THEORY OF HIGH-GAIN TRANSIENT ENERGY-TRANSFER IN GAAS AND SI

Rate equations for carrier number densities and wave equations for optical fields are solved numerically to investigate transient energy transfer (TET) from a strong pump beam to a weak probe via the free-carrier nonlinearity in GaAs and Si. Our calculations of TET include, for the first time we believe, arbitrary ratio of pulse length to diffusion time, pump depletion, free-carrier absorption, and twophoton absorption. The calculations reproduce all qualitative features of our experimental results. In silicon, excellent quantitative agreement can be obtained, but one must assume that the ambipolar diffusion coefficient is substantially smaller than implied by conventional electronic measurements. In GaAs, obtaining good quantitative agreement requires both a decreased diffusion coefficient and a saturation of the free-carrier nonlinearity. Our calculations provide guidance on the optimal choice of sample thickness, free-carrier cross section, and two-photon absorption coefficient for obtaining high TET gains in semiconductors. © 1990 IEEE