Piezo-optical response of Ge in the visible–uv range

Using rotating-analyzer ellipsometry we have measured the three complex components P₁₁({ω}), P₁₂({ω}), and P₄₄({ω}) of the linear piezo-optical tensor Pᵢⱼₖₗ({ω}) of Ge in the 1.6--5.6 eV photon energy range. This was accomplished by applying static uniaxial stress to Ge crystals along the [111] and [001] crystallographic directions, and monitoring the stress-induced changes in the dielectric function {ε}({ω}) at room temperature. The real and imaginary parts of each component were directly obtained. They show, in general, good Kramers-Kronig consistency. A comparison with pseudopotential calculations of P₁₁({ω}), P₁₂({ω}), and P₄₄({ω}) for strained Ge is also given. In addition, deformation-potential constants (D₁¹,D₁⁵,D₃³,D₃⁵) and spin-exchange parameters (δJ1,δJ2) were determined for the E₁-E₁+Δ₁ transitions; they show good agreement with prior work.