Is there a link between very high strain and metastable phases in semiconductors: cases of Si and GaAs?

Silicon and gallium arsenide indentations have been investigated by using Raman spectroscopy. This perfect tool permits the study of the strain field within and around the indentation with 3D-micrometric resolution. By mapping both indented materials, we show that the strain varies strongly in GaAs and is constant in Si within indentations. With the selected orientation of GaAs, the two observed phonons provide a way to determine the local symmetry of the strain in all the area of the fingerprint. In Si, the quite constant value within the indentation, always reported in the literature with low laser power, seems to be correlated with the metastable phases created. To provide evidence for this fact, we have selected samples which favour metastable phases over amorphous, allowing the study of the correlation of the Raman peaks associated with metastable crystalline Si phases (Si-XII) and associated with diamond Si-I. The frequency shift plot of the 355 cm -1 band as a function of the Si-I Raman band frequency at 522 cm -1 exhibits a negative slope. The strains in both phases have an opposite sign. This accurate observation provides an insight into the origin of the surprising high strain in silicon.