Study of a-Si crystallization dependence on power and irradiation time using a CW green laser

ABSTRACT An advantage of laser crystallization over conventional heating methods is its ability to limit rapid heating and cooling to thin surface layers. Laser energy is used to heat the a- Si thin film to change th e microstructure to poly-Si. Thin film samples of a-Si were irradiated with a CW-green laser source. Laser irradiated spots were produced by using different laser powers and irradiation times. These parameters are identified as key variables in the crystallization process. The power threshold for crystallization is reduced as the irradiation time is increased. When this threshold is reached the crystalline fraction increases lineally with power for each irradiation time. The experimental results are analysed w ith the aid of a numerical thermal mode l and the presence of two crystallization mechanisms are observed: one du e to melting and the other due to solid phase transformation. Keywords: amorphous silicon, polycrystalline silicon, cr ystallization, annealing, laser, simulation