Direct absorption inside the electron‐hole liquid in Ge: Warping effects and final state interactions

Earlier absorption experiments in highly excited Ge are successfully explained and quantitatively fitted by a theory including Moss‐Burstein shift in warped hole bands, self‐energy effects, and multiple electron‐hole scattering via screened Coulomb potential. The corresponding Bethe‐Salpeter equation is solved numerically in momentum space. At frequencies above Moss‐Burstein influence, calculated absorption spectra are close to the exciton continuum independent of excited carrier concentration in agreement with experiment, which disqualifies a one‐particle description of direct absorption in the electron‐hole liquid of Ge.