Effect of pressure and time on the self catalyzed growth of epitaxial GaAs nanostructures by MOCVD

Epitaxial GaAs nanostructures have been grown on GaAs (111)B surface by metal organic chemical vapor deposition (MOCVD) using in situ self assembled Gallium (Ga) droplets as catalyst. The effect of growth pressure and time on the shape, size, and surface density of nanostructures grown under Arsenic (As) deficient conditions has been studied in detail. Good optical quality nanostructures in high yield and uniformity could be grown at 420 °C using catalyst droplets having a size of 350 nm. The optical quality of the nanostructures was confirmed with photoluminescence (PL) and Raman measurements. An unconventional decrease in the size of the nanostructures and formation of undesired streaky features were noticed on prolonging the growth from 10 to 20 min under Arsenic deficient conditions used in this study. Lowering the growth pressure from near atmospheric to 100 Torr has also led to a drastic decrease in the size and density of the nanostructures. At 450 °C, interestingly, almost flat hexagonal GaAs nanostructures with thickness ∼25 nm have been obtained in surplus yield in samples grown under 100 Torr. A growth model on the basis of progressive consumption of catalyst droplet during the growth has been proposed to explain these findings. The droplet consumption rate ∼25 nm/min has been estimated at 420 °C and 660 Torr from detailed analysis of the growth results.