Mode Gruneisen parameters and stress-induced changes in the infrared spectrum of silicon

The results of a theoretical and experimental investigation of the effects of uniaxial stresses on some two-phonon infrared absorption feature of silicon are presented. The lifting of degeneracies at the X and L points and modified section rules are derived for (001) and (111) stresses. Expressions for the frequency shifts in terms of mode Gruneisen parameters ( gamma s) are presented. Experimental results are given for the shifts and splittings of three infrared features associated with critical points on the two phonon dispersion curves. These data are insufficient to determine any gamma s, but values of omega j gamma j +or- omega j' gamma j' , for three branch combinations j+or-j' at the X and L points have been obtained and are compared with the theoretical values of other workers.