Compositional dependence of the exciton reduced mass in GaAs1-xBix (x=0-10%)

We report the compositional dependence of the exciton reduced mass, mu(exc), of GaAs1-xBix in a very large Bi concentration range (x=0-10.6%). Photoluminescence under high magnetic fields (B up to 30 T) shows that mu(exc) increases rapidly until x similar to 1.5% and then oscillates around similar to 0.08 m(0), m(0) being the electron mass in vacuum, up to about x=6%. Surprisingly, for x > 8% the exciton reduced mass decreases below the GaAs value, in agreement with the expectations of a k.p model. Such a behavior reveals the existence of different concentration intervals, where continuum states of the valence and conduction band hybridize with Bi-related levels at different extents, thus conferring to the band edges a localized or bandlike character for x < 6% and x > 8%, respectively.