INFLUENCE OF ELECTRON-HOLE CORRELATIONS ON THE ABSORPTION OF GAAS IN THE PRESENCE OF NONTHERMALIZED CARRIERS

We study, both theoretically and experimentally, the variations of the absorption coefficient of bulk GaAs in the presence of a nonthermaliz ed electron-hole plasma. We investigate the changes of the Coulomb enh ancement factor (CEF) due to nonthermal carrier distributions. For com parison with experimental data, time-dependent nonlinear absorption sp ectra are calculated using carrier distributions obtained from the num erical solution of Boltzmann's equations. Experimental absorption spec tra are derived from differential transmission and reflectivity measur ements of GaAs thin films in the subpicosecond regime. Both experiment al and theoretical spectra show a redshift of the transient-hole-burni ng peak that can be attributed to the spectral dependence of the CEF c hanges. An induced absorption above the spectral hole is predicted for narrow distributions. This effect, which critically depends on the wi dth of the carrier distributions, is strongly suppressed by fast colli sional broadening in accordance with the experimental results.