Development of Morphological Instability and Cells During Rapid Solidification of Laser Annealed Silicon Alloys

ABSTRACTThe details of morphological instability occurring during rapid solidification have been studied in In+, Ga+, Sb+, Bi+, Ge+, Fe+ and Cr+ implanted silicon specimens after pulsed laser annealing. The average cell sizes were determined at the onset of instability and in the region of well-developed instability using x-section and plan-view electron microscopy. The total and substitutional solute concentration profiles were determined using Rutherford backscattering and channeling techniques. The formation of cells and the critical solute concentrations associated with instability were studied as a function of velocity of solidification, which was varied by controlling the substrate temperature or the laser parameters. The results on the cell formation and the critical solute concentrations were compared with the predictions of the perturbation theory which took into account the dependence of distribution coefficients on the velocity of solidification. A good agreement between the calculations and the experimental results was obtained. We also examined theoretically the effect of reduction in surface tension due to segregation of impurities on cell sizes and critical solute concentrations associated with instability.