Isotropic TFT Characteristics in the {100}-Oriented Grain-Boundary-Free Laser-Crystallized Si Thin Films

Isotropic TFT characteristics are realized in the {100}-oriented grain-boundary-free 60 nm thick Si film obtained by the continuous-wave laser lateral crystallization, where the grain- and sub-boundaries are defined as the crystallographic boundaries having misfit angles of theta > 15 degrees and theta < 15 degrees, respectively. Sub-boundaries are observed in the film parallel to the scan directions; the misfit angles were 5-10 degrees and the sub-boundary density was 0.02956 mu m(-1). Sub-grains, joined by the sub-boundaries, have widths of 8 similar to 69 mu m. The cumulative distributions of mobility, threshold voltage, and subthreshold swing agree well between the parallel and perpendicular TFTs in the film, where parallel or perpendicular means the source-to-drain directions to the laser scan direction. The maximum mobilities of the parallel and perpendicular TFTs are 695 and 663 cm(2)/Vs, respectively. The trap-state density N-T in the sub-boundaries estimated from the product of the bond efficiency eta and the dangling bond density decreases by two decades from those of the grain boundaries. A new carrier transport model of the current flow across the sub-boundary is proposed instead of the thermionic emission model for the grain boundaries.

Automated summary

Isotropic TFT characteristics are achieved in a {100}-oriented grain-boundary-free 60 nm thick Si film obtained by continuous-wave laser lateral crystallization. The film contains both grain boundaries and sub-boundaries, with misfit angles of theta > 15 degrees and theta < 15 degrees, respectively. The mobility, threshold voltage, and subthreshold swing in the parallel and perpendicular TFTs exhibit similar behavior, with maximum mobilities of 695 and 663 cm(2)/Vs, respectively. The trap-state density in the sub-boundaries is significantly lower than that in the grain boundaries, and a new carrier transport model is proposed for current flow across the sub-boundary.