DYNAMICAL SCREENING OF EXCITONS IN A SEMICONDUCTOR ELECTRON-HOLE PLASMA

A single-particle Hamiltonian approach is used for describing dynamical screening of excitons in optically excited semiconductors. Upon considering a particular electron-hole pair, the excitation spectrum of all the other electrons and holes is replaced by a single plasmon mode omega(q). From a Frohlich-type Hamiltonian, 1s exciton binding energy and wavefunctions are calculated variationally with a generalization of the Lee-Low-Pines transformation. The advantage of the method, beside the simplicity, is that bandgap renormalization is accounted for within the same Hamiltonian so that a consistent comparison with experimental data is possible. In particular, our model reproduces both the remarkable persistence of the 1s GaAs exciton line under strong optical excitation and the measured transition density from bound to unbound states.