Subject classification: 71.55.Eq; 78.20.Ci; S7.11 Energy shifts of optical interband transition edges, E 0 0 , E 1 , E 1 þ D 1 , and E 2 , of Te and Ge codoped In 0:5 Ga 0:5 P alloys have been studied with varying the Te mole fraction in the solution using their complex dielectric functions measured by spectroscopic ellipsometry at room temperature. The interband transition edges were resolved by a line shape analysis on the numerical second derivative spectra of the dielectric functions. The E 1 and E 1 þ D 1 edges are found to shift to low energies with increasing doping concentration. It is interpreted as due to the doping-related bandgap renormalization.

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