Morphological characterization of GaAs islands grown on InGaAs by droplet epitaxy

•Droplet epitaxy of Ga(As) on InGaAs buffers lattice-matched to InP substrates.•Explored growth conditions resulting in unexpected morphology of GaAs droplet epitaxy on InGaAs.•Found shorter diffusion length for Ga adatoms compared with In.•Co-deposition of In- and Ga-droplets on InGaAs resulted in separate InAs and GaAs features. We investigated droplet epitaxy of Ga(As) on In0.53Ga0.47As as a method to extract Ga-adatom diffusion lengths with the aim of better understanding the underlying cause of phase separation in bulk In0.53Ga0.47As. However, instead of the expected morphology of a dot and a halo (the radius of which is directly related to adatom diffusion length), we found the deposited Ga etched into the underlying material, forming pits, tracks, and mounds with jagged edges. To understand the cause of this morphology, we varied several growth conditions including the substrate temperature, the Ga effective thickness, and depositing with/without As crystallization. Effective thickness and substrate temperature investigations revealed expected density trends in spite of the unusual morphology. This allowed us to compare densities of In halos (from our previous work) and Ga mounds, revealing a longer adatom diffusion length for In than Ga. We believe that the etching of the underlying In0.53Ga0.47As material led to scavenged In incorporating into the Ga droplet resulting in a low-In-content InGa alloy droplet. The irregular morphology then arose from competing In- and Ga-adatom diffusion lengths in Ga-rich conditions. Finally, we co-deposited In and Ga on In0.53Ga0.47As and found that instead of a uniform alloyed droplet morphology, the two group-III species formed separate In halos and Ga mounds. The inability of In and Ga to form an alloyed droplet under the growth conditions explored suggests that In-and Ga-adatoms may self-segregate under bulk growth conditions as well, leading to phase separation.