Localization behavior at bound Bi complex states in GaAs1-xBix

While bismuth-related states are known to localize carriers in GaAs_1-xBi_x alloys, the localization behavior of distinct Bi pair, triplet and cluster states bound above the valence band is less well understood. We probe localization at three different Bi complex states in dilute GaAs_1-xBi_x alloys using magneto-photoluminescence and time-resolved photoluminescence spectroscopy. The mass of electrons Coulomb-bound to holes trapped at Bi pair states is found to increase relative to the average electron mass in the alloy. This increase is attributed to enhanced local compressive strain in the immediate vicinity of the pairs. The dependence of energy transfer between these states on composition is also explored.