Free-Energy Barrier to Crystallite Nucleation in Solid-Phase Crystallized Poly-Silicon Thin Films

ABSTRACTWe introduce a non-Arrhenius method for measuring free-energy barrier to nucleation, W*, directly from size distribution of crystallites. W* is determined independent of any model for the nucleation barrier and independent of energy barrier to growth. The method is applicable to three-dimensionally growing crystallites, planar crystallites in thin films, and both compact and fractal crystallites. We apply the method to dendritic crystallites obtained by solid-phase crystallization of amorphous Si thin films into which Si+ ions are implanted at various conditions prior to the isothermal annealing. The ion implantation suppresses the nucleation of the crystallites and enhances the crystallite size of the resulting polycrystalline films. The directly measured W* increases as the accelerating energy or the dose of the Si+ ions increases. This result suggests that the observed suppression of the nucleation could not be accounted for simply by the amor-phization of the preexisting crystallites by the ion bombardment.

Fundamental Aspects of High Speed Crystal Growth from the Melt

ABSTRACTAdvances in the study of high speed crystal growth from the melt are reviewed, with special emphasis on the fast melting and solidification of silicon achieved by use of Q-switched laser radiation pulses. Rapid melting of amorphous Si is confirmed to yield a liquid undercooled by several hundred Kelvins and, under suitable conditions, explosive crystal growth processes can occur. The latter involve the self-sustaining propagation of melt bands buried within the initially amorphous material. When the highest quench-rate conditions are established melting of even crystalline Si can yield a final amorphous solid phase. This breakdown in crystal growth is orientation dependent and can give regimes of crystal defect formation when amor-phization does not take place. The processes which characterize this limiting growth behaviour are discussed.