Angular distortion of Si clusters in a-SiC

In this letter we report on the unusually large bond angle distortion of silicon clusters in an amorphous silicon carbide matrix. The samples, produced by Ar+ ion irradiation of single crystal 6H-SiC, have been analyzed by Raman spectroscopy. The apperance of both Si-Si and C-C related bands points to the formation of silicon and carbon clusters in the amorphous SiC matrix. The width of the Si-Si Raman band was found to be almost twice that of ion-implanted amorphous silicon. In terms of root-mean-square bond angle distortion, we found a value of Delta theta similar to 22.5 degrees. Upon annealing, Delta theta increases up to 27 degrees at 700 degreesC, while in amorphous silicon it decreases from 12.3 degrees to 9.5 degrees. It is the relaxation of the a-SiC matrix that provides the energy required to increase the distortion of the silicon clusters. Taking into account the variation of the number of clusters with annealing, the total energy stored in the distortion of the clusters decreases from 20 kJ/mole to 10 kJ/mole.