Piezoreflectance in Ge

Observation of the change in position of identified reflectance peaks caused by the application of uniaxial stress along various directions can yield information concerning the shift of band edges under hydrostatic pressure and, in principle, of deformation potential constants. The reflectance peaks of Ge and Si below 5 eV have been studied in crystals subjected to four-point bending. A measurable effect was observed only in the 2-eV peaks associated with the ${L_3}^{\prime }\to L_1$ transitions in Ge. The shift for principal stress along the [111] direction was somewhat larger than that for stress along the [100] direction. Values are obtained for the pressure shift of the ${L_3}^{\prime }\to L_1$ gap, the pressure shift of individual band edges, ${{\Gamma }_{25}}^{\prime }$, ${L_3}^{\prime }$, and $L_1$, and for the deformation potentials associated with the ${L_3}^{\prime }$ minima.