Femtosecond transmission spectroscopy at the direct band edge of germanium

Abstract

We time-resolve the transient, photoinduced transmission near the direct band edge of crystalline germanium (at 295 K) with 120-fs, tunable, infrared pulses from a 76-MHz optical parametric oscillator. The data show a rich collection of phenomena including band-gap renormalization, carrier-carrier scattering, carrier cooling, and \ensuremath{\Gamma}\ensuremath{\rightarrow}L intervalley scattering. An apparent carrier-density dependence in the measured intervalley scattering time is attributed to plasma screening of the Coulomb enhanced continuum absorption.