Nonequilibrium model of laser-induced phase change processes in amorphous silicon thin films

Abstract

A mathematical model of nonequilibrium phase change processes in amorphous silicon induced by pulsed lasers, which includes explosive crystallization, melting, evaporation, and crystallization from the solid/liquid interface and takes into account the thermophysical properties of polycrystalline silicon in dependence on the grain size, is formulated in the paper. The computational implementation of the model is used to simulate phase changes in a typical case of XeCl excimer laser irradiation of 50 nm to 8 m thick amorphous silicon layers deposited on the quartz substrate, where characteristic thermal and optical effects accompanying the irradiation process are demonstrated. The experimental verification of the model is discussed, and a comparison of simulated data with experimental measurements of various groups is performed. The model is shown to achieve agreement with experimental data in a variety of experimental situations. It can also be employed to provide estimated values of thermophysical and optical parameters of polycrystalline silicon in dependence on the grain size.

Phase field modeling of excimer laser crystallization of thin silicon films on amorphous substrates

“…͑2͒ The present PFM only considered the coupled relation of the interface and heat transfer, while many other physical phenomena, such as explosive crystallization, heat radiation from the surface, and nucleation phenomena, were not included. 12,13,15 Indeed, most of the physical phenomena can be integrated into the PFM, and a set of best-fitted parameters can be obtained after some computational trials. For the present model, as explained in the previous analysis, we have verified that it is possible to simulate reasonably well the melting and solidification processes by using our PFM.…”

“…For the simulation of laser induced melting and solidification of materials, many nonequilibrium models ͑i.e., where the interface temperature is far from the melting point, and materials may exist highly supercooling or superheating͒ [10][11][12][13][14][15] have been proposed. Simulations of nucleation 12,15 and explosive crystallization with double moving fronts 13 have also been conducted. However, to solve the problem of free boundary movement, these models are all based on the enthalpy model 16 and they only introduce an equation of thermal transport.…”

Multicrystalline silicon films with large grains on glass: preparation and applications

“…Typical are a pulse duration of 25 ns and a cooling rate of 10 9 to 10 10 K/s [32]. So the system undercools by several 100 K within 100 ns and small grains in the 10 to 100 nm range result necessarily.…”