FRACTAL FORMATION IN A-SI-HAGA-SI-H FILMS AFTER ANNEALING

The crystallization behavior of a-Si:H/Ag/a-Si:H sandwich films has been studied in detail. Fractals of Si caused by metal enhanced crystallization appear after annealing at 350-600-degrees-C. The fractal dimension decreases (the Si fractals become more open) with the increasing annealing temperature. The number density of fractals increases at 350-450-degrees-C and turns to decrease at 500-600-degrees-C. The average fractal size increases from 350 to 550-degrees-C and shows a decreasing tendency at 600-degrees-C. The formation of fractals can be explained by a random successive nucleation and growth model. The x-ray energy dispersive spectroscopy (EDS) microanalysis indicates that although there is lateral interdiffusion of Ag and Si atoms, the thicknesses of the fractal region and the matrix remain nearly the same. At the same time, EDS shows that there are also Ag aggregates extending out of the films. It is suggested that besides the preferred nucleation at the Ag/Si interface the break of Si-H bonds may also stimulate the crystallization of a-Si:H so that the crystallization temperature of an a-Si:H/Ag system is much lower than that of an a-Si/Ag system.