Transition mechanism of the thin Si-films obtained by the CW laser lateral crystallization from the grain-boundary free highly {100} oriented crystal to the twinned {211} crystal depending on the laser power

Abstract

Surface texture transition from grain-boundary free {100} crystals to twinned {211} was observed with increasing laser power in the crystal growth of low-temperature silicon films by the cw laser lateral crystallization of a-Si. This transition is explained by two step mechanism. Firstly a crystal having ∼{110} texture grows in the scan direction (SD) rotated from {100} texture keeping the {100} surface normal texture with increasing laser power, and secondly the deformation twinning occurs in the solidified crystal having an in-plane rotation angle of 35°–45° by the compressive stress due to the Si volume expansion with further increasing power, but the twinning does not occur even with the same compressive stress in the crystal having an in-plane rotation angle of 0°–33.5°, where the rotation angle is defined as the angle between 〈100〉 axis of the grown crystal and the SD. The reason is explained by the Schmidt factor calculated as a function of the in-grain rotation with the laser power, assuming the compressive stress is applied parallel to the isotherms. The maximum value in the Schmidt factors for possible partial dislocation glides was 0.471 for the crystal having {110} texture in the SD and 0.236 for the crystal having {100} texture in the SD. Resolved stress to move the twinning partial dislocation in the crystal having {110} texture in the SD is higher than that in the crystal having {100} texture in the SD by a factor of 2.