Identification ofΓTransitions in theE0′Region of Germanium by Piezoreflectance Measurements

The reflectance of germanium and its logarithmic derivative $\frac{\left(\frac{\mathrm{dR}}{\mathrm{dE}}\right)}{R}$ in the 2.8- to 4.0-eV spectral region have been reexamined as a function of temperature (2 to 300 K) and uniaxial stress. Two relatively sharp structures at 3.00 and 3.19 eV are seen in the unstressed derivative data at 2 K. The observed splittings and polarizations of these two structures for large uniaxial stress along [001] or [111] directions agree well with the behavior calculated for ${\Gamma }_8^v\to {\Gamma }_7^c$ and ${\Gamma }_8^v\to {\Gamma }_8^c$ transitions, respectively. The data are incompatible with a $\Delta$ symmetry assignment for these two structures. A third broader structure is seen near 3.5 eV, the expected energy for a ${\Gamma }_7^v\to {\Gamma }_8^c$ transition; however, the temperature independence and strength of this structure indicate that it is not a $\Gamma$ transition.