Direct observation of the E- resonant state in GaAs1-xBix

Bismuth-derived resonant states with T-2 symmetry are detected in the valence band of GaAs1-xBix using electromodulated reflectance. A doublet is located 42 meV below the valence-band edge of GaAs that is split by local strain around isolated Bi impurity atoms. A transition associated with a singlet is also observed just above the GaAs spin-orbit split-off band. These states move deeper into the valence band with increasing Bi concentration but at a much slower rate than the well-known giant upward movement of the valence-band edge in GaAs1-xBix. Our results provide key insight for clarifying the mechanisms by which isovalent impurities alter the band structure of the host semiconductor.