier transport in amorphous silicon-based thin-film transistors studied by spin-dependent transport

Carrier transport processes in hydrogenated amorphous silicon-based thin-film transistors (a-Si:H TFT's) are investigated by spin-dependent transport (SDT). Spin-dependent photoconductivity (SDPC) signals arising from less than 10(6) spins in a small transistor are detected with an adequate signal-to-noise ratio. SDPC measurements reveal two different limiting steps for the light-induced leakage current in TFT's depending on the gate voltage: bulk recombination in undoped a-Si:H and recombination near the source junction. Also, the leakage current mechanism under high source-drain fields is identified by SDT measurements in the dark as electron hopping via defect states located at the interface between undoped a-Si:H and the passivation silicon nitride layer. Both silicon dangling bonds and nitrogen dangling bonds seem to be involved in the electron hopping process. At temperatures below 100 K, spin-dependent hopping of electrons in conduction-band tail states is observed. The change of the dominant transport path from extended state conduction to variable range hopping conduction with decreasing temperature is confirmed by SDT measurements.