Analysis of the activation energy of the subthreshold current in laser- and solid-phase-crystallized polycrystalline silicon thin-film transistors

Analysis of the thermal and gate-voltage dependences of the current in the subthreshold region is performed on both low-temperature laser-crystallized and solid-phase-crystallized polycrystalline silicon (polysilicon) thin-film transistors (TFTs). Temperature measurements are made at first in order to extract the variations of the activation energy EA of the drain current with the gate voltage. The plot of the subthreshold current versus the measured activation energy leads to an apparent activation energy EA/n, where the n factor is extracted from the slope of this plot. The n factor is close to 1 for laser-crystallized polysilicon TFTs while it is rather close to 2 for solid-phase-crystallized ones. These two values can be attributed to a different defect distribution in the two differently crystallized TFTs polysilicon active layers.