Variable strain energy in amorphous silicon

Different Raman experiments on structural relaxation ofa-Si anda-Ge are reviewed and discussed in relation to calorimetric measurements ona-Ge. On the basis of the correlation found between results from Raman spectroscopy and results from calorimetry in the case ofa-Ge and of the strong similarity betweena-Si anda-Ge in terms of their Raman spectra, it is suggested that the strain energy ina-Si may vary considerably with preparation conditions and subsequent treatments. Under this assumption thea-Si Gibbs free energy versus temperature has been constructed for material in different initial states of relaxation. It is shown that the melting temperature of amorphous silicon should increase when relaxation occurs during the heating phase prior to melting. Thus differences in apparent melting temperature, as observed under different laser heating conditions, may be explained.