Picosecond imaging of photoexcited carriers in quantum wells: Anomalous lateral confinement at high densities.

Abstract

We have measured the in-plane motion of photoexcited carriers in semiconductor quantum wells and have discovered several surprising results. The effective diffusivity of the carriers at densities below $n=2\ifmmode\times\else\texttimes\fi{}{10}^{11}$ ${\mathrm{cm}}^{\ensuremath{-}2}$ is found to depend upon the excitation level, possibly indicating defect-limited diffusion or phonon-wind effects. Above this density the spatial profiles exhibit two distinct components with widely differing diffusivities. We postulate that the slowly diffusing component represents carriers which are "thermally confined" to a phonon hot spot.