The effect of growth conditions to the optical quality of GaAsBi alloy

The quality of GaAsBi samples grown under various conditions were investigated by photoluminescence (PL) and atomic force microscopy (AFM). The samples were grown by molecular beam epitaxy at a rate of 0.36 and 0.61 μm/h. For each growth rates, three samples were grown under different Bi fluxes. For samples grown at a rate of 0.36 μm/h, the PL peak wavelength was red-shifted from 1103 to 1241 nm as the Bi flux was increased from 0.53 to 1.0 × 10^-7 mBar. However, for sample grown with the highest Bi flux, the optical quality degraded showing a weak and broad PL spectrum. The AFM image shows that the sample grown with Bi flux of 0.53 × 10^-7 mBar has a smooth surface with rms roughness of 0.78 nm. However, the presence of Bi droplets was observed for samples grown with higher Bi fluxes. A similar PL trend was also observed for samples grown at 0.61 μm/h. The results indicate that high Bi flux may increase the incorporation of Bi into GaAs but it is limited by the formation of Bi droplets.