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We present a Raman spectroscopic study of GaAs_1-xBi_x epilayers grown by molecular beam epitaxy. We have investigated the anharmonic effect on the GaAs-like longitudinal optical phonon mode (LO'_GaAs) of GaAs_1-xBi_x for different Bi concentrations at various temperatures. The results are analyzed in terms of the anharmonic damping effect induced by thermal and compositional disorder. We have observed that the anharmonicity increases with Bi concentration in GaAs_1-xBi_x as evident from the increase in the anharmonicity constants. Additionally, the anharmonic lifetime of the optical phonon decreases with increasing Bi concentration in GaAs_1-xBi_x.

We present measurements of the THz emission from GaAs_1–xBi_x epilayers excited with femtosecond laser pulses (λ ~ 800 nm). Here, we observed an increase in the peak-to-peak amplitude of the THz electric field with increasing Bi concentration. We also observed a polarity reversal of the THz transient in the epilayers with higher Bi concentration (x ≳ 1.4%). Taking into account the band gap reduction due to Bi incorporation and the excess energy of the carriers, our measurements suggest that there is a cross-over from a predominantly surface field emitter at low Bi concentrations (x ≲ 0.5%) to a predominantly photo-Dembermore » field emitter at higher concentrations (x ≳ 1.4%).« less