Degradation mechanisms of annealed GaAsPBi films grown by molecular beam epitaxy

GaAsPBi is a novel semiconductor that can broaden the bandgap range of III-V compounds, but its growth on GaAs(001) by molecular beam epitaxy is complicated by the presence of Bi. To avoid the nucleation of Bi droplets, the growth temperature must be low (<400 & DEG;C), resulting in GaAsPBi films with poor photoluminescent yields. It is shown here that while post-growth annealing of GaAsPBi improves its optical quality, the GaAsPBi surface and the underlying GaAsPBi/GaAs interface undergo structural and chemical changes that limit the usefulness of annealing. Using synchrotron radiation-based spectromicroscopy, morphological and chemical changes on the surface are followed in situ, allowing the temperature limit to be estimated at -510 & DEG;C. Beyond this, the GaAsPBi film degrades, first by the nucleation of interfacial dislocations at -520 & DEG;C, then by the desorption of surface oxides at -580 & DEG;C, and by congruent sublimation of the film itself at -670 & DEG;C. The damages are spatially correlated and inhomogeneous, with areas above the dislocations being the preferential damage sites. These in situ observed events provide critical insights to the mechanisms and chronology of surface and interfacial degradation during high-temperature processing of GaAsPBi/GaAs structure, with implications for the process and device designs of heteroepitaxial III-V films prevalence in optoelectronics.