Time- and angle-resolved photoemission spectroscopy for the saddle-point excitons in GaAs

Time- and angle-resolved photoemission spectroscopy reveals the electronic structures and dynamics of saddle-point excitons formed at 2.95 eV above the valence-band maximum in GaAs. The exciton wave function is composed of electron-hole pair states with wave vectors of 0.23\ifmmode\pm\else\textpm\fi{}0.04 \AA{}${}^{\ensuremath{-}1}$ along the $G$-$L$ line of the Brillouin zone. The excitons decay with a 11-fs lifetime by the autoionization into noncorrelated electron-hole pair states. Thus, the method provides far deeper insight into the nature of excitonic states in semiconductors.