It has been theoretically predicted that isolated Bi forms a resonant state in the valence band of the dilute bismide alloy, ${\mathrm{GaAs}}_{1-x}{\mathrm{Bi}}_x$. We present ultrafast pump-probe reflectivity measurements of this interesting alloy system, which provide experimental evidence for the resonant state. The reflectivity transients for pump/probe wavelengths λ ∼ 860–900 nm have negative amplitude, which we attribute to the absorption of the probe pulse by the pump induced carriers that are localized at the Bi-resonant state. Our measurements show that the lifetime of carriers localized at the resonant state is ∼200 ps at 10 K.

• Received 27 October 2013
• Revised 29 September 2014

DOI:https://doi.org/10.1103/PhysRevB.90.165203