Ion assisted crystal grain nucleation in a-Si: a low temperature route towards poly-Si formation

The processes of nucleation and growth of crystalline silicon grains in amorphous Si layers irradiated at temperatures between 450 and 530 degrees C with different ion beams have been investigated in details using transmission electron microscopy. The crystal growth kinetics exhibits a behavior similar to that observed during ion-assisted epitaxial crystallization, ie, it increases by increasing the energy deposited into nuclear elastic collisions by the impinging ions, and weakly decreases by increasing the irradiation dose rate. Viceversa, the nucleation rate decreases by increasing the energy deposition of the ion and strongly decreases by increasing the dose rate. Although the experiments span over a very wide range of process conditions, i.e, temperatures and ion beam parameters, we demonstrate that a single description, based on the classical nucleation theory, can explain all the experimental results, allowing an accurate evaluation of all the kinetics parameters.