Degradation mechanisms of annealed GaAsPBi films grown by molecular beam epitaxy

•GaAsPBi films grown by MBE are annealed to improve their optical properties.•Optimum temperature for ex situ annealing differs from in situ annealing.•Degradation of the film as a result of over-annealing is observed in situ.•Interfacial dislocations at GaAsPBi/GaAs are created before the surface oxides desorb.•The underlying dislocations are spatially correlated with surface oxide desorption. 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 (