Spontaneous nanostructure formation in GaAsBi alloys

Bismuth containing semiconductor alloys are of increasing interest for their potential applications as infrared devices, though material quality in these materials has often proven problematic. This work shows a series of GaAsBi films grown by molecular beam epitaxy over a range of temperatures, 340 °C-315 °C, with all other parameters equal. Atomic force microscopy shows that there is an increase in the surface roughness of the films from 0.8 nm to 2.7 nm RMS. Transmission electron microscopy and atom probe tomography reveals the onset of spontaneous nanostructure formation in the films including nanopores, lateral composition modulation, and Bi rich GaAsBi clusters. The phenomena are shown to correlate and linked to reaching a growth instability due to the differences in surface diffusivity of Bi and As adatoms.