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We investigate the surface morphologies of two series of homoepitaxial GaSb(100) thin films grown on GaSb(100) substrates by molecular beam epitaxy in a Veeco GENxplor system. The first series was grown at temperatures ranging from 290 to 490°C and serves as a control. The second series was grown using the same growth parameters with bismuth used as a surfactant during growth. We compared the two series to examine the impacts of bismuth over the range of growth temperatures on the GaSb surface morphologies using atomic force microscopy and the film properties using Raman spectroscopy and scanning electron microscopy. High-resolution x-ray diffraction was performed to confirm that bismuth was not incorporated into the films. We found that the morphological evolution of the GaSb series grown without bismuth is consistent with the standard surface nucleation theory and identified the 2D-3D transition temperature as close to 290° C. In contrast, the presence of a Bi surfactant during growth was found to significantly alter the surface morphology and prevent undesired 3D islands at low temperatures. We also observed a preference for hillocks over step morphology at high growth temperatures, antistep bunching effects at intermediate temperatures, and the evolution from step-meandering to mound morphologies at low temperatures. This morphological divergence from the first series indicates that bismuth significantly increases in the 2D Erlich–Schwöebel potential barrier of the atomic terraces, inducing an uphill adatom flux that can smoothen the surface. Our findings demonstrate that bismuth surfactant can improve the surface morphology and film structure of low-temperature grown GaSb. Bismuth surfactant may also improve other homoepitaxial III-V systems grown in nonideal conditions. 

Variable‐angle spectroscopic ellipsometry is used to determine the room temperature complex refractive index of molecular beam epitaxy grown GaSb_1−xBi_xfilms withx ≤ 4.25% over a spectral range of 0.47–6.2 eV. By correlating to critical points in the extinction coefficientk, the energies of several interband transitions are extracted as functions of Bi content. The observed change in the fundamental bandgap energy (E₀, −36.5 meV per %Bi) agrees well with previously published values; however, the samples examined here show a much more rapid increase in the spin‐orbit splitting energy (Δ₀, +30.1 meV per Bi) than previous calculations have predicted. As in the related GaAsBi, the energy of transitions involving the top of the valence band are observed to have a much stronger dependence on Bi content than those that do not, suggesting the valence band maximum is most sensitive to Bi alloying. Finally, the effects of surface droplets on both the complex refractive index and the critical point energies are examined.