Experimental investigation of the amorphous silicon melting temperature by fast heating processes

The recrystallization of amorphous Si layers on Si crystal substrates after laser irradiation was investigated to test previous experimental evidence that both the melting point and the melting enthalpy of the amorphous are lower than the corresponding crystalline values. The irradiation was performed in some cases from the back side of 100-μm-thick Si wafers to obtain a temperature distribution in the amorphous layer with a small spatial gradient. In the case of front irradiation the threshold energy density was measured as a function of the amorphous layer thickness, for the polycrystalline formation, crystallization with residual disorder, and good annealing, respectively. The experimental data agree quite well with heat flow calculations assuming a reduction of about 30% in the melting point and enthalpy of amorphous silicon with respect to crystalline silicon.