PIEZO-RAMAN MEASUREMENTS AND ANHARMONIC PARAMETERS IN SILICON AND DIAMOND

Measurements of the frequency shift of optical phonons in Si with uniaxial stress have been performed by Raman spectroscopy using a laser frequency in the region of transparency. A mean deviation of 25% has been found in the phonon deformation potentials as compared with previous results obtained with laser frequencies above the absorption edge. The new values are p/02=-1.85+0.06, q/02=-2.31+0.06, and r/02=-0.71+0.02, and 1.08+0.06 for the Gr̈neisen parameter G. A valence-force-field model with five anharmonic parameters provides a consistency check between the phonon deformation potentials and the third-order elastic constants of Si. On the basis of this model, existing uniaxial-stress data for the optical phonons of diamond and for the pressure dependence of the second-order elastic constants have been reanalyzed and the corresponding five anharmonic parameters have been determined. In this manner, reliable values for the third-order elastic constants have been obtained for diamond. © 1990 The American Physical Society.