METAL-MEDIATED CRYSTALLIZATION OF AMORPHOUS-SILICON IN SILICON SILVER LAYERED SYSTEMS

We report on the crystallization behaviour of amorphous Si(a-Si) in a-Si/Ag/a-Si trilayer and a-Si/Ag multilayer systems using in situ transmission electron microscopy (TEM) and differential scanning calorimetry. The crystallization temperature of a-Si in these Si/Ag layered systems is 385-415 degrees C, about 200 degrees C lower than that found in pure a-Si, whereas the heat of crystallization is 12 +/- 1 kJ mol(-1), in good agreement with published values. During the reaction, in situ cross-section TEM showed that Ag grains border the a-Si matrix and the crystallized Si(c-Si) grains and that the Ag grains migrate toward the a-Si region, leaving the c-Si phase behind. In situ atomic resolution TEM also revealed that the lattice points of the migrating Ag grains are stationary during this process and that the interface between the c-Si and Ag phases advances by a ledge mechanism. These observations indicated that the Si atoms diffuse through the Ag grains and precipitate onto the c-Si phase, whereas the migration of the Ag grains is caused by the counter self-diffusion of the Ag atoms.