Dynamics of electron–hole liquid condensation in CVD diamond studied by femtosecond pump and probe spectroscopy

Abstract

We report on the femtosecond pump and probe study of the condensation dynamics of electron–hole liquid in CVD IIa type diamond. The parameters of electron–hole liquid created after carrier excitation by one- and two-photon absorption were determined on the basis of the analysis of spectral shape of time-integrated photoluminescence. The dynamics of condensation of carriers into electron–hole liquid was probed by measuring the time evolution of changes in infrared light absorption. These changes were interpreted in terms of the density dependent carrier scattering time according to the Drude model of free-carrier absorption. Measured condensation times range from 50 to 500ps depending on the initial carrier density (3×1016cm−3–5×1018cm−3) and the sample temperature (13–130K). The measured dynamics was reproduced very well by a rate equation model of electron–hole droplet formation for low photoexcited carrier densities. A ~10ps delay in initial stage of condensation observed for high carier densities was interpreted in terms of density dependent carrier cooling rate.