T-Matrix Approach to the Linear Optical Response of Highly Excited Semiconductors

Using Green's function techniques the optical susceptibility is expressed in terms of the T-matrix taking into account self-energies of the carriers depending both on wave number and energy. The influence of a real excitonic fraction in the electron–hole plasma onto single particle properties and optical response is studied investigating numerically the T-matrix. For temperatures T ≳ 40 K the chemical potential is strongly reduced due to an excitonic fraction. Finally, we find for this temperature region, that the Mott transition has already finished when the chemical potential crosses the exciton, preventing excitonic gain discussed for II–VI semiconductors.