Decoupling the Effects of Surface Morphology and Bulk Substitutionality on Dilute-Bismide Optical Quality

The growth of bismuth-containing III–V alloys is often accompanied by the formation of metallic surface droplets owing to the extreme growth conditions necessary for bismuth incorporation as well as the atom’s preference for surface segregation. However, the effects of droplet formation on III–V–Bi optical quality, a telling metric for optoelectronic device performance, have remained remarkably underexplored. By comparing InSbBi films that were grown under nearly identical parameters but exhibited dissimilar surfaces as-grown, the effects of droplet formation on optical quality were systematically studied. As grown, a smooth InSbBi film exhibited ∼2.5× the photoluminescence intensity of a droplet-containing film. However, with etching by dilute HCl, not only were the droplets effectively removed, but the photoluminescence intensity of the droplet-containing film recovered to within ∼10% of the strength of the as-grown smooth film. This dramatic increase in photoluminescence intensity with droplet removal may be attributed to the removal of surface recombination sites. Both films exhibited ≥99% substitutionally incorporated bismuth atoms on anion sublattice sites indicative of high-quality material. These results illustrate that, as grown, the material quality of the bulk of the droplet-containing sample was comparable to that of the smooth sample. A third sample grown under a greater bismuth flux also underwent droplet formation during growth, but did not exhibit photoluminescence as-grown or following droplet removal. Rutherford backscattering spectrometry measurements revealed that this sample only contained ∼75% substitutionally incorporated bismuth atoms. Altogether, these results present bulk substitutionality as a more accurate measure of dilute-bismide optical and material quality than the occurrence of droplet formation during growth.