1：Experimental Design and Method Selection:

Micro-Raman scattering experiments were performed in a quasi-backscattering geometry with a 50× microscope. The 514.5 nm, 532 nm, and 633 nm laser lines were used as excitation lasers. The laser power was changed using neutral density filters. Polarized Raman spectra were measured using appropriate polarizers and waveplates. The scattering signal was dispersed by a spectrometer and detected by a liquid nitrogen-cooled Si-CCD camera.

2：5 nm, 532 nm, and 633 nm laser lines were used as excitation lasers. The laser power was changed using neutral density filters. Polarized Raman spectra were measured using appropriate polarizers and waveplates. The scattering signal was dispersed by a spectrometer and detected by a liquid nitrogen-cooled Si-CCD camera. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: The studied GaAs1-xBix samples with thicknesses ~450 nm (x=0.4%, 0.8%, 2.6%, and 3.7%) were grown on GaAs (100) substrates by molecular beam epitaxy. These compositions were determined by X-ray diffraction and optical data.

3：4%, 8%, 6%, and 7%) were grown on GaAs (100) substrates by molecular beam epitaxy. These compositions were determined by X-ray diffraction and optical data. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: A spectrometer, a liquid nitrogen-cooled Si-CCD camera, neutral density filters, polarizers, and waveplates were used.

4：Experimental Procedures and Operational Workflow:

The samples were housed in a liquid nitrogen cryostat for low-temperature measurements. Hall measurements were performed in Van der Pauw geometry in a magnetic field of 0.2 T at room temperature. Ti (50 nm)/Pt (100 nm)/Au (100 nm) metal films were deposited on GaAsBi film by magnetron sputtering method for providing ohmic contacts.

5：2 T at room temperature. Ti (50 nm)/Pt (100 nm)/Au (100 nm) metal films were deposited on GaAsBi film by magnetron sputtering method for providing ohmic contacts. Data Analysis Methods:

5. Data Analysis Methods: The Raman spectra were analyzed using the dielectric theory model to simulate the line-shape of the LOPC modes. The ULO and TO phonon modes were fitted with two Lorentzian oscillators.