Terahertz gain in optically excited biased semiconductor superlattices

We investigate the terahertz-driven dynamics of excitons in an undoped optically excited biased semiconductor superlattice, including exciton-LO phonon scattering. We calculate the THz gain spectrum for a 820 fs THz pulse when the superlattice is excited by a 590 fs optical pulse. The gain arises because, in contrast to the single-electron case, the excitonic Wannier-Stark ladder is asymmetric with respect to absorption and emission. We find that gain coefficients greater than 100 cm(-1) can be achieved at excitation densities for which domain formation should not occur. (c) 2005 American Institute of Physics.